A THEORETICAL-STUDY OF CONFORMATIONS AND VIBRATIONAL FREQUENCIES IN (NH2)2C=X COMPOUNDS (X=O, S, AND SE)

Results of ab initio SCF and MP2 calculations of urea (NH2)2C=O, thiourea ((NH2)2C=S) and selenourea ((NH2)2C=Se) have been reported. The non-planar transoid structure turned out to be more stable than the cissoid form, and the planar form is characterized as the transition structure throughout. Harmonic force field and vibrational frequencies have been calculated for the normal species as well as the corresponding deuterated ones. Experimental IR spectra and assignments of previous empirical and semiempirical studies have been critically examined, and the electronic structures of three species are compared by calculating some molecular properties.