Conformational equilibrium isotope effects on selectively deuterated cyclooctanone

Conformational equilibrium isotope effects (CEIEs) are found in selectively deuterated cyclooctanone isotopomers (cyclooctanone-2-D, cyclooctanone-2,2 -D-2, cyclooctanone-2,8-D-2, cyclooctanone-2,2,7,7-D-4, and cy clooctanone- 2,2,8-D-3) by observing equilibrium NMIR isotope shifts in C-13 spectra. Th e temperature dependence of the isotope shifts are included for the complet e analysis of cyclooctanone conformation. Equilibrium constants and the cha nges in the free energies, enthalpies, and entropies are also reported for these cyclooctanone isotopomers. Molecular mechanics (MM2) calculations of steric interactions and molecular geometry strongly support the steric and hyperconjugative origin of the observed isotope shift results.