Organic Chemistry Flashcards
1
Q
CH4
A
Methane
2
Q
C2H6
A
Ethane
3
Q
C3H8
A
Propane
4
Q
C4H10
A
Butane
5
Q
C5H12
A
Pentane
6
Q
C6H14
A
Hexane
7
Q
C7H16
A
Heptane
8
Q
C8H18
A
Octane
9
Q
C9H20
A
Nonane
10
Q
C10H22
A
Decane
11
Q
Diol
A
Alcohols with 2 hydroxyl groups
Is a protecting group for aldehyde and ketone carbonyls
12
Q
Geminal diols
A
Alcohols with 2 hydroxyl groups on the same carbon
13
Q
Vicinal diols
A
Alcohols with 2 hydroxyl groups on adjacent carbons
14
Q
2-propanol common name
A
Isopropyl alcohol
15
Q
Ethanol common name
A
Ethyl alcohol
16
Q
Aldehyde
A
Has a carbonyl group at the end of the chain that has at least one bond to hydrogen
17
Q
Ketone
A
Has a carbonyl group in the middle of the chain that has two bonds to carbons
18
Q
Aldehyde suffix
A
-al
19
Q
Aldehyde substituent prefix
A
oxo-
20
Q
Ketone suffix
A
-one
21
Q
Ketone substituent prefix
A
oxo- OR keto-
22
Q
Methanal common name
A
Formaldehyde
23
Q
Ethanal common name
A
Acetaldehyde
24
Q
Propanal common name
A
Propionaldehyde
25
Propanone common name
Acetone
26
What is the ester derivative of pentanoic acid?
Pentanoate
27
What is the amide derivative of pentanoic acid?
Pentanamide
28
What is the anhydride derivative of pentanoic acid?
Pentanoic anhydride
29
Alkanes
Hydrocarbons without any double or triple bonds
30
Alkanes formula
C (n) H (2 n + 2)
31
Alkanes suffix
-ane
32
Alkenes
Hydrocarbons with double bonds
33
Alkynes
Hydrocarbons with triple bonds
34
Alkene suffix
-ene
35
Alkyne suffix
-yne
36
Alcohols
Contain a hydroxyl (-OH) group
37
Alcohol suffix
-ol
38
Alcohol substituent prefix
Hydroxy-
39
Alcohol common nomenclature
Carbon chain name + alcohol
40
Ketone common nomenclature
Alkyl groups on either side in alphabetical order + ketone
41
What is the smallest ketone?
Acetone (a.k.a propanone)
42
Alpha-carbon
The carbon adjacent to the carbonyl carbon
43
What is the highest priority functional group?
Carboxylic acids
44
Carboxylic acid suffix
-oic acid
45
Methanoic acid common name
Formic acid
46
Ethanoic acid common name
Acetic acid
47
Propanoic acid common name
Propionic acid
48
Esters
Carboxylic acid derivatives where -OH is replaced with -OR
| They are the condensation products of carboxylic acids with alcohols
49
Alkoxy group
-OR
50
Ester suffix
-oate
51
Ester substituent prefix
alkoxycarbonyl-
52
Ester common name
Alcohol name + carboxylic acid name used during synthesis
53
Carboxylic acid + alcohol =
Ester
54
Amides
Carboxylic acid derivatives where -OH is replaced with an amino group
They are the condensation products of carboxylic acids and ammonia or amines
55
Amide suffix
-amide
56
Amide substituent prefix
carbamoyl- OR amido-
57
How are substituents attached to the amide nitrogen designated?
N-
58
Anhydrides
Carboxylic acid derivates formed from two carboxylic acids by dehydration
They are the condensation dimers of carboxylic acids
59
Carboxylic acid + carboxylic acid (in dehydration process) =
Anhydride
60
Symmetric anhydride
Made of 2 of the same carboxylic acid
61
Asymmetric anhydride
Made of 2 different carboxylic acids
62
What is a cyclic anhydride made of?
Made from an intramolecular reaction of a dicarboxylic acid
63
Anhydride suffix
Anhydride in place of acid
64
The order of priority in functional groups
1. Carboxylic acid
2. Anhydride
3. Ester
4. Amide
5. Aldehyde
6. Ketone
7. Alcohol
8. Alkene or alkyne
9. Alkane
65
Structural (constitutional) isomers
Have the same molecular formula, but different physical and chemical properties
66
Is melting point a physical or chemical property?
Physical
67
Is boiling point a physical or chemical property?
Physical
68
Is solubility a physical or chemical property?
Physical
69
Is density a physical or chemical property?
Physical
70
Conformational isomers
Stereoisomers with the same molecular connectivity at different points of rotation around a single (sigma) bond
71
Configurational isomers
Stereoisomers with differing molecular connectivity
72
Enantiomers
Non-superimposable mirror images
| Differ at all chiral carbons, with no plane of symmetry
73
Do enantiomers have internal planes of symmetry?
No
74
Do enantiomers have the same physical properties
Yes, except rotation of plane-polarized light
75
Do enantiomers have the same chemical properties
Yes, except reactions in chiral environments
76
Diastereomers
Non-mirror-image optical isomers
| Differ by at least one, but not all chiral carbons
77
Do diastereomers have the same physical properties?
No
78
Do diastereomers have the same chemical properties?
No
79
Enantiomer rotation in plane-polarized light
Each enantiomer's rotation is the opposite of the other
80
Enantiomer reactions in chiral environments
React differently because the environment is seeking to react with only one of the enantiomers
81
Meso compound
Contains chiral centers and an internal plane of symmetry, the molecule is therefore achiral overall and will not rotate in plane-polarized light
82
Do meso compounds have an internal plane of symmetry?
Yes
83
Do meso compounds rotate in plane-polarized light?
No
84
Are meso compounds chiral?
No
85
E / Z isomers
Refer to arrangement of groups around a double bond
86
Z isomer
When the two highest priority groups are on the same side
87
E isomer
When the two highest priority groups are on opposite sides
88
Cahn-Ingold-Prelog priority rules
1. Priority is assigned by atomic number
2. The atom connected to the stereo center or double-bonded carbon with the highest atomic number gets the highest priority
3. If there is a tie, one works outward from the stereo center or double-bonded carbon until the tie is broken
89
Is stereochemistry retained or inverted in a Fischer projection if we switched a pair of substituents?
Inverted
90
Is stereochemistry retained or inverted in a Fischer projection if we switched two pairs of substituents?
Retained
91
Is stereochemistry retained or inverted in a Fischer projection if we rotated the molecule 90 degrees?
Inverted
92
Is stereochemistry retained or inverted in a Fischer projection if we rotated the molecule 180 degrees?
Retained
93
Staggered conformations
Have groups 60 degrees apart
94
Anti-staggered conformations
The two largest groups are 180 degrees apart
| Strain is minimized
95
Is strain minimized or maximized in anti-staggered conformations?
Minimized
96
Gauche staggered conformations
The two largest groups are 60 degrees apart
97
Types of staggered conformations
Anti and gauche
98
Eclipsed conformations
Groups are directly in front of each other (120 degrees apart)
99
Totally eclipsed conformations
The two largest groups are directly in front of each other
| Strain is maximized (0 degrees apart)
100
Is strain minimized or maximized in totally eclipsed conformations?
Maximized
101
Where does the strain in cyclic molecules come from?
