Theoretical studies of protonation and lithiation of first- and second-row aldehydes

Abstract

We investigate the effects of protonation and lithiation upon the atomic apd molecular properties of formaldehyde and thioformaldehyde. At the HF/6-311 ++ G** level, protonation is much more exothermic than lithiation in both systems; protonation of the thioformaldehyde is favoured over formaldehyde, while lithiation of the aldehyde is favoured over the thioaldehyde. Lithiation results in a much larger dipole polarization and quadrupole depolarization of the H₂CX| fragment than does protonation. On the atomic level, protonation is favoured by the large transfer of charge to the proton and its subsequent stabilization, while lithiation is driven by the inter-atomic stabilization afforded X by the proximity of Li⁺. Lithiation of either aldehyde is well approximated by an electrostatic model, but protonation is not.