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Organic Chemistry I > Chapter 4 > Flashcards

Chapter 4 Flashcards

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1
Q

what are conformations

A

different spatial arrangements of a molecule that are generated by rotation about single bonds

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2
Q

what is conformational analysis

A

the study of how conformational factors affect the structure of a molecule and its properties

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3
Q

steric hindurence

A

when large atoms restrict the amount of possible arrangments

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4
Q

what is anticonformations

A

when large mols are 180 degrees apart instead of 60

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5
Q

what are the 3 most common ways to show conformations

A

wedge and dash
sawhorse
newman projection

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6
Q

dashes, wedges and lines in wedge and dash drawings

A

dash - going “dashing” away from you
wedge - coming towards you
straight line - on the plane

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7
Q

what are the basics of newman projections

A

bonds on the back carbon are shown sticking out of the circle, those with lines on top of the circle are on the front of the carbon

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8
Q

stagged

A

when bonds to the axis of rotation are not aligned

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9
Q

eclipse

A

when bonds to the axis of rotation ARE alligned

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10
Q

how do Newman projections differ

A

by their rotations of the front and back carbon atoms (angles basically)

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11
Q

what type of newman projection has the highest energy repulsion between bonds

A

eclipsed

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12
Q

what type of newman projection has the lowest energy repulsion between bonds

A

anti

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13
Q

which newman projection is least stable and why

A

eclipsed

because it has the highest energy

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14
Q

which newman projection is the most stable and why

A

anti

because it has the lowest NG

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15
Q

0 degree NP

A

eclipsed

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16
Q

60 degree NP

A

gauche

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17
Q

180 degree NP

A

anti

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18
Q

ethane conformations

A

are infinite and correspond to changes in the torsional angle

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19
Q

what do conformations that are not staggered have

A

torsional strain

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20
Q

in newman projections, what conformation are molecules usually in

A

staggered conformations, hardly ever in eclipsed conformations

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21
Q

what are the two different staggered conformations for butane

A

gauche (higher NG, steric strain on CH3, least stable)

anti (most stable, least NG)

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22
Q

types of strains in newman projections

A

3

torsional strain
steric hindrance
steric strain

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23
Q

torsional strain

A

results from eclipsed bonds

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24
Q

steric hindrance

A

when 2 atoms are too close together (AKA van der Waals strain)

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25
steric strain
the combination of torsional strain and steric hindrance
26
energy of an eclipse
high (less stable)
27
energy of staggered
low (more stable)
28
what characteristics do the lowest energy conformation of alkanes have
all bonds staggered with simple alkanes, has zig-zag arrangement of carbon atoms
29
what bond angle do tetrahedral carbons prefer
109.5
30
what type of cycloalkane has the highest angle strain and what is the bond angle
cyclopropane 60 degrees
31
what do all other cycloalkanes besides tetrahedral carbons try to do to the angle strain
minimize it, and are therefore not planar
32
why is heat of combustion important
gives us a way to measure the relative stability of cycloalkanes
33
what does the lowest heat of combustion per CH2 group correspond to
the most stable cycloalkane
34
bent/banana bonds
when strong sp3-sp3-s bonds cannot be formed because of 60 degree bond angles, the bonds are called bent/banana
35
how is torsional strain in cyclopropane
it is high because the C-H bonds are eclipsed
36
what is the general conformation for cyclobutane and why
a nonplanar "puckered" conformation to minimize the torsional strain
37
how is the angle strain of planar cyclopentane and why
low angle strain because the natural bond angle is 108
38
what type of strain do cyclopentane have and why
torsional strain because the C-H bonds are eclipsed
39
cyclopentane and stability
2nd most stable cycloalkane, they relieve some of the torsional strain but not all
40
what is the most stable cycloalkane and what conformation is it most stable in
cyclohexane, chair conformation
41
what are the two groups of bonds in cyclohexanes
- axial | - equitorial
42
equitorial hydrogens
horizontal
43
axial hydrogens
vertical up and down
44
how many chair conformations of cyclohexane are there and what do they do
there are 2, and they rapidly interconvert
45
what happens when cyclohexane inverts from original chair conformation
the original conformation becomes equitorial in the inverted form, and vice versa
46
general rule for ring inversions
procedes through highest energy half-chair conformations and the twist and boat conformations
47
general rule for interconversion of methylcyclohexanes
methyl group is either equatorial or axial
48
what confirmation of methylcyclohexane is most favored
equatorial methyl
49
what destabilizes the conformation of methylcyclohexane
van der waals strain between the methyl and axial hydrogen atoms destabilizes an axial methyl
50
where is methyl more stable in inversions
when it is equitorial and has 0 interactions
51
chair inversion of fluorocyclohexane (vs. methyl)
less crowding because F is a smaller substituent difference in energy is lower than methyl
52
chair inversion of t-butylcyclohexane (vs. methyl)
more crowding because butyl is a larger substituent (tertiary butyl) difference in energy is much higher than methyl
53
isomers
different compounds that have the same molecular formula
54
constitutional isomers
differ in connectivity
55
stereoisomers
have the same connectivity but different arrangements of the atoms in space
56
what are the 2 possible orientations for sustituents
trans and cis
57
cis substituents
on the same side of the ring
58
trans substituents
on the opposite sides of the ring
59
which type of substituent has higher energy and why
cis, because van der waals strain, more hindrance, less stable, more NG
60
what type of stereoisomer is most stable
trans
61
cis-1,4-dimethylcyclohexane
both cis isomers when inverted, have the same energy
62
diaxial and stability relationship
least diaxial is most stable
63
trans-1,4-Dimethylcyclohexane
one chair conformation of trans isomers has both methyls equatorial more stable more stable than cis chair conformations
64
cis conformations of 1,2-dimethylcyclohexane
are equal in NG, one methyl group is equatorial and the other is axial
65
what does the lowest chair conformation of the trans isomer of dimethylcyclohexane have
both methyls equitorial
66
with 2 different substituents, what will happen with conformation
the lowest conformation will have a larger substituent in the equatorial postion
67
spirocyclic systems
have 2 rings with one common atom
68
how do you name spirocyclic systems
spiro(number.number)alkane alkane = number of carbons in the rings
69
how do you number the carbons in spirocyclic systems
increasing order starting from the top of the left ring, going counter clockwise and up to the top of the right ring
70
what are bridged compounds
2 nonadjacent atoms common to 2 or more rings
71
how do you name bridged compounds
bycyclo(number.number.number)alkane parent alkane = number of carbons numbers: number of carbon atoms between the bridgehead atoms in descending order
72
fused ring compounds
where two rings share a common side
73
how to name fused rings
bicyclo(number.number.number)alkane same as bridges compounds pretty much
74
heterocyclic compounds
contains an atom other than carbon in the ring (heteroatoms)

Organic Chemistry I (9 decks)

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