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Chelate-type intramolecular hydrogen bridging in 2,4-diaryl-6-(2-hydroxy-4-methoxyphenyl)-1,3,5-triazines. A dynamic 1H/13C NMR study

✍ Scribed by P. Fischer; A. Fettig

Publisher: John Wiley and Sons
Year: 1997
Tongue: English
Weight: 272 KB
Volume: 35
Category: Article
ISSN: 0749-1581
DOI: 10.1002/(sici)1097-458x(199712)35:12<839::aid-omr182>3.0.co;2-g

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✦ Synopsis

The energy for breaking the intramolecular hydrogen bond between the phenolic OH and an aza nitrogen in two 2,4-diaryl-6-(2-hydroxy-4-methoxyphenyl)-1,3,5-triazines was determined, by dynamic 1H and 13C NMR spectroscopy, as 55 » 5 kJ mol-1. The activation parameters DHt and DSt for the corresponding internal rotation were derived from a plot. The strength of the chelate-type hydrogen bond is the rationale for the excellent DG C t-T C photostabilizing capacity of this class of triazines. It is demonstrated explicitly that the line separation Dm of the signals under exchange must be extrapolated to the coalescence temperature when values are to be calculated DG C t by the Gutowsky-Holm equation. Correct lineshape analysis likewise depends on employing the requisite Dm value for each temperature.

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