jo020377i_si_003.pdf (1.49 MB)
Stereochemical Analysis by Solid-State NMR: Structural Predictions in Ambuic Acid
journal contribution
posted on 2003-01-24, 00:00 authored by James K. Harper, Dewey H. Barich, Jian Z. Hu, Gary A. Strobel, David M. GrantRelative stereochemistry is predicted for ambuic acid using a novel solid-state NMR approach.
This NMR technique entails a comparison of measured shift tensor principal values with computed
values for all diastereomers, allowing the selection of a best-fit structure. The proposed method
extends previous solution NMR structural data by simultaneously modeling with high statistical
probability hydrogen-bonding arrangements and molecular conformation at two positions. A dimeric
structure is proposed for ambuic acid based on the initial poor fit of the carboxyl carbon tensors to
a monomeric model. The dimer model, consisting of hydrogen bonding between pairs of neighboring
carboxyl groups, reduces the root mean square error at the carboxy tensor by a factor of 2.7. Lattice
details are thus also described by the proposed approach. The structural characterization method
presented is of general applicability and may be especially useful for characterizing difficult to
crystallize or hydrogen-poor materials.