title: NMR spin-spin coupling constants: bond angle dependence of the sign and magnitude of the vicinal (3)JHF coupling.
abstract: The dependence of the magnitude and sign of (3)JHFF on the bond angle in fluoro-cycloalkene compounds is evaluated by electronic structure calculations using different levels of theory, viz. DFT, SOPPA(CCSD) and SOPPA(CC2). Localized molecular orbital contributions to (3)JHFF are analyzed to assess which orbitals are responsible for (3)JHFF and which are the most important coupling transmission mechanisms for each compound. Fluoro-ethylene is used as a model system to evaluate the dependence of the (3)JHFF coupling constant on the angle between the σCα-F and σCα'-HF vectors. Through-space and hyperconjugative transmission pathways and ring strain are identified as responsible for the opposite trend between (3)JHFF and bond angle, and for the negative signs obtained for the two molecules, respectively. One of the fluorine lone pairs, σCα'-HF, σCα-F, σCα'-Cβ' bonding orbitals and the σ*Cα-F antibonding orbital are involved in the J-coupling pathways, according to analyses of pairwise-steric and hyperconjugative energies.
authors.affiliation: Institute of Chemistry, University of Campinas - UNICAMP, P. O. Box 6154, 13083-970 Campinas, SP, Brazil.
authors.forename: Renan V
authors.initials: RV
authors.lastname: Viesser
authors.affiliation: Department of Fundamental Chemistry, Institute of Chemistry, University of São Paulo, Av. Prof. Lineu Prestes, 748, 05508-000, São Paulo, SP, Brazil. ducati@iq.usp.br.
authors.forename: Lucas C
authors.initials: LC
authors.lastname: Ducati
authors.affiliation: Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14260-3000, USA. jochena@buffalo.edu.
authors.forename: Jochen
authors.initials: J
authors.lastname: Autschbach
authors.affiliation: Institute of Chemistry, University of Campinas - UNICAMP, P. O. Box 6154, 13083-970 Campinas, SP, Brazil.
authors.forename: Cláudio F
authors.initials: CF
authors.lastname: Tormena