Abinitio study on radical anions of nitro compounds

Abstract

This paper is dedirnted to Professor Sigeru Huzinaga on the occasion of his 65th birthdayFABIO RAMONDO. Can. J. Chem. 70, 3 14 (1992).The results of ab itritio molecular orbital calculations on some nitro compounds, RN02 (R = CH,, CF,, CH,F, BH,, BF,, BHF, C6H5) and on the corresponding radical anions are reported. The geometries of the neutral and charged species were optimized at the SCF and MP2 levels of theory employing the 6-31G* and the 6-3 1 +G* basis sets. The rotation about the CN and BN bonds reveals distinct conformations for each molecule and vibrational frequencies were determined for such structures. All the employed levels of theory predict structural differences between neutral and charged molecules. The major geometrical changes occurring by electron adding to R N 0 2 consist in the lengthening of the NO bonds and in the shortening of the CN and BN bonds. The radical anions are calculated to be pyramidal at nitrogen in the stable conformers of CH,NO,-, CF3N02-, CH,FNO,-, while, for the T-electron-accepting substituents (BH,, BHF, BF,, C6H5), the anion is planar. Electron correlation energy corrections in the framework of Moiler-Plesset perturbation theory were included to determine relative stabilities between different conformations. At the MP4/6-3 1G*//MP2/ 6-31G* level, an easy rotation of the NO, group is predicted for all the radical anions and neutral molecules with the exception of BH?NO,-, BF2N02-, and BHFN0,-, which show high torsional barriers about the BN bond.

Revisiting the heterogeneous electron-transfer kinetics of nitro compounds

“…Thus the nitrogen center is more than halfway toward tetrahedral geometry in the radical anions, as predicted by DFT. This pyramidalization has been predicted in earlier calculations [26,27]. Again, the explanation is rather straightforward.…”

On the binding of electrons to nitromethane: Dipole and valence bound anions

“…The CN torsion frequency for the CH 3 NO 2 molecule corresponds to 2.6 meV and increases to 27 meV in the valence anion as a result of the tetrahedral structure of the ground state of the anion ͑increased hindrance of the torsional motion͒. 3 Thus we assign the ''breaks'' in the field detachment curves to field ionization of a mixed dipole-valence state in which the low energy torsional frequency gives rise to fast vibrational FIG. 5.…”

“…This is consistent with a number of theoretical and experimental studies of the nitromethane anion. 3,25 Since the main goal in performing these experiments was the determination of the adiabatic electron affinity of nitromethane, it was necessary to identify the origin ͑vЈϭ0, vЉϭ0͒ of the vibrational progressions for CH 3 NO 2 Ϫ and CD 3 NO 2 Ϫ spectra. The photoelectron spectra presented in Fig.…”

“…There, the following values of the EA's were reported: 0.43Ϯ0.2 and 0.35Ϯ0.2 eV for CH 3 NO 2 colliding with Cs and K atoms, respectively, and 0.39Ϯ0.2 eV for CD 3 NO 2 colliding with Cs atoms. Thus, we assign the peaks at the arrows marked on the spectra as the origin transitions for CH 3 ror bar in this case reflects the uncertainty in choosing the origin peak.…”

“…2 For the specific case of nitromethane, Adamowicz has calculated a dipole-bound electron affinity of Ϸ3 meV. Other studies 3 show that in the CH 3 NO 2 Ϫ valence state the -CNO 2 group becomes nonplanar with a dihedral angle of 148.5°between the NO 2 plane and the CN bond. Thus, the dipole and valence adiabatic states are coupled through a breakdown of the Born-Oppenheimer approximation perhaps as a result of the wagging motion of the -NO 2 group.…”