Organic chemistry Flashcards
1
Q
what is hybridisation?
A
mixing orbitals to form new hybrid orbitals with different shapes and energies
- in covalent bonding
2
Q
what is the hybridisation in linear?
A
SP (1S + 1P)
- triple bond (2pi and 2 sigma bonds)
- 180 degrees
3
Q
what is the hybridisation in trigonal planar?
A
SP2 (1S and 2P)
- for C=C (1pi and 1 sigma)
- 120 degrees
4
Q
how many pi and sigma bonds in a triple bond?
A
2 pi and 2 sigma
5
Q
how many pi and sigma bonds in a double bond?
A
1 pi and 2 sigma
6
Q
what is hybridisation in tetrahedral?
A
SP3 (1S and 3P)
- 109.5 degrees
- only in c-c not double bonds
- 4 sigma bonds
7
Q
what is trigonal bipyramidal?
A
- has sp3d hybridisation
- has 2 bond angles: 120 and 90
- Axial Positions:
The two axial positions are above and below the equatorial plane - 90 degrees - equatorial positions are perpendicular to axial plane so to the sides - 120 degrees
8
Q
what is hybridisation in octahedral?
A
SP3d2 (1s 3P and 2d)
8
Q
what is hybridisation in trigonal bypyramidal?
A
SP3d (1S 3p and 1 d)
- 90 degrees and 120 degrees
9
Q
what is hybridisation in a double c bond?
A
sp2 - trigonal planar
- 2s overlap with p orbital to form pi bond
- dumbell shape, doesn’t rotate
10
Q
what is hybridisation in a single c bond?
A
sp3 - tetrahedral
- form 4 equivalent sp3 hybrid orbitals - mix of 2s and 3p forms 4 sp3 bc taking electrons up to 2- takes too much energy so just mix electrons instead
11
Q
what is hybridisation in a triple c bond?
A
sp - linear
- sigma bonds overlap
- and pi bonds overlap
- can’t rotate
12
Q
what is a constitutional isomer?
A
same molecular formula but different structural formula (type of structural isomer)
13
Q
what is an electrophile?
A
electron pair acceptor
14
Q
what is a nucleophile?
A
electron pair donor
15
Q
what is a radical?
A
species with an unpaired electron
16
Q
why are radicals bad in the body?
A
- they break peptide bonds - leads to protein degradation especially if high in methionine/cysteine, or membrane proteins
- they damage DNA - break bonds - lead to cancer
- they oxidise amino acids - alters function
17
Q
what are the most susceptible amino acids to radicals?
A
- cysteine due to thiol (SH) group
- methionine due to S
- tryptophan due to indole ring
- tyrosine due to phenol group
18
Q
what are the best amino acids that control radicals?
A
- cysteine too bc of disulphide bonds that stabilise radicals
- methionine too bc they’re radical scavengers
- tyrosine too bc of antioxidant enzyme activity
- histidine bc of metal binding which removes radials
19
Q
where are radicals useful?
A
in NO signalling which:
- relaxes blood vessels
- used in neurotransmission
- immune response as macrophages produce NO which kills pathogens
20
Q
what are the 2 types of stereoisomers?
A
conformational (geometric or optical) and configurational (bonds move so different planes)
21
Q
what is conformational stereoisomerism?
A
caused by rotation around a single bond
- carbon classification - secondary preferred to primary as more stable
22
Q
what is hyperconjugation?
A
delocalisation of electron from sigma bond to partially filled p orbital or pi system
- stabilises
23
Q
what is the D isomer?
A
where OH group on chiral carbon furthest from carbonyl group is on the right
24
what is the L isomer?
where OH group on chiral carbon furthest from carbonyl group is on the left
25
what is syn-addition?
groups are added on the same side, like cis or Z
26
what is anti-addition?
groups are added on the opposite sides, like trans or E
27
What happens when you hydrate an alkene?
