Correlations of geometric and spectroscopic parameters of intramolecular hydrogen bonds in porphyrin-like macrocycles

Abstract

Chemical bond lengths and angles are characteristic structural parameters that describe a molecule. Likewise, the frequencies of the vibration modes and the NMR chemical shift are unique and referred to as "chemical fingerprints" specific to the compound. These are the basic parameters describing and allowing the identification of newly obtained compounds. In macrocyclic compounds with a porphyrin-like structure, intramolecular hydrogen bonding significantly influences the physicochemical properties. This paper presents the correlations between geometric and spectroscopic parameters related to hydrogen bonds in this type of macrocyclic compound. In particular, these relationships were demonstrated for a large group of porphyrin, porphycene, and dibenzotetraaza[14]annulene derivatives and the group of other macrocycles with a similar structure. A very strong linear relationship is found between the frequencies of vibrations of the NH groups of the hydrogen bond and the length of this bond, which is common for all macrocyclic compounds of this type. Several other relationships are shown between spectroscopic (IR, Raman, NMR) and geometric (X-ray) parameters indicating differences and similarities between different families of macrocycles. Apart from a better understanding of the nature of hydrogen bonds and their characteristics in porphyrin-like macrocyclic compounds, these relationships will facilitate the identification of new macrocycles and the extrapolation of their spectroscopic properties.