Effects of structural differences on the NMR chemical shifts in cinnamic acid derivatives: Comparison of GIAO and GIPAW calculations.

In this article we report the results of combined theoretical and experimental structural studies on cinnamic acid derivatives (CADs), one of the main groups of secondary metabolites present in various medicinal plant species and food products of plant origin. The effects of structural differences in CADs on their spectroscopic properties were studied in detail by both: solid-state NMR and GIAO/GIPAW calculations. Theoretical computations were used in order to perform signal assignment in 13 C CP/MAS NMR spectra of the cinnamic, o-coumaric, m-coumaric, p-coumaric, caffeic, ferulic, sinapic and 3,4-dimethoxycinnamic acids, and to evaluate the accuracy of GIPAW and GIAO methodology. [ABSTRACT FROM AUTHOR]