title: Theoretical study on effects of hydrogen bonding on the ring stretching modes of pyridine.
abstract: Pyridine generally acts as the proton acceptors in the hydrogen bonding interaction by using its lone pair n(N) or pi-electrons. Some previous research indicated that for the N-type H-bond, the ring breathing mode v(1), the N-para-C stretching mode v(6a) and the meta-CC stretching mode v(8a) of pyridine showed a frequency blueshift but the triangle mode v(12) had no change in frequency. Both electrostatic interaction and charge transfer caused by intermolecular hyperconjugation n(N)-->sigma( *)(HX) have contributions to the frequency blue shifts, while charge transfer is predominant at equilibrium intermolecular distance. An intramolecular hyperconjugation between the lone pair n(N) and the two sigma( *)(meta-CC) orbitals in the pyridine ring provides a reasonable interpretation for the effect of charge transfer on the ring stretching modes upon formation of the N-type H-bonding.
authors.affiliation: School of Chemistry and Chemical Engineering, Southwest University, Beibei District, 400715 Chongqing, People's Republic of China. aylifnsy@swu.edu.cn
authors.forename: An Yong
authors.initials: AY
authors.lastname: Li
authors.forename: Hong Bo
authors.initials: HB
authors.lastname: Ji
authors.forename: Li Juan
authors.initials: LJ
authors.lastname: Cao