Chapter 3 Flashcards
(286 cards)
1
Q
what are the prefixes of compounds from 1 to 12 carbons in a chain (no branching)
A
2
Q
What is the MF for non branching carbon chains
A
3
Q
what are alkanes
A
*only carbon and hydrogen atoms
*only single bonds (saturated of H atoms)
4
Q
what suffix does groups take when in the form of substituents?
A
-yl
5
Q
From which end of the parent chain do you have to start numbering?
A
end that has the highest priority group
6
Q
What’s the decreasing order of priority for numbering the main chain?
A
carboxylic acid>aldehyde>ketone>alcohol>amine>alkene>alkyne>alkyl (R) and halides
7
Q
when name of compound given how do we determine the end where we start numbering?
A
the end with the last suffix in the name
8
Q
What exactly is considered the parent chain?
A
longest continuous carbon chain with the most substituents connected to it
9
Q
How do you determine the order which to name substituents? How/where is it named?
A
alphabetically
as prefix(-yl) of the main chain
10
Q
When is unsaturation named?
A
immediately after the parent chain in the name
11
Q
When are functional groups named in the name? And how do they appear?
A
after unsaturation
as suffixes
12
Q
When is stereoisomerism named?
A
they appear first before substituents
13
Q
What are the rules for putting the names together?
A
14
Q
What should you do first when trying to name a compound?
A
15
Q
What is the classification of carbon atoms?
A
*not to be confused with the numbering of carbon atoms
16
Q
name this
A
17
Q
name this
A
18
Q
name this
A
19
Q
How do you name a substituent that has two or more of the same group on the same carbon?
A
20
Q
name this
A
21
Q
What do we do of the substituents are at equal distance from either end of the main chain?
A
chose the name that gives the lower numbering at the first point of difference
22
Q
How do you decide which subst takes the lowest number when equidistant from either ends of main chain?
A
alphabetical order: lower alphabet=lower number
23
Q
what is the general formula for cycloalkanes?
A
24
Q
how do you name cycloalkanes?
A
25
what do you change from the name of cycloalkanes when they are alkyl groups?
26
How else do you call E/Z isomers for cyclics?
just cis and trans
27
what is the difference between naming a compound cycloalkyl-alkane or alkyl-cycloalkane?
28
name this
29
name this
30
what happens when both alkane and cyclalkane have the same number of c atoms?
the naming system is alkyl-cycloalkane
31
What is a rule of rings that have more than one substituents when it comes to the direction of numbering?
32
Explain this:
33
hoe do you name branched (complex substituents)?
*name of the branch is 6-(2-methylbutyl)
34
name this
35
how do you use common acceptable IUPAC names?
36
what to do when more than one ring is attached to an alkane?
name the compound cycloalkylalkane
37
how do you name alkyl halides?
38
How do alcohols appear as bondline and how are they written in the name?
39
what is the general formula for alkenes?
40
what type of bonds are found in alkene and cycloalkenes?
double bonds
41
When and how does the numbering of alkenes is named?
42
How do you number cycloalkenes?
43
How do you name alkenes and cycloalkenes with two or more double bonds?
44
how do you name alcohols containing double bonds? priority? suffix?
45
Explain the stereochemistry of double bonds:
what is cis and trans
46
Explain the stereochemistry of cyclics:
what is cis and trans
47
What is E/Z and when are they typically used?
48
How do you name alkynes? suffix? priority?
49
general formula of alkynes
50
51
what are the five columns? (general format of names)
52
What is functional class naming system?
53
what are the three non covalent interractions?
London dispersion forces, dipole–dipole interactions, and hydrogen bonding.
54
What determines the boiling point of a compound, and why is it essential for vaporization to occur?
determined by the strength of the attractive forces between individual molecules. For vaporization to occur, these forces must be overcome
55
How do strong attractive forces between molecules influence the boiling point of a compound?
If a compound's molecules are held together by strong forces, a significant amount of energy is required to pull the molecules away from each other. Consequently, the compound will have a high boiling point.
56
Are alkanes polar? why?
Alkanes, composed of carbon and hydrogen, have nonpolar bonds due to the similar electronegativities of carbon and hydrogen. The lack of significant partial charges on the atoms results in alkanes being neutral nonpolar molecules, giving them an oily feel.
57
What factors determine the strength of London dispersion forces in alkane molecules?
epends on the area of contact between the molecules. The greater the area of contact, the stronger the London dispersion forces. Boiling points of alkanes increase with molecular weight as each additional methylene (CH2) group increases the area of contact.
58
ow does branching affect the boiling point of alkane molecules, and why does branching reduce the boiling point?
Branching lowers a compound’s boiling point by reducing the area of contact between molecules. Highly branched molecules have less surface area in contact compared to their unbranched counterparts. As a result, if two alkanes have the same molecular weight, the more highly branched one will have a lower boiling point.
59
How do hydrogen bonds' strength compare to other dipole-dipole interactions and LDF?
Hydrogen bonds are stronger than other dipole–dipole interactions, which are stronger than
London dispersion forces.
60
in what arrangement are the strongest hydrogen bonds?
linear - the two electronegative atoms and the hydrogen between them lie on a straight line.
61
What makes alcohols have higher boiling points than ethers despite their similar weight?
they have many hydrogen bonds and overall requires more energy to break the bonds
62
Do molecules with net dipole moments repel or attract each other in space?
Attract
63
how do hydrogen bonding work?
64
Why would two constitutional isomers have very different BP?
one has hydrogen bonds and the other dipole-dipole interactions only
65
What type of interactions do hydrocarbons mainly have?