You add water to make it an alcohol
28
what is an R isomer?
priority groups around chiral centre go clockwise
29
what is an L isomer?
priority groups around chiral centre go anticlockwise
30
what is molecule called if not an enantiomer?
a diastomer
31
which isomers are used in human protein structures?
only L bc gives uniformity in secondary and tertiary structures
32
which enzyme converts L amino acids to D amino acids?
racemases, flips chiral centre
33
which amino acid isomers are used in bacteria?
D isomers so they are resistant to proteases so are more protected from human immune system
34
what are the 2 types of nucleophilic substitution?
Sn1 and Sn2
35
what is Sn1?
unimolecular nucleophilic sub.
2 step mechanism - goes through 2 transition stages
Bond breaks, leaving group leaves, then nucleophile comes in to attack
- have 2 bumps on the graph
- first step is larger if uses more energy to make intermediate
35
what does an Sn1 curve show?
first peak is normally largest whereas second curve energy only goes from first trough to second peak
(if first curve largest energy = rate determining step)
36
what does Sn1 favour?
secondary and tertiary carbocations, more R groups mean less space for attack
37
what is bad about sn1?
it destroys the enantiomeric purity so molecule is not the same, e.g get R enantiomers if start with S
38
what is Sn2?
biomolecular nucleophilic sub - one step mechanism - nucleophile attacks before leaving group has fully left, creating transition state
- 2 things happen at once
- causes trigonal bipyramidal transition state to lengthen
- forms radicals bc C-hal bond breaks
39
when does Sn2 occur?
when have a strong nucleophile e.g OH-
40
what's good about Sn2?
maintains enantiomeric purity. but can still cause S/R inversion
41
what is a strong nucleophile?
attaches to H (so its a strong base)
- needed for elimination
42
what is a weak nucleophile?
attaches to C (so its a weak base)
43
what are the two types of elimination?
E1 and E2
44
what is E1?
unimolecular elimination
The leaving group leaves first, forming a carbocation (a lonely carbon with a positive charge)
Then a base comes in and removes a hydrogen from a neighboring carbon
The electrons form a double bond
45
when does E1 occur?
when there's a weak base or a stable carbocation intermediate or with heat
46
what does an E1 graph show?
peak of first curve is when bond stretches, at trough the bond breaks and then second peak is where H is removed
47
Define nucleophilic substitution
Nucleophilic substitution is a type of reaction in which a nucleophile replaces a leaving group in a molecule. It commonly occurs in haloalkanes
48
What is Sn1 favoured by?
Tertiary carbons (stable carbocations)
Polar protic solvents (e.g., water, alcohol)
Weak nucleophiles
49
What is Sn2 favoured by?
Methyl or primary carbons (less steric hindrance)
Strong nucleophiles
Polar aprotic solvents (e.g., acetone, DMSO)
50
Describe the energy profile for Sn1
Two energy barriers (transition states)
Intermediate = carbocation
51
Describe the energy profile for Sn2
One energy barrier
No intermediates, only a transition state
52
Describe the transition state of Sn2
Five atoms arranged around the carbon center (a trigonal bipyramidal-like structure)
Partially formed bonds to nucleophile and leaving group
53
In terms of substitution, define primary carbon and explain why this gives rise to Sn2
The carbon bonded to the leaving group is attached to 1 other carbon
Means the nucleophile has space to come in and attack without the leaving group leaving first
54
Which has higher electronegativity, hydrogen or fluorine?
Fluorine
55
Define elimination
A single reactant is split into two products
56
Simply explain an elimination reaction
You have a molecule with:
A carbon chain
A leaving group (like Br⁻ or Cl⁻)
A nearby hydrogen
Now you're adding a base (like OH⁻ or OEt⁻), and instead of replacing the leaving group (substitution), you're eliminating both the leaving group and a hydrogen, creating a double bond (C=C).
That’s an elimination reaction.
57
Explain E2
Strong base comes in and grabs a hydrogen (H)
At the same time:
A double bond forms
The leaving group leaves
It all happens in one move
58
What kind of base is used in E2 vs E2?
Strong in E2, weak or absent in E1
59
What kind of carbon does E1 favour?
