The x˜¹A₁ and ã³B₂States of o-Benzyne: A Theoretical Characterization of Equilibrium Geometries, Harmonic Vibrational Frequencies, and the Singlet-Triplet Energy Gap

Using the methods of ab initio electronic structure theory, we have characterized the equilibrium geometries for the ground state and first excited state of the important organic reaction intermediate o-benzyne. Additionally, a complete set of harmonic vibrational frequencies and infrared absorption intensities has been determined at the ground-state equilibrium. of great interest here is the character of the dehydrogenated C—C bond. Our best prediction for this bond distance is 1.25-1.26 Å, and for the harmonic vibrational frequency corresponding to the normal mode involving the stretch of this bond 1965–2010 cm−1. This result is consistent with the gas-phase photodetachment study of Leopold, Miller, and Lineberger but is inconsistent with four independent matrix isolation infrared studies of o-benzyne. Several reassignments of observed fundamental vibrational frequencies are suggested. Also of interest is the energy gap between the X˜1A1 state and the low-lying ã3B2 state which has been predicted herein to lie at 33.3 kcal/mol. © 1989, American Chemical Society. All rights reserved.