29Si NMR spectra of trimethylsilylated cyclic acyloins and ketones. 29Si chemical shifts as a measure of ring size

²⁹Si chemical shifts are reported for nine 1,2-bis(trimethylsiloxy)cycloalkenes and four 1-trimethylsiloxycycloalkenes, (Me₃SiO)_xC_nH_2n–2–x (x=1, 2). For cycloalkene derivatives with n?8 the silicon shift exhibits a strong dependence on the ring size, although the silicon is exocyclic and is separated by two bonds from the olefinic carbon atom. The dependence can be exploited for ring size determination of cyclic ketones after trimethylsilylation.