Angle strain, torsional strain and non-bonded strain
102
How is angle strain created?
By stretching or compressing angles from their normal size
103
How is torsional strain created?
By eclipsing conformations
104
Non-bonded strain
Created by interactions between substituents attached to non-adjacent carbons
105
How do cyclic molecules minimize strain?
By adopting non-planar shapes
106
How are substituents on a cyclohexane classified?
Axial and equatorial
107
Axial
Substituents are sticking up or down from the plane of the molecule
108
Equatorial
Substituents are in the plane of the molecule
109
What creates more non-bonded strain axial or equatorial?
Axial
110
Why do the largest substituents take the equatorial position?
To minimize strain
111
Types of conformational isomers
Staggered, anti-staggered, gauche staggered, eclipsed and totally eclipsed
112
How to switch between conformational isomers?
Change substituent rotation. No bond-breaking is required
113
How to switch between configurational isomers?
Bond-breaking is required
114
Types of configurational isomers
Enantiomers, meso compounds, diastereomers and cis-trans isomers
115
Optical activity
The ability of a molecule to rotate in plane-polarized light
116
d- OR (+)
Molecules rotate light to the right
117
l- OR (-)
Molecules rotate light to the left
118
Racemic mixture
Have equal concentrations of two enantiomers and are, therefore inactive in plane-polarized light
119
Cis-trans isomers
A subtype of diastereomers in which groups differ in position about an immovable bond
120
Chiral centers
Have four different groups attached to the central carbon
121
Relative configuration
Gives the stereochemistry of a compound in comparison to another molecule
122
Absolute configuration
Gives the stereochemistry of a compound without having to compare to other molecules
Uses the Cahn-Ingold-Prelog priority rules
123
(R) configuration
The substituents in a seterocenter rotate clockwise
124
(S) configuration
The substituents in a stereocenter rotate counterclockwise
125
Specific rotation [alpha]
= alpha observed / c l
alpha observed = angle observed
c = concentration in g/mL
l = diameter in dm
126
The maximum number of stereoisomers of a compound
2^n
| n = number of chiral carbons
127
Quantum number n name
Principal quantum number
128
What does quantum number n describe?
Size
129
What is the organizational level of quantum number n?
Shell
130
What are the possible values for quantum number n?
1 to infinity
131
Quantum number l name
Azimuthal quantum number
132
What does quantum number l describe?
Shape
133
What is the organizational level of quantum number l?
Sub-shell
134
What are the possible values for quantum number l?
0 to n - 1
135
Quantum number ml name
Magnetic quantum number
136
What does quantum number ml describe?
Orientation
137
What is the organizational level of quantum number ml?
Orbital
138
What are the possible values for quantum number ml?
-l to +l
139
Quantum number ms name
Spin quantum number
140
What does quantum number ms describe?
Spin
141
What are the possible values for quantum number ms?
-1/2 or +1/2
142
Which is more stable: bonding or anti-bonding orbitals?
Bonding
143
Which has higher energy: bonding or anti-bonding orbitals?
Anti-bonding
144
Which has shorter bond length: double or single bonds?
Double
145
Which has higher bond energy: double or single bonds?
Double
146
Which has more molecular rigidity: double or single bonds?
Double
147
Which bond is strongest: sigma bond, pi bond, double bond or triple bond?
Triple bond
148
Which bond is weakest: sigma bond, pi bond, double bond or triple bond?
Pi bond
149
Which bond is stronger: sigma bond or double bond?
Double bond
150
What is the s character of sp hybridized orbitals?
50%
151
What is the s character of sp2 hybridized orbitals?
33%
152
What is the s character of sp3 hybridized orbitals?
25%
153
What is the p character of sp hybridized orbitals?
50%
154
What is the p character of sp2 hybridized orbitals?
67%
155
What is the p character of sp3 hybridized orbitals?
75%
156
Resonance structures
Differ in their placement of electrons in hybridized p-orbitals and require bond conjugation to delocalize electrons in a molecule
157
l = 0
Sub-shell s
158
l = 1
Sub-shell p
159
l = 2
Sub-shell d
160
l = 3
Sub-shell f
161
Shape of s orbital
Spherical
162
Shape of p orbital
Dumbbell
163
Bonding orbitals
Created by head-to-head or tail-to-tail overlap of atomic orbitals of the same sign and are energetically favorable
164
Anti-bonding orbitals
Created by head-to-head or tail-to-tail overlap of atomic orbitals that have opposite signs and are energetically unfavorable
165
Single (sigma) bonds
Contain 2 electrons
166
Double bonds
Contain one sigma bond and one pi bond
167
Pi bonds
Created by sharing electrons between two unhybridized p-orbitals that align side-by-side
168
Triple bonds
Contain one sigma bond and two pi bonds
169
Why are multiple bonds less flexible?
Because rotation is not possible when pi bonds are present
170
sp3 geometry
Tetrahedral, 109.5 degree angles, central carbon with 4 single bonds
171
sp2 geometry
Trigonal planar, 120 degree angles, central carbon with 2 single bonds and 1 double bond
172
sp geometry
Linear, 180 degree angles, central carbon with 1 single bond and 1 triple bond OR 2 double bonds
173
Conjugation
Occurs when single and multiple bonds alternate, creating a system of unhybridized p-orbitals down the backbone of the molecule through which pi electrons can delocalize
174
Why is resonance useful?
It increases the stability of a molecule
175
When will an acid-base reaction proceed?
When the acid and base react to form conjugate products that are weaker than the reactants
176
Amphoteric molecules
Species that can act as either acids or bases
177
Is water amphoteric?
Yes
178
Is bicarbonate amphoteric?
Yes
179
Is dihydrogen phosphate amphoteric?
Yes
180
pKa
= - log Ka
| Ka = the equilibrium constant for the dissociation of an acid
181
What does pKa indicate?
The strength of an acid
182
What does a low pKa indicate?
Strong acid
183
Are alcohols acids or bases?
Acids
184
Are aldehydes acids or bases?
Acids
185
Are ketones acids or bases?
Acids
186
Are carboxylic acids acids or bases?
Acids
187
Are amines acids or bases?
Bases
188
Are amides acids or bases?
Bases
189
Nucleophilicity and electrophilicity
Based on relative rates of reactions and are therefore kinetic properties
190
Acidity and basicity
Measured by the position of equilibrium in a protonation or deprotonation reaction and are therefore thermodynamic properties
191
Is nucleophilicity a thermodynamic or kinetic property?
Kinetic
192
Is electrophilicity a thermodynamic or kinetic property?
Kinetic
193
Is acidity a thermodynamic or kinetic property?
Thermodynamic
194
Is basicity a thermodynamic or kinetic property?
Thermodynamic
195
What determines nucleophilicity?
Charge, electronegativity, steric hindrance and the solvent
196
Does a strong nucleophile have a more negative or more positive charge?
More negative
197
Is a strong nucleophile more electronegative or less electronegative?
Less electronegative
198
Is a strong nucleophile large or small?
Small
199
How does the solvent change a nucleophile's reactivity?
Protic solvents protonate or hydrogen bond with the nucleophile, decreasing its reactivity
200
How does a substitution reaction proceed?
The nucleophile has to be stronger (more reactive) than the leaving group
201
Does a strong electrophile have a more negative or more positive charge?
More positive
202
How do better leaving groups increase electrophilicity?
