1,2-Cyclopentanediols

Epoxides, like other ethers, are cleaved by nucleophiles under acidic conditions. For example, cyclopentene oxide produces a mixture of 1,2-cyclopentanediol stereoisomers when treated with water and sulfuric acid. 

How many stereoisomers of 1,2-cyclopentanediol are there What are their stereochemical relationships Are they enantiomers ... 

The product of nucleophilic attack can be anticipated by examining the lowest-unoccupied molecular orbital (LUMO) on protonated cyclopentene oxide. From which direction (top or bottom) would a nucleophile be more likely to approach each epoxide carbon in order to transfer electrons into this orbital Explain. Does one carbon contribute more to the LUMO, or is the orbital evenly spread out over both epoxide carbons Assuming that LUMO shape dictates product stereochemistry, predict which stereoisomers will be obtained, and their approximate relative amounts. Is the anticipated kinetic product also the thermodynamic product (Compare energies of 1,2-cyclopentanediol stereoisomers to tell.)... 

Strong support for the cyclic ester intermediate comes from the measurement of the relative rates of oxidation by chromic acid of cis- and // fl/w-l,2-dimethyl-1,2-cyclopentanediol. In water and in 90 % acetic acid is 17,000 and... 

Glycols and related alcohols In contrast to aliphatic monoalcohols (1), 1,2-glycols and related compounds (2-methoxy alcohols, 1,2-amino alcohols) can be easily oxidized by the direct electrochemical method [12]. For example, 1,2-cyclopentanediol (9) affords diacetal (10) in 56% yield as the main product (Eq. 3). 

The study of oxo-Cr(V)-diols complexes formed by reduction of Cr(VI) by GSH in the presence of m-cyclopentanediol (8) or Iram-cyclopentanediol (9) expanded the EPR analysis of oxo-Cr(V)-diols species to five-membered ring 1,2-diols.66 Unlike the Cr(V) complexes formed with 6 and 7, the 1,2-cyclopentanediols 8 and 9 lead to oxo-Cr(V) complexes having very similar EPR spectral patterns (Fig. 6). The spectra are in both instances the sum of two EPR components, both split by the hyperfine interaction with nonequivalent carbinolic protons (Table II). 

Chlorocyclopentanol has been prepared by the reaction of dry hydrogen chloride with 1,2-cyclopentanediol and by the addition of hypochlorous acid to cyclopentene. -... 

Me3M+ cations (M = C, Si, Ge, Sn) were used as a stereochemical probe in gas-phase reactions with 1,2-cyclopentanediol isomers98. The decomposition pattern of the [1,2-cyclopentanediol + Me3M]+ adducts depended on the stereochemistry of the diol. For c/.v-diol the decomposition led readily to hydrated [Me3M(OH2)]+ cations, while for frans-diol the adduct was significantly more stable the Me3Ge+ cation was a more sensitive and selective reactant than other group 14 cations. 

Problem 13.4 The ir spectra of trans- and cis-1,2-cyclopentanediol show a broad band in the region 3450-3570 cm-1. On dilution with CC14, 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. ... 

The relative binding strength of the adducts follows the qualitative trend of the gas-phase basicities of the donor base, i.e. f-BuOH > i-PrOH > EtOH > MeOH > H2O. The binding to alcohols can be sufficiently selective to the point where 1,2-cyclopentanediols isomers have been distinguished by their reactivity towards Me3Ge+ in tandem mass spectrometry ". The actual binding energy has been measured for H2O (equation 22) ... 

We shall begin with the glycol of cyclopentene, 1,2-cyclopentanediol. Using models, we find that we can anangc the atoms of this molecule as in I, in which both hydroxyls lie below (or above) the plane of the ring, and as in II, in which one hydroxyl lies above and the other lies belpw the plