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A DFT/GIAO/NBO and experimental study of 13 C SCSs in 1‐X‐bicyclo[1.1.1]pentanes
Author(s) -
Della Ernest W.,
Lochert Ian J.,
Peralta Juan E.,
Contreras Rubén H.
Publication year - 2000
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 - 10.1002/1097-458x(200006)38:6<395::aid-mrc656>3.0.co;2-n
Subject(s) - natural bond orbital , chemistry , intramolecular force , density functional theory , atomic orbital , chemical shift , delocalized electron , computational chemistry , substituent , stereochemistry , electron , organic chemistry , physics , quantum mechanics
The 13 C NMR spectra of 24 members of a series of 1‐X‐bicyclo[1.1.1]pentanes were measured. SCSs on 13 C 1 were found to linearly correlated with those on 13 C 3 , although the former correspond to deshielding effects and the latter to shielding effects. Even though the 13 C 1 SCSs follow the same trend as α‐SCSs in other types of substrates, they are significantly smaller. In order to provide an insight into the different intramolecular interactions that define such a trend, theoretical studies that include SCSs calculated at the GIAO B3LYP/6–311G** level, electron delocalization analysis within the NBO approach at the same level and electrostatic interaction effects on chemical shifts were carried out. Important halogen heavy‐atom effects on C 3 were observed, suggesting that the spin–orbit interaction is transmitted through space between the bridgehead carbon atoms. Additionally, in a few members of the series X = H, F, CH 3 , NH 2 , OCH 3 , CN, COOH, COCH 3 ), theoretical calculations of the substituent chemical shifts, 13 C SCSs, were carried out with particular reference to the C 1 position. These theoretical calculations included: (a) full geometry optimizations, (b) magnetic shielding constant calculations using the GIAO (gauge‐included atomic orbitals) method within the DFT (density functional theory) approach and (c) natural bond orbital (NBO) analysis of intramolecular charge transfer interactions. Copyright © 2000 John Wiley & Sons, Ltd.