1,3-H-shift pathways in C 2H 4O [rad]+ and C 2H 4O

Abstract

The 1,3-H-shifts that would interconvert the C 2H 4O aldehyde and enol isomers and the corresponding radical cations are characterized by theory to examine further the influence of Woodward–Hoffmann (WH) orbital symmetry constraints on those reactions. Reaction pathways are traced using intrinsic reaction coordinate methods. The interconversion of the ions avoids WH restraints by rotation of the methylene such that the transition state is neither suprafacial nor antarafacial. However, the neutrals appear to interconvert through a “forbidden” suprafacial transition state with an associated avoided curve crossing such that electronic ground state reactants give products in their ground electronic state. This is the first violation of WH constraints found in a 1,3-H-shift. Present results together with previous work demonstrates that 1,3-H-shifts across double bonds can be antarafacial, suprafacial or in between.