They make the reaction more likely to proceed
203
Good leaving groups characteristics
1. Can stabilize the extra electrons that result from heterolysis
2. Are weak bases (the conjugate bases of strong acids)
3. Resonance stabilization
4. Have inductive effects from electron-withdrawing groups
204
Good oxidizing agents characteristics
1. Have high affinities for electrons
2. Have high oxidation states
3. Get reduced as they accept electrons
4. Contain a metal and a large number of oxygen
205
Good oxidizing agents
O2, O3, Cl2, MnO4-, CrO4-, CrO7^2-, pyridinium chlorochromate, metal + large number of oxygen atoms
206
Good reducing agents characteristics
1. Have low electronegativities
2. Have low ionization energies
3. Contain a metal and a large number of hydrides
4. Donate electrons while getting oxidized
207
Good reducing agents
Na, Mg, Al, Zn, NaH, CaH2, LiAlH4, NaBH4, metal + large number of hydrides
208
What are the two reactive centers of carbonyl-containing compounds?
Carbonyl carbon (electrophilic) and alpha-hydrogens (acidic)
209
Are carbonyl carbs electrophilic or nucleophilic?
Electrophilic
210
Are alpha-hydrogens acidic or basic?
Acidic
211
When do SN1 reactions occur?
They occur on tertiary carbons because there can be most easily stabilized
212
When do SN2 reactions occur?
They occur on methyl or primary carbons because these reactions are easily inhibited by steric hindrance
213
How to solve organic chemistry reactions?
1. Know the nomenclature
2. Identify the functional groups
3. Identify the other reagents
4. Identify the most reactive functional group(s)
5. Identify the first step of the reaction
6. Consider stereoselectivity
214
If there are no reaction conditions listed, what determines how the reaction will proceed?
The properties of the functional groups on the reactants themselves (acid-base; nucleophile-electrophile) will determine the outcome
215
Lewis acids
Electron acceptors
Have vacant orbitals
Positively polarized
216
Lewis bases
Electron donors
Have a lone pair of electrons
Anions
217
Bronsted-Lowry acids
Proton donors
218
Bronsted-Lowry bases
Proton acceptors
219
Acid dissociation constant (Ka)
= ([H+] [A-]) / [HA]
A measure of acidity
The equilibrium constant corresponding to the dissociation of an acid into a proton an its conjugate base
220
In which direction does pKa increase on the periodic table?
Bottom to top and left to right
221
Nucleophiles characteristics
Nucleus-loving
Contain lone pairs or pi bonds
High electron density
Carry negative charge
222
Are nucleophiles similar to acids or bases?
Bases
223
Are nucleophiles positively or negatively charged?
Negatively charge
224
Are amino groups nucleophilic or electrophilic?
Nucleophilic
225
Electrophiles characteristics
Electron-loving
| Positively charged
226
Are electrophiles positively or negatively charged?
Positive
227
Are alcohols nucleophiles or electrophiles?
Electrophiles
228
Are aldehydes nucleophiles or electrophiles?
Electrophiles
229
Are ketones nucleophiles or electrophiles?
Electrophiles
230
Are carboxylic acids nucleophiles or electrophiles?
Electrophiles
231
Are carboxylic acid derivatives nucleophiles or electrophiles?
Electrophiles
232
Why are alkanes and hydrogen ions never leaving groups?
Because they form reactive anions
233
Unimolecular nucleophilic substitution (Sn1) reaction steps
1. Leaving group leaves
2. Carbocation forms b/c leaving group is gone
3. Nucleophiles attacks the planner carbocation from either side
The result is a racemic mixture of products
234
Do SN1 reactions make racemic mixtures?
Yes
235
Conditions that facilitate Sn1 reactions
More substituted carbons (because the alkyl groups can donate electron density and stabilize the positive charge of the carbocation)
236
What does the rate of an SN1 reaction depend on?
The concentration of the substrate
rate = k [R - L]
237
Bimolecular nucleophilic substitution (Sn2) reaction steps
1. Nucleophile attacks at the same time the leaving group leaves
Nucleophile must perform backside attack, which leads to an inversion of stereochemistry
238
Do SN2 reactions invert stereochemistry?
Yes
239
Conditions that facilitate Sn2 reactions
Less substituted carbons (because the alkyl groups create steric hinderance and inhibit the nucleophile from accessing the electrophilic substrate carbon)
240
What does the rate of an SN2 reaction depend on?
The concentrations of both the substrate and the nucleophile
rate = k [Nu] [R - L]
241
Oxidation state
The charge an atom would have if all its bonds were completely ionic
242
Which are the most oxidized functional groups?
Carboxylic acids and their derivatives
243
Which are the second most oxidized functional groups?
Aldehydes, ketones and imines
244
Which are the least oxidized functional groups?
Alcohols, alkyl halides and amines
245
Oxidation
An increase in oxidation state, assisted by oxidizing agents
246
Primary alcohol + pyridinium chlorochromate (PCC)
= Aldehyde
247
Primary alcohol + CrO3
= Carboxylic acid
248
Primary alcohol + sodium dichromate (Na2Cr2O7)
= Carboxylic acid
249
Primary alcohol + potassium dichromate (K2Cr2O7)
= Carboxylic acid
250
Secondary alcohol + oxidizing agent (weak or strong)
= Ketone
251
Aldehyde + oxidizing agent (weak or strong)
= Carboxylic acid
252
Reduction
Decrease in oxidation state, assisted by reducing agents
253
Aldehyde + lithium aluminum hydride (LiAlH4)
= Alcohol
254
Ketone + lithium aluminum hydride (LiAlH4)
= Alcohol
255
Carboxylic acid + lithium aluminum hydride (LiAlH4)
= Alcohol
256
Amide + lithium aluminum hydride (LiAlH4)
= Amine
257
Ester + lithium aluminum hydride (LiAlH4)
= 2 alcohols
258
What do diols protect?
Carbonyl carbons in aldehydes and ketones
259
How to protect alcohol groups?
Convert them to tert-butyl ethers
260
Does a large nucleophile make a strong or weak conjugate acid?
Strong (the nucleophile is therefore a strong nucleophile)
261
Why are aldehydes more reactive than ketones?
Have one alkyl group connected to the carbonyl, whereas ketones have two, creating more steric hindrance, lowering their reactivity
262
Reactivity hierarchy of carboxylic acid derivatives towards nucleophilic attacks
Anhydrides > carboxylic acids and esters > amides
| Derivatives of higher reactivity can form derivatives of lower reactivity, but not vice-versa
263
Which has a lower pKa: ethanol or p-ethylphenol?
p-ethylphenol
264
Why is p-ethylphenol a stonier acid (lower pKa) than ethanol?
Because its phenol group provides resonance and the phenol group is aromatic and an electron-withdrawing group
265
Primary alcohol + strong oxidizing agent
= Carboxylic acid
266
Primary alcohol + weak oxidizing agent
= Aldehyde
267
Mesylate and tosylate
Convert an alcohol into a better leaving group
Useful for nucleophilic substitution reactions because it increases the stability of the product
They are alcohol protecting groups because oxidizing agents cannot react with them
268
Pyridinium chlorochromate (PCC)
Weak oxidizing agent
269
Aldehyde + 2 alcohol
= acetal
270
Ketone + 2 alcohol
= ketal
271
Acetals and ketals
Less reactive than aldehydes and ketones (especially to reducing agents), thereby protecting the functional groups from reacting
272
How can an acetal or ketal be reverted back to aldehyde or ketone?
