Chapter 3

Question 1

how do atoms relative to reach other move

Answer 1

by rotations about single bonds

Question 2

are molecules in constant motion under standard conditions

Answer 2

YES

Question 3

what does rotations around c-c single bonds NOT change

Answer 3

the overlap between the orbitals =

Question 4

does the sigma bond between C-C single bonds break during rotations

Answer 4

NO

Question 5

conformations

Answer 5

the different spatial arrangements produced by rotation about single bonds

Question 6

why are newman projections used

Answer 6

to clearly show the arrangement around a single bond

Question 7

what is the first atom depicted as in a newman projection? the second?

Answer 7

first = dot

second = circle

Question 8

do different conformations have the same or different energies

Answer 8

different energies

Question 9

eclipsed conformation

Answer 9

when the bonds of the front carbon atom align with those of the back carbon atom

Question 10

type of conformation (LEFT)

Answer 10

eclipsed

Question 11

type of conformation (RIGHT)

Answer 11

staggered

Question 12

staggered conformation

Answer 12

when the groups attached to the front carbon are AS FAR AS possible from the back groups

Question 13

what type of conformation has higher energy? lower?

Answer 13

lower energy = staggered

higher energy = eclipsed

Question 14

why does an eclipsed conformation have higher energy

Answer 14

because there is repulsion between the adjacent bonds which creates torsion strain and raises the energy

Question 15

is a conformation with higher or lower energy more stable?

Answer 15

lower energy = more stable

Question 16

which conformation is more stable

Answer 16

staggered

Question 17

why do staggered conformations have lower energy

Answer 17

because with further rotation around the c-c bond the atoms move farther apart which lowers the torsion strain = lower energy

Question 18

what is the relationship between the torsion angle and torsional strain

Answer 18

the GREATER the torsion angle = less torsional strain

Question 19

what conformation has the GREATEST torsional strain

Answer 19

eclipsed

Question 20

what is the angle between atoms in an eclipsed conformation

Answer 20

0 degrees

Question 21

what is the angle between atoms in an staggered conformation

Answer 21

60 degrees

Question 22

what is the most stable conformation for a molecule

Answer 22

staggered with the major substituents 180 degrees from each other

Question 23

what happens if a staggered conformation is rotated by 60 degrees

Answer 23

it becomes eclipsed

Question 24

steric strain

Answer 24

repulsive force between electron clouds of atoms that are close to each other BUT NOT directly bonded

Question 25

types of conformations in regards to steric strain

Answer 25

1. anti-conformations 2. gauche conformations 3. eclipsed conformation

Question 26

what conformation has the highest steric strain

Answer 26

eclipsed conformation

Question 27

what can lowered the steric strain of an eclipsed molecule

Answer 27

when the large atoms are not eclipsing each other (Cl eclipses H not another Cl)

Question 28

what conformation has no torsional strain

Answer 28

anti conformation

Question 29

how does anti conformations minimize steric strain

Answer 29

by placing large groups as far apart as possible (180 degrees)

Question 30

what conformation has NO steric strain

Answer 30

anti conformation

Question 31

what conformation has small steric strain but not the most

Answer 31

gauche conformation

Question 32

what gives gauche conformations small steric strain

Answer 32

major atom groups are side to side but NOT eclipsed

Question 33

is gauche conformations higher or lower in energy than anti? eclipsed?

Answer 33

higher in energy than anti conformations lower in energy than eclipsed

Question 34

angle in gauche conformations that the atoms are apart

Answer 34

60 degrees

Question 35

type of conformation

Answer 35

anti-conformation

Question 36

type of conformation

Answer 36

gauche conformation

Question 37

what is the relationship between electron cloud and steric strain

Answer 37

the bigger the electron cloud (bigger the group) the MORE steric strain there is in the molecule

Question 38

what conformation with steric strain is the LOWEST and MOST stable

Answer 38

anti conformation

Question 39

what is the issue with depicting cyclic molecules as polygons

Answer 39

neglects their 3D structures

Question 40

what is angle strain

Answer 40

arises from bond angles NOT permitting maximum orbital overlap (deviations from angles predicted by VESPR)

Question 41

what cyclic molecules have the MOST strain

Answer 41

3 membered rings

Question 42

what strain do 3 member rings experiece

Answer 42

1. angle strain 2. steric strain 3. torsional strain

Question 43

how do 3 membered rings exhibit the different types of strain

Answer 43

1. angle strain by not having angles close to the predicted (109 degrees) 2. torsional strain with the eclipsed C-H bonds 3. eclipsed conformation increases steric strain

Question 44

do the triangular way of drawing 3 member rings reduce or increase overlap between SP3 orbitals

Answer 44

REDUCES the overlap

Question 45

are 4 membered ring more or less stable than 3 membered rings

Answer 45

more stable

Question 46

do 4 membered rings show more or less strain than 3 membered rings

Answer 46

LESS

Question 47

what is the most stable conformation for 5 membered rings

Answer 47

envelope conformation

Question 48

are 5 member rings more or less stable than BOTH 3 and 4 membered rings

Answer 48

MORE stable

Question 49

type of conformation

Answer 49

envelope

Question 50

what is the ONLY ring that is relatively free of strain

Answer 50

6 membered rings

Question 51

what is the most stable conformation for a 6 membered ring

Answer 51

chair conformation

Question 52

where are axial bonds in chair conformation

Answer 52

straight above or below the plane

Question 53

direction of equatorial bonds in chair conformation

Answer 53

parallel to the bond two bonds away from it

Question 54

type of conformation

Answer 54

chair

Question 55

how many chair conformations are there for a molecule

Answer 55

2

Question 56

what is it called when inverting a chair conformation

Answer 56

ring flip

Question 57

do ring flips of 6 cyclohexane have same energy or different

Answer 57

same energy

Question 58

what happens to axial bonds in a ring flip

Answer 58

turn equatorial

Question 59

what happens to equatorial bonds in a ring flip

Answer 59

turn axial

Question 60

when do two conformers in chair conformation NOT have the same energy

Answer 60

when there are substituents added to the 6 member ring

Question 61

what position in a 6 membered ring are substituents LESS favorable

Answer 61

substituents found in AXIAL position

Question 62

why are substituents in axial positions less favorable

Answer 62

1,3 - diaxial interactions

Question 63

what is the relationship between strain from 1,3-diaxial interactions and size of substituents

Answer 63

the strain caused by 1,3-diaxial interactions INCREASES as the size of the substituent increases

Question 64

what is 1,3-diaxial interactions

Answer 64

when substituents react with hydrogens and other atoms in the same PHASE as it

Question 65

in general, what is considered the more stable chair conformation

Answer 65

the one where the larger substituents are placed in equatorial positions

Question 66

how can the most stable 6 membered ring be found when it has multiple substituents

Answer 66

draw the ring inversion of the ring and decide which has the least 1,3-diaxial interactions

Question 67

do dashes and wedges give insight into whether the atom is axial or equatorial

Answer 67

NO - shows whether top or bottom phase