Nucleophilic reactivity. Part VIII. A comparison of 1,2- and 1,4-elimination

Abstract

The relative rates of the iodide-promoted 1,2- and 1,4-eliminations of ethylene dichloride and 1,4-di-iodobut-2-ene and of the base-promoted elimination of ethylene dichloride and 1,4-dichlorobut-2-ene are similar. The somewhat higher reactivity of the 1,2-dihalides is attributed to differences in rotational entropy of the terminal halogenomethyl groups. The cis- and trans-dimethanesulphonates of but-2-ene were found to react at comparable rates with iodide ions. These and previous results for the analogous dimethanesulphonate esters are discussed in terms of the probable transition-state structures.