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

Abstract

Density functional method B3LYP plus the AUG-cc-pVDZ and AUG-cc-pVTZ basis sets is used to investigate ring normal modes of halogen-substituted pyridines involved in the NÁÁÁHAX H-bonds with HX (X ¼ F, Cl). The results demonstrated that the formation of hydrogen bond leads to an increase in the frequencies of the ring breathing mode v 1 , the N-para-C stretching mode v 6a and the meta-CC stretching mode v 8a , whereas there is no change in the triangle mode v 12 for free pyridine and a smaller blue shift for substituted pyridines. There is a strong coupling between the CAY stretching vibration and the triangle mode (ortho-and para-substituted) or the breathing mode (metasubstituted) in substituted pyridines, which leads to the frequency decrease in the triangle or breathing modes. The natural bond orbital analysis suggests that electrostatic interaction and charge transfer caused by the intermolecular and intramolecular hyperconjugations are the origin of the frequency blue shift in the ring stretching modes.

Origin of the blue‐shifted hydrogen bond in the vibrational Raman spectra of pyridine–water complexes: A density functional theory study

“…[60,61] For N-heterocyclic compounds such as pyridine and pyrimidine hydrogen bonding to water has been studied by several groups using Raman spectroscopy, often in a concentration-dependent manner and in combination with DFT calculations for interpreting the associated spectral changes. [37,[62][63][64][65][66][67][68][69] The Raman spectra of the corresponding binary mixtures, specifically the ringbreathing mode of the N-heterocycle, exhibit significant changes with increasing water mole fraction, which can be explained with the help of DFT-computed Raman spectra from individual isolated hydrogen-bonded complexes. For pyridine as the most widely investigated N-heterocyclic compound involved in hydrogen bonding with water, Kreyenschmidt et al [70] studied pyridinemethanol binary solutions using four channel Raman spectroscopy and reported continuous blue-shift with changing solvent concentrations.…”

Cycloaddition of CO2 to epoxides by highly nucleophilic 4-aminopyridines: establishing a relationship between carbon basicity and catalytic performance by experimental and DFT investigations

“…The in situ IR spectrum of the solution in 1545-1600 cm -1 (Figure S47a) initially displayed only a signal at 1585 cm -1 attributed to one of the C=C stretching modes of the pyridine ring and observed also in the FT-IR spectrum of pure 4 (Figure S47b). 89 Within 1 h, we observed the appearance of a new strong signal at 1645 cm -1 attributed to the C=C ring stretching of a pyridinium moiety 90 as expected for the formation of the adduct of ring-opening of the epoxide by the nucleophilic nitrogen atom (Scheme 1, cycle A and Figure S47c). 91,92 Additionally, the peak initially centered at 1585 cm -1 was replaced by a new signal centered at 1577 cm -1 .…”

Probing the Ag, Au, and Cu electrode/pyridine-α-hydroxymethyl biphenyl phosphine oxide isomer interface with SERS

“…The pyridine molecule (Py) immobilized onto these substrates produces a large enhancement because of the electromagnetic field and chemical enhancements [12]. The SERS spectra of free pyridine with C 2v symmetry possess five A 1 ring stretching vibrations: asymmetric ring deformation [ 6a ; according to Wilson's numbering scheme], ring breathing mode [ 1 ], symmetric ring deformation mode [ 12 ], C-H in-plane bending vibration [ 9a ], and a ring C-C stretching mode [ 8a ] [12,17,18]. The bands of the above modes appear in the Py SERS spectrum at approximately 624, 1010, 1035, 1218, and 1598 cm −1 , respectively [12].…”