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Conjugation of two functional groups through an unsaturated system
Author(s) -
Exner Otto,
Böhm Stanislav
Publication year - 2006
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.998
Subject(s) - chemistry , isodesmic reaction , substituent , resonance (particle physics) , acceptor , interaction energy , conjugated system , stereochemistry , dipole , computational chemistry , crystallography , molecule , density functional theory , organic chemistry , quantum mechanics , physics , polymer
Abstract Energies of 51 1‐( E ),4‐( E )‐disubstituted 1,3‐butadienes ( 1 ), 36 1,4‐disubstituted benzenes ( 2 ) and 36 ( E )‐1,2‐disubstituted ethenes ( 3 ) with dipolar substituents were calculated at the B3LYP/6–311 + G(d,p) level and evaluated in terms of isodesmic reactions expressing the interaction of substituents through the conjugated system. The energy of interaction reaches up to 40 kJ mol −1 , it is roughly similar in the three series and most regular in the series 1 . While its correlation within the framework of dual substituent parameter analysis lacks physical meaning, it is possible to separate the conjugative (resonance) component by subtracting the inductive component with reference to 1,4‐disubstituted bicyclo[2.2.2]octanes 4 . The conjugative interaction is strongly stabilizing for the combination acceptor–donor and destabilizing for two donors; in these cases it is parallel to changes of geometry as they are predicted by the common resonance equations. Interaction of two acceptors is weak; in addition, there are groups that cannot be classified either as donors or as acceptors. Therefore, one can construct a scale of the resonance ability of donors in conjugation with an acceptor and vice versa, but it is not possible to express the interaction of two donors or of two acceptors on a unified scale for all substituents. The resonance description is certainly appropriate for the typical examples (interaction of NO 2 and NH 2 ) but should not be generalized to all possible structures. Copyright © 2005 John Wiley & Sons, Ltd.