DFT and topological study on the rearrangement observed in the mass spectra of N,N-dimethylhydrazones of unsaturated aldehyde

Density functional theory(DFF) and topological analysis have been employed to study the rearrangement mechanisms observed in the mass spectra of N,N-dimethyldrazone derivatives of 5-unsaturated straight-chain aldehydes. There are two types of rearrangement mechanisms: cycloalkene budding and McLafferty. All the stationary points were optimized at B3LYP/6-31G* level. Transition states were further confirmed with vibrational analysis. For cycloalkene budding rearrangement, a stable two-ring intermediate was found along the reaction process. The transition states are asynchronous, i.e. one bond is formed. (or broken) first. McLafferty rearrangement is also a two-step process. These two reactions are feasible in the mass spectra of gas phase with excessive energies. Our results are in agreement with the experimental suggestions. (C) 2001 Elsevier Science B.V. All rights reserved.