Tertiary carbon
60
What kind of molecule does elimination form?
An alkene - double bond
61
What is reduction of carbon?
When carbon atoms are reduced they often form additional bonds to hydrogen
62
Define addition
Two reactants add together to form a single product (opposite to elimination)
63
What is the general formula for open-chain alkanes?
CₙH₂ₙ₊₂
64
What type of bonding exists in alkanes?
Only single covalent (sigma) bonds between carbon atoms
65
What is a homologous series?
A series of compounds where each member differs by CH₂
66
What is the IUPAC naming convention for alkanes?
Prefix (substituent location) – Parent (carbon chain) – Suffix (family, e.g., -ane)
67
What are constitutional (structural) isomers?
Isomers that differ in the connectivity of their atoms
68
What are conformational isomers?
Isomers that differ by rotation around a single bond
69
What is the key difference between conformational and constitutional isomers?
Constitutional isomers have different connectivity; conformational isomers have the same connectivity but differ in spatial arrangement due to bond rotation
70
What is required for conformational isomerism to occur?
Free rotation around single (sigma) bonds
71
What type of intermolecular forces do alkanes have?
Van der Waals (London dispersion) forces
72
How does branching affect boiling point in alkanes?
More branching lowers boiling point due to reduced surface area
73
What are primary, secondary, and tertiary radicals?
Radicals formed when a hydrogen is removed from a primary, secondary, or tertiary carbon
74
What stabilizes alkyl radicals?
Hyperconjugation – delocalization of bonding electrons from adjacent C-H sigma bonds into the empty p orbital
75
What change in hybridization occurs during radical formation?
The carbon changes from sp³ to sp² hybridized
76
What is hyperconjugation?
The stabilizing interaction of sigma C-H bonds with an adjacent empty p orbital on a radical center
77
List four types of reactions alkanes undergo.
1. Combustion
2. Cracking
3. Dehydrogenation
4. Halogenation
78
What is combustion in alkanes?
Burning in oxygen to produce CO₂ and H₂O
79
What is cracking?
Breaking large alkanes into smaller alkanes and alkenes
80
What is dehydrogenation?
Removal of H₂ to form an alkene from an alkane
81
What is halogenation?
A radical reaction replacing a hydrogen with a halogen atom
82
What type of fission occurs in halogenation?
Homolytic fission
83
Why do tertiary carbons form radicals more easily?
They are more stabilized by hyperconjugation and electron-donating alkyl groups
84
What determines product distribution in radical halogenation?
The type of carbon (primary, secondary, tertiary) where hydrogen is abstracted
85
Why does the type of carbon matter in alkane reactions?
Because it affects radical stability and reaction pathway energetics
86
What are the key steps in naming an alkane?
1. Identify the longest carbon chain
2. Number the chain to give substituents lowest numbers
3. Name and locate substituents
4. Arrange substituents alphabetically
87
What are di-, tri-, and tetra- prefixes used for?
Indicating multiple identical substituents (e.g. 2,3-diethyl)
88
How do you handle naming when two substituents are on the same carbon?
List both with correct locant (e.g., 2-methyl-2-propyl-octane)
89
What is meant by the parent name in IUPAC naming?
The root name based on the number of carbons in the longest continuous chain
90
What is the general formula for alkenes?
CₙH₂ₙ (for open-chain alkenes with one double bond)
91
How are alkenes named according to IUPAC?
Prefix – Parent – Suffix (-ene), with the position of the double bond indicated (e.g. octa-1-ene)
92
What is the priority in alkene naming?
The carbon chain containing the double bond gets priority in numbering, and the double bond is given the lowest possible number.
93
What is a constitutional isomer of an alkene?
An isomer with the same molecular formula but a different connectivity of atoms.
94
What is a geometric isomer?
An isomer that differs in spatial arrangement around a double bond due to restricted rotation. Cis/trans, E/Z
95
Why can’t alkenes rotate around the double bond?
Because of the π bond — rotation would break the π orbital overlap, which requires a large amount of energy.
