Density Functional Theory Modeling and Calculation of NMR Parameters: An ab Initio Study of the Polymorphs of Bulk Glycine

The three forms of glycine in the solid state, α, β, and γ, are described and modeled by means of generalized-gradient approximation (GGA) ab initio calculations. In particular, the location of the protons in each structure is studied. The vibrational frequencies and the NMR chemical shifts of 1H, 13C, and 15N in the three polymorphs are calculated and compared to experimental data (IR and Raman, solid-state magic angle spinning NMR, respectively). 13C chemical shift differences on the order of 1 ppm, which constitute the most accurate way to discriminate between the three structures when X-ray diffraction is not available, can be satisfactorily predicted.