Using a catalytic acid
273
Phenol oxidation =
Quinone
274
Quinone oxidation + addition of hydroxyl groups =
Hydroxyquinone
275
What chemical properties of ubiquinone (coenzyme Q) allow it to carry out its biological functions?
Ubiquinone has conjugated rings, which stabilize the molecule when accepting electrons
The long alkyl chain in the molecule allows for lipid solubility, which allows the molecule to function in the phospholipid bilayer
276
Phenol
Benzene ring with hydroxyl groups
277
Phenol prefixes
Ortho-, meta-, para-
278
Ortho-
Phenol prefix that indicates the hydroxyl groups are on adjacent carbons
279
Meta-
Phenol prefix that indicates the hydroxyl groups are separated by one carbon
280
Para-
Phenol prefix that indicates the hydroxyl groups are on opposite sides of the ring
281
Why do alcohols have high boiling and melting points?
Because they participate in hydrogen bonding
282
Why do alcohols have high solubility?
Because they participate in hydrogen bonding
283
Why are phenols more acidic than other alcohols?
Because the aromatic ring can delocalize the charge of the conjugate base
284
Example of electron-donating group
Alkyl groups
285
Why do alkyl groups decrease acidity?
They destabilize negative charges due to their electron-donating nature
286
Example of electron-withdrawing group
Electronegative atoms and aromatic rings
287
Why do electron-withdrawing groups increase acidity?
They stabilize negative charges
288
What is mesylate's functional group?
-SO3CH3
289
What is mesylate derived from?
Methanesulfonic acid
290
What is tosylate's functional group?
-SO3C6H4CH3
291
What is tosylate's derived from?
Toluenesulfonic acid
292
Deprotection reaction
Converting acetal or ketal back to aldehyde or ketone by a catalytic acid
293
Quinone
Resonance-stabilized electrophile
294
Examples of quinones
Vitamin K1 (phylloquinone) and Vitamin K2 (menaquinone)
295
Vitamin K1
Phylloquinone
296
Vitamin K2
Menaquinone
297
Ubiquinone (coenzyme Q)
Acts as an electron acceptor in Complexes I, II and III of the electron transport chain
298
Ubiquinol
The reduced version of ubiquinone (coenzyme Q)
299
Why are tertiary alcohols difficult to oxidize?
Because there is no hydrogen attached to the carbon with the hydroxyl group
300
Factors increasing the boiling point
Increasing size of alkyl chain because of increased van der Waals attractions
Hydrogen bonding
301
What is the oxidizing agent in a Jones oxidation reaction?
Dilute sulfuric acid
302
How to convert phenols into hydroxyquinones?
1. Phenol --> quinone through oxidation
| 2. Quinone --> hydroxyquinone through oxidation
303
How to convert acetal to a carbonyl and a dialcohol?
Treatment with aqueous acid
304
Given an alkane, an aldehyde and alcohol with equal-length carbon chains: what is their arrangement in increasing boiling points?
1. Alkane
2. Aldehyde: has dipole
3. Alcohol: can hydrogen bond
305
Is the carbonyl carbon electrophilic or nucleophilic and why?
Electrophilic, because it's partially positive since the oxygen pulls the electrons away from the oxygen
306
How to form an aldehyde?
Primary alcohol + PCC
| Carboxylic acid + reducing agent
307
How to form a ketone?
Secondary alcohol + any oxidizing agent
308
What happens when an aldehyde or ketone is reacted with one equivalent of an alcohol in acidic conditions? What kind of reaction is it?
Aldehyde: Hemiacetal
Ketone: Hemiketal
Nucleophilic addition
309
What happens an an aldehyde or ketone is reacted with two equivalents of alcohol in acidic conditions? What kind of reaction is it?
Aldehyde: Acetal
Ketone: Ketal
Nucleophilic addition (first step to hemiacetal or hemiketal) then nucleophilic substitution (second step to acetal or ketal)
310
What type of reaction occurs when nitrogen, or nitrogen-containing derivates react with aldehydes and ketones?
Nucleophilic substitution and dehydration
311
What functional group forms when nitrogen, or nitrogen-containing derivates react with aldehydes and ketones?
Imine, oximes, hydrazones and semicarbazones
312
What functional group forms when HCN reacts with an aldehyde or ketone?
Cyanohydrin
313
Is the product of a reaction between HCN and an aldehyde or ketone stable?
Yes
314
What functional group is formed when an aldehyde is oxidized?
Carboxylic acid
315
What are common oxidizing agents that can oxidize an aldehyde to a carboxylic acid?
KMnO4, CrO3, Ag2O and H2O2
316
What functional group is formed when aldehydes and ketones are reduced?
Aldehyde: Primary alcohol
Ketone: Secondary alcohol
317
What are common reducing agents that can reduce aldehydes and ketones to alcohols?
NaBH4 and LiAlH4
318
Are aldehydes terminal or internal functional groups?
Terminal
319
Aldehyde suffice if they are in a ring
-carbaldehyde
320
Are ketones terminal or internal functional groups?
Internal
321
Why do carbonyl-containing compounds have higher boiling points than equivalent alkanes?
Because they have dipole interactions
322
Why do alcohols have higher boiling points than compounds containing carbonyls?
Because they can participate in hydrogen bonding
323
What happens when a nucleophile attacks and forms a bond with a carbonyl carbon?
Electrons in the pi bond are pushed to the oxygen atom
If there is no good leaving group (aldehydes and ketones), the carbonyl will remain open and is protonated to form an alcohol
If there is a good leaving group (carboxylic acids and derivates), the carbonyl will reform and kick off the leaving group
324
Hydration reaction
Water adds to a carbonyl, forming a geminal diol
325
What functional group results when an immune tautomerizes?
Enamine
326
Why are hemiacetals and hemiketals difficult to isolate?
They keep reacting to form acetals and ketals because they are very unstable. The hydroxyl group is rapidly protonated and is lost as water under acidic conditions, leaving behind a reactive carbocation. Once the alcohol has been added, the acetal and ketal become more stable as the newly added group is more stable since it is less likely to become protonated and leave, unlike -OH.
327
Can PCC completely oxidize a secondary alcohol?
Yes (to ketone)
328
Water + Carbonyl carbon
= Geminal diol
329
Why are the alpha-hydrogens of aldehydes and ketones acidic (i.e. they deprotonate easily)?
Due to the inductive and resonance effects the carbonyl group offers. The electronegative oxygen atom pulls electron density from the C-H bond, weening it. Once deprotonated, the resonance stabilization of the negative charge between the alpha-carbon, carbonyl carbon and electron-withdrawing carbonyl oxygen increases the stability of this form.
330
Which alpha-hydrogens are more acidic: the ones on aldehydes or the ones on ketones?
Aldehydes
331
Why are the alpha-hydrogens on aldehydes more acidic than the ones on ketones?
Due to the electron-donating characteristics of the second alkyl group in ketones, the carbanion is destabilized, which slightly disfavors the loss of the alpha-hydrogens in ketones as compared to aldehydes
332
How does steric hindrance affect the relative reactivity of aldehydes and ketones?
Aldehydes are more reactive than ketones because they are less stericaly hindered since they have one R group and one H group, while ketones have 2 R groups. The additional alkyl group in ketones gets in the way and makes for a higher-energy, crowded intermediate.
