1,2-Cyclopentanediol trans isomer

Probtem 13.5 The ir spectra of trans- and cu-l,2-cyclopentanediol show a broad band in the region 3450-3570 cm On dilution with CCI, this band of the cis isomer remains unchanged, but the band of the trans isomer shifts to a higher frequency and becomes sharper. Account for this difference in behavior. M... 

Aqueous acetic acid (rate of oxidation) [1, 145, after citation of ref. 5], Rocek and Westheimer58 reported that the oxidation of cm-l,2-dimethyl-1,2-cyclopentanediol (1) by chromic acid in water or 90% acetic acid to 2,6-heptanedione (2) is much faster than oxidation of the trans isomer (3). In water the oxidation of (1) to (2) is 17,000... 

Cyclopentanediol also has two chiral centers therefore, the 2" rule predicts a maximum of 2 = 4 stereoisomers. As shown in the following stereodrawings, only three stereoisomers exist for this compound. The ds isomer is achiral (meso) because it and its mirror image are superposable. An alternative way to identify the ds isomer as achiral is to notice that it possesses a plane of symmetry that bisects the molecule into two mirror halves. The trans isomer is chiral and exists as a pair of enantiomers. 

The ion-molecule reactions of MesSi have been employed to distingnish between the cis- and trans- isomers of 1,2-cyclopentanediol. The formation of a [Me3SiOH2]+ cation (equation 26, top) was found to be indicative for a c -structure of the reacted diol 37. Thus the formation of the [Mc3SiOH2]+ cation from the addnct 38 proceeds without a barrier, whereas the production of this ion from the frawi-diol 39 via adduct 40 (equation 26, bottom) was shown to be an endothermic process which possesses a translational energy onset. These studies are the first to use the reactivity of the Me3Si+ ion as a probe of the stereochemistry of the reacted neutrals in a mass spectrometer. 

When two substituents are on the same side of a ring skeleton, they are said to be cis, and when on opposite sides, trans (analogous to use of those terms with 1,2-disubstituted alkene isomers). Consider stereoisomeric forms of 1,2-cyclopentanediol (compounds having a five-membered ring and hydroxyl groups on two adjacent carbons that are cis in one isomer and trans in the other). At high dilution, both isomers have an infrared absorption band at approximately 3626 cm but only one isomer has a band at 3572 cm . 

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