Subject: Proton affinities for non-nitrogens

From: "Hr. Dr. S. Shapiro" <[email-masked]>
Date: Tue, 04 Feb 1997 09:39:02 +0100

Dear Colleagues;

        Recently there has been some discussion in this group about the
calculation of proton affinities using semi-empirical QM methods.  A quick
perusal (admittedly not comprehensive) of the literature has turned up
numerous articles on the subject, but all of these seem to be concerned with
amines of some sort: RR'R"N: + H+ <==> RR'R"N:H+, where RR'R"N: can be a
primary, secondary, or tertiary amine.

        Whilst reading these articles, it occurred to me that a similar
approach should be applicable for any Lewis base for which parametrisations
exist for the elements of interest.  For example, one might be able to 
_rank_ the Lewis acidities of various RX: derivatives (where X: =
non-nitrogen heteroatom) by performing calculations on these species
analogous to the abovementioned protonation reaction of amines.  Even if
species such as RX:H+ aren't _practically_ realistic, at least one should be
able to compare the proton affinities of analogous Lewis bases and rank them
accordingly.

        From those out there who are more knowledgeable about area than I
am: is this a reasonable way of ranking the basicities within an analogous
series of non-nitrogenous Lewis bases for which no experimental data are
available?  If not, why not?  If so, then does anyone know of any
publications directly addressing this matter?

        Thanks in advance to all responders.

Sincerely,

S. Shapiro
[email-masked]