96
What is the difference between 'cis' and 'trans' isomers?
Cis: substituents are on the same side of the double bond; Trans: substituents are on opposite sides.
97
What are 'E' and 'Z' isomers?
Z (zusammen): high-priority groups are on the same side; E (entgegen): high-priority groups are on opposite sides.
98
How is priority determined in E/Z isomerism?
By atomic number — the atom with the higher atomic number gets higher priority.
99
Why do cis double bonds in fatty acids cause kinks?
They disrupt linear packing, introducing bends in the fatty acid chain.
100
How do alkenes react in general?
They undergo electrophilic addition reactions due to electron-rich double bonds. They are more reactive than alkanes due to the Pi bond
101
What types of addition reactions do alkenes undergo? Addition - combining with a positive electrophile
Hydrohalogenation, halogenation, hydration, and hydrogenation.
102
What is hydrohalogenation?
Addition of HX (e.g., HBr) to an alkene, forming a haloalkane.
103
What is halogenation of an alkene?
Addition of X₂ (e.g., Br₂), forming a dihalide.
104
What is hydration of an alkene?
Addition of H₂O (often catalyzed by acid), forming an alcohol.
105
What is hydrogenation of an alkene?
Addition of H₂ across the double bond, forming an alkane.
106
What is Markovnikov’s Rule?
In HX (hydrohalogen) addition, the H attaches to the carbon with more hydrogens, and the X attaches to the more substituted carbon. “The rich get richer” - the hydrogen goes to the side that already has more hydrogens
107
Why does Markovnikov’s Rule work?
Because the more stable carbocation intermediate (more substituted) forms during the reaction.
108
Which carbocation is most stable: primary, secondary, or tertiary?
Tertiary > Secondary > Primary.
109
What stabilizes carbocations?
Hyperconjugation — delocalization of electrons from adjacent C–H sigma bonds.
110
What is syn-addition?
Both atoms add to the same face of the double bond.
111
What is anti-addition?
Atoms add to opposite faces of the double bond.
112
How do alkynes compare to alkenes in reactivity?
They behave similarly but are generally more reactive due to higher π electron density.
113
Can alkynes undergo electrophilic addition?
Yes — alkynes also undergo reactions like halogenation, hydrohalogenation, and hydration. Alkynes do it twice when alkenes do it once
114
What is a π bond?
A sideways overlap of p orbitals above and below the sigma bond plane, found in double and triple bonds.
115
What’s the difference between a sigma (σ) and a pi (π) bond?
Sigma bonds are head-on overlaps of orbitals (stronger, always present), while pi bonds are sideways overlaps and are weaker.
116
Why are alkenes more reactive than alkanes?
Due to the presence of a π bond, which is more exposed and more reactive than σ bonds.
117
Why don’t alkanes have geometric isomers?
Because their single bonds allow free rotation.
118
What is the role of the double bond in alkene reactions?
It acts as a nucleophile, attacking electrophiles in addition reactions.
119
What is an electrophilic addition?
A reaction where an electrophile (positive) reacts with the double bond, adding atoms across it.
120
What is a carbocation?
A carbon with a positive charge
121
What does hyperconjugation stabilise?
Carbocations
122
Why is a methyl group more stable than a hydroxyl group?
Hyperconjugation - the methyl group can donate negative charge
123
What is a haloalkane?
An alkane in which one or more hydrogen atoms have been replaced by halogen atoms (F, Cl, Br, I)
124
What makes haloalkanes polar?
The carbon–halogen bond is polar due to the electronegativity difference between C and the halogen
125
How are haloalkanes named in IUPAC?
Halogen substituents are named as prefixes (e.g., fluoro-, chloro-, bromo-, iodo-) with locants to indicate position
126
Give an example of a properly named haloalkane.
1-chloro-2-fluoroethane
127
What types of isomers can haloalkanes have?
Constitutional, conformational, and optical (enantiomers)
128
What is a conformational isomer?
Isomers with the same connectivity but differ by rotation around a single bond
129
What is an optical isomer?
