title: Influence of sigma-hyperconjugative interactions on 13C substituent chemical shifts: experimental and theoretical study in 1-X,3-CH3-bicyclo[1.1.1]pentanes.
abstract: (13)C chemical shifts were measured for 18 1-X,3-CH(3)-bicyclo[1.1.1]pentanes and the corresponding (13)C substituent chemical shifts (SCSs) were compared with those measured previously for the corresponding 1-X-bicyclo[1.1.1]pentanes. DFT-B3LYP calculations of GIAO magnetic shielding constants and of natural bond orbitals were carried out in order to gain an insight into factors defining the observed differences in (13)C SCSs in both series. These differences are rationalized in terms of substituent effects on sigma-hyperconjugative interactions.
authors.affiliation: Departamento de Física, FCEyN, Universidad de Buenos Aires, and CONICET, Ciudad Universitaria, Pabellón 1 (C1428EHA) Buenos Aires, Argentina. contrera@df.uba.ar
authors.forename: Rubén H
authors.initials: RH
authors.lastname: Contreras
authors.forename: Angel L
authors.initials: AL
authors.lastname: Esteban
authors.forename: Ernesto
authors.initials: E
authors.lastname: Díez
authors.forename: Ernest W
authors.initials: EW
authors.lastname: Della
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Lochert