Lecture 22

1. (a) There are 3 chiral centres in menthol (denoted by *).

(b) The number of stereoisomers possible for this molecule is 2³ or 8.

(d) The structure of naturally occurring menthol is given below.

(e) The structure of (+)-isomenthol is given below.

(f) The structure of (+)-neomenthol is given below.

(g) The chair forms of the three isomers (-)-menthol, (+)-isomenthol and (+)-neomenthol are given below.

Hence the order of stability is (-)-menthol > (+)-neomenthol > (+)-isomenthol.

Lecture 23

1. The product in this reaction may be predicted by following the Felkin Anh model. According to this model, the attack by a nucleophile takes place through a conformation where the largest group is perpendicular to the carbonyl group.

2. This is the manifestation of the criteria of antiperiplanar elimination in an E2 reaction. Of the two hydrogens 1 and 2 only the 1 are in suitable position to be abstracted by base in a transition state for E2 reaction.

Lecture 24

Lecture 25

The relationship between reduced mass (μ) of a bond between two atoms of masses m1 and m2 is given by

In this case, this may be written as

Here m O = 15.999 and m H =1.008, then,

If m H is replaced by m D then,