Non-superimposable mirror image molecules due to a chiral centre
130
How do we label enantiomers using the R/S system?
1. Identify chiral carbon
2. Assign priorities based on atomic number
3. Orient lowest priority group away
4. Trace 1→2→3 path:
Clockwise = R; Anti-clockwise = S
131
What determines group priority in R/S nomenclature?
Atomic number — higher atomic number = higher priority
132
What is the difference between R and S enantiomers?
They are mirror images with different spatial arrangements, affecting smell, taste, and biological activity
133
How does the body distinguish between enantiomers?
Biological receptors are chiral and interact differently with R and S forms
134
What is inversion of configuration in SN2?
The stereochemistry of the product is flipped (Walden inversion)
135
What is an elimination reaction?
A reaction where atoms are removed from a molecule, forming a double bond
136
What happens in an E1 reaction?
1. Leaving group leaves → carbocation forms
2. Base removes proton → alkene forms
137
What happens in an E2 reaction?
Base removes a proton while leaving group leaves simultaneously
(one concerted step)
138
What kind of base favors E2?
Strong bases like OH⁻ or tert-butoxide
139
How are E1 and SN1 related?
Both involve carbocation intermediates and favor similar conditions
140
How are E2 and SN2 related?
Both are one-step reactions, influenced by sterics and base/nucleophile strength
141
What decides between substitution vs. elimination?
- Nucleophile = substitution
- Base = elimination
Also depends on carbon type and reaction conditions
142
Why is stereochemistry important in haloalkane reactions?
Because SN2 and optical isomerism affect the 3D shape and behavior of products
143
What are enantiomers and why are they important in drugs?
Enantiomers are mirror images; one form may be therapeutic, the other toxic (e.g., thalidomide disaster)
144
What is the thalidomide case?
A drug used for morning sickness caused birth defects because one enantiomer was harmful
145
How does the body make D-amino acids if nature uses L-amino acids?
Through specialized enzymes; D-forms are used in bacteria and specific immune functions
146
What’s an example of enantiomers affecting senses?
R-carvone smells like spearmint, S-carvone smells like caraway
147
Why is C–Cl bond more polar than C–F?
Cl is less electronegative than F, but has a longer bond length, resulting in a stronger dipole
148
What is the functional group in alkanols?
–OH (hydroxyl group)
149
How are alkanols named in IUPAC nomenclature?
By identifying the longest carbon chain and replacing the -e of the alkane with -ol; number the chain to give –OH the lowest number.
150
Give the IUPAC name of CH₃CH₂CH₂OH.
Propan-1-ol
151
What does (e)-4-bromobut-2-en-1-ol mean?
Four-carbon chain with:
- Br on carbon 4
- Double bond between C2 & C3 in E configuration
- OH on carbon 1
152
What are the physical properties of alkanols?
They are hydrophilic, polar, reactive, and capable of hydrogen bonding.
153
What happens to solubility of alkanols as chain length increases?
Solubility in water decreases because the non-polar alkyl portion increases.
154
What is a diol?
A molecule with two hydroxyl (–OH) groups.
155
What are the chemical properties of alkanols?
They can act as acids (donate H⁺), bases (accept H⁺), be oxidised, and undergo substitution or elimination.
156
How do alkanols act as acids?
Alcohol + alkali metal → alkoxide + hydrogen gas.
157
How do alkanols act as bases?
Alcohol + acid (e.g., H⁺) → oxonium ion (ROH₂⁺).
158
What happens when a primary alcohol is oxidised?
Alcohol → Aldehyde → Carboxylic acid.
159
What happens when a secondary alcohol is oxidised?
Secondary alcohol → Ketone.
160
Why don’t tertiary alcohols undergo oxidation easily?
They lack a hydrogen on the carbon bonded to the –OH group.
161
What is an example of alcohol oxidation in biology?
Ethanol is oxidised to ethanal (acetaldehyde), which contributes to hangovers.
162
What is the elimination reaction of alkanols?
Alcohol → Alkene + H₂O (requires acid and heat).
