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Electron Delocalization in Electron‐Deficient Alkenes and Push‐Pull Alkenes
Author(s) -
Džambaski Zdravko,
BaranacStojanović Marija
Publication year - 2017
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.201601661
Subject(s) - delocalized electron , chemistry , electron , electron delocalization , double bond , alkene , reactivity (psychology) , electron donor , crystallography , photochemistry , stereochemistry , organic chemistry , physics , catalysis , medicine , alternative medicine , quantum mechanics , pathology
We have studied π electron delocalization in electron‐deficient alkenes and push‐pull alkenes by means of natural bond orbital analysis at the B3LYP/6‐311+G(d,p) level. The study revealed that the rarely mentioned π electron donation from an electron‐accepting group (Acc) toward the C=C double bond in push‐pull alkenes and electron‐deficient alkenes can provide up to 10 % of total π electron stabilizing energy of a push‐pull system and as much as 45 % in a strongly electron‐deficient tetracyanoethene. The Acc → C=C bond π electron donation is more intense in s‐trans than in s‐cis conformational arrangement, but is less dependent on Z/E isomerism in push‐pull alkenes, being slightly more pronounced in Z isomers. Among different Acc substituents, CN and COO ‐ groups contribute the largest percent of stabilizing energy and NO 2 the smallest. Increase in the number of Acc groups increases percentage contribution of Acc → C=C bond π electron delocalization to a system stabilization. A difference in π * C=C orbital occupancy between isomers can be related with their chemical reactivity.