Conformational analysis of 2-halocyclopentanones by NMR and IR spectroscopies and theoretical calculations.
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.
Martins
Carina R
CR
Physical Organic Chemistry Laboratory, Chemistry Institute, State University of Campinas, Caixa Postal 6154; 13084-971 Campinas, SP, Brazil.
Ducati
Lucas C
LC
Tormena
Cláudio F
CF
Rittner
Roberto
R
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
D003517:Cyclopentanes; D006219:Halogens; C007201:cyclopentanone