Spectroscopic and computational insight into weak noncovalent interactions in crystalline pyrimidine

Effects of weak C–H⋯N interactions on the vibrational spectrum of crystalline pyrimidine are studied using Raman spectroscopy and electronic structure computations. When pyrimidine transitions from the liquid to solid state, peaks in the Raman spectrum exhibit non-uniform shifts. Calculations performed on a cluster of nine pyrimidine molecules (one pyrimidine molecule embedded in a field of its eight nearest neighbors in the crystalline geometry) predict that modes involving the movement of hydrogen atoms are associated with the observed shifts. Assignments of fundamentals and combination bands in both the liquid and solid states are also revised in the complicated C–H stretching region.