LDF
66
What does the strength of LDF depend on?
surface area of hydrocarbons:
67
Are hydrocarbons polar molecules?
no
68
As hydrocarbons get large, the more _______ and higher _______
more polarizable
higher MP and BP
69
What is polarizability of a molecule?
70
How do cycloalkanes compare to their corresponding alkanes in terms of BP and MP?
71
Which is more stable ? branched or unbranched molecules? why?
72
What are the solubility rules?
73
What are the solubility trends of alcohols, amines and carboxilic acid?
74
Compare branched to unbranched by contact surface, LDF, BP, MP, delta H and stability
75
answer by most linear or more branched
most linear, most branched
76
what are conformations
77
what are conformers?
78
Which molecular stucture is used for conformers
newman projection
79
How are compounds only containing carbon and hydrogen called?
hydrocarbons
80
What are homologous series?
family of compounds in which each member differs from the one before it in the series by one methylene (CH2) group.
81
What are the members of a homologous series called?
homologues
82
Name CH3CH2CH2CH3
butane
83
Name CH3CH3
ethane
84
Name CH3CH3
ethane
85
Name CH4
methane
86
Which of the four has one alternate structure. How is it called?
methane CH4; ethane C2H6; propane C3H8; butane C4H10
butane C4H10
isobutane
87
What is a carbon bonded to 1 H and 2 CH3 groups called?
an ”iso“ structural unit
88
What is the systematic name of isoheptane?
2-methylhexane
89
What is an alkyl group?
Removing a hydrogen from an alkane
90
What is another name for an alkyl group?
alkyl substituent
91
What does the R- in some structure represent?
an alkyl group
92
If a hydrogen in an alkane is replaced by an OH, the compound becomes an ________.
alcohol
93
If a hydrogen in an alkane is replaced by an NH2, the compound becomes an ________.
amine
94
If a hydrogen in an alkane is replaced by an halogen, the compound becomes an ________.
alkyl halide
95
If a hydrogen in an alkane is replaced by an OR, the compound becomes an ________.
ether
96
how do you make a propyl group versus an isopropyl group?
97
What is up with these two structures?
They are identical
98
What are the rules for naming butyl groups?
*butyl and isobutyl groups, have a hydrogen removed from a primary carbon.
*sec-butyl group has a hydrogen removed from a secondary carbon (sec-, sometimes abbreviated s-, stands for secondary)
*tert-butyl group has a hydrogen removed from a tertiary carbon (tert-, often abbreviated t-, stands for tertiary). A tertiary carbon is bonded to three other carbons.
99
Why can the "sec-" be only used by the butyl group?
*A chemical name must specify one compound only.
100
Why can't "sec-pentyl" group exist?
*removing a hydrogen from a secondary carbon of pentane produces one of two different alkyl groups, depending on which hydrogen is removed
ex: sec-pentyl chloride would specify two different alkyl chlorides, so it is not a correct name.
101
Which alkyls can use the prefix "tert-"?
both tert-butyl and tert-pentyl compounds
*“tert-hexyl” cannot be used because it describes two different alkyl groups.
102
What does tert-butyl and tert-pentyl look like in bondline?
103
What does sec-butyl look like in bondline?
104
Whenever the prefix “iso” is used, how are the iso structural unit and the group replacing a hydrogen placed?
the iso structural unit is at one end of the molecule and the group replacing a hydrogen is at the other end
105
What exactly is an iso group?
a methyl group on the next-to-the-last carbon in the chain
106
What is the same for substituent placement for all isoalkyl compounds but different for isopropyl?
all isoalkyl compounds have the substituent (OH, Cl, NH2, and so on) on a primary carbon, except for isopropyl, which has the substituent on a secondary carbon.
107
How can a sec-propyl also be called?
isopropyl
108
How is the substituent in red called?
1. using common name
2. using IUPAC (systematic)
1. isopropyl
2. 1-methylethyl
109
How is the substituent in red called?
1. using common name
2. using IUPAC (systematic)
1. isobutyl
2. 2-methylpropyl
110
How is the substituent in red called?
1. using common name
2. using IUPAC (systematic)
1. sec-butyl
2. 1-methylpropyl
111
How is the substituent in red called?
1. using common name
2. using IUPAC (systematic)
1. tert-butyl
2. 1,1-methylethyl
112
How is the substituent in red called?
1. using common name
2. using IUPAC (systematic)
1. isopentyl
2. 3-methylbutyl
113
How is the substituent in red called?
1. using common name
2. using IUPAC (systematic)
1. isohexyl
2. 4-methylpentyl
114
Do common names require numbering?
Only systematic names have numbers; common names never contain numbers.
115
Which one is a correct name?
B
116
What are general rules of numbering an alkyl chain attached to a main chain (when it is a substituent).
1. the carbon attached to the main chain is always carbon-1 of the substituent
2. number outside the parenthesis is the placement on the main chain and the number inside the parenthesis is a placement on the substituent chain
3. unlike alphabetical naming on the main chain, the prefixes are included in the alphabetization; ex: "diethyl" we would consider "d" in opposed to "e"
117
In what situation does a substituent on a carbon ring don't need a number?
when it is the only one
118
How do you name and number substituents on a carbon ring when there is two or more?
*listed in alphabetical order, and the substituent given the number-1 position is the one that results in a second substituent getting as low a number as possible.
*If two substituents have the same low numbers, the ring is numbered—either clockwise or counterclockwise—in the direction that gives the third substituent the lowest possible number.