163
What is substitution in alcohols?
The –OH group is replaced by another group, often forming an ether.
164
What is an ether?
A compound with a C–O–C linkage, where both sides of the oxygen are alkyl groups.
165
How are ethers named in IUPAC?
Name the smaller alkyl group as an alkoxy substituent, then name the main chain (e.g., methoxyethane).
166
Why are ethers relatively unreactive?
Although they have polar bonds, they lack a good leaving group and are poor nucleophiles.
167
Can ethers form hydrogen bonds with themselves?
No, because they lack an –OH group.
168
Can ethers hydrogen bond with water?
Yes, via the lone pairs on oxygen.
169
What is an amine?
An organic compound derived from ammonia (NH₃), where one or more H atoms are replaced with alkyl or aryl groups.
170
What are the types of amines?
Primary (1°), Secondary (2°), and Tertiary (3°), based on how many alkyl groups are attached to the nitrogen.
171
Give an example of a primary amine.
Methylamine (CH₃NH₂).
172
What is a quaternary ammonium ion?
A nitrogen atom bonded to four alkyl groups, carrying a positive charge (e.g., tetramethylammonium).
173
How are amines named?
Name the alkyl groups attached to nitrogen and add “-amine” or “ammonium” if positively charged.
174
What is N-methyl-ethanamine?
A secondary amine with a methyl group and an ethyl group on nitrogen.
Methyl group, then Nitrogen, then 2 carbons
175
Why do amines have relatively high boiling points?
Because they can form hydrogen bonds via their nitrogen lone pair.
176
What are the properties of the ammonium ion?
Positively charged, highly polar, often soluble in water.
177
What kind of reaction do amines undergo?
Nucleophilic addition-elimination, where the nitrogen lone pair attacks an electrophilic carbon.
178
What is the importance of the nitrogen lone pair in amine chemistry?
It makes amines good nucleophiles and bases.
179
What is an imine?
A compound formed when an amine reacts with a carbonyl compound (C=N bond).
180
Why does the effect of –OH diminish with a longer carbon chain in alcohols?
Because the growing hydrophobic alkyl chain reduces the overall polarity and hydrogen bonding ability.
181
Why are amines more reactive than alcohols?
Due to the higher basicity and nucleophilicity of the nitrogen lone pair compared to the oxygen in alcohols.
182
Why is methanoic acid related to being “blind-drunk”?
Methanol is oxidised in the body to formaldehyde and formic acid, which are toxic to the optic nerve.
183
What is the result of oxidation in primary, secondary, and tertiary alcohols?
Primary alcohol → Aldehyde → Carboxylic acid
Secondary alcohol → Ketone
Tertiary alcohol → No reaction (no hydrogen to remove)
184
What is an amine?
An amine is a molecule where one or more hydrogens from ammonia (NH₃) are replaced by alkyl groups
185
What is the functional group in carboxylic acids?
–COOH (carboxyl group)
186
Why is the carbon in the carboxyl group partially positive?
Because both oxygens are more electronegative and pull electrons away from the carbon
187
Why is the OH hydrogen in a carboxylic acid acidic?
Because the electron-withdrawing effect of the carbonyl oxygen makes the O–H bond weaker and more polar
188
How are carboxylic acids named in IUPAC?
By replacing the -e in the parent alkane name with -oic acid
189
Give the IUPAC name for CH₃COOH.
Ethanoic acid
190
What does '2-hydroxypropanoic acid' mean?
A 3-carbon carboxylic acid with an –OH group on carbon 2
191
What does '2-ketopropanoic acid' mean?
A 3-carbon carboxylic acid with a C=O group (ketone) on carbon 2
192
What does '2-aminopropanoic acid' mean?
A 3-carbon carboxylic acid with an –NH₂ group on carbon 2
193
What does the Greek letter α (alpha) mean in naming?
The carbon adjacent to the carboxylic acid group
194
What are the physical properties of carboxylic acids?
They are polar, hydrophilic (short chains), reactive, and can hydrogen bond
195
Why do carboxylic acids have high boiling points?
