The evaluation of the electronic charge distribution in metal complexes enables more precise interpretation of mechanism by which particular metal ions affect biochemical properties of ligands [J. Inorg. Biochem. 99 (2005), 1407–1423, J. Mol. Struct. 919 (2009), 284–289]. In this paper we investigated the influence of alkali metal cations (lithium, sodium, potassium, rubidium and cesium) on the electronic structure of p-coumaric acid (p-CA). It allowed to observe the systematic changes in the spectra of investigated complexes depending on the position of the element in the periodic table. p-Coumaric acid is a derivative of cinnamic acid that occurs in several plant species. Li, Na, K, Rb and Cs p-coumarates were synthesized and the experimental and theoretical FT-IR, FT-Raman, 1H and 13C NMR spectra of p-coumaric acid and its salts were registered and analyzed. The structures, atomic charges, infrared and NMR spectra of p-coumaric acid and Li, Na, K salts were calculated by B3LYP/6-311++G** method.