1!

17

Conformational analysis

4. Conformational analysis

(E)-dodec-10-en-1-yl acetate

18

Conformational analysis of ethane

What does a rotaional barrier of 12 kJ/mol mean?

k= 48.9 x 109 s-1

conformer

4. Conformational analysis

H

HHH

HH

2!

19

Conformational analysis of butane

4. Conformational analysis

What does a rotaional barrier of 20 kJ/mol mean?

k= 48.9 x 109 s-1

20

Conformational analysis of cyclobutane - not a flat molecule!

4. Conformational analysis

Ring strain is caused by:

(i)  deviation from ideal bond angels (109.5°)

(ii)  non-optimal conformations

3!

21

Conformational analysis of cyclohexane

4. Conformational analysis

22

Conformations and Configurations -never mistake them!

4. Conformational analysis

•  structures that can be interconverted by rotation about single bonds are conformations of the same molecule. [Conformations representing energy minima are termed conformers]

•  structures that can only be interconverted by breaking bonds have different configurations; they are stereoisomers.

4!

23 23

Concepts

•  conformation/configuration •  Newman projection •  staggered, eclipsed •  anti-periplanar, syn-periplanar, gauche •  chair, twisted

4. Conformational analysis