Decomposition of methylamino and aminomethyl radicals. The heats of formation of methyleneimine (CH_2=NH) and hydrazyl (N_2H_3) radical

Abstract

A kinetic analysis of the thermal decomposition of methylamino and aminomethyl radicals into methyleneimine, reactions (1) and (2): (1) CH_3N^•H → CH_2=NH + H (2) C^•H_2NH_2 → CH_2=NH + H leads to ΔH_f^0(CH_2=NH) = 25.0 ± 3 kcal/mol in excellent agreement with ion cyclotron resonance spectroscopy measurements and to a pi bond energy of E_π = 55.0 kcal/mol in CH_2=NH which is comparable but smaller than to the corresponding value in CH_2=CH_2 (63.7 kcal/mol). Assuming that E_π (CH_2=NH) = 0.5 [E_π (CH_2=CH_2) + E_π (NH=NH)] then requires that E_π (NH=NH) = 46.8 kcal/mol in diimine and BDE(N_2H_3-H) = 87.5 kcal/mol i.e. about 11.5 kcal/mol larger than current data for hydrazine but otherwise consistent with additional evidence. The entropy and heat capacity of methyleneimine, calculated from recent infrared and microwave spectroscopic data using the rigid rotor harmonic oscillator approximation, are also reported.

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