Steric Hindrance and Geometrical Isomerism

Abstract

IT is not often that evidence in the form of steric hindrance is available for confirming the configurations of geometrical isomers among ethylenic compounds. The following observations are thus of interest. cis--Dibromocinnamic acid¹ (m.p. 100°) esterifies to the extent of only 6 per cent in one hour, and 33 per cent in 16 hours, by the Fischer-Speier method, whereas the trans-acid¹ (m.p. 136°) is esterified completely in one hour. This is in conformity with my earlier observation² in regard to the different modes of addition of bromine to phenylpropiolic acid and its methyl ester.