Introduction To Stereochemistry

Question 1

Conformation=

Answer 1

Different arrangements caused by rotations alone

Question 2

Conformers

Answer 2

Different conformations which are energy minima

Question 3

Karplus equation

Answer 3

Determines size of coupling constant between 2 protons

-varies with dihedral angle

Question 4

Constitutional/structural isomers

Answer 4

Different connectivity between atoms

Question 5

Configurational isomers (stereoisomers)

Answer 5

All have same constitution but structures have different shape and can’t be inter-converted by rotating single bonds

Question 6

If stereoisomers are non-superimposable mirror images=

Answer 6

Enantiomers

Question 7

If stereoisomers aren’t enantiomers=

Answer 7

Diastereomers

Question 8

Properties of enantiomers

Answer 8

Same chemical and physical properties

Question 9

Properties of diastereomers

Answer 9

Properties aren’t the same

Question 10

Non-optically active diastereomer=

Answer 10

Meso form

Question 11

If there are 2 stereogenic centres

Answer 11

Have two sets of enantiomers

The sets are diastereomers of each other

Question 12

Chiral if:

Answer 12

• no symmetry

- only rotational symmetry

Question 13

Achiral if:

Answer 13

• plane of symmetry
• centre of inversion
• improper rotation axis (rotate then reflect)

Question 14

Achiral molecules

Answer 14

Can be superimposed onto their mirror image

Question 15

How to resolve enantiomers

Answer 15

1) Add enantiomerically pure amine
- > diastereomeric salts (different properties)
2) dissolve in ethanol (one dissolves, the other does not)
3) filter
- >seperate

Question 16

Diastereotopic protons

Answer 16

If compare molecule where Ha is replaced with D with one where Hb is replaced with D, they are diastereomers

• never in exactly the same environment
• are strongly coupled to each other

Question 17

Energy of alkenes

Answer 17

More substituted= lower in energy

Question 18

Elimination tends to be

Answer 18

Antiperiplanar

Question 19

A-value

Answer 19

A group’s preference for an equatorial position

Question 20

Trans decalin

Answer 20

Locks ring conformation

Question 21

3J (ax-ax)

Answer 21

9-13Hz

Question 22

3J (eq-eq)

Answer 22

1.5-6.5Hz

Question 23

3J (ax-eq)

Answer 23

1.5-6.5Hz

Question 24

2J (geminal)

Answer 24

11-14Hz

Question 25

4J (w)

Answer 25

1-4Hz

Question 26

Substitution in a ring favours

Answer 26

Axial leaving group

- nucleophile approach less hindered, static relief from axial leaving group

Question 27

Epoxide opening

Answer 27

Transdiaxial

Question 28

Ring stability

Answer 28

5>6>3»4~7