3rd

Question 1

staggered confirmation

Answer 1

drawing molecules with dashes and wedges to show their shape.

Question 2

wedges

Answer 2

towards u

Question 3

dashes

Answer 3

away

Question 4

newmans projection

Answer 4

looking at a molecule down the C-C bonds
each atom attached to the C should have a number
should look like a pirate ship wheel with numbers corresponding to the different atoms

Question 5

dihedral angle

Answer 5

angle between 2 H’s on adjacent carbon atoms

Question 6

staggered conformation

Answer 6

more stable
energetically favourable
groups are as far as possible
nothing is overlapping
☸️
60*

Question 7

eclipsed conformation

Answer 7

less stable arrangement
groups are directly aligned
groups overlap
higher energy, less stable
potential repulsion between atoms

Question 8

from staggered to eclipsed conformation

Answer 8

energy is needed to swap conformations.

low energy needed: at room temp they interconvert frequently.

Question 9

three groups on the carbon

Answer 9

3 troughs on the conformed energy change graph

Question 10

conformed energy change graph

Answer 10

peaks : eclipsed conformation
troughs : staggered conformation 60*

Question 11

why is staggered conformation more stable

Answer 11

• atoms are as far as possible reducing repulsion!!
• electron density is donated from a CH sigma bonding orbital to the adjacent CH anti bonding orbital. (stabilises it)

Question 12

antibonding orbital **

Answer 12

• orbital with higher energy than normal ones
• work against bonding orbitals + try to prevent atoms holding together
• weaken bonds as they have nodes in between atoms which weakens the bond between atoms.

Question 13

anti conformation

Answer 13

when bigger groups are staggered in conformation and are placed as far apart as possible from one another.

one at the top, one at the bottom.

180* dihedral angle

Question 14

difference between staggered and anti conformational

Answer 14

staggered: overall arrangement is overlapping

anti conformational: specific arrangements of substituents ( 2 Methyl groups at opposite sides with 180 dihedral angle)

Question 15

Me-Me eclipsed conformation

Answer 15

least stable conformation for butane
both methyl groups are eclipsed

Question 16

Gauche conformation

Answer 16

slightly higher energy than anti conformation

when groups are 60* apart (dihedral angle)

7.5 mins apart from one another 🕣

Question 17

another conformation high in energy

Answer 17

when the bigger group is eclipsed with a smaller one

Question 18

ranking : high to low energy

Answer 18

Me Me eclipsed (big group eclipse)
gauche (7.5 mins away )
Me H eclipse (big+small group eclipse)
anti conformational

Question 19

why is eclipsed highest in energy

Answer 19

sterics: putting two groups together takes energy due to unfavourable steric interactions
electronic: torsial strain due to electrostatic repulsion of electrons involved in the eclipsed bonds

Question 20

is benzene flat or is cyclohexane flat

Answer 20

benzene is flat
cyclohexane is 3D in structure

Question 21

most stable conformation for cyclohexane

Answer 21

chair conformation 🪑

Question 22

how many chair confirmations are there

Answer 22

2

Question 23

the two chair conformations are

Answer 23

enantiomers of eachother

non superimposable mirror images of eachother

inter conversion between the two is rapid (racemization causes them to flip)

Question 24

axial groups on the cyclohexane chair point

Answer 24

up and down
corners + middle area up and down

Question 25

equatorial groups on cyclohexane chair point

Answer 25

towards / away from u
to the sides (parallel to C-C bonds)
they point inwards on the sides

Question 26

cyclohexane ring chair flip

Answer 26

chair 1
half chair
twist boat
boat
twistboat
half chair
chair 2

Question 27

cyclohexane chair flip vids

Answer 27

j mol videos on internet

Question 28

larger groups substituted on a cyclohexane should be placed

Answer 28

equatorially
this is almost always lower in energy

Question 29

energy penalty is placed when larger groups are placed

Answer 29

axial position

Question 30

why is an energy penalty placed when big groups are axial

Answer 30

flagpole interactions (unfavourable) between the big group and the two axial Hs

unfavourable gauche interaction between CX and C-C bonds

Question 31

when two or more substituents are added to the cyclohexane,,

Answer 31

isomers could form

we need to see which group should be placed equitorially so it’s more stable.

Question 32

cis… cyclohexane

Answer 32

both groups have dashed or slashed lines

Question 33

trans… cyclohexane

Answer 33

one has slashed
one has dashed lines

Question 34

CIS + two diff groups

Answer 34

larger group is equatorial
smaller group is axial

Question 35

TRANS + two diff groups

Answer 35

both can sit equatorially

Question 36

trisubstituted + group is in the middle

Answer 36

it cannot be equatorial as in that place (not the corners) it can only be axial as C can only make 4 bonds

Question 37

two cyclohexanes fused together

Answer 37

DECALINS

Question 38

trans decalins are

Answer 38

conformationally locked
cannot undergo ring flip

nice looking ones that make sense, look like a sweet 🍬

Question 39

what does conformationally locked mean

Answer 39

rings are fused
rigid
defined 3D structure
used by cholesterol + estrogen

Question 40

can cis decalins undergo chair flip

Answer 40

yes!!!

cis decalins is the odd looking one that just flips down

Question 41

cyclopentane

Answer 41

less conformationally rigid than cyclohexane - smaller ring = more strain = more ability to move and twist to different conformations.

envelope like shape

each carbon takes turns being the top of the envelope (4 are in the same plane, one is slightly propped up) 💌

Question 42

cyclohexane had conformations that can interconvert but the bond angles won’t the the same :( so we refer to the hs as

Answer 42

pseudo axial
pseudo equatorial

larger groups should still be placed equatorially

Question 43

how do we measure ring stability

Answer 43

compare heat of combustion from carbocycles and // by number of Cs.

compare this with linear alkanes to see which ring is most stable.

most stable = cyclohexane

3 + 4 C rings : sp3 rings are forced to adopt a conformation with no ideal bond angles (high in energy) RING STRAIN