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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
Q

steric strain

A

the combination of torsional strain and steric hindrance

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26
Q

energy of an eclipse

A

high (less stable)

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27
Q

energy of staggered

A

low (more stable)

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28
Q

what characteristics do the lowest energy conformation of alkanes have

A

all bonds staggered

with simple alkanes, has zig-zag arrangement of carbon atoms

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29
Q

what bond angle do tetrahedral carbons prefer

A

109.5

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30
Q

what type of cycloalkane has the highest angle strain and what is the bond angle

A

cyclopropane

60 degrees

31
Q

what do all other cycloalkanes besides tetrahedral carbons try to do to the angle strain

A

minimize it, and are therefore not planar

32
Q

why is heat of combustion important

A

gives us a way to measure the relative stability of cycloalkanes

33
Q

what does the lowest heat of combustion per CH2 group correspond to

A

the most stable cycloalkane

34
Q

bent/banana bonds

A

when strong sp3-sp3-s bonds cannot be formed because of 60 degree bond angles, the bonds are called bent/banana

35
Q

how is torsional strain in cyclopropane

A

it is high because the C-H bonds are eclipsed

36
Q

what is the general conformation for cyclobutane and why

A

a nonplanar “puckered” conformation

to minimize the torsional strain

37
Q

how is the angle strain of planar cyclopentane and why

A

low angle strain because the natural bond angle is 108

38
Q

what type of strain do cyclopentane have and why

A

torsional strain because the C-H bonds are eclipsed

39
Q

cyclopentane and stability

A

2nd most stable cycloalkane, they relieve some of the torsional strain but not all

40
Q

what is the most stable cycloalkane and what conformation is it most stable in

A

cyclohexane, chair conformation

41
Q

what are the two groups of bonds in cyclohexanes

A
  • axial

- equitorial

42
Q

equitorial hydrogens

A

horizontal

43
Q

axial hydrogens

A

vertical up and down

44
Q

how many chair conformations of cyclohexane are there and what do they do

A

there are 2, and they rapidly interconvert

45
Q

what happens when cyclohexane inverts from original chair conformation

A

the original conformation becomes equitorial in the inverted form, and vice versa

46
Q

general rule for ring inversions

A

procedes through highest energy half-chair conformations and the twist and boat conformations

47
Q

general rule for interconversion of methylcyclohexanes

A

methyl group is either equatorial or axial

48
Q

what confirmation of methylcyclohexane is most favored

A

equatorial methyl

49
Q

what destabilizes the conformation of methylcyclohexane

A

van der waals strain between the methyl and axial hydrogen atoms destabilizes an axial methyl

50
Q

where is methyl more stable in inversions

A

when it is equitorial and has 0 interactions

51
Q

chair inversion of fluorocyclohexane (vs. methyl)

A

less crowding because F is a smaller substituent

difference in energy is lower than methyl

52
Q

chair inversion of t-butylcyclohexane (vs. methyl)

A

more crowding because butyl is a larger substituent (tertiary butyl)

difference in energy is much higher than methyl

53
Q

isomers

A

different compounds that have the same molecular formula

54
Q

constitutional isomers

A

differ in connectivity

55
Q

stereoisomers

A

have the same connectivity but different arrangements of the atoms in space

56
Q

what are the 2 possible orientations for sustituents

A

trans and cis

57
Q

cis substituents

A

on the same side of the ring

58
Q

trans substituents

A

on the opposite sides of the ring

59
Q

which type of substituent has higher energy and why

A

cis, because van der waals strain, more hindrance, less stable, more NG

60
Q

what type of stereoisomer is most stable

A

trans

61
Q

cis-1,4-dimethylcyclohexane

A

both cis isomers when inverted, have the same energy

62
Q

diaxial and stability relationship

A

least diaxial is most stable

63
Q

trans-1,4-Dimethylcyclohexane

A

one chair conformation of trans isomers has both methyls equatorial

more stable

more stable than cis chair conformations

64
Q

cis conformations of 1,2-dimethylcyclohexane

A

are equal in NG, one methyl group is equatorial and the other is axial

65
Q

what does the lowest chair conformation of the trans isomer of dimethylcyclohexane have

A

both methyls equitorial

66
Q

with 2 different substituents, what will happen with conformation

A

the lowest conformation will have a larger substituent in the equatorial postion

67
Q

spirocyclic systems

A

have 2 rings with one common atom

68
Q

how do you name spirocyclic systems

A

spiro(number.number)alkane

alkane = number of carbons in the rings

69
Q

how do you number the carbons in spirocyclic systems

A

increasing order starting from the top of the left ring, going counter clockwise and up to the top of the right ring

70
Q

what are bridged compounds

A

2 nonadjacent atoms common to 2 or more rings

71
Q

how do you name bridged compounds

A

bycyclo(number.number.number)alkane

parent alkane = number of carbons

numbers: number of carbon atoms between the bridgehead atoms in descending order

72
Q

fused ring compounds

A

where two rings share a common side

73
Q

how to name fused rings

A

bicyclo(number.number.number)alkane

same as bridges compounds pretty much

74
Q

heterocyclic compounds

A

contains an atom other than carbon in the ring (heteroatoms)

Organic Chemistry I (9 decks)

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