M. Herreros

The intrinsic basicity of urea. An experimental (FT ICR) and theoretical (G2) study

Abstract The gas phase basicity of urea (1), GB(1), [i.e. the standard Gibbs energy change for the reaction 1H + (g) ⇄ 1 (g) + H + (g) ] has been determined experimentally for the first time. This was achieved by means of Fourier Transform Ion Cyclotron Resonance Spectroscopy (FT ICR). 1 and 1H+ have been treated at the G2 level. This study suggests that 1(g) is very nearly a 1:1 mixture of two conformers of C2 and Cs symmetries. 1(g) is an oxygen base. The calculated and experimental values of GB(1) are in excellent agreement. An equally excellent agreement also exists between the experimental and calculated standard enthalpies of formation of 1(g). The vibrational frequencies of the conformers of 1 and of 1H+ have been calculated. This information, as well as the structures optimized at the MP2(FULL)/6-31G(d) level have been examined and compared to the available experimental data. The results thus obtained shed light on the mechanism of the stabilizing effect of 1H+(g) provided by the amino groups.

Is there a hydride transfer between N2OH+ and saturated hydrocarbons?

Various reaction mechanisms for the reaction between N2OH + and CH 4 have been explored theoretically at the MP26-31G** level. Also computed were the structure and thermodynamic state functions for several neutral molecules, notably N20, CH4 and C2H 6 and ions (CH~, C2H~, C2H~-, N2OH ÷ ). These results were combined with a Fourier transform ion cyclotron resonance study of the reactions of N2OH ÷ with CH4 or C2H6. Both studies suggest that the title hydride transfer, while thermodynamically favorable, is not kinetically preferred under thermal conditions in the gas phase.