title: Conformational analysis of 2-halocyclopentanones by NMR and IR spectroscopies and theoretical calculations.
abstract: The conformational isomerism of 2-chlorocyclopentanone and 2-bromocyclopentanone has been determined through the solvent dependence of the (1)H NMR (3)J(HH) coupling constants, theoretical calculations and infrared data, using the solvation theory for the treatment of NMR data. In 2-chlorocyclopentanone, the energy difference (E(Psi-e)-E(Psi-a)), in the isolated molecule at B3LYP level of theory, between the pseudo-equatorial (Psi-e) and pseudo-axial (Psi-a) conformers is 0.42kcalmol(-1), which decreases in CCl(4) and in acetonitrile solutions, in good agreement with infrared data (nu(CO)), despite the uncertainties of the latter method. The conformational equilibrium for 2-bromocyclopentanone is also between the Psi-e and Psi-a conformations, with an energy difference (E(Psi-e)-E(Psi-a)), in the isolated molecule at B3LYP level of theory, is 0.85kcalmol(-1) which decreases in CCl(4) and in acetonitrile solutions, also in good agreement with infrared data.
authors.affiliation: Physical Organic Chemistry Laboratory, Chemistry Institute, State University of Campinas, Caixa Postal 6154; 13084-971 Campinas, SP, Brazil.
authors.forename: Carina R
authors.initials: CR
authors.lastname: Martins
authors.forename: Lucas C
authors.initials: LC
authors.lastname: Ducati
authors.forename: Cláudio F
authors.initials: CF
authors.lastname: Tormena
authors.forename: Roberto
authors.initials: R
authors.lastname: Rittner
mesh_terms: D003517:Cyclopentanes / Q000737:chemistry*; D006219:Halogens / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008962:Models, Theoretical; D008968:Molecular Conformation; D013055:Spectrophotometry, Infrared / Q000379:methods*; D013237:Stereoisomerism
chemical_list: D003517:Cyclopentanes; D006219:Halogens; C007201:cyclopentanone