Heavy Halogen Atom Effect on C-13 NMR Chemical Shifts in Monohalo Derivatives of Cyclohexane and Pyran. Experimental and Theoretical Study

Author(s)

Cunha Neto, Alvaro ^[1] ; Ducati, Lucas C. ^[1] ; Rittner, Roberto ^[1] ; Tormena, Claudio F. ^[1] ; Contreras, Ruben H. ^{[2, 3]} ; Frenking, Gernot ^[4]

Affiliation

^[1] Univ Estadual Campinas, Inst Chem, BR-13084971 Campinas, SP - Brazil

^[2] Consejo Nacl Invest Cient & Tecn, RA-1033 Buenos Aires, DF - Argentina

^[3] Univ Buenos Aires, Dept Phys, FCEyN, Buenos Aires, DF - Argentina

^[4] Univ Marburg, D-35032 Marburg - Germany

• Document type: Journal article
• Source: JOURNAL OF CHEMICAL THEORY AND COMPUTATION; v. 5, n. 9, p. 2222-2228, SEP 2009.
• Web of Science Citations: 25

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 sigma(star)(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. (AU)