Subject: Hammett ortho substituent constants?

From: "Hr. Dr. S. Shapiro" <[email-masked]>
Date: Thu, 30 Jan 1997 13:40:21 +0100

Dear Colleagues;

        It is my understanding that Hammett sigma constants are restricted
to substituents at meta and para positions because steric influences on the
functionality at C-1 (e.g., COOH, OH) cannot be clearly distinguished from
electronic influences, whereas steric influences on the functionality at C-1
by substituents in the meta or para positions is negligible.

        Has anyone ever undertaken (and pubished) a detailed analysis of the
influence of ortho substituents in an effort to factor the influence of
ortho substituents in to electronic and steric components?  I note that in
the 1982 book "pKa Prediction for Organic Acids and Bases" by D. D. Perrin,
B. Bempsey, and E. P. Serjeant Appendix A.5 is a small list of apparent
sigma ortho values.  Does anyone know of a more recent and/or extensive
lists, particularly ones containing values factored into steric and
electronic components for benzoic acids and phenols?

Thanks in advance to all responders,

S. Shapiro
[email-masked]

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From: "Paul G. Tratnyek" <[email-masked]>
Date: Sat, 1 Feb 1997 08:33:18 -0700

>ortho substituents in to electronic and steric components?

As of when I did the literature search for this (where we found remarkable
little "ortho effect"):

Tratnyek, P. G., and J. Hoigné. 1994. Kinetics of reactions of chlorine
dioxide (OClO) in water. II. Quantitative structure-activity relationships
for phenolic compounds. Water Res.  28(1): 57-66.

The best/latest refs on the "ortho effect" were this:

Charton, M. 1971. The nature of the ortho effect. VII. Nuclear magnetic
resonance spectra. J. Org. Chem.  36(2): 266-272.

Charton, M. 1971. The quantitative treatment of the ortho effect. Progr.
Phys. Org. Chem.  8: 235-317.

Charton, M., and B. I. Charton. 1971. The nature of the ortho effect. VI.
Polarographic half-wave potentials. J. Org. Chem.  36(2): 260-265.

Fujita, T., and T. Nishioka. 1976. The analysis of the ortho effect. Progr.
Phys. Org. Chem.  12: 49-89.

>electronic components for benzoic acids and phenols?

Try the paper by Fujita.

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Paul Tratnyek, Department of Environmental Science and Engineering
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