Subject: Summary & change of the question: simple way to measure delocalization

From: YONG HUANG <[email-masked]>
Date: Mon, 17 Feb 1997 22:33:40 -0600 (CST)

I asked a question a few days ago. First, my original question:

>A quick question. Is there any simple way to measure electronic delocaliza-
>tion? We know tryptophan is probably the most delocalized in terms of
>electron density among all the naturally occurring amino acids. Phenyl-
>alanine may be second, glycine and proline very localized and so on. Any
>quantitation has been done? Thanks for your help.
>

Dr. Dave Winkler ([email-masked]) says:
--------------------
I would be interested in the replies.  In some QSAR studies, where
delocalization is important (compounds active against electron transport
systems) simply counting the length of the longest conjugated path worked
quite well.
--------------------
I'd like to know some references and/or tutorials on this, Dr. Winkler.

No other responses except one saying "No", three saying "Please summarize".

Let's see. The significance of this question lies in the fact that the more
electronically delocalized, the less solvation stabilization you get when the
molecule is put in solvent. A direct measurement in this regard is obviously a
measurement of the actual solvation energy. Any work has been done,
experimental or computational? This won't be a simple way of measuring
delocalization. In fact it's not a way to quantitate it at all (unless the
cause-effect relation is one-to-one and not many-to-one).

A related property of molecules is polarizability, isn't it? Anybody knows any 
published work on polarizability of amino acids? Or refractive indeces? Or
Raman spectroscopy work? I guess there must an answer to one of these
questions. Thanks for any reply.

Yong