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The origin of an unusually large 19 F chemical shift difference between the diastereomeric α‐cyano‐α‐fluoro‐ p ‐tolylacetic acid (CFTA) esters of 3′,4′,5,7‐tetra‐ O ‐methylepicatechin
Author(s) -
Brand Dirk J.,
Steenkamp Jacobus A.,
Omata Kenji,
Kabuto Kuninobu,
Fujiwara Tomoya,
Takeuchi Yoshio
Publication year - 2008
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.20447
Subject(s) - chemistry , diastereomer , chemical shift , stereochemistry , aryl , fluorine , dihedral angle , computational chemistry , crystallography , molecule , organic chemistry , hydrogen bond , alkyl
During a study on the relationship between the 19 F chemical shift difference for the diastereomeric α‐cyano‐α‐fluoro‐ p ‐tolylacetic acid (CFTA) esters of chiral secondary alcohols and the absolute configurations of the alcohols, an unusually large 19 F chemical shift difference has been observed for the CFTA esters of 3',4',5,7‐tetra‐ O ‐methylepicatechin. This large chemical shift difference has been reproduced by ab initio calculations of molecular geometry and GIAO calculations of 19 F chemical shifts on the stable conformations of the diastereomeric α‐cyano‐α‐fluorophenylacetic acid (CFPA) esters of cis ‐flavan‐3‐ol as model systems. The origin of the large chemical shift difference has been further investigated using NBO analysis. This revealed that the interaction between π(CC) of the aryl group in the chiral auxiliary and σ*(CF) is a very important determinant of the 19 F chemical shifts and this interaction depends on the torsion angle between the plane of aryl group and the CF bond. Chirality, 2008. © 2007 Wiley‐Liss, Inc.