THE INTRINSIC BASICITY OF UREA - AN EXPERIMENTAL (FT ICR) AND THEORETICAL (G2) STUDY

The gas phase basicity of urea (1), GB(1), [i.e. the standard Gibbs en ergy change for the reaction 1H(+)(g) reversible arrow 1(g) + H+(g)] h as been determined experimentally for the first time. This was achieve d by means of Fourier Transform Ion Cyclotron Resonance Spectroscopy ( FT ICR). 1 and 1H(+) have been treated at the G2 level. This study sug gests that 1(g) is very nearly a 1:1 mixture of two conformers of C-2 and C-s symmetries. 1(g) is an oxygen base. The calculated and experim ental values of GB(1) are in excellent agreement. An equally excellent agreement also exists between the experimental and calculated standar d enthalpies of formation of I(g). The vibrational frequencies of the conformers of 1 and of 1H(+) have been calculated. This information, a s well as the structures optimized at the MP2(FULL)/6-31G(d) level hav e been examined and compared to the available experimental data. The r esults thus obtained shed light on the mechanism of the stabilizing ef fect of 1HC(g) provided by the amino groups.