Table of Contents
ISRN Physical Chemistry
Volume 2012 (2012), Article ID 431367, 7 pages
http://dx.doi.org/10.5402/2012/431367
Research Article

Formation of Van Der Waals Complexes in Concerted Unimolecular Elimination Processes

The Institute of Chemistry, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Jerusalem 91904, Israel

Received 8 January 2012; Accepted 1 February 2012

Academic Editors: A. M. Koster and S. Sasaki

Copyright © 2012 Faina Dubnikova and Assa Lifshitz. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Potential energy surfaces for three unimolecular elimination reactions: ( C H 3 ) 3 C O H ( C H 3 ) 3 = C = C H 2 + H 2 O , C H 3 C F 3 C H 2 = C F 2 + H F , and C H 3 C H 2 C H 2 C 1 C H 3 C H = C H 2 + H C 1 were calculated using a variety of quantum chemical methods. It was shown that, in all the three cases, the transition state in the first step of the reaction leads to the production of the complex intermediates based on van der Waals interactions. In addition to the fact that the three complexes appear as intermediates on the potential energy surfaces, which means that they are not free entities, the entropy values of the two elimination products are far above those of the complexes due to their additional Sackur-Tetrode entropy. Moreover, the three vibrational frequencies of the H2O group in the (CH3)3COH complex and the H–Cl and H–F stretch frequencies in CH3CF3 and CH3CH2CH2Cl are quite different (see the various tables). The energy levels of the complexes were found to be below those of the corresponding decomposition products. Rate constants for the elimination processes were calculated from the potential energy surfaces using transition-state theory and were compared to available experimental data.