119
What is an alkyl halide?
How are they classified?
*compound in which a hydrogen of an alkane has been replaced by a halogen
*primary, secondary, or tertiary, depending on the carbon to which the halogen is attached
120
How do you name alkyl halides?
- common name
- systematic name
*common name:
name of the alkyl group, followed by the name of the halogen—with the “ine” ending of the halogen name (fluorine, chlorine, bromine, and iodine) replaced by “ide” (fluoride, chloride, bromide, and iodide)
*systematic name:
alkyl halides are named as substituted alkanes. The prefixes for the halogens end with “o” (that is, fluoro, chloro, bromo, and iodo).
121
What is another name for alkyl halides?
haloalkanes
122
What is an ether?
What are the two types?
123
How do you name ethers?
1. common name
2. systematic name
1. names of the two alkyl substituents (in alphabetical order), followed by the word “ether”
2. as an alkane with an RO substituent. The substituents are named by replacing the “yl” ending in the name of the alkyl substituent with “oxy.”
124
How do you name alcohols?
1. common name
2. systematic name
1. name of the alkyl group to which the OH group is attached, followed by the word “alcohol.”
2. replacing the “e” at the end of the name of the parent hydrocarbon with “ol.”
When necessary, the position of the functional group is indicated by a number immediately preceding the name of the parent hydrocarbon or immediately preceding the suffix.
If there are two OH groups, the suffix “diol” is added to the name of the parent hydrocarbon.
125
What is the difference between primary, secondary and tertiary amines?
depending on how many alkyl groups are attached to the nitrogen:
126
What is an amine?
compound in which one or more hydrogens of ammonia have been replaced by alkyl groups.
127
How do you name amines?
1. common name
2. systematic name
1. names of the alkyl groups bonded to the nitrogen, in alphabetical order, followed by “amine.” The entire name is written as one word (unlike the common names of alcohols, ethers, and alkyl halides
2. The “e” at the end of the name of the parent hydrocarbon is replaced by “amine”
a number identifies the carbon to which the nitrogen is attached, and the number can appear before the name of the parent hydrocarbon or before “amine.”
The name of any alkyl group bonded to nitrogen is preceded by an “N” (in italics) to indicate that the group is bonded to a nitrogen rather than to a carbon.
doesn't matter substituent on a carbon or a nitrogen, they are placed in alphabetical order.
128
How do you name nitrogen compounds with four alkyl groups attached to the nitrogen—thereby giving the nitrogen a positive formal charge?
they are quaternary ammonium salts
Their names consist of the names of the alkyl groups in alphabetical order, followed by “ammonium” (all one word) and then the name of the accompanying anion as a separate word.
129
What is the bond strength trend in alkyl halides?
the C ¬ X bond becomes longer and weaker as the size of the halogen increases because the electron density of the orbital decreases with increasing volume.
130
What is the structure of an alcohol?
the geometry of the oxygen in an alcohol; it is the same as the geometry of the oxygen in water
oxygen in an alcohol is sp3 hybridized, as it is in water. Of the four sp3 orbitals of oxygen, one overlaps an sp3 orbital of a carbon, one overlaps the s orbital of a hydrogen, and the other two each contain a lone pair.
131
What is the structure of alkyl halides?
like alkanes but a halogen replaces a hydrogen
132
What is the structure in ethers?
oxygen in an ether same geometry as the oxygen in water.
same structure as a water molecule with alkyl groups in place of both hydrogens
133
What is the structure of amines?
nitrogen in an amine same geometry as the nitrogen in ammonia
nitrogen is sp3 hybridized as in ammonia, with one, two, or three of the hydrogens replaced by alkyl groups. (primary, secondary, or tertiary)
134
What is the boiling point (bp) of a compound?
temperature at which a compound's liquid form becomes a gas (vaporizes).
135
What determines the boiling point of a compound?
on the strength of the attractive forces between individual molecules
136
How do strong attractive forces affect the boiling point?
Strong forces result in a high boiling point because more energy is needed to pull molecules away from each other.
137
What are London dispersion forces?
weak induced-dipole–induced-dipole interactions that hold neutral nonpolar molecules together.
138
How does molecular weight affect London dispersion forces? Due to what?
The greater the molecular weight, the stronger the London dispersion forces
due to increased area of contact between molecules.
139
Why do alkanes with higher molecular weights have higher boiling points?
Higher molecular weights mean more methylene (CH2) groups, increasing the area of contact between molecules and strengthening London dispersion forces.
140
How does branching affect boiling points?
Branching decreases boiling points by reducing the area of contact between molecules.
Highly branched molecules have lower boiling points compared to their unbranched counterparts of the same molecular weight.
141
What other force than LDF affect the boiling points of a series of ethers, alkyl halides, alcohols, or amines?
dipole-dipole interactions
the polar C ¬ Z bond. Recall that the C ¬ Z bond is polar because nitrogen, oxygen, and the halogens are more electronegative than the carbon to which they are attached
142
Why are molecules with polar bonds attracted to one another?
because they can align themselves in such a way that the positive end of one dipole is adjacent to the negative end of another dipole.
143
Do ethers or alkanes have higher bp for the same molecular weight? Why?
Ethers generally have higher boiling points than alkanes of comparable molecular weight
because both London dispersion forces and dipole–dipole interactions must be overcome for an ether to boil.
144
What must be overcome for an alkyl halide to boil?
Both London dispersion forces and dipole–dipole interactions
145
How do both interactions strengthen as the halogen atom increases in size?
