Cyclopentenones substituted in position 4, and 3, 5‐cis or ‐trans disubstituted cyclopentenes have been studied by NMR. and by IR. spectroscopy. Cyclopentenone derivatives and cyclopentene derivatives adopt a quasi‐coplanar and an envelope conformation, respectively. The preferential orientation of the substituents has been established according to their nature and to the solvents by correlation to the vicinal and the long‐range coupling constants.

VI 70)Suinmary. Several mono-, di-, and tr-hydroxy d-rivatives of cyclopentanc and cyclopentene have been studied by NMR. spectroscopy. The chemical shifts and thc coupling constants of the OH groups have been correlated with their position, with their configuration and, in some cases, with their conformation. do, est constant pour des concentrations infkrieures B 0,12M; chaque OH est alors associC uniquement avec le solvant. La valeur de 6, pour un hydroxyle donnC, dCpend de la force de la liaison OH . . . DMSO : grosso modo, plus cette liaison est forte, plus la rCsonance du proton OH est dCplacCe vers des champs faibles. Si la molCcule contient 1)Adresse pern-anente : DBpartement de Chimie organique de l'Universit6 de Bucarest.

Two new cyclopentane‐pentols, namely the 1, 2, 3, 4/5‐ and 1, 2, 3/4, 5‐isomers have been prepared by hydroxylation of the three 3, 4, 5‐trihydroxy‐1‐cyclopentenes. The stereoselectivity of some hydroxylating agents is discussed.

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