ISSN:
1573-8353
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Chemie und Pharmazie
Notizen:
Abstract A comparison of the frequencies of the valence vibrations of the OH group and of the chemical shifts of the protons of the hydroxyl groups in α-naphthol derivatives containing the nitrogen atom of the condensed ring of pyridine, pyrazine, 1,2,5-selenadiazole, 1,2,5-thiadiazole, 1,2,5-oxadiazole, and imidazole in the peri position to the hydroxyl group is indicative of the decisive effect of the molecular geometry on intramolecular hydrogen bonding in systems with rigidly fixed configurations. All conditions being equal, the intramolecular hydrogen bond is considerably weaker when the nitrogen atom is part of a five-membered rather than a six-membered heterocycle. This is explained not only by an increase in the distance between the proton donor and acceptor (which may be the same in some cases), but also by the greater deviation of the orbital of the unshared electron pair of the nitrogen of the five-membered heterocycle from the O...N line and, thus, by its greater distance from the hydrogen atom. For the same favorable molecular geometry, the OH...N bond is stronger than the OH...O bond because of the high basicity of the nitrogen atom.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00473093
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