Both interactions strengthen because a larger halogen atom results in a larger electron cloud, leading to increased contact area and polarizability.
146
What is polarizability, and how does it relate to electron cloud size?
Polarizability refers to how readily an electron cloud can be distorted to create an induced dipole.
Larger electron clouds have greater polarizability.
147
Why do alkyl halides with larger halogen atoms have higher boiling points?
due to stronger London dispersion forces and dipole–dipole interactions resulting from larger electron clouds and greater polarizability.
148
How does the boiling point of alkyl halides change as the size of the halogen atom increases?
Comparing alkyl halides with the same alkyl group, an alkyl fluoride has a lower boiling point than an alkyl chloride, which has a lower boiling point than an alkyl bromide.
149
Why do alcohols have higher boiling points than ethers with similar molecular weights?
because, in addition to London dispersion forces and dipole–dipole interactions, they can form hydrogen bonds.
150
What is a hydrogen bond?
a special type of dipole–dipole interaction between a hydrogen atom attached to an electronegative atom (such as oxygen, nitrogen, or fluorine) and a lone pair of electrons on another electronegative atom.
151
How does the strength of a hydrogen bond compare to other dipole–dipole interactions?
stronger than other dipole–dipole interactions but weaker than covalent bonds.
152
What type of hydrogen bonds are the strongest?
The strongest hydrogen bonds are linear, where the two electronegative atoms and the hydrogen between them lie on a straight line.
153
Why do alcohols have much higher boiling points than ethers with similar molecular weights?
due to the presence of hydrogen bonds. Although each individual hydrogen bond is weak, the cumulative effect of many hydrogen bonds in alcohols requires extra energy to break, resulting in higher boiling points.
154
How does the strength of individual hydrogen bonds compare to covalent bonds?
Individual hydrogen bonds are weak, requiring only about 5 kcal/mol to break, whereas covalent bonds are much stronger.
155
What is the dramatic effect of hydrogen bonding on the boiling point of water?
Hydrogen bonding significantly raises the boiling point of water. Despite its low molecular weight (18), water has a boiling point of 100°C due to the extensive network of hydrogen bonds between water molecules.
156
How does the boiling point of water compare to that of methane, and why?
Water has a much higher boiling point (100°C) compared to methane (-167.7°C) despite their similar molecular weights because water molecules can form hydrogen bonds, whereas methane molecules cannot.
157
By what type of bonds do the two strands in DNA hold together?
H-bond
158
Why do primary and secondary amines have higher boiling points than ethers with similar molecular weights?
Primary and secondary amines have higher boiling points due to the formation of hydrogen bonds between amine molecules.
159
Why can't tertiary amines form hydrogen bonds between their own molecules?
Tertiary amines do not have a hydrogen atom attached to the nitrogen atom, so they cannot form hydrogen bonds between their own molecules.
159
How do the strength of hydrogen bonds in amines compare to those in alcohols?
Hydrogen bonds between amine molecules are weaker than those between alcohol molecules because nitrogen is less electronegative than oxygen.
159
Why do primary amines have higher boiling points than secondary amines?
Primary amines have stronger dipole–dipole interactions than secondary amines, making hydrogen bonding more significant. Consequently, primary amines have higher boiling points than secondary amines.
160
How do the boiling points of primary, secondary, and tertiary amines compare when they have the same molecular weight?
the primary amine has the highest boiling point, followed by the secondary amine, and then the tertiary amine.
161
How are hydrogen bonds involved in DNA?
making it possible for DNA to copy all its hereditary information
holding proteins chains in the correct three-dimensional shape
162
How can you tell if a compound can make hydrogen bonds with itself? Why?
must have a hydrogen directly attached on a O, N, or F
so this hydrogen can interact with a lone pair on a O,N, or F of another molecule of the compound.
163
How can you tell if a compound can be dissolved in solvents such as ethanol?
Ethanol has an H attached to an O, so it is able to form hydrogen bonds with a compound that has a lone pair on an O, N, or F.
164
Explain why H2O has a higher boiling point than CH30H
165
Explain why H2O has higher boiling point than NH3
166
167
How do the melting points of alkanes change with increasing molecular weight?
melting points of alkanes increase as molecular weight increases, with a few exceptions.
168
Why is the increase in melting point less regular than the increase in boiling point?
The increase in melting point is influenced not only by intermolecular attractions but also by the packing in the crystal lattice, which affects the energy required to break the lattice and melt the compound.
169
What influences the melting point in addition to intermolecular attractions?
The arrangement, closeness, and compactness of molecules in the crystal lattice
170
How do the melting points of straight-chain alkanes with even and odd numbers of carbons differ?
alkanes with an odd number of carbons pack less tightly than alkanes with an even number of carbons
171
Why do alkanes with an odd number of carbons pack less tightly?
because the molecules (each a zigzag chain with its ends tilted the same way) can lie next to each other with a methyl group on the end of one facing and repelling the methyl group on the end of the other, thus increasing the average distance between the chains.
Consequently, they have weaker intermolecular attractions and correspondingly lower melting points.
172
Why does "polar dissolves polar" occur?
because a polar solvent, such as water, has partial charges that can interact with the partial charges on a polar compound.
173
How do solvent molecules interact with polar compounds?
The negative poles of solvent molecules surround the positive pole of the polar compound, and the positive poles of solvent molecules surround the negative pole of the polar compound.
174
What is solvation?
interaction between solvent molecules and solute molecules (molecules dissolved in a solvent).
175
How does solvation enable dissolution?
Solvation involves the clustering of solvent molecules around solute molecules, which separates them from each other and facilitates dissolution.
