PROTON AFFINITY AND HEAT OF FORMATION OF VINYLIMINE CH2=CHCH=NH

The vinylimmonium cation [CH2=CHCHNH2](+), [1H](+), originating from cyclopentylamine has been studied by photoionization, ion cyclotron resonance mass spectrometry and ab initio molecular orbital calculations. A heat of formation, Delta H degrees(1300)[CH2=CHCHNH2](+) of 747 +/- 7 kJ/mol has been deduced from photoionization experiments, after correction for the thermal energy of the precursor molecules, The proton affinity of vinylimine, CH2=CHCHNH, 1, (PA(1)=908 +/- 4 kJ/mol) has been deduced from proton exchange experiments using the 'bracketing' technique. This latter, combined with the previously determined Delta H degrees(1300) [CH2=CHCHNH2](+) leads to Delta H degrees(1300)(CH2=CHCHNH)=125 kJ/mol with a possible error of +/- kJ/mol. Molecular orbital calculations, conducted at the MP2/6-311++G**//MP2/6-31G*+ZPE level, lead to comparable estimates (Delta H degrees(1300)(CH2=CHCHNH2)(+)=746 kJ/mol and Delta H degrees(1300)(CH2=CHCHNH)=128-135 kJ/mol).