333
Tautomers
Isomers that can be interconverted by the movement of a hydrogen and a double bond
334
Which tautomer of aldehydes and ketones is thermodynamically favored: keto or enol?
Keto
335
Which role does the enolate carbanion play in organic reactions: nucleophile, electrophile, oxidizing agent or reducing agent?
Nucleophiles
336
What conditions favor the kinetic enolate form?
Because the kinetic enolate forms rapidly and can interconvert with the thermodynamic form if given time, the kinetic form is favored by fast, irreversible reactions, such as with a strong, sterically hindered base, and lower temperatures.
337
What conditions favor the thermodynamic enolate form?
The thermodynamic enolate is favored by slower, reversible reactions, with weaker or smaller bases, and higher temperatures.
338
What species acts as the nucleophile in aldol condensation?
The enolate carbanion (the deprotonated aldehyde or ketone)
339
What species acts as the electrophile in an aldol condensation?
The keto form of the aldehyde or ketone
340
Retro-aldol reaction
The reverse of an aldol reaction: a bond between the alpha- and beta-carbons of a carbonyl is broken
341
What conditions favor retro-aldol reactions?
The addition of base and heat
342
Which reactions can aldol condensation be classified under?
Condensation reaction (two molecules are joined to form a single molecule with the loss of a small molecule), dehydration reaction (water is lost), nucleophile-electrophile reaction (a nucleophile pushes an electron pair to form a bond with an electrophile)
343
Alpha-hydrogens
Hydrogens attached to the alpha-carbon
344
Are alpha-hydrogens acidic or basic?
Acidic
345
How can alpha-hydrogens be removed?
With a strong base
346
Does the electron-withdrawing oxygen of the carbonyl strengthen or weaken the C-H bonds on the alpha-carbon?
Weaken
347
Enolate
Results from the deprotonation of the alpha-carbon and is stabilized by resonance with the carbonyl
348
How is the enolate form stabilized?
Resonance due to the carbonyl carbon
349
Do aldehydes and ketones exist in the keto form or the enol form?
Keto
350
How can the enol form become enolate?
It can be deprotonated
351
Are enolates good nucleophiles or electrophiles?
Nucleophiles
352
Michael addition
An enolate attacks and alpha,beta-unsaturated carbonyl, creating a bond
353
Does an imine have a tautomer?
Yes, enamine
354
Which tautomer is more common: imine or enamine?
Enamine
355
Aldol condensation
The aldehyde or ketone acts as both nucleophile and electrophile, resulting in the formation of a carbon-carbon bond in a new molecule called an aldol
In the presence of a base, the alpha-hydrogen is abstracted from an aldehyde, forming the enolate ion (RCHO-). This enolate ion then attacks the carbonyl group of the other aldehyde molecule, forming the aldol
356
Aldol
Contains both an aldehyde and an alcohol functional group
357
Steps of an aldol condensation reaction
1. Condensation
2. Dehydration
Result: alpha,beta-unsaturated carbonyl
358
Aldehyde or ketone + lithium diisopropylamide (LDA)
= More nucleophilic enolate carbanion
359
Lithium diisopropylamide (LDA)
Strong base
360
How to stop an aldol condensation after the aldol formation (i.e. skipping the dehydration step)?
Adding a strong acid
361
What is the most important step in a retro-aldol reaction?
Breaking the carbon-carbon bond to form two aldehydes, two ketones or one of each
362
What is the most important step in an aldol condensation reaction?
Combining two aldehydes, two ketones or one of each
363
What causes the relatively high acidity of carboxylic acids?
The electron-withdrawing oxygen atoms in the functional group and the high stability of the carboxylate anion, which is resonance stabilized by delocalization with two electronegative oxygen atoms
364
Between a monocarboxylic acid, a dicarboxylic acid, and a dicorboxylix acid that has been deprotonated once, which will be the most acidic?
A dicaboxylic acid would be the most acidic, as the second carboxyl group is electron-withdrawing and, therefore, contributes to even higher stability of the anion after loss of the first hydrogen.
A monocarboxylic acid is more acidic than a deprotonated dicarboxylic acid because the carboxylate anion is electron-donating and destabilizes the product of the second deprotonation step, resulting in decreased acidity.
365
What effects do additional substituents have on the acidity of carboxylic acids?
Electron-withdrawing substituents make the anion more stable and, therefore, increase acidity.
Electron-donating substituents destabilize the anion, causing the carboxylic acid to be less acidic.
The closer the substituent is to the carboxylic acid on the molecule, the stronger the effect will be.
366
Amides are formed by reaction with:
Ammonia or an amine
367
Esters are formed by reaction with:
Alcohol
368
Anhydrides are formed by reaction with
Another carboxylic acid
369
Mechanism of nucleophilic acyl substitution reaction
The nucleophile attacks, opening the carbonyl and forming a tetrahedral intermediate --> The carbonyl then reforms, kicking off the leaving group
(The reaction is favored by acidic or basic conditions)
370
Can carboxylic acids be reduced by sodium borohydride?
No
371
Under what conditions will a carboxylic acid spontaneously decarboxylate?
1,3-dicarboxylic acids will spontaneously decarboxylate when heated, due to the stable cyclic intermediate step
372
Cyclic form of amide
Lactam
373
Cyclic form of ester
Lactone
374
Cyclic form of anhydride
Anhydride
375
Nucleophilic acyl substitution
The substitution of an attacking nucleophile for the leaving group of an acyl compound, which includes carboxylic acids, amides, esters and anhydrides
376
Is nucleophilic acyl substitution favored under basic or acidic conditions?
Both
377
Can carboxylic acids be reduced by lithium aluminum hydride?
Yes, they get reduced to primary alcohols
378
Carboxylic acid
Contains a carbonyl and a hydroxyl group connected to the same carbon
379
Are carboxylic acids terminal groups?
Yes
380
Carboxylic acid suffix
-oic acid
381
Salts suffix
-oate
382
Dicarboxylic acid suffix
-dioic acid
383
Physical properties of carboxylic acids
Polar
Participate in hydrogen bonding
Have high boiling points due to the hydrogen bonding
Exist as dimers in solution
Their acidity is enhanced by the resonance between the oxygen atoms
Their acidity can be enhanced by substituents that are electron-withdrawing
Their acidity can be decreased by substituents that are electron-donating
384
Beta-dicarboxylic acids
Like other 1,3 dicarbonyl compounds, they have am alpha-hydrogen that is also highly acidic
385
Are carboxylic acids polar or non-polar?
Polar
386
Can carboxylic acids participate in hydrogen bonding?
Yes
387
Do carboxylic acids have high boiling points?
Yes
388
Why do carboxylic acids have high boiling points?
Because they can form hydrogen bonds
389
How do carboxylic acids exist in solution?
As dimers
390
How do carboxylic acids gain their acidity?
By the resonance between the oxygen atoms and by adding electron-withdrawing substituents to the compound. The closer the substituent is to the carbonyl carbon, the more acidic the compound will be.
391
How can carboxylic acids' acidity be reduced?
By adding electron-donating substituents to the compound. The closer the substituent is to the carbonyl carbon, the less acidic the compound will be.
392
How can carboxylic acids be made?
