Intramolecular homolytic substitution in selenoxides and selenones

G3(MP2)-RAD calculations provide activation energies for intramolecular homolytic substitution in the 4-(alkylselenoxo)butyl and 4-(alkylselendioxo)butyl radicals ranging from 21-39 kJ mol(-1), and 143-170 kJ mol(-1) for the selenoxide and selenone, respectively. Arrhenius data translate into rate constants for ring-closure of 1.5 x 10(5)-2.5x 10(8) s(-1) (80 degrees) for the selenoxides, and 5.4 x 10(-14)-5.1 x10(-11) s(-1) (80 degrees) for the corresponding selenones. NBO analyses show alkyl radicals are electrophilic during homolytic substitution at selenoxide selenium. The dominant orbital interaction in the transition state is worth 2413 kJ mol(-1) and involves the SOMO and the lone-pair of electrons on selenium. The corresponding selenones are calculated to ring-close through transition states in which alkyl radicals are nucleophilic, but involve weak (SOMO-> sigma* and SOMO-> pi*) interactions. Consequently, this chemistry is not viable for selenones because of the lack of lone-pairs of electrons on the chalcogen. Crown Copyright (C) 2016 Published by Elsevier Ltd. All rights reserved.