Theoretical study of structure of alkali metal cyanates and isocyanates and their related ion pair SN2 reactions

The structure of lithium and sodium cyanates and isocyanates and their related ion pair SN2 reactions were investigated using molecular quantum mechanics at the Hartree–Fock (HF)/6-31G**//HF/6-31G** level. Extensive further calculations of some of the lithium systems at higher levels gave no significant changes in relative properties. The isocyanate ion pairs are the most stable monomeric forms. The lowest energy dimers are planar eight-membered rings. For the ionic SN2 reaction of cyanate ion and methyl fluoride and chloride, methyl isocyanate is the predicted major product. The monomer ion pair inversion mechanism is predicted to preferentially form methyl cyanate but the calculations also indicate that reaction with dimeric ion pairs have no clear preference for forming methyl cyanate or isocyanate.