title: Heavy Halogen Atom Effect on (13)C NMR Chemical Shifts in Monohalo Derivatives of Cyclohexane and Pyran. Experimental and Theoretical Study.
abstract: As a first step, a qualitative analysis of the spin-orbit operator was performed to predict the kind of organic compounds, where it could be expected that the SO/FC (spin-orbit/Fermi contact) and SO/SD (spin-orbit/spin dipolar) yield unusually small contributions to the "heavy atom effect" on (13)C SCSs (substituent chemical shifts). This analysis led to the conclusion that compounds presenting strong hyperconjugative interactions involving the σ*C-X orbital (X = halogen) are good examples where such effects can be expected to take place. On the basis of such results, the following set of model compounds was chosen: 2-eq-halocyclohexane (2-eq), 2-ax-halocyclohexane (2-ax), and 2-ax-halopyran (3), to measure (13)C SCSs. Such experimental values, as well as those of methane and halomethanes taken from the literature, were compared to calculated values at a nonrelativistic approach using B3LYP, and at a relativistic approach with BP86 using scalar ZORA, spin-orbit ZORA, scalar PAULI, and spin-orbit PAULI. Results from relativistic calculations are in agreement with the trends predicted by the qualitative model discussed in this work.
authors.affiliation: Chemistry Institute, State University of Campinas, Caixa Postal 6154, 13084-971 Campinas, SP, Brazil, Department of Physics, FCEyN, University of Buenos Aires and CONICET, Buenos Aires, Argentina, and Philipps-Universität Marburg, Hans-Meerwein-Strasse, D-35032 Marburg, Germany.
authors.forename: Alvaro Cunha
authors.initials: AC
authors.lastname: Neto
authors.affiliation: Chemistry Institute, State University of Campinas, Caixa Postal 6154, 13084-971 Campinas, SP, Brazil, Department of Physics, FCEyN, University of Buenos Aires and CONICET, Buenos Aires, Argentina, and Philipps-Universität Marburg, Hans-Meerwein-Strasse, D-35032 Marburg, Germany.
authors.forename: Lucas C
authors.initials: LC
authors.lastname: Ducati
authors.affiliation: Chemistry Institute, State University of Campinas, Caixa Postal 6154, 13084-971 Campinas, SP, Brazil, Department of Physics, FCEyN, University of Buenos Aires and CONICET, Buenos Aires, Argentina, and Philipps-Universität Marburg, Hans-Meerwein-Strasse, D-35032 Marburg, Germany.
authors.forename: Roberto
authors.initials: R
authors.lastname: Rittner
authors.affiliation: Chemistry Institute, State University of Campinas, Caixa Postal 6154, 13084-971 Campinas, SP, Brazil, Department of Physics, FCEyN, University of Buenos Aires and CONICET, Buenos Aires, Argentina, and Philipps-Universität Marburg, Hans-Meerwein-Strasse, D-35032 Marburg, Germany.
authors.forename: Cláudio F
authors.initials: CF
authors.lastname: Tormena
authors.affiliation: Chemistry Institute, State University of Campinas, Caixa Postal 6154, 13084-971 Campinas, SP, Brazil, Department of Physics, FCEyN, University of Buenos Aires and CONICET, Buenos Aires, Argentina, and Philipps-Universität Marburg, Hans-Meerwein-Strasse, D-35032 Marburg, Germany.
authors.forename: Rubén H
authors.initials: RH
authors.lastname: Contreras
authors.affiliation: Chemistry Institute, State University of Campinas, Caixa Postal 6154, 13084-971 Campinas, SP, Brazil, Department of Physics, FCEyN, University of Buenos Aires and CONICET, Buenos Aires, Argentina, and Philipps-Universität Marburg, Hans-Meerwein-Strasse, D-35032 Marburg, Germany.
authors.forename: Gernot
authors.initials: G
authors.lastname: Frenking