Due to hydrogen bonding between the –OH and C=O groups
196
Why do longer-chain carboxylic acids become less soluble?
The non-polar alkyl chain becomes dominant, making the molecule more hydrophobic
197
What happens in esterification?
A carboxylic acid reacts with an alcohol to form an ester and water
198
What is the general reaction for esterification?
Carboxylic acid + alcohol → ester + water (in acid, with heat)
199
What is the name of the ester formed from ethanol and ethanoic acid?
Ethyl ethanoate
200
What is the functional group in esters?
–COO– (carbonyl carbon bonded to another oxygen)
201
What is ester hydrolysis?
Breaking an ester into a carboxylic acid and alcohol using water
202
What is saponification?
Ester hydrolysis using a base, forming a carboxylate salt and alcohol
203
What are some uses of esters?
Fragrances, flavors, solvents, plasticizers, fats, and oils
204
What happens in amide formation?
A carboxylic acid reacts with an amine to form an amide and water
205
What is the functional group of an amide?
–CONH₂
206
What is amide cyclisation?
When a molecule with both an amine and carboxylic acid reacts with itself to form a cyclic amide (lactam)
207
What is a peptide bond?
An amide bond between two amino acids (–CO–NH–), formed during protein synthesis
208
What two groups react to form a peptide bond?
Amino group (–NH₂) of one amino acid and carboxyl group (–COOH) of another
209
What determines the acidity of a carboxylic acid?
The stability of the carboxylate ion formed after losing H⁺
210
What stabilizes the carboxylate ion?
Resonance: the negative charge is delocalized between the two oxygen atoms
211
Why is lactic acid more acidic than propanol?
Because the carboxylic acid can stabilize the negative charge; alcohols cannot
212
What does 'amide formation is a condensation reaction' mean?
It means water is lost when the amine and acid join to form the amide bond
213
Why does the amine group get protonated before the carboxyl group in cyclisation?
Because the nitrogen has a higher pKa and acts as a better base
214
What is the Ramachandran plot?
A graph showing allowed angles of backbone rotation in proteins (ϕ and ψ angles)
215
Where do α-helices and β-sheets appear on a Ramachandran plot?
α-helices: bottom left region
β-sheets: top left region
216
Why are glycine and proline structurally unique?
Glycine is very flexible (no side chain); proline is rigid (cyclic side chain)
217
What are the two 'non-standard' natural amino acids?
Selenocysteine and pyrrolysine
218
Where are selenocysteine and pyrrolysine found?
In some bacteria and archaea; they are genetically encoded by UGA and UAG codons
219
What is an amide functional group?
–CONH₂, or more generally:
R–C(=O)–NR'R"
It has:
A carbonyl group (C=O)
Directly bonded to a nitrogen atom (N)
220
What group is lactic acid?
Carboxylic acid
221
What is the functional group in aldehydes and ketones?
The carbonyl group: C=O
222
How is a ketone defined?
A molecule where the C=O group is within a carbon chain
223
How is an aldehyde defined?
A molecule where the C=O group is at the end of a carbon chain
224
How are ketones named in IUPAC?
Replace -e with -one; number the chain to give the C=O the lowest number
## Footnote
Example: propanone
225
How are aldehydes named in IUPAC?
Replace -e with -al; no number is needed because the C=O is always at carbon 1
## Footnote
Example: ethanal
226
Why are aldehydes more reactive than ketones?
Because the carbon in aldehydes is less hindered and more electrophilic due to having only one alkyl group
227
Can aldehydes be oxidised?
Yes, to form carboxylic acids
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Can ketones be oxidised?
Not easily; they generally do not oxidise further without breaking the carbon chain
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What happens when a ketone or aldehyde is reduced?
They form alcohols:
- Aldehyde → primary alcohol
- Ketone → secondary alcohol
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What type of reaction do aldehydes and ketones undergo?
Nucleophilic addition to the carbonyl group
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Why does nucleophilic addition occur at the carbonyl carbon?
