Premium
The Basicity of Unsaturated Hydrocarbons as Probed by Hydrogen‐Bond‐Acceptor Ability: Bifurcated NH + ⋅⋅⋅π Hydrogen Bonding
Author(s) -
Stoyanov Evgenii S.,
Stoyanova Irina V.,
Reed Christopher A.
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200800337
Subject(s) - chemistry , hexamethylbenzene , mesitylene , hydrogen bond , medicinal chemistry , benzene , protonation , toluene , photochemistry , hydrogen , pyridine , conjugated system , ion , molecule , organic chemistry , polymer
The competitive substitution of the anion (A − ) in contact ion pairs of the type [Oct 3 NH + ]B(C 6 F 5 ) 4 − by unsaturated hydrocarbons (L) in accordance with the equilibrium Oct 3 NH + ⋅⋅⋅A − + n L ⇄ [Oct 3 NH + ⋅⋅⋅L n ]A − has been studied in CCl 4 . On the basis of equilibrium constants, K , and shifts of ν NH to low frequency, it has been established that complexed Oct 3 NH + ⋅⋅⋅L n cations with n =1 and 2 are formed and have unidentate and bifurcated NH + ⋅⋅⋅π hydrogen bonds, respectively. Bifurcated hydrogen bonds to unsaturated hydrocarbons have not been observed previously. The unsaturated hydrocarbons studied include benzene and methylbenzenes, fused‐ring aromatics, alkenes, conjugated dienes, and alkynes. From the magnitude of the redshifts in the NH stretching frequencies, Δ ν NH, a new scale for ranking the π basicity of unsaturated hydrocarbons is proposed: fused‐ring aromatics≤benzene