176
What is the significance of solvation in the dissolution process?
Solvation is what enables polar compounds to dissolve in polar solvents by allowing solvent molecules to interact with and surround solute molecules, thereby breaking them apart and dispersing them throughout the solvent.
177
Why aren't polar solvents attracted to non polar molecules?
because they have no charge
For a nonpolar molecule to dissolve in a polar solvent such as water, the nonpolar molecule would have to push the water molecules apart, disrupting their hydrogen bonding. Hydrogen bonding, how- ever, is strong enough to exclude the nonpolar compound.
178
How can non polar solvents dissolve non polar molecules?
because the London dispersion forces between solvent molecules and solute molecules are about the same as those between solvent molecules or those between solute molecules.
179
What is the density trend in alkanes when it comes to molecular weight?
densities increase wit increasing molecular weight
180
Are alkanes soluble in water? Why?
No, since they are non polar
181
What would happen if we mix a solution of alkane with water?
even a 30-carbon alkane is less dense than water so the mixture would separate into two distinct layers.
182
Is an alcohol nonpolar because of its alkyl group, or is it polar because of its OH group?
It depends on the size of the alkyl group
alcohols with fewer than four carbons are soluble in water, but alcohols with more than four carbons are insoluble in water.
Thus, an OH group can drag about three or four carbons into solution in water.
183
Are tert-butyl alcohol or n-butyl alcohol more soluble in water? Why?
tert-butyl alcohol is more soluble than n-butyl alcohol
Alcohols with branched alkyl groups are more soluble in water than alcohols with unbranched alkyl groups with the same number of carbons (branching minimizes the contact surface of the non- polar portion of the molecule.)
184
How many carbons can ethers drag into water?
about 3, (4 it becomes a bit insoluble)
185
Why are low-molecular-weight amines soluble in water?
Low-molecular-weight amines are soluble in water because they have a lone pair that can form hydrogen bonds with water molecules.
186
How do primary, secondary, and tertiary amines differ in solubility in water?
Primary amines are more soluble than secondary amines with the same number of carbons because primary amines have two hydrogens that can engage in hydrogen bonding with water.
Tertiary amines are less soluble in water than secondary amines with the same number of carbons because they do not have hydrogens available to donate for hydrogen bonding.
187
Why are primary amines more soluble than secondary amines?
Primary amines have two hydrogens available to engage in hydrogen bonding with water, whereas secondary amines have only one hydrogen available for hydrogen bonding.
188
Why are tertiary amines less soluble than secondary amines?
Tertiary amines do not have any hydrogens available to donate for hydrogen bonding with water, making them less soluble in water than secondary amines.
189
Are alkyl halides all soluble in water, since they all have some polar character?
No, only alkyl fluorides have an atom that can form a hydrogen bond with water. Alkyl fluorides, therefore, are the most water soluble of the alkyl halides. The other alkyl halides are less soluble in water than ethers or alcohols with the same number of carbons
190
What type of bond is formed when an sp3 orbital of one carbon overlaps an sp3 orbital of another carbon?
A carbon-carbon single bond (σ bond)
191
How does rotation about a carbon-carbon single bond affect orbital overlap?
Rotation about a carbon-carbon single bond can occur without any change in the amount of orbital overlap.
192
What is the term used to describe the different spatial arrangements of atoms resulting from rotation about a single bond?
conformational isomers or conformers.
193
What is Newman projection?
Way of representing three-dimensional structures that result from rotation about a σ bond.
viewer is looking along the longitudinal axis of a particular C¬C bond.
carbon in front is represented by a point (where three lines are seen to intersect), and the carbon at the back is represented by a circle. The three lines emanating from each of the carbons represent its other three bonds.
194
What are the staggered and eclipsed conformer?
The staggered conformer and the eclipsed conformer represent two extremes resulting from rotation about a C-C bond.
195
How do the staggered conformer and the eclipsed conformer differ in stability and energy level?
The staggered conformer is more stable and lower in energy compared to the eclipsed conformer.
196
Is rotation about a C-C bond completely free? If not, why?
No, rotation about a C-C bond is not completely free because an energy barrier must be overcome during rotation.
197
What is the significance of the energy barrier associated with rotation about a C-C bond?
What is its strength at room temperature?
The energy barrier, though present, is small enough to allow continuous rotation at room temperature.
2.9 kcal/mol
198
How frequently does a molecule's conformation change from staggered to eclipsed at room temperature?
millions of times per second at room temperature
199
Why is it challenging to separate conformers from each other?
Conformers cannot be separated from each other because their interconversion occurs at a rapid pace, making it practically impossible to isolate individual conformations.
200
What percentage of ethane molecules typically exist in a staggered conformation at room temperature, and why?
Approximately 99%
due to its greater stability compared to the eclipsed conformation.
201
What contributes to the stability difference between staggered and eclipsed conformers?
Stabilizing interactions between the bonding and antibonding molecular orbitals of adjacent C-H bonds are the major contributors to the energy difference: the electrons in the bonding MO move partially into the unoccupied antibonding MO.
only in the staggered conformation the two orbitals are parallel, and these interactions are maximized.
202
What is hyperconjugation, and how does it relate to the stability of staggered conformers?
the delocalization of electrons by the overlap of a σ orbital with an empty orbital.
In staggered conformers, hyperconjugation maximizes stabilizing interactions between adjacent C-H bonds, contributing to their greater stability.
203
How many C-C single bonds on which rotation can occur is there in butane?
Butane has three carbon–carbon single bonds, and rotation can occur about each of them.