By the oxidation of primary alcohols or aldehydes using an oxidizing agent like potassium permanganate (KMnO4)m dichromate salted (Na2Cr2O7 or K2Cr2O7) or chromium trioxide (CrO3)
393
What is the product of nucleophilic acyl substitution if the nucleophile is an amine?
Amide
394
What is the product of nucleophilic acyl substitution if the nucleophile is an alcohol?
Ester
395
What is the product of nucleophilic acyl substitution if the nucleophile is another carboxylic acid?
Anhydride
396
How can a carboxylic acid be reduced to a primary alcohol?
Strong reducing agents like lithium aluminum hydride (LiAlH4)
397
Is sodium borohydride (NaBH4) strong enough to reduce a carboxylic acid to a primary alcohol?
No
398
Which species can undergo spontaneous decarboxylation when heated?
Beta-dicarboxylic acids and other beta-keto acids
399
Decarboxylation
Beta-dicarboxylic acids and other beta-keto acids are heated and lose a carbon as carbon dioxide
400
What is the intermediate in a decarboxylation reaction?
A six-membered cyclic intermediate
401
Saponification
Mixing of long-chain carboxylic acids (fatty acids) with a strong base, resulting in the salt we call soap
402
Soap
Contain a hydrophilic carboxylate head and hydrophobic alkyl chain tail
Organize in hydrophilic environments to form micelles
403
Micelle
Dissolves non polar organic molecules in its interior and can be solvated with water due to its exterior shell of hydrophilic groups
404
Jones reagent
Chromium trioxide in aqueous sulfuric acid
405
Is the Jones reagent oxidizing or reducing?
Oxidizing
406
Is the Jones reagent a strong or weak oxidant?
Strong
407
Esterification
Using an acid catalyst, the nucleophilic oxygen of an alcohol attacks the electrophilic carboxyl carbon of a carboxylic acid, ultimately displacing water to form an ester
408
Is the alpha-hydrogen of a carboxylic acid more or less acidic than the hydroxyl hydrogen?
Less
409
What kind of reaction occurs when a carboxylic acid reacts with ammonia to form an amide?
Condensation
410
What is the byproduct of amide formation through reacting carboxylic acids with ammonia?
Water
411
Condensation reaction
Two molecules are joined with the loss of a small molecule, like water
412
What is responsible for the increased rate of hydrolysis in beta-lactams?
Beta-lactams are susceptible to hydrolysis due to the high level of ring strain, which is due to both torsional strain (eclipsing interactions) and angle strain (deviation from 109.5 degrees)
413
What properties account for the differences in reactivity seen between anhydrides, esters and amides with nucleophiles?
Electronic effects like induction have some effect on the reactivity of carbonyl in these three functional groups. Differences in resonance also explain the increased reactivity of anhydrides, in particular. Steric effects could also be significant, depending on the specific leaving group present.
414
Torsional strain
Comes from eclipsing interactions
415
Angle strain
Comes from deviation from 109.5 degrees
416
In the formation of an amide from ammonia and an anhydride, what serves as the nucleophile?
Ammonia
417
In the formation of an amide from ammonia and an anhydride, what serves as the electrophile?
One of the carbonyl carbons of the anhydride
418
Transesterification
The exchange of one esterifying group for another in an ester
Requires an alcohol as a nucleophile
419
How do strongly acidic conditions catalyze the hydrolysis of an amide?
Catalyze amide hydrolysis by protonating the oxygen in the carbonyl
This increases the electrophilicity of the carbon, making it more susceptible to nucleophilic attack
420
How do strongly basic conditions catalyze the hydrolysis of an amide?
Greatly increase the concentration of OH-, which can act as a nucleophile on amide carbonyls
421
How are lactams named?
By the Greek letter of the carbon forming the bond with the nitrogen
422
Fischer esterification reaction
The condensation of carboxylic acids with alcohols to form esters
423
How are lactones named?
By the number of carbons in the ring and the Greek letter of the carbon forming the bond with the oxygen
424
Triacylglycerols
A form of fat storage
| Include 3 ester bonds between glycerol and fatty acids
425
Steric hindrance
When a reaction cannot proceed (or is significantly slowed) because of substituents crowding the reactive site
426
Protecting groups
E.g. acetals
| Are used to increase steric hindrance or otherwise decrease the reactivity of a particular portion of a molecule
427
Induction
Uneven distribution of charge across a sigma bond because of differences in electronegativity
The more electronegative groups in a carbonyl-containing compound, the greater its reactivity
428
Resonance
Experienced through unhybridized p-orbitals, increasing stability
429
Why are conjugated carbonyl-containing compounds more reactive?
Because they can stabilize their transition states
430
Would increasing strain in a molecule make it more or less reactive?
More
431
What causes ring strain?
Torsional strain (eclipsing interactions) and angle strain (deviation from 109.5 degrees)
432
Which carboxylic acid derivatives cannot under nucleophilic substitution reactions?
None
433
How can anhydrides be cleaved?
By the addition of a nucleophile
434
Anhydride + ammonia
Amide + carboxylic acid
435
Anhydride + amine
Amide + carboxylic acid
436
Anhydride + alcohol
Ester + carboxylic acid
437
Anhydride + water
Two carboxylic acids
438
How can amides be hydrolyzed to carboxylic acids?
Under strongly acidic or basic conditions, where the attacking nucleophile is water or a the hydroxide anion
439
Why should esterification reactions not be carried out in water?
Water molecules would hydrolyze the desired products back into the parent carboxylic acid
440
What makes glycine unique among the amino acids?
All amino acids, except glycine, have chiral alpha-carbons. Because the R group of glycine is a hydrogen atom, it is not chiral and therefore is not optically active.
441
What functional groups make amino acids amphoteric?
Carboxylic acids give amino acids their acidic properties because they can be deprotonated
Amino groups give amino acids their basic properties because they can be protonated
442
How are peptide bonds formed?
A condensation reaction, in which water is lost
443
How are peptide bonds cleaved?
Hydrolytic reaction with a strong acid or base
444
Why is the C-N bond of an amide planar?
It has partial double-bond character due to resonance, making it planar
Double bonds exist in a planar conformation and restrict movement
445
What are the four reactants in the Strecker synthesis of an amino acid?
Aldehyde, ammonium chloride (NH4Cl), and potassium cyanide (KCN) are used to make the aminonitrile; water is used to hydrolyze the aminonitrile to form the amino acid.
446
What are the reaction types used in the Strecker synthesis?
Streicher synthesis is a condensation reaction (formation of an imine from a carbonyl-containing compound and ammonia, with loss of water), follow by nucleophilic addition *addition of the nitrile group), follow by hydrolysis
447
What are the four main reactants in the Gabriel synthesis of an amino acid?
Gabriel synthesis begins with potassium phthalimide and diethyl bromomalonate, followed by an alkyl halide. Water is then used to hydrolyze the resulting compound to form the amino acid. While acid and bases are used at various times as catalysts, they are not main reactants.
448
What are the reaction types used in the Gabriel synthesis?
Gabriel synthesis proceeds through two SN2 reactions, hydrolysis and decarboxylation
449
What characteristics make inorganic phosphate so useful for energy transfer biologically?
It contains a very negative charge
When bonded to other phosphate groups in a nucleotide triphosphate, this creates repulsion with adjacent phosphate groups, increasing the energy of the bond
It can be resonance stabilized
450
What is an organic phosphate?
