THEORETICAL STUDY OF THE REACTION MECHANISM OF SUBSTITUTED ISOCYANATES AND ALCOHOLS

Reactions of substituted alcohols (R-OH, where R = CH3, (CH3)2CH, SiH3CH2, NH2CH2, or FCH2) and isocyanates (X-NCO where X = CH3, CH2F, C6H5, SiH3 or SiH3CH2) were studied using B3LYP/6-31G * calculations. Activation energies of the four-membered cyclic transition complexes (TS) were calculated. In case of substituted methanols and methyl isocyanate the activation energy and Gibbs free energy was found to increase in the following order: CH3 < (CH3)2CH < SiH3CH2 < NH2CH2 < FCH2. Substituting the isocyanates changed the order with respect to the activation energy and Gibbs free energy: FCH2 < SiH3CH2 < C6H5 < CH3 < SiH3. Solvent effect was also studied for the reaction of CH3NCO with CH3OH as an example using the SCRF (CPCM) method and chlorobenzene as solvent. The activation energy was found to be very similar in an environment of a low permittivity solvent (G(sol)=38.00 kcal/mol) and in the gas phase (G(g)=37.77 kcal/mol). Vibrational frequencies and forces in transition state were calculated. Enthalpies (H) and Gibbs-free energies (G) were determined at 298.16 K and 1 atm