Quantum chemical studies on acidity-basicity behaviors of some bipyridine derivatives

Abstract

The protonation of six isomeric forms of bipyridine has been investigated by means of different quantum chemical methods (i.e. semi-empirical (PM5), DFT (B3LYP/6-31G(d)) and ab initio (HF/6-31G(d)). It is concluded that 2,2'-bipyridine exists as transoid isomer, 2,3'-bipyridine as cisoid isomer and 3,3'-bipyridine coexist in equal amount of cisoid and transoid isomeric forms.

Hydrogen-Bonding Trends in a Bithiophene with 3- and/or 4-Pyridyl Substituents

“…When 2 equiv of triflic acid was added to 5 , however, the signals for the 3-pyridyl subunit shifted more than those of the 4-pyridyl subunit, with a downfield shift of ∼0.2 ppm for the two iminic α protons and ∼0.4 ppm for the aryl protons for the 3-pyridyl ring and only a ∼0.1 ppm shift of the 4-pyridyl signals. These data suggested that the 4-pyridyl subunit was being protonated with the first equivalent of triflic acid in these trials and that it was the more basic of the two nitrogen atoms, as has been observed by others before. , With the second equivalent of triflic acid, the 3-pyridyl N atom was then expected to be protonated. The increased basicity of the 4-pyridyl ring is consistent with the increased N atom electron density originating from the in-resonance thiophene rings.…”

“…These data suggested that the 4-pyridyl subunit was being protonated with the first equivalent of triflic acid in these trials and that it was the more basic of the two nitrogen atoms, as has been observed by others before. 24 , 25 With the second equivalent of triflic acid, the 3-pyridyl N atom was then expected to be protonated. The increased basicity of the 4-pyridyl ring is consistent with the increased N atom electron density originating from the in-resonance thiophene rings.…”