Carbon-containing molecule with phosphate group (e.g. DNA, ATP, GTP)
451
What characteristics of phosphoric acids make them good buffers?
The three hydrogens in phosphoric acid have very different pKa values. This allows phosphoric acid to pick ip or give off protons in a wide pH range, making it a good buffer over most of the pH scale
452
What is the alpha carbon of an amino acid attached to?
An amino group, a carboxyl group, a hydrogen atom and an R group
It is a chiral center (except in glycine)
453
Are eukaryotic amino acids L-amino acids or D-amino acids?
L-amino acids
454
Do eukaryotic amino acids have (S) stereochemistry or (R) stereochemistry?
(S) stereochemistry (except cysteine is (R))
455
All eukaryotic amino acids have (S) stereochemistry, except:
Cysteine
456
How do amino acids exist in neutral solution?
As zwitterions
457
Zwitterions
Dipolar ions
458
Nonpolar, nonaromatic amino acids
Glycine, alanine, valine, leucine, isoleucine, methionine and proline
459
Nonpolar, aromatic amino acids
Tryptophan and phenylalanine
460
Polar, aromatic amino acids
Tyrosine
461
Polar, nonaromatic amino acids
Serine, threonine, asparagine, glutamine and cysteine
462
Negatively charged (acidic) amino acids
Aspartic acid and glutamic acid
463
Positively charged (basic) amino acids
Lysine, arginine and histidine
464
Polypeptides
Made up of multiple amino acids linked by peptide bonds
465
Proteins
Large, folded, functional polypeptides
466
Strecker synthesis
Generates an amino acid from an aldehyde
1. An aldehyde is mixed with ammonium chloride (NH4Cl) and potassium cyanide (KCN)
2. The ammonia attacks the carbonyl carbon, generating an imine
3. The imine is then attacked by cyanide, generating aminonitrile
4. The amininitrile is hydrolyzed by two equivalents of water, generating an amino acid
467
Gabriel synthesis
Generates an amino acid from potassium phtbalimide, diethyl bromomalonate and an alkyl halide
1. Phthalimide attacks the diethyl bromomalonate, generating a phthalimidomalonic ester
2. The pthalimidomalonic ester attacks an alkyl halide, batting an alkyl group to the ester
3. The product is hydrolyzed, creating pthalic acid (with two carboxyl groups) and converting the esters into carboxylic acids
4. One carboxylic acid of the resulting 1,3-dicarbonyl is removed by decarboxylation
468
Inorganic phosphate (Pi)
A buffered mixture of hydrogen phosphate (HPO4^2-) and dihydrogen phosphate (H2PO4-)
469
What forms the backbone of DNA?
Phosphorus in phosphodiester bonds
470
How are phosphodiester bonds formed?
A pyrophosphate (PPi, P2O7^4-) is released and pyrophosphate can then be hydrated to two inorganic phosphates
471
Which amino acids contain sulfur?
Cysteine and methionine
472
Can Strecker synthesis result in an optically active solution?
No, because it contains a planar intermediate that can be attacked from either side by a nucleophile, resulting in a racemic mixture of enantiomers and the solution will therefore be optically inactive
473
Can Gabriel synthesis result in an optically active solution?
No, because it contains a planar intermediate that can be attacked from either side by a nucleophile, resulting in a racemic mixture of enantiomers and the solution will therefore be optically inactive
474
What does infrared (IR) spectroscopy measure?
The absorption of infrared light by specific bonds, which vibrate. These vibrations cause changes in the dipole moment if the molecule that can be measured.
475
What is IR spectroscopy generally used for?
The presence of functional groups to determine the identity of a molecule
476
What two peaks would you expect to see in the IR spectrum of a carboxylic acid?
Broad O-H peak (2800 - 3200 1/cm)
| Sharp carbonyl peak (1700 - 1750 1/cm)
477
What types of molecules can be detected by UV spectroscopy?
Molecules with pi or nonbonding electrons and conjugated systems
478
HOMO in UV spectroscopy
Highest occupied molecular orbital
479
LUMO in UV spectroscopy
Lowest unoccupied molecular orbital
480
In UV spectroscopy, how are HOMO and LUMO related to the absorption wavelength?
The smaller the difference in energy between HOMO and LUMO, the longer the wavelengths that can be absorbed by the molecule
481
What does nuclear magnetic resonance (NMR) spectroscopy measure?
NMR measures alignment of the spin of a nucleus with an applied magnetic field
482
What is NMR spectroscopy generally used for?
Identifying the different types and magnetic environments of protons in a molecule, which allows us to infer the connectivity (backbone) of a molecule
483
What are the units for chemical shift on a standardized NMR spectrum?
Parts per million (ppm)
484
What does it mean for a proton to be deshielded?
Deshielding occurs in molecules that have electronegative atoms that pull electron density away from the hydrogens being measured
485
How does proton deshielding affect its peak in NMR spectroscopy?
Downfield (leftward) shift of the proton peak
486
Spin-spin coupling
Occurs when two protons close to one another have an effect on the other's magnetic environment. This results in the splitting of peaks into doublets, triplets or multiplets, depending on the environment
487
Infrared (IR) spectroscopy
Measures absorption of infrared light, which causes molecular vibration (stretching, bending, twisting and folding)
488
How are IR spectra plotted?
Percent transmittance v. wavenumber (1 / lambda)
489
What is the normal range of an IR spectrum?
4000 to 400 1/cm
490
Where is the fingerprint region of an IR spectrum?
1500 to 400 1/cm
491
Fingerprint region of IR spectrum
1500 to 400 1/cm
| Contains a number of peaks that can be used by experts to identify the compound
492
How would a functional group appear on an IR spectrum?
Vibration of a bond must change the double bond moment
493
O-H peak on IR spectrum
Broad
| 3300 1/cm
494
OH peak of a carboxylic acid on IR spectrum
Broad
| 3000 1/cm
495
N-H peak on IR spectrum
Sharp
| 3300 1/cm
496
C=O peak on IR spectrum
Sharp
| 1750 1/cm
497
Ultraviolet (UV) spectroscopy
Measures absorption of ultraviolet light, which causes movement of electrons between molecular orbitals
498
How are UV spectra plotted?
Percent transmittance or absorbance v. wavelength
499
How would a molecule appear on a UV spectrum?
It must have small enough energy difference between its highest occupied molecular orbital (HOMO) and its lowest unoccupied molecular orbital (LUMO) to permit an electron to move from one orbital to the other
500
Conjugation
Occurs in molecules with unhybridized p-orbitals
501
How does conjugation change a UV spectrum?
It shifts the absorption spectrum to higher maximum wavelengths (i.e. lower frequencies)
502
Nuclear magnetic resonance (NMR) spectroscopy
Measures alignment of nuclear spin with an applied magnetic field, which depends on the magnetic environment of the nucleus itself
Nuclei may be in the lower-energy alpha-state or higher-energy beta-state; radio frequency pulses push the nucleus from the alpha-state to the beta-state, and these frequencies can be measured
503
How are NMR spectra plotted?
Frequency v. absorption of energy
They are standardized by using chemical shift (delta)
They are calibrated during tetramethylsilane (TMS)
504
What is the chemical shift of TMS?
0 ppm
505
Where are higher chemical shifts located on an NMR spectrum?
Downfield (to the left)
506
Where are lower chemical shifts located on an NMR spectrum?
