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13C CP/MAS NMR studies of vitamin E model compounds

✍ Scribed by Stanislaw Witkowski; Katarzyna Paradowska; Iwona Wawer

Publisher
John Wiley and Sons
Year
2004
Tongue
English
Weight
232 KB
Volume
42
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

^13^C cross‐polarization magic angle spinning (CP/MAS) NMR data for 2,2,5,7,8‐pentamethylchroman‐6‐ol (2), 6‐hydroxy‐2,5,7,8‐tetramethylchroman‐2‐carboxylic acid (Trolox c) (3) and its acetate (4), 2‐methoxy‐2,2,5,7,8‐pentamethylchroman‐6‐ol (5), 2‐hydroxy‐2,2,5,7,8‐pentamethylchroman‐6‐ol (6) and 2,2,5,7,8‐pentamethylchroman (7) are reported. A deshielding of 7.7 ppm for the carboxylic carbon was observed in solid Trolox due to formation of intermolecular hydrogen bonds within cyclic dimers. Such crystal packing permits effective cross‐polarization and fast relaxation (short T~1ρ~^H^). The impact of the proton concentration on the CP dynamics is reflected by the longer T~CP~ and T~1ρ~^H^ for Trolox‐d~2~ (deuterated at mobile proton sites). The calculated GIAO RHF shielding constants are sensitive to intramolecular effects: rotation around the C‐6O bond (changes of σ up to 8 ppm) and conformation at C‐2. Copyright © 2004 John Wiley & Sons, Ltd.

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