Conference paper

Semiempirical Study of Intramolecular Hydrogen Bond in Naphthazarin

Z. B. Maksić ; Ruđer Bošković Institute, Bijenička c. 54, 41001 Zagreb, Croatia, Yugoslavia
M. Eckert-Maksić ; Ruđer Bošković Institute, Bijenička c. 54, 41001 Zagreb, Croatia, Yugoslavia
D. Kovaček ; Ruđer Bošković Institute, Bijenička c. 54, 41001 Zagreb, Croatia, Yugoslavia

Abstract

It is found that MINDO/3, MNDO and AMI give a reasonable
description of intramolecular hydrogen bonds in malonaldehyde,
acetylacetone and naphtazarin tautomers as evidenced
by comparison with the available ab initio results and reliable
experimental f'indings. MINDO/3 and MNDO procedures of'Ier
information at a qualitative level, whilst AMI yields semiquantitative
resuIts after some empirical adjustements.
The main result of this study is a strong indication that
all studied systems possess asymmetric H-bond(s) at least in the
gas phase. The most stable tautomer of naphthazarin has 1,4-
-quinoid structure. It is found that single proton (two step) tunnelling
is energetically much more favourable than concerted
(simultaneous) transfer of both protons. Tunnelling barrier heights,
of internal H-bonds are thoroughly discussed and interpreted in
terms of the micro- and gross-energy partitioning method. Variation
in structural parameters and changes in atomic charges
are elaborated. It is established that keto- and hydroxy-oxygens
have substantially different electron densities, which necessarily
lead to appreciable differences in their ls ESCA shifts.

Keywords

Hrčak ID:

175823

URI

https://hrcak.srce.hr/175823

Publication date:

25.2.1990.

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