13C NMR, infrared, solvation and theoretical investigation of the conformational isomerism in 1-haloacetones (X = Cl, Br and I).
The solvent dependence of the 13C NMR spectra of chloroacetone (CA), bromoacetone (BA) and iodoacetone (IA) are reported and the 3J(CH) couplings analysed using ab initio calculations and solvation theory. In CA the energy difference (E(cis) - E(gauche)) between the cis (Cl-C-C=O 0 degrees) and gauche (Cl-C-C=O 155 degrees) conformers is 1.7 kcal mol(-1) in the vapour, decreasing to 0.8 kcal mol(-1) in CCl4 solution and to -1.0 kcal mol(-1) in the pure liquid. The conformational equilibrium, in BA, is between the more polar cis (Br-C-C=O 0 degrees) and gauche (Br-C-C=O 132 degrees) conformations. The energy difference (E(cis) - E(gauche)) is 1.8 kcal mol(-1) in the vapour, decreasing to 0.9 kcal mol(-1) in CCl4 solution and to -0.4 kcal mol(-1) in the pure liquid. The energy difference (E(cis) - E(gauche)), in IA, between the cis (I-C-C=O 0 degrees) and gauche (I-C-C=O 104 degrees) conformers is 1.1 kcal mol(-1) in the vapour phase, decreasing to 0.5 kcal mol(-1) in CCl4 solution and to -0.5 kcal mol(-1) in the pure liquid. The vapour state energy difference for BA [1.4 kcal mol(-1) at B3LYP/6-311++G(d,p)] and for IA [1.6 kcal mol(-1) at B3LYP/6-311++G(d,p)/LANL2DZ)] are in very good agreement with the above values. For CA the agreement is also satisfactory [1.4 kcal mol(-1) at B3LYP/6-311++G(d,p)].
Doi
Telma R
TR
Physical Organic Chemistry Laboratory, Chemistry Institute-State University of Campinas, Caixa Postal 6154, 13084-971 Campinas, SP, Brazil.
Yoshinaga
Fabiana
F
Tormena
Cláudio F
CF
Rittner
Roberto
R
Abraham
Raymond J
RJ
D000096:Acetone / Q000031:analogs & derivatives* / Q000737:chemistry; D001965:Bromides / Q000737:chemistry; D002247:Carbon Isotopes; D002713:Chlorine / Q000737:chemistry; D007454:Iodides / Q000737:chemistry; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008968:Molecular Conformation; D012997:Solvents / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013816:Thermodynamics
D001965:Bromides; D002247:Carbon Isotopes; D007454:Iodides; D012997:Solvents; D000096:Acetone; C018235:bromoacetone; C418987:fluoroacetone; D002713:Chlorine; C006973:chloroacetone