The 13C NMR spectra of 24 members of a series of 1-X-bicyclo[1.1.1]pentanes were measured. SCSs on 13C1 were found to linearly correlated with those on 13C3, although the former correspond to deshielding effects and the latter to shielding effects. Even though the 13C1 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 C3 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, CH3, NH2, OCH3, CN, COOH, COCH3), theoretical calculations of the substituent chemical shifts, 13C SCSs, were carried out with particular reference to the C1 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.
|Number of pages||8|
|Journal||Magnetic Resonance in Chemistry|
|State||Published - Jun 2000|
- C NMR
- Substituent chemical shifts