204
How do you draw newman projection? use butane as an example
the carbon with the lower number is placed in the foreground
205
Are all staggered conformers resulting from rotation about the C₁-C₂ bond in butane energetically equivalent?
Yes
206
Are staggered conformers resulting from rotation about the C₂-C₃ bond in butane energetically equivalent?
No
207
What are the staggered and eclipsed conformers that result from rotation about the C₂-C₃ bond in butane?
208
What are the relative energies of these conformers?
209
What does the degree of rotation of each conformer correspond to?
the dihedral angle, which is the angle formed in a Newman projection by a bond on the front carbon and a bond on the back carbon.
210
Can you provide an example of how the dihedral angle varies between conformers?
in conformer (A) where one methyl group stands directly in front of the other, the dihedral angle is 0°. In contrast, in conformer (D) where the methyl groups are opposite each other, the dihedral angle is 180°.
211
What distinguishes the anti conformer from the gauche conformers among the three staggered conformers?
The anti conformer, labeled as D, has the two methyl groups positioned as far apart as possible, making it more stable and lower in energy compared to the gauche conformers (B and F).
212
Why are the two gauche conformers (B and F) considered to have the same energy?
The two gauche conformers (B and F) are considered to have the same energy because they share a similar spatial arrangement where the two methyl groups are closer together compared to the anti conformer, resulting in identical steric strain.
213
What is steric strain, and how does it relate to the energy difference between anti and gauche conformers?
the additional energy experienced by a molecule due to close proximity of atoms or groups.
In the gauche conformers, the two methyl groups are closer, leading to a gauche interaction and higher steric strain compared to the anti conformer, which contributes to the energy difference between them.
214
How do the energies of eclipsed conformers vary based on the positioning of the methyl groups?
The eclipsed conformer where the two methyl groups are closest (labeled as A) is less stable than eclipsed conformers where they are farther apart (labeled as C and E).
215
Why do carbon chains adopt zigzag arrangement? From what it this due?
They are in a zigzag formation as they are staggered
being staggered rather that in eclipse makes them more stable
therefore, leading to a higher number of molecules in staggered conformations compared to eclipsed conformations
216
What are the ideal bond angles for an sp3 carbon?
109.5°
217
How did Baeyer suggest determining the stability of a cycloalkane based on bond angles?
by calculating the difference between the ideal bond angle (109.5°) and the actual bond angle in the planar cycloalkane.
For example, the bond angles in cyclopropane are 60°, representing a 49.5° deviation from 109.5°
218
What is the relationship between the bond angles in cyclopropane and its stability according to Baeyer's proposal?
For example, the bond angles in cyclopropane are 60°, representing a 49.5° deviation from 109.5°
this deviation causes angle strain, thereby decreasing cyclopropane's stability.
219
Represent the angle strain in cyclopropane by drawing the overlap of the orbitals compared to a normal σ bond.
Typically, σ bonds are formed by the direct overlap of two sp3 orbitals.
However, in cyclopropane, the overlapping orbitals cannot point directly at each other due to the cyclical structure. As a result, the amount of overlap between the orbitals forming the C-C bonds is reduced compared to a normal C-C bond.
220
How does the reduced overlap of orbitals in cyclopropane affect the strength of C-C bonds? What is the erm for it?
it weakens the C-C bonds.
This weakening due to decreased overlap is what is referred to as angle strain.
221
What is angle strain, and why does it occur in cyclopropane?
the strain caused by deviation from the ideal bond angle.
In cyclopropane, the deviation from the ideal bond angle of 109.5° results in reduced overlap between orbitals forming the C-C bonds, leading to weaker bonds and angle strain.
222
What else than angle strain affects the stability of cyclopropane?
In addition to angle strain in the C-C bonds, all the adjacent C-H bonds in cyclopropane are eclipsed rather than staggered, further contributing to its instability.
223
How does the angle strain in cyclobutane compare to that in cyclopropane?
Cyclobutane would have less angle strain than cyclopropane because its bond angles would deviate by only 19.5° from the ideal bond angle, compared to the 49.5° deviation in cyclopropane.
224
Why is cyclobutane not planar despite having less angle strain than cyclopropane?
because of the presence of eight pairs of eclipsed hydrogens, resulting in structural distortion. One of the CH2 groups in cyclobutane is bent away from the plane made by the three other carbons
225
How does the presence of eclipsed hydrogens affect the stability of cyclobutane?
Although the bent conformation of cyclobutane introduces more angle strain compared to a planar configuration, the increase in angle strain is outweighed by the decrease in the number of eclipsed hydrogens. This results in an overall increase in stability despite the distortion.
aka less eclipsed hydrogens = better at stability than less angle strain (of orbitals)
226
What would be the consequences if cyclopentane were planar according to Baeyer's prediction?
it would have essentially no angle strain but would possess 10 pairs of eclipsed hydrogens due to the cyclic structure, leading to instability.
227
How does cyclopentane address the issue of eclipsed hydrogens to increase stability?
Cyclopentane puckers, causing the molecule to bend out of a planar arrangement.
This puckering allows some of the hydrogens to become nearly staggered, reducing the number of eclipsed hydrogens and increasing stability.
However, this process introduces some degree of angle strain to the molecule.
228
Why is cyclohexane more stable than cyclopentane, contrary to Baeyer's prediction?
because cyclohexane molecules adopt a non-planar conformation, allowing for a more optimal arrangement that minimizes ring strain and the number of eclipsed hydrogens. (chair conformer)
229
What was the error in Baeyer's assumption regarding the planarity of cyclic molecules?
assuming that all cyclic molecules are planar. In reality, cyclic compounds twist and bend out of a planar arrangement to achieve structures that maximize stability by minimizing ring strain and the number of eclipsed hydrogens.
