Stereochemistry and Stereoelectronics of Azines. 13. Conformational Effects on the Quadrupolarity of Azines. An Ab Initio Quantum-mechanical Study of a Lateral Synthon

Author

Rainer Glaser, Missouri University of Science and TechnologyFollow
Michael A. Lewis
Zhengyu Wu

Abstract

The quadrupole moment of formaldazine, H₂C=N-N=CH₂, has been studied for the trans structure (∠(C-N-N-C) = τ = 180°) and a series of gauche structures (τ > 120°). Restricted Hartree-Fock theory, second-order Møller-Plesset theory, and quadratic CI theory have been used in conjunction with the basis sets 6-31G*, 6-31G**, 6-311G**, and 6-311++G**. Formaldazine is a quadrupolar molecule with primitive quadrupole moment tensor components of Q_xx = -22.4, Q_yy = -20.4 and Q_zz = -25.6 DÅ at the theoretical level QCISD/6-311++G**. The examination of the theoretical level dependency shows that the reliable computation of a quadrupole moment requires the use of a flexible basis set. A large part of the component Q_zz = -25.6 DÅ is due to the π-system and compares, on a per electron basis, with the Q_zz value of benzene. Conformational changes of the azines in the range 120° < τ < 180° have but a minute effect on the energy and are associated with only minor electronic relaxation. These conformational changes alter the quadrupole moment tensor components less than ΔQ_xx = +0.4, ΔQ_yy = +1.6 and ΔQ_zz = -1.0 DÅ at QCISD/6-311++G**//QCISD/6-31G*. The direction of these changes is explained by consideration of the rotation of the CN-π-systems and a small reduction of the CN bond polarity in the gauche structures. The Q_zz component of formaldazine is representative of the quadrupole moment tensor component along the direction of the C2 axis of the azine bridge as such. Hence, the results of this study suggest that azines can engage in strong quadrupole-quadrupole interactions and can be employed as lateral synthons in crystal engineering.

Recommended Citation

R. Glaser et al., "Stereochemistry and Stereoelectronics of Azines. 13. Conformational Effects on the Quadrupolarity of Azines. An Ab Initio Quantum-mechanical Study of a Lateral Synthon," Journal of Molecular Modeling, vol. 6, no. 2, pp. 86 - 98, Springer Verlag, Feb 2000.

The definitive version is available at https://doi.org/10.1007/s0089400060086

Department(s)

Chemistry

Keywords and Phrases

Azine; Conformational analysis; Crystal engineering; Potential energy surface analysis; Quadrupole; Synthon

International Standard Serial Number (ISSN)

1610-2940; 0948-5023

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2000 Springer Verlag, All rights reserved.

Publication Date

01 Feb 2000