SEMI-EXPERIMENTAL $(r_s/r_e)$ STRUCTURES FOR THE HEAVY ATOM BACKBONES OF TWO MODERATELY LARGE MOLECULES OBTAINED FROM MICROWAVE SPECTROSCOPY AND QUANTUM CHEMICAL CALCULATIONS
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Date
2011
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Publisher
Ohio State University
Abstract
From recent microwave investigations of 1-methyl-4-piperidone and tropinone ground state rotational constants are available for the equatorial conformers of the normal species and the isotopologues with single substitution of all the heavy atoms. Vibration-rotation constants (alphas) were computed with Gaussian 03 (G03) for the B3LYP/cc-pVTZ model and used to convert ground state rotational constants into equilibrium rotational constants. Using the Kraitchman equations ({\em r}$_{s}$ method), the equilibrium ({\em r}$_{e}$) Cartesian coordinates were determined for all the heavy atoms in the principal axis framework. Equilibrium bond lengths and bond angles are compared with those computed with the B3LYP/cc-pVTZ model. We have compared the ground state rotational constants computed with G03, after scaling by factors based on the normal species, with observed values. The agreement is within 0.1\% for the full set of constants (0.04\% for methyl-piperidone and 0.1\% for tropinone). This agreement between experiment and theory is so good that it seems possible to use calculated ground state rotational constants in place of experimental ones for determining {\em r}$_{s}$/{\em r}$_{e}$ structures for organic molecules of this size.
Description
Author Institution: Department of Chemistry and Biochemistry, Oberlin College, Oberlin, OH 44074; Departamento de Quimica Fisica y Quimica Inorganica, Facultad de Ciencias, Universidad de Valladolid, E-47011 Valladolid, Spain; Departamento de Química Física y Química Inorganica, Facultad de Ciencia y; Tecnologia, Universidad del Pais Vasco, Ap. 644, E-48080 Bilbao, Spain; Institut fur Physikalische Chemie und Elektrochemie, Gottfried-Wilhelm-Leibniz-Universitat Hannover, Callinstrasse 3A, D30167 Hannover, Germany.