Surfing π clouds for noncovalent interactions: arenes versus alkenes.
A comparative study of molecular balances by NMR spectroscopy indicates that noncovalent functional-group interactions with an arene dominate over those with an alkene, and that a π-facial intramolecular hydrogen bond from a hydroxy group to an arene is favored by approximately 1.2 kJ mol(-1). The strongest interaction observed in this study was with the cyano group. Analysis of the series of groups CH2CH3, CH=CH2, C≡CH, and C≡N shows a correlation between conformational free-energy differences and the calculated charge on the C(α) atom of these substituents, which is indicative of the electrostatic nature of their π interactions. Changes in the free-energy differences of conformers show a linear dependence on the solvent hydrogen bond acceptor parameter β.
Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ (UK). a.e.aliev@ucl.ac.uk.
Abil E
AE
Aliev
Josephine R T
JR
Arendorf
Ilias
I
Pavlakos
Rafael B
RB
Moreno
Michael J
MJ
Porter
Henry S
HS
Rzepa
William B
WB
Motherwell
D000475:Alkenes / Q000737:chemistry*; D006838:Hydrocarbons / Q000737:chemistry*; D008958:Models, Molecular
D000475:Alkenes; D006838:Hydrocarbons
NMR spectroscopy; conformational analysis; molecular balances; noncovalent interactions; π interactions