UNIMOLECULAR REARRANGEMENTS CONNECTING HYDROXYETHYLIDENE (CH3-C-OH), ACETALDEHYDE (CH3-CH=O), AND VINYL ALCOHOL (CH2=CH-OH)

Ab initio molecular orbital theory at uniform and high levels has been used to study hydroxyethylidene and its isomers acetaldehyde and vinyl alcohol. Vinyl alcohol and hydroxyethylidene are predicted to lie 47 and 213 kJ mol-1, respectively, above acetaldehyde. Hydroxyethylidene, despite its high relative energy, is predicted to be separated by significant barriers (118 and 98 kJ mol-1, respectively) from its lower energy isomers acetaldehyde and vinyl alcohol. The transition structure for rearrangement of vinyl alcohol to acetaldehyde is found to lie lower in energy than the transition structures connecting hydroxyethylidene to acetaldehyde or vinyl alcohol. The rate-determining step for the production of CO from any of the three isomers is predicted to correspond to methane elimination from acetaldehyde, and this is consistent with observed effects.