Relative Rates of Transesterification vis-à-vis Newman’s Rule of Six

The relative reactivity of a systematic
series of simple aliphatic
acetate esters has been measured. Exposure of pairs of esters of increasing
remote steric hindrance (by altering the degree of branching of the
ester alkyl group) to a methanolic solution of Cs2CO3 proved to be a reliable (and general) method for quantitating
the rate differences in these base-catalyzed transesterification reactions.
The trends in relative rates are in accordance with the qualitative
“Rule of Six” put forward by Melvin S. Newman in 1950,
as deduced then from interpretation of earlier reports of ease of
Fischer esterification reactions.