THEORETICAL-STUDIES OF PROTONATION AND LITHIATION OF FIRST-ROW AND 2ND-ROW ALDEHYDES

We investigate the effects of protonation and lithiation upon the atom ic and molecular properties of formaldehyde and thioformaldehyde. At t he HF/6-311 + + G* level, protonation is much more exothermic than li thiation in both systems; protonation of the thioformaldehyde is favou red over formaldehyde. while lithiation of the aldehyde is favoured ov er the thioaldehyde. Lithiation results in a much larger dipole polari zation and quadrupole depolarization of the H(2)CX\ fragment than does protonation. On the atomic level, protonation is favoured by the larg e transfer of charge to the proton and its subsequent stabilization. w hile lithiation is driven by the inter-atomic stabilization afforded X by the proximity of Li+. Lithiation of either aldehyde is well approx imated by an electrostatic model, but protonation is not.