Current Organic Chemistry - Volume 13, Issue 2, 2009

Polyphenols are a very diverse class of compounds. In the present volume the emphasis is on Schiff bases and azo compounds containing one or more hydroxy group. Such polyphenols have many interesting properties and uses. Many Schiff bases with hydroxy groups have a hydroxy group in ortho position to the imine function resulting in intra molecular hydrogen bonding and possibly tautomerism. This can happen both in the liquid and solid state. The hydrogen bond is often of the low barrier type and Schiff bases are therefore valuable models in order to describe this phenomenon in particular because the N…O distance can conveniently be varied as a function of substituents in the vicinity. The Schiff bases and azo compounds have interesting biological properties and it is vital to understand how this is a function of the structure. Schiff bases are clearly of great importance in material science in general and in optical materials in particular. Schiff base metal complexes have become important catalysts. The contributions cover all these aspects and give a thorough overview of theoretical calculations. Spectroscopic approaches such as NMR and IR are clearly important in order to elucidate the properties not the least in order to understand the biological properties. The present contributions will shortly be followed by another volume dealing with further aspects of Schiff bases and azo compounds.

Aza-derivatives of phenols such as Schiff bases and hydrazones are an important and interesting group of chemical compounds. They exhibit a number of biological activities and play an important role in the regulation of many biochemical processes. Due to these properties, these compounds are potentialy useful for the design and production of novel anticancer, antimalaria, antivirus and antimicrobial drugs. The primary aim of the present review is to compare selected groups of phenol-derivatives containing azo-, heterocyclic, aromatic, alkyl and sugar moieties in view of their potential use and undesired effects, since some of them are widely used as dyes in the industry. Despite the vast number of azo derivatives of phenols which were synthesized and tested with respect to their biological activities, there is a continuous search for compounds of this group which might exhibit interesting, new biological effects.

A brief overview of computational chemistry methods for the design of Schiff base derivatives with certain materials properties is presented. The problem of azo - hydrazo or imino enol - enaminone tautomerism, especially calculations on its influence on dying properties/dye stability of hydroxy azo dyes is described. Design strategies for nonlinear optic materials based on Schiff bases and their metal complexes, guided by semi-empirical INDO/1 and, partly, DFT calculations as well as computational results for Schiff base metal complexes as catalysts for a variety of organic and biomimetic reactions are discussed. Insights from theoretical methods into the aggregation/self-assembly behaviour of Schiff bases and their complexes are reviewed.

This review is composed of several chapters dealing with research on the o-hydroxy aryl Schiff bases. The introduction comments on modern problems of quasi-aromatic formation which participates in o-hydroxy aryl Schiff bases as well as some potential applications of compounds of this type. The main part of the paper describes quantummechanical calculations of potential curves, electron-topological parameters depending on tautomeric equilibrium, the influence of substitution in the phenol ring and imine moiety, and the influence of environment on the potential curves. A difference between the impact of steric effect in o-hydroxy aryl Schiff bases and o-hydroxy benzoyl compounds is presented based on calculations of potential curve. A method of calculating the isotopic effect is described. A scheme of the “thermodynamic cycle” is presented estimating steric interrelations in the molecule and, in particular, the intramolecular hydrogen bonding energy.

The review covers the use of chemical shifts, isotope effects on chemical shifts and coupling constants in the description of Schiff bases. o-Hydroxy Schiff bases are often tautomeric and special attention is devoted to this feature. Nuclei in question are 1H, 13C, 15N, 19F and 17O. As well primary as secondary isotope effects are treated. Deuterium isotope effects on 13C and 15N chemical shifts are treated in detail and the theoretical background is dealt with. Finally, various applications of Schiff bases in biology and stereochemistry are discussed.