Precise Equilibrium Structure of Benzene

• Published in: Journal of the American Chemical Society 2023-10, Vol.145 (40), p.21785-21797
• Main Authors: Esselman, Brian J., Zdanovskaia, Maria A., Owen, Andrew N., Stanton, John F., Woods, R. Claude, McMahon, Robert J.
• Format: Article
• Language: English
• Subjects: Chemistry
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.3c03109

Recent advances in gas-phase structure determination afford outstanding agreement between the CCSD­(T)/cc-pCVTZ-corrected semi-experimental (re SE) equilibrium structures and their corresponding best theoretical estimates (BTEs) of the equilibrium structures (re ) based upon corrections to the CCSD­(T)/cc-pCV5Z geometries for the aromatic heterocycles pyrimidine and pyridazine. Herein, that same analysis is extended to the fundamental aromatic molecule benzene, using published experimental spectroscopic data for a total of 11 available isotopologues. The incorporation of rotational constants from all of these isotopologues and CCSD­(T) corrections to address the impacts of both the vibration-rotation interaction and electron-mass distribution results in a highly precise and accurate re SE structure. The CCSD­(T)/cc-pCV5Z optimized geometry has been further corrected to address a finite basis set, untreated electron correlation, relativistic effects, and a breakdown of the Born–Oppenheimer approximation. This analysis achieves outstanding agreement between the re (BTE) and re SE structural parameters of benzene to a highly satisfying level (0.0001 Å), an agreement that surpasses our recently published structures of the aforementioned nitrogen-substituted benzene analogues. The D 6h geometry of benzene is now known to an unprecedented precision: R C–C = 1.3913 (1) Å and R C–H = 1.0809 (1) Å. The mutual agreement between theory and experiment presented in this work validates both, substantially resolving all discrepancies between the re SE and theoretical re structures available in the literature.