230
Why are six-membered rings commonly found in natural cyclic compounds?
because they can adopt a conformation known as a chair conformer, which is almost completely free of strain.
231
How does a chair conformer differ from a planar structure?
A chair conformer is not planar; instead, it forms a three-dimensional shape resembling a lounge chair.
Unlike a planar structure with bond angles of 120°, all the bond angles in a chair conformer are approximately 111°, which is very close to the ideal tetrahedral bond angle of 109.5°.
232
What is the significance of the bond angles in a chair conformer?
In a chair conformer, all the bond angles are approximately 111°, which closely resembles the ideal tetrahedral bond angle of 109.5°. This arrangement minimizes strain within the molecule.
233
How are the bonds arranged in a chair conformer?
all the adjacent bonds are staggered, contributing to the stability of the structure.
234
Draw the newman projection of the chair conformer looking down the
C-1---C-2 and C-5---C-4 bonds
235
What are axial and equatorial bonds in cyclohexane chair conformers and how do you draw them?
236
What is the process known as when cyclohexane interconverts between two stable chair conformers?
ring flip
237
How does ring flip occur in cyclohexane, and what changes take place during this process?
Ring flip occurs due to the ease of rotation about the C-C bonds in cyclohexane. During ring flip, bonds that are equatorial in one chair conformer become axial in the other chair conformer, and vice versa.
This interchange allows the molecule to adopt different stable conformations.
238
What happens to equatorial and axial bonds during the ring flip of cyclohexane?
During ring flip, equatorial bonds become axial, and axial bonds become equatorial
239
How does ring flip contribute to the stability of cyclohexane?
Ring flip allows cyclohexane to access two stable chair conformers, which helps distribute any potential strain more evenly throughout the molecule, contributing to its overall stability.
240
What is the alternative conformation to the chair conformer for cyclohexane, and what is it called?
boat conformer
241
What strain is absent in the boat conformer of cyclohexane?
Similar to the chair conformer, the boat conformer of cyclohexane is free of angle strain.
242
Why is the boat conformer less stable compared to the chair conformer?
because it contains some eclipsed C-H bonds, unlike the chair conformer.
Additionally, the boat conformer experiences steric strain due to the close proximity of the flagpole hydrogens located at the "bow" and "stern" of the boat conformation.
243
How does steric strain arise in the boat conformer of cyclohexane?
due to the close proximity of the flagpole hydrogens, causing repulsive interactions and destabilizing the conformation.
244
How does cyclohexane interconvert between the boat conformer and the chair conformer?
one of the topmost carbons of the boat conformer must be pulled down to become the bottommost carbon of the chair conformer.
245
What is the intermediate conformation between the boat and chair conformers, and why is it more stable than the boat conformer?
the twist-boat conformer.
(When the carbon is pulled down just a little)
It is more stable than the boat conformer because the movement of the top carbon away from the other top carbon reduces the steric strain caused by the flagpole hydrogens.
246
What happens when the carbon in the twist-boat conformation aligns with the sides of the boat?
When the carbon in the twist-boat conformation aligns with the sides of the boat, it forms the half-chair conformation, which is highly unstable due to the strained geometry.
247
How frequently does cyclohexane undergo ring flips at room temperature, and what does this indicate about the two chair conformers?
approximately 105 ring flips per second at room temperature, indicating that the two chair conformers are in rapid equilibrium.
248
What is the predominant conformation adopted by cyclohexane molecules at any given moment?
chair conformer.
249
How does the population of chair conformers compare to other conformers, such as the twist-boat conformer?
The population of chair conformers greatly outweighs that of other conformers.
For every 10,000 chair conformers of cyclohexane, there is no more than one twist-boat conformer, which is the next most stable conformer.
250
What does the predominance of chair conformers imply about the stability of cyclohexane conformations?
it implies that they are significantly more stable than any other conformers of cyclohexane.
251
How does the population distribution of cyclohexane conformers reflect their relative stability?
The population distribution of cyclohexane conformers reflects their relative stability, with the chair conformers being overwhelmingly more stable and thus more prevalent compared to other conformers.
252
How do the two chair conformers of a monosubstituted cyclohexane, like methylcyclohexane, differ?
the two chair conformers of a monosubstituted cyclohexane, such as methylcyclohexane, differ in the position of the methyl substituent. In one conformer, the methyl substituent is in an equatorial position, while in the other conformer, it is in an axial position.
253
What determines the position of substituents in chair conformers of cyclohexanes?
The position of substituents in chair conformers of cyclohexanes is determined by the necessity to minimize steric interactions.
Substituents preferentially occupy equatorial positions to minimize steric hindrance.
254
How does the position of the substituent in one chair conformer relate to its position in the other chair conformer?
The position of the substituent in one chair conformer is opposite to its position in the other chair conformer. If the substituent is equatorial in one chair conformer, it will be axial in the other, and vice versa. This relationship ensures that substituents alternate between equatorial and axial positions as the cyclohexane ring interconverts between its two chair conformers.
255
How does the position of the methyl group in an equatorial position minimize steric interactions?
it extends into space away from the rest of the molecule, reducing steric hindrance with adjacent atoms or groups and minimizing repulsive interactions.
