Conformational Studies on 2,2-Bispropane Diacetate and 2,2'-Oxydi-N-carbethoxycarbazole
The influences of temperature and solvent polarity on the relative population of conformational states about CH2-CH2 bonds in the model compounds dyanol 22 4-(2-hydroxyethoxy)phenyl>propane> diacetate (DDA) and 2,2'-oxydi-N-carbethoxycarbazole (ONCC) are studied by NMR spectroscopy and dipole moment measurements.The study suggests that solvent effects are not important and the fraction of gauche states about CH2-CH2 is above 0.90.Both compounds have similar polarity, but the temperature coefficient of the mean-square dipole moment d ln 2>/dT is positive for DDA and negative for ONCC.The critical interpretation of the polarity of ONCC suggests that the orientation of the dipole associated with the carbethoxycarbazole residue forms an angle of 65 +/- 5 deg with the N-CO bond.Theoretical calculations of 2> for both model compounds indicate that the experimental values of this quantity can be reproduced by assuming that gauche states about CH2-CH2 bonds have an energy 0.8 kcal mol-1 below that of the alternative trans states, a value that is somewhat larger than that suggested by NMR spectroscopic analysis.
Riande, Evaristo,Jimeno, Maria L.,Salvador, Rosa,Abajo, Javier de,Guzman, Julio
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