Conformational study of trans-cyclododecene by dynamic NMR spectroscopy and computational methods

The C-13 spectrum of trans-cyclododecene (1) dissolved in propane showed se ven peaks for the olefinic carbons at -164.5 degrees C, corresponding to th ree conformations of C-1 symmetry and a fourth conformation, with a populat ion of 20.1%, of C-2 symmetry. The populations of the C-1 conformations wer e 57.0, 18.6, and 4.3%. Conformational space was searched for 1 using MM2. Free energies and populations were calculated by MM3, and the results of th e low-temperature NMR study are discussed in terms of these calculations an d the C-13 chemical shifts calculated for eight conformations by the GIAO m ethod at the HF/6-311G* level. The conformations of 1 and cyclododecane (2) are compared.