An experimental and theoretical study of the interaction of n-butylmercaptan with phenylacetylene in acid medium

Abstract

The geometric and electronic structure of phenylacetylene (PA), its carbocations formed in the addition of the proton to PA, n-butylmercaptan (BM), the products of the addition of BM to PA carbocations, and the final products of the electrophilic addition of BM to PA was studied using the B3LYP hybrid density functional and the 6-31G* basis set. The proton affinity of the molecules studied and the products of the addition of BM to PA was calculated. The conclusion was drawn that an important role in nonradical reactions of the addition of BM to PA was played by the structure of PA carbocations, which determined the structure of the products of the interaction of BM with PA. The classic form of the PA carbocation led to the formation of only 1,1-substituted ethylene, and the nonclassic form, to the formation of either the trans or cis form. The addition of BM to carbocations was shown to be an activationless reaction. The energy difference between the final products was small, and conclusions of the formation of only one isomer could not be drawn with confidence. The same follows from a comparison of the calculated vibrational frequencies of the products of the interaction of BM with PA with the experimental IR spectra.