Unimolecular reactions of isolated C4H8O+˙ ions derived from unbranched butenols

Abstract

The slow dissociations of C₄H₈O⁺˙ radical cations produced by ionisation of CH₂CHCH₂CH₂OH, CH₃CHCHCH₂OH, CH₂CHCH(CH₃)OH and numerous ²H-labelled analogues are reported and discussed. Each of these C₄H₈O⁺˙ species undergoes three main reactions: loss of water, a methyl radical, and an ethyl radical. However, the labelling results reveal that the specificity of hydrogen selection is different for decomposition of each of the three ionised alkenols. Extensive exchange occurs between the hydroxylic and carbon-bound hydrogens of ionised homoallyl alcohol before decomposition takes place. In contrast, the hydroxylic hydrogen of ionised but-2-en-1-ol and but-3-en-2-ol participates with a high specificity in water and ethyl radical expulsion, but not in methyl radical loss. Moreover, there is only limited interchange of the carbon-bound hydrogens in the reactions of the ionised allylic alcohols. The results of these studies are compared with those of previous investigations of the C₄H₈O⁺˙ system; in general, the agreement with earlier work is good.