256
What visual representation supports the idea that a methyl group in an equatorial position extends into space?
a methyl group in an equatorial position extends into space away from the rest of the molecule, demonstrating the increased room available for the substituent.
257
Why does a substituent prefer an equatorial position in a chair conformer?
because it experiences fewer steric interactions and has more room to move freely, contributing to the overall stability of the molecule.
258
What is the consequence of having an axial substituent in a cyclohexane chair conformer in terms of steric interactions?
it results in the substituent being relatively close to the axial substituents on the other two carbons on the same side of the ring.
This proximity leads to unfavorable steric interactions known as 1,3-diaxial interactions.
259
How do axial substituents interact with each other in a cyclohexane chair conformer?
because all three axial bonds are parallel to each other. This arrangement brings the substituents on the same side of the ring (1,3-positions relative to each other) into close proximity, resulting in steric hindrance.
260
Why are steric interactions between axial substituents in a cyclohexane chair conformer termed 1,3-diaxial interactions?
because the interacting axial substituents are positioned at 1,3-positions relative to each other along the ring structure.
261
What makes 1,3-diaxial interactions unfavorable?
because they lead to repulsive forces between the axial substituents due to their close proximity, contributing to the destabilization of the molecule.
262
To what type of "chain" strain can 1,3-diaxial interactions be compared to?
the gauche interaction in butane
263
What contributes to the stability difference between the chair conformers of methylcyclohexane with the methyl group in equatorial and axial positions?
The stability difference between the chair conformers of methylcyclohexane with the methyl group in equatorial and axial positions is due to the presence of gauche interactions.
The axial position leads to unfavorable 1,3-diaxial interactions between the methyl group and other axial substituents, resulting in decreased stability compared to the equatorial position.
264
How do the relative amounts of chair conformers of monosubstituted cyclohexanes vary based on the substituent?
it depends on the nature of the substituent.
Different substituents may exhibit different steric effects, influencing the stability of the chair conformers and thereby affecting their population distribution.
265
The _____ the group attached on a cyclohexane is, the more they are prone to be in _____ position when it comes to their population distribution.
Give an example:
bigger; axial
95% of methylcyclohexane molecules have their methyl group in equatorial position at 25ºC, whereas in tert-butylcyclohexane, 99.9%, since tert-butyl group is larger than a methyl group
266
What is the cis isomer in cyclohexanes?
both substituents are positioned on the same side of the cyclohexane ring.
267
What is the trans isomer in cyclohexanes?
the two substituents are positioned on opposite sides of the cyclohexane ring.
268
What are geometric isomers?
using the terms cis and trans to designate two isomers that have the same atoms, and that atoms are connected to each other in the same order, but they have different spatial arrangements
269
Are there ways of differenciating geometric isomers?
yes; the cis and trans isomers are different compounds with different melt- ing and boiling points, so they can be separated from each other.
270
How to differentiate cis-trans isomers
(textbook p.169 if unclear)
*If the bonds bearing the substituents both point upward or both point downward, then the compound is the cis isomer; if one bond points upward and the other downward, then the compound is the trans isomer. (axial)
*if not evident, look at the axial H (or other substituent), if they are cis, the substituents are also vive versa
271
What is another name fr cis-trans isomers?
geometric isomers
272
How do you draw the most stable conformer?
273
How are two cyclohexane rings fused, and what does this imply regarding substituents?
Two cyclohexane rings are fused when they share two adjacent carbons. In this arrangement, one ring can be considered as a pair of substituents bonded to the other ring.
274
What distinguishes the trans and cis isomers in fused cyclohexane rings?
In the trans isomer of fused cyclohexane rings, one substituent bond points upward and the other downward, both in the equatorial position. In the cis isomer, one substituent is in the equatorial position, while the other is in the axial position.
275
Which isomer, cis or trans, is more stable in fused cyclohexane rings?
The trans-fused rings are more stable than the cis-fused rings.
276
Why are trans-fused rings more stable than cis-fused rings?
because both substituents are in the equatorial position, which minimizes steric interactions and ring strain. In contrast, the cis-fused rings have one substituent in the axial position, which increases steric hindrance and destabilizes the structure.
277
What are hormones, and what is their function?
Hormones are chemical messengers synthesized in glands and transported by the bloodstream to target tissues.
They stimulate or inhibit various processes within the body.
278
What is a common structural feature of many hormones?
Many hormones are steroids, which are organic compounds characterized by a four-ring structure. These rings are designated as A, B, C, and D.
279
How are the B, C, and D rings arranged in steroids?
In steroids, the B, C, and D rings are all trans-fused, meaning they share two adjacent carbons and have a stable, planar configuration.
280
What is the typical arrangement of the A and B rings in most naturally occurring steroids?
he A and B rings are also trans-fused, similar to the B, C, and D rings. This arrangement contributes to the overall stability and structural integrity of the steroid molecule.
281
What is the most abundant member of the steroid family in animals, and what is its role?
Cholesterol: serves as the precursor for the synthesis of all other steroids and plays a crucial role as an important component of cell membranes.
282
How does the structure of cholesterol contribute to its function in cell membranes?
with its rigid and specific conformation due to locked rings: enhances membrane stability and fluidity by interacting with phospholipids, affecting their arrangement and preventing excessive fluidity or rigidity in the membrane.
283
What distinguishes the rigidity of cholesterol from other membrane components?
conformation of its rings, which are locked in place.
This rigidity allows cholesterol to maintain the structural integrity of the membrane while modulating its fluidity.
284
What is the precursor for all steroids such as cortisol, estrogen, and testosterone, as well as vitamin D?
cholesterol
