A Theoretical Investigation of the Structure and Bonding of Diazomethane, CH₂N₂

Abstract

We have investigated the electronic ground-state structure and binding mode of CH 2 N 2 by ab initio multireference perturbation calculations CASPT2 and CASPT3, using correlation consistent cc-pVTZ basis sets. Our calculations suggest that the CH 2 -N 2 binding between the CH 2 (ã 1 A 1 ) and N 2 (X 1 Σ g + ) moieties consists of a "harpooning" σ, bond from N 2 to CH 2 and a π-like bond due to the back-transfer of electrons from CH 2 to N 2 . Despite the popular dipolar resonance structures employed to represent the CH 2 N 2 binding no charge transfer between the in situ CH 2 and N 2 is observed. Our CH 2 -N 2 dissociation energy is D e ) 38.2 kcal/mol with respect to the CH 2 (ã 1 A 1 ) + N 2 (X 1 Σ g + ) adiabatic products or D e ) 27.2 kcal/mol with respect to the ground X 3 B 1 state of CH 2 . Taking into account zero point energy corrections, this value is reduced to D o ) 21.6 kcal/mol.

Atmospheric chemistry of diazomethane – an experimental and theoretical study

“…The bonding in diazomethane has previously been thoroughly characterised in CASPT2 and CASPT3 calculations showing that there is virtually no total charge transfer between the -CH 2 and -N 2 moieties, that the carbon and terminal nitrogen atoms have net negative charges, and that the CN bond consists of a single σbond, originating from the σ electrons of central nitrogen and a π -like bond due to the back-transfer of the carbon π electrons: [29] The electronic structures obtained in our MP2/augcc-pVTZ and M062X/aug-cc-pVTZ calculations of CH 2 NN comply with this depiction although the Mulliken charges obtained at the MP2 and M062X levels are significantly larger than the CASPT2 values [29]. Nonetheless, the MP2/M062X calculated dipole moments (1.47 / 1.53 D) and the structural parameters (r CH = 1.073 / 1.074 A, r CN = 1.310 / 1.292 A, r NN = 1.138 / 1.124 A and α HCH = 126 / 125°) agree as well as can be expected with experiment (μ = 1.45 D and (r 0 -structure) r CH = 1.08 A, r CN = 1.32 A, r NN = 1.12 A and α HCH = 127°) [30].…”

A theoretical study on CH2N2 isomers: structure and energetics

“…These can be considered as conservative estimates, which also account for the approximations made and for neglecting higher-order correlation effects. From Tables 1, 2, 3, 4 and 5, it is evident that all isomers considered have been previously studied at different levels of theory [11,[41][42][43][44][45][46][47][48], but we report the first systematic investigation of their molecular structure. As in most cases the method and/or the basis set used are inferior to ours, a detailed comparison of these results to ours is not too meaningful.…”

Photodissociation dynamics of the CNN free radical

“…Our heat of formation is just outside the error bars of the value derived from recent photoelectron and proton affinity measurements of Clifford et al However, the value obtained by Clifford et al involves a thermochemical cycle referenced to ⌬ r H 0 (H 2 CNN) for which the authors adopt a value of 2.85 eV based upon ab initio calculations, and this may be the cause of the discrepancy. Experimental 13,[38][39][40][41][42] and theoretical 15,[43][44][45][46][47] values for the heat of formation of diazomethane (H 2 CNN) vary from 2.2-3.3 eV.…”

“…Using our ⌬ f H 0 (CNN), ground state frequencies from IR matrix studies, 6 and tabulated values for N 2 and C, 30 41 and theoretical values, ⌬ f H 0 ͑H 2 CNN͒ ϭ3.09 eV ͑Ref. 44͒ and 3.06 eV, 47 based upon ab initio calculations of D 0 (CH 2 -N 2 ).…”