Stereochemistry

Question 1

wedge’s denote?

Answer 1

denotes a group pointing “out of the page”

Question 2

dash’s denote?

Answer 2

denotes a group pointing “into the page”

Question 3

anti

Answer 3

two groups on adjacent carbons oriented at 180° to each other

Question 4

syn

Answer 4

two groups on adjacent carbons oriented at 0° to each other

Question 5

gauche

Answer 5

two groups on adjacent carbons oriented at 60° to each other

Question 6

eclipsed

Answer 6

when all 3 substituents overlap completely with all 3 substituents on a neighbouring carbon.

(Generally, eclipsed conformations have the highest torsional strain)

Question 7

staggered

Answer 7

refers to the orientation when all 3 substituents on a carbon are arranged at
a 60 deg angle to all 3 substituents on another carbon.

Question 8

isomers

Answer 8

two molecules with the same molecular formula, but different in their structures

Question 9

configuration

Answer 9

the 3-D arrangement of bonds around a carbon.

Question 10

racemic mixture

Answer 10

a 50:50 mixture of two enantiomers

Question 11

Meso compound

Answer 11

A molecule with chiral centers, but a plane of symmetry that makes the molecule achiral

Question 12

Cis

Answer 12

on the same side of a double bond or ring

Question 13

Trans

Answer 13

on opposite sides of a double bond or ring.

Question 14

Chiral molecule

Answer 14

a molecule with an enantiomer; cannot possess a plane of symmetry

Question 15

Chiral Center

Answer 15

Has 4 different constituents

Question 16

Torsional Strain

Answer 16

Strain that arises from the proximity of bonds (and the electrons in them) - generally eclipsing)

Question 17

Conformational isomers

Answer 17

same connectivity, same configuration, different 3-D shape.

Physical properties: Identical, as long as they can interconvert through bond rotation

Question 18

constitutional isomers

Answer 18

isomers that differ in the oder their atoms are bonded

same molecular formula but different structural formula (bonding arrangements)

Question 19

Enantiomers

Answer 19

Stereoisomers that are non- superimposable mirror images

Question 20

Diastereomers

Answer 20

Stereoisomers that are NOT non- superimposable mirror images

Question 21

The R,S convention

Answer 21

Rank according to CIP protocol Put #4 ranked substituent in back
1,2,3 goes CW: R
1,2,3 goes CCW: S

Question 22

The R,S convention - What if #4 is in the front?

Answer 22

One approach is to trace 1,2 and 3 as you normally would. Then flip!

Question 23

The single swap rule:

Answer 23

Single swap rule: switching any two groups on a chiral center will flip (R) to (S) and vice versa.

Question 24

Cyclohexane chair conformations

Answer 24

n the cyclohexane chair conformation: all C–C bonds staggered

Question 25

Chair flips

Answer 25

all axial groups become equatorial, and all equatorial groups become axial.

BUT all groups that are “up” stay “up” and all groups that are “down” stay “dow

Question 26

what do bulkier groups prefer in chairs?

Answer 26

Bulky groups prefer the equatorial position

The bulkier the group, the greater the energy difference will be.

Question 27

chair confirmation - what is the order of bulkiness?

Answer 27

Bulkiness:
tertiary C (3°) > secondary C (2°) > primary C (1°), methyl (CH3) >> H

Question 28

Explain the three different ways of representing conformations

Answer 28

(Dash and Wedge, Newman projections, sawhorse projection)