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.

Salivary gland disorders and diseases: Diagnosis and management

“…The frequency blue shift of the pyridine ring vibration modes caused by formation of the H‐bonding can be interpreted based on two theories. (1) In the N‐type H‐bonds XH ··· N, the intermolecular charge transfer caused by the intermolecular hyperconjugation n (N) → σ*(HX) induces intramolecular charge redistribution, mainly the intramolecular charge transfer from the two antibonding orbitals σ*(meta‐CC) to n (N) 14, 21, 22. This intramolecular charge transfer is just the inverse process of the intramolecular hyperconjugation n (N) → σ*(meta‐CC).…”

“…In our previous works, we have studied the N‐type hydrogen bonds of pyridine with proton donors such as CHX 3 (X = F, Cl, Br), HCONH 2 , H 2 O, and CH 3 COOH 21, 22 and discussed the effects of hydrogen bonding on the ring stretching mode of pyridine. We found that the frequency blue shift in the ring stretching mode was related to the sigma meta‐CC bonds of the pyridine ring, whereas the π bond was not involved.…”

Soft X-ray Absorption Spectroscopy of Liquids for Understanding Chemical Processes in Solution

“…[42][43][44] The HB structures of pyridine-water mixtures in aqueous solutions have been also studied by neutron diffraction, 45 nuclear magnetic resonance (NMR), 46,47 and theoretical methods. [48][49][50][51][52][53] Although local structures of aqueous pyridine solutions are extensively studied by experimental and theoretical methods, the concentration-dependent structural changes of the pyridinewater mixtures have not yet been fully understood. It is because the molecular interactions of pyridine are not easily observed separately from those of solvent water.…”

A computational study on the ring stretching modes of halogen‐substituted pyridine involved in H‐bonding

“…(1) In the N-type H-bonds XAHÁÁÁN, the intermolecular charge transfer caused by the intermolecular hyperconjugation n(N) ! r*(HX) induces intramolecular charge redistribution, mainly the intramolecular charge transfer from the two antibonding orbitals r*(meta-CC) to n(N) [14,21,22]. This intramolecular charge transfer is just the inverse process of the intramolecular hyperconjugation n(N) !…”

“…In our previous works, we have studied the N-type hydrogen bonds of pyridine with proton donors such as CHX 3 (X ¼ F, Cl, Br), HCONH 2 , H 2 O, and CH 3 COOH [21,22] and discussed the effects of hydrogen bonding on the ring stretching mode of pyridine. We found that the frequency blue shift in the ring stretching mode was related to the sigma meta-CC bonds of the pyridine ring, whereas the p 6 6 bond was not involved.…”