Premium
Chelate‐type intramolecular hydrogen bridging in 2,4‐diaryl‐6‐(2‐hydroxy‐4‐methoxyphenyl)‐1,3,5‐triazines. A dynamic 1 H/ 13 C NMR study
Author(s) -
Fischer P.,
Fettig A.
Publication year - 1997
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/(sici)1097-458x(199712)35:12<839::aid-omr182>3.0.co;2-g
Subject(s) - chemistry , intramolecular force , hydrogen bond , chelation , hydrogen , coalescence (physics) , nuclear magnetic resonance spectroscopy , proton nmr , computational chemistry , stereochemistry , organic chemistry , molecule , physics , astrobiology
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 1 H and 13 C NMR spectroscopy, as 55±5 kJ mol ‐1 . The activation parameters Δ H ‡ and Δ S ‡ for the corresponding internal rotation were derived from a Δ G C ‡ – T C plot. The strength of the chelate‐type hydrogen bond is the rationale for the excellent photostabilizing capacity of this class of triazines. It is demonstrated explicitly that the line separation Δν of the signals under exchange must be extrapolated to the coalescence temperature when Δ G C ‡ values are to be calculated by the Gutowsky–Holm equation. Correct lineshape analysis likewise depends on employing the requisite Δν value for each temperature. © 1997 John Wiley & Sons, Ltd.