The proton NMR spectrum of partially deuterated cyclooctane dissolved in a nematic solvent has been studied in detail. The direct coupling constants between proton pairs and between carbonhyphen;13 and a proton have been measured and assigned. Of the many conformations that have been suggested for cyclooctane, the boathyphen;chair is the only one for which the calculated coupling constants will reproduce the observed ones, and it is concluded that this is the dominant conformation. It has been shown by Anet and Basus that another conformation, probably the crown, is present to an amount of about 6percnt; at room temperature. The present results seem to confirm this, but the method is not very sensitive for small admixtures of other conformations, and the actual fraction present, though clearly small, could not be determined. The carbon bond angles were found to deviate very appreciably from tetrahedral. The average Cndash;Cndash;C angle was determined as 118deg; and the Hndash;Cndash;H angle as 103deg;, with an estimated uncertainty of plusmn;2deg;.
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