Upfield (to the right)
507
Integration on NMR
Area under the curve
| Proportional to the number of protons contained under this peak
508
How is a proton's (or group of protons') peak split?
n + 1 subpeaks
| n = the number of protons that are three bonds away from the proton of interest
509
Splitting patterns
Doublets, triplets and multiplets
Occur due to coupling between protons on adjacent carbon atoms
510
Where are protons on sp3-hybridized carbons located on NMR?
0 to 3 ppm range
511
Where are protons on sp2-hybridized carbons located on NMR?
4.6 to 6.0 ppm range
512
Where are protons on sp-hybridized carbons located on NMR?
2.0 to 3.0 ppm range
513
Where are aldehydes located on NMR?
9 to 10 ppm range
514
Where are carboxylic acids located on NMR?
10.5 to 12 ppm range
515
Where are aromatic hydrogens located on NMR?
6.0 to 8.5 ppm range
516
In an IR spectrum, how does extended conjugation of double bonds affect the absorbance band of carbonyl (C=O) stretches compared with normal absorption?
The absorbance band will occur at a lower wavenumber
Carbonyl groups in conjugation with double bonds tend to absorb at lower wavenumber because the delocalization of pi electrons causes the C=O bond to lose double bond character, shifting the stretching frequency closer to C-O stretches. Remember that higher-order bonds tend to have higher absorption frequencies, so loss of double-bond character should decrease the absorption frequency of the group.
517
Coupling constant (J)
A measure of the degree of splitting caused by other atoms in the molecule
518
The IR spectrum of a fully protonated amino acid would likely contain:
A sharp peak at 1750 1/cm and a sharp peak at 3300 1/cm
519
What must be true about the two solvents used for an extraction to work?
The two solvents must be immiscible and must have different polarity or acid-base properties that allow a compound of interest to dissolve more easily in one than the other
520
When doing an extraction, would it be better to do three extractions with 10 mL of solvent, or one extraction with 30 mL?
It is better to do three washes with 10 mL than to do one with 30 mL; more of the compound of interest would be extracted with multiple sequential extractions than one large one
521
Would acid dissolve better in aqueous acid or aqueous base?
Acid dissolves better in aqueous base because it will dissociate to form the conjugate base and, being more highly charged, will become more soluble.
Note that like dissolves like applies to polarity; acids and bases dissolve more easily in solutions with the opposite acid-base characteristics.
522
Distillation separates compounds based on what property?
Differences in boiling points
523
If we are given a solution of ether, with a boiling point of 308 K, and methylene chloride, with a boiling point of 313 K, which type of distillation should be used to separate them?
Fractional distillation
524
If we are given a solution of bromobenzene, with a boiling point of 156 C, and camphor, with a boiling point of 204 C, which type of distillation should be used to separate them?
Vacuum distillation because the chemicals have very high boiling points and the decreased ambient pressure will allow them to boil at a lower temperature
525
What properties of molecules do thin-layer chromatography, paper chromatography and standard column chromatography take advantage of to separate compounds?
Charge and polarity
526
Types of column chromatography
Ion-exchange, size-exclusion, and affinity
527
In what way is gas chromatography distinct from all of the other techniques of chromatography?
The same technique of mobile and stationary phases are performed with a gaseous eluent (instead of liquid). The stationary phase is usually a crushed metal or polymer.
528
What is the major historical distinction between HPLC and column chromatography?
HPLC was performed at high pressures, whereas column chromatography uses gravity to pill the solution through the column
529
What is the major modern distinction between HPLC and column chromatography?
HPLC is performed with sophisticated and variable solvent and temperature gradients, allowing for much more specific separation of compounds than column chromatography. High pressures are no longer required.
530
Ion-exchange column chromatography
Column is given a charge, which attracts molecules with the opposite charge
531
Size-exclusion column chromatography
Small pores are used; smaller molecules are trapped, while larger molecules pass through the column
532
Affinity column chromatography
Specific receptors or antibodies can trap the target in the column; the target must then be washed out using other solutions
533
Retardation factor (Rf)
= (distance spot moved) / (distance solvent front moved)
534
Extraction
Combines two immiscible liquids, one of which easily dissolves the compound of interest
Carried out in a separatory funnel : one phase is collected, and the solvent is then evaporated
Acid-base properties can be used to increase solubility
535
Aqueous phase
```
The polar (water) layer
Dissolves compounds with hydrogen bonding or polarity
```
536
Organic phase
The nonpolar layer
| Dissolves nonpolar compounds
537
Wash
The reverse of extraction
| A small amount of solute that dissolves impurities is run over the compound of interest
538
Filtration
Isolates a solid (residue) from a liquid (filtrate)
539
Gravity filtration
Used when the product of interest is in the filtrate
| Hot solvent is used to maintain solubility
540
Vacuum filtration
Used when the product of interest is the solid
| Vacuum is connected to the flask to pull the solvent through more quickly
541
Recrystallization
The product is dissolved in a minimum amount of hot solvent. If the impurities are more soluble, the crystals will reform while the flask cools, excluding the impurities.
542
Distillation
Separates liquids according to differences in their boiling points; the liquid with the lowest bolding point vaporizes first and is collected as the distillate
543
Simple distillation
Can be used if the boiling points are under 150 C and are at least 25 C apart
544
Vacuum distillation
Should be used if the boiling points are over 150 C to prevent degradation of the product
545
Fractional distillation
Should be used if the boiling points are less than 25 C apart because it allows more refined separation of liquids by boiling point
546
Chromatography
Uses two phases to separate compounds based on physical or chemical properties
547
Stationary (absorbent) phase
Usually a polar solid
548
Mobile phase
Runs though the stationary phase and is usually a liquid or gas
Elutes the sample though the stationary phase
549
Do compounds with a higher affinity for the stationary phase have smaller or larger retardation factors?
Smaller
| Therefore, they take longer to pass through, if at all
550
Partitioning
Separating compounds in chromatography, but having one stick to the stationary phase due to its higher affinity for it, while the other one passing through the stationary phase due to its high affinity to the mobile phase
551
Thin-layer and paper chromatography
Used to identify a sample
The card is spotted and developed
Rf values can be calculated and compared to reference values
552
What is the stationary phase in thin-layer and paper chromatography?
Polar material, such as silica, alumina or paper
553
What is the mobile phase in thin-layer and paper chromatography?
Nonpolar solvent, which climbs the card though capillary action
554
Reverse-phase chromatography
Uses a nonpolar card with a polar solvent
555
Column chromatography
Utilizes polarity, size, or affinity to separate compounds based on their physical or chemical properties
556
What is the stationary phase in column chromatography?
Silica or alumina beads
557
What is the mobile phase in column chromatography?
Nonpolar solvent, which travels though the column by gravity
558
Gas chromatography
Separates vaporizable compounds according to how well they adhere to the adsorbent in the column
Can be combined in sequence with mass spectrometry, which ionizes and fragments molecules and passes these fragments through a magnetic field to determine molecular weight or structure
559
What is the stationary phase in gas chromatography?
Crushed metal or a polymer
560
What is the mobile phase in gas chromatography?
Nonreactive gas
561
High-performance liquid chromatography (HPLC)
Similar to column chromatography but uses sophisticated computer-mediated solvent and temperature gradients. It is used if the sample side is small or if forces such as capillary action will affect results. It was formerly called high-pressure liquid chromatography
