Definitive Heat of Formation of Methylenimine, Ch 2 =nh, and of Methylenimmonium Ion, Ch 2 Nh

A long-standing controversy concerning the heat of formation of methylenimine has been addressed by means of the W2 (Weizmann-2) thermochemical approach. Our best calculated values, ∆H◦ f,298(CH2NH)=21.1±0.5 kcal/mol and ∆H◦ f,298(CH2NH + 2 )=179.4±0.5 kcal/mol, are in good agreement with the most recent measurements but carry a much smaller uncertainty. As a byproduct, we obtain the first-ever accurate anharmonic force field for methylenimine: upon consideration of the appropriate resonances, the experimental gas-phase band origins are all reproduced to better than 10 cm−1. Consideration of the difference between a fully anharmonic zero-point vibrational energy and B3LYP/cc-pVTZ harmonic frequencies scaled by 0.985 suggests ∗Dedicated to Prof. Paul von Ragué Schleyer on the occasion of his 70th birthday †Present address: Chemistry Department, Pensacola Christian College, 250 Brent Lane, Pensacola, FL 32503 ‡Author to whom correspondence should be addressed. E-mail: [email protected]