A Karplus Equation for the Conformational Analysis of Organic Molecular Crystals

In the liquid state, vicinal J couplings (3J) have been extensively used for conformational analysis of organic compounds, peptides and proteins through the use of empirical Karplus equations. Contrastingly, there are essentially no examples of the use of 3J for quantitative structural investigation of solids. With the support of DFT calculations, we show that 13C-13C 3J couplings measured on a series of 13C-enriched solids can be related to the dihedral angle of the corresponding molecular fragment by a simple Karplus relationship. We show that such function could be successfully used to deduce dihedral angles on a solid compound with known structure.