•The interactions of nicotinamide with H2O were investigated.•Hydrogen bonding and π-π stacking were formed in nicotinamide/H2O mixtures.•Experimental results were supported by theoretical calculations.The interactions between nicotinamide (NA) and H2O were studied using UV–visible spectra (UV–Vis), cyclic voltammetry (CV), nuclear magnetic resonance (NMR), density functional theory (DFT) and atoms in molecules (AIM) analysis. According to the changes of the UV–Vis spectra and the oxidation and reduction potentials in cyclic voltammograms of NA in aqueous solution, it was found that hydrogen bonding occurred between NA and H2O molecules. Quantum chemistry calculations and AIM analysis further confirmed the existence of hydrogen bonding between H2O molecules and the amide group, the nitrogen atom, and hydrogen atoms on the pyridine ring of NA molecules. In addition, the NMR results demonstrated that the π-π stacking between NA pyridine rings could be formed at higher concentrations.Download high-res image (154KB)Download full-size image

•2-Acetylpyridine is an important food additive and a flavoring substance.•Vibrational spectra of 2-acetylpyridine have been determined and assigned for the observed bands.•The cis conformer of 2-acetylpyridine is most stable according to DFT calculations.The molecular geometries, FT-IR and Raman spectra of 2-acetylpyridine were studied using Density functional theory (DFT-B3LYP) with the large basis sets. Theoretical calculations indicate the cis conformer of 2-acetylpyridine is most stable though this conformation was seldom found in the crystal structures of coordinated compounds. Based on the stable conformer, comprehensive assignments of the experimental bands were made. The observed and calculated positions are found to be in good agreement with an average deviation of <4 cm−1. The assignments provide valuable information for the fingerprint and identification of 2-acetylpyridine.Graphical abstract

•The FT-IR and FT-Raman spectra of N4-acetylcytosine were recorded and analyzed.•Different conformers of N4-acetylcytosine have been given.•The complete vibrational assignments and spectroscopic analysis were made.The infrared and FT-Raman spectra of N4-acetylcytosine in the solid phase have been recorded, and the molecular geometrical parameters were optimized using B3LYP and MP2 methods with 6-311++G(d,p) basis set. The theoretical calculations indicate the presence of four stable conformers of N4-acetylcytosine, and the one containing an intramoleuclar six-membered ring is the most stable. The vibrational wavenumbers, infrared intensities, Raman scattering activities and the corresponding assignments of the observed bands based on the most optimized conformer were performed by B3LYP methods using the aug-cc-pvtz basis set. The observed and calculated frequencies are found to be in good agreement.Graphical abstract