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Turn: Weak Interactions and Rotational Barriers in Molecules-Insights from Substituted Butynes.
- Source :
-
Journal of Physical Chemistry A . Nov2016, Vol. 120 Issue 44, p8896-8906. 11p. - Publication Year :
- 2016
-
Abstract
- The nature of the bonding and a definite preference for an eclipsed geometry in several substituted but-2-ynes, including certain novel derivatives are uncovered and examined. In particular, we consider the molecular species R3C-C-C-CR3 (where R= H, F, Cl, Br, I, and CN), their R3C-B-N-CR3 analogues, and a few novel exo-bridge systems with intramolecular hydrogen bonds running parallel to the C-C-C-C chain. In some cases, the potential energy surfaces are remarkably flat-so flat, in fact, that free rotation is predicted for those molecules at very low temperatures. A systematic investigation of the bonding in the halogenated butynes demonstrates that the eclipsed conformation actually becomes more stable relative to the staggered form as R becomes larger and less electron-withdrawing. The rotational barriers (the differences in energy between the eclipsed and staggered geometries) are magnified significantly, however, in a special case where selected R groups at the ends of the R3C-C-C-CR'3 molecule form hydrogen bonds parallel to the C-C-C-C core. In those systems, the hydrogen bonds serve as a weak locking mechanism that favors the eclipsed conformation. A comparison of HF and uncorrected DFT methods versus the MP2(full), CCSD(T), and other dispersion-corrected methods confirms that correlation accounts to a significant extent for barriers in substituted butyne compounds. In the hydrogen-bonded systems, the barriers are comparable to and larger in some cases than the barriers observed for the more extensively studied ethane molecule. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 10895639
- Volume :
- 120
- Issue :
- 44
- Database :
- Academic Search Index
- Journal :
- Journal of Physical Chemistry A
- Publication Type :
- Academic Journal
- Accession number :
- 119521142
- Full Text :
- https://doi.org/10.1021/acs.jpca.6b09155