Exploring rare chemical phenomena using fractional nuclear charges: The cis-effect in N2F2

• Type: Article in International Scientific Journal
• Date: 2018

Authors

Teixeira, F (Author) Other; Andre Melo (Author) FCUP; Natalia N D S Cordeiro (Author) FCUP

Journal

Title: International Journal of Quantum Chemistry

Vol. 118

ISSN: 0020-7608

Publisher: Wiley-Blackwell

Indexing

ISI Web of Knowledge - 3 Citations

Scopus - 2 Citations

Other information

Authenticus ID: P-00P-HBM

DOI: 10.1002/qua.25662

Abstract (EN): The so called cis-effect, in which the cis form of an ethylenic compound is more stable than its trans-isomer. is a good example of a rare phenomenon described only for a few isomeric pairs. In this work, a novel approach to the study of this rare effect is attempted by changing the nuclear charges of the fluoride and nitrogen in cis- and trans-N2F2. This allowed the survey of a large number of isomeric pairs composed sharing the same molecular topology, while varying the electronegativity of selected atoms. The results show an increasing stabilization of the cis-isomers when increasing the electronegativity of the fluoride atoms. in line with the accepted zeitgeist linking this effect to the electronegativity of the peripheral groups. However, a similar behavior was also found when varying the nuclear charge of the nitrogen atoms. This prompted a more in-depth look at the electronic structure of these compounds, gathering descriptors from Bader's Quantum Theory of Atoms in Molecules. A descriptive linear model was derived from these descriptors using a two-stage step-wise linear regression. Further inspection of the model linked the destabilization of the trans-isomers with a deviation from the idealized trigonal planar geometry predicted by the Valence Shell Electron Pair Repulsion model. This tendency was explained by an increase in the ionic character of the N-F bonds. Furthermore, the current model suggests that the Coulombic repulsion between the two peripheral atoms in the cis-isomers prevents such large deviations from the idealized geometry, thus, contributing to their relative stabilization. The qualitative rules governing the cis-effect in N2F2 were further tested on other compounds with a similar bond topology.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 15