Because the C=O bond is polar; the carbon is partially positive and attracts nucleophiles
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What is a hemiacetal?
A molecule formed when an alcohol adds to an aldehyde
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What is a hemiketal?
A molecule formed when an alcohol adds to a ketone
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What is an acetal?
Formed when a second alcohol adds to a hemiacetal, replacing the –OH with –OR
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What is a ketal?
Formed when a second alcohol adds to a hemiketal, replacing the –OH with –OR
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What is the difference between a hemiacetal and an acetal?
Hemiacetal: has –OH and –OR groups;
Acetal: has two –OR groups
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What is keto-enol tautomerism?
A reversible reaction between a ketone (or aldehyde) and its enol form (C=C–OH)
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What is the enol form of a carbonyl compound?
It contains a double bond and an alcohol group: C=C–OH
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Why is tautomerism biologically important?
It allows carbonyl groups to move and facilitates biochemical reactions like glycolysis
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What is the aldol reaction?
A reaction where an enolate ion attacks another carbonyl compound, forming a β-hydroxy carbonyl compound
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What functional group does an enolate ion contain?
A negatively charged oxygen and a double bond: C=C–O⁻
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What molecule forms from the aldol reaction in glycolysis?
Fructose-1,6-bisphosphate, from G3P and DHAP
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What is an imine?
A compound with a C=N double bond formed from an aldehyde/ketone + a primary amine
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What is transamination?
The process of transferring an amino group from one molecule to another
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What enzyme helps with transamination in humans?
Pyridoxal phosphate (PLP), derived from vitamin B6
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What’s the difference between internal and external aldimines?
External: amine from the substrate binds to PLP;
Internal: amine from the enzyme is still bound to PLP
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What is a Schiff base?
Another name for an imine, especially when used in enzyme catalysis
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Why is propanone the smallest possible ketone?
Because it’s the smallest molecule with a carbonyl between two carbons (3 total atoms)
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What are the key roles of hemiacetal and hemiketal formation?
They help form cyclic structures of sugars like glucose and fructose
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What is the defining feature of an aromatic compound?
A planar ring structure with delocalised π electrons (conjugated system), following Hückel’s rule
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What is benzene?
A 6-carbon aromatic ring with alternating double bonds (delocalised electrons in a π system)
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What is Hückel’s Rule?
A molecule is aromatic if it has (4n + 2) π electrons (where n is a whole number)
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Why is benzene unusually stable?
Because of resonance — the electrons are delocalised over the ring, reducing reactivity
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What are common aromatic compounds?
Benzene, toluene, phenol, aniline, benzoic acid
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What are the names for substituted benzenes?
Methylbenzene = toluene
Benzenol = phenol
Benzenamine = aniline
Benzenecarboxylic acid = benzoic acid
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What is the difference between phenyl and benzyl groups?
Phenyl = benzene ring directly attached
Benzyl = benzene ring attached via a CH₂ group
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What are ortho, meta, and para positions on a benzene ring?
Ortho (o-) = positions 1,2
Meta (m-) = positions 1,3
Para (p-) = positions 1,4
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What is 2-hydroxybenzoic acid also called?
o-hydroxybenzoic acid or salicylic acid
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How is aromaticity different from just having a ring?
Aromaticity requires a cyclic, planar structure with delocalised π electrons obeying Hückel’s rule
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What makes aromatic compounds less reactive than alkenes?
Their π electrons are stabilised (delocalised), so they don't readily participate in addition reactions
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What type of reactions do aromatic compounds undergo?
Electrophilic substitution reactions
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Why doesn’t benzene do addition reactions like alkenes?
Because it would destroy its aromatic stability
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What is electrophilic aromatic substitution (EAS)?
A reaction where an electrophile replaces a hydrogen on the benzene ring
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What is required for EAS reactions to occur?
A very strong electrophile, often with acid catalysts (like AlCl₃ or H₂SO₄)
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What is Friedel–Crafts alkylation?
EAS reaction where an alkyl group is added to benzene using an alkyl halide and AlCl₃
