trans: cis Olefin ratios in the elimination reactions of 1-benzylethyl halides and toluene-p-sulphonate in different base–solvent systems

Abstract

trans:cis Olefin ratios have been determined for the elimination reactions of 1-benzylethyl halides and tosylate PhCH₂CHXMe (X = Br, I, or OTs) in different base–solvent systems. The trans : cis ratio is substantially the same for X = Br and I, whereas a lower value is observed for X = OTs. The basicity of the nuclecphile does not appear significantly to affect the trans : cis ratio. However, an increase in this ratio is observed in going from a protic to a dipolar aprotic solvent and from EtONa–EtOH to Bu^tOK–Bu^tOH. Ion association increases the trans : cis ratio when X = I and Br. whereas it has practically no effect on the geometrical orientation when X = OTs. The present results are discussed by comparison with those obtained in the corresponding reactions of non-activated substrates.