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GIAO/DFT evaluation of 13 C NMR chemical shifts of selected acetals based on DFT optimized geometries
Author(s) -
Migda Wojciech,
Rys Barbara
Publication year - 2004
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/mrc.1366
Subject(s) - chemical shift , chemistry , computational chemistry , density functional theory , ground state , carbon 13 nmr , isotropy , stereochemistry , atomic physics , physics , quantum mechanics
DFT/B3LYP calculations of the ground‐state conformation of eight cyclic and acyclic acetals are presented and compared with experimental data. Results of single‐point GIAO/DFT calculations at five different levels of theory show that isotropic shieldings need to be empirically scaled to achieve agreement with experimental chemical shifts. Statistical evaluation of data indicates that the most accurate prediction of 13 C chemical shifts is achieved at the MPW1PW91/6–311G** level of theory. An empirical equation describing the relationship between δ values and shielding constants is postulated. This equation has been applied to the non‐chair ground‐state conformation of the six‐membered acetonide and to the conformationally flexible benzodioxonine derivative. The agreement observed between the experimental and predicted chemical shifts shows that calculations at the MPW1PW91/6–311G** level of theory are adequate for addressing questions of conformation. Copyright © 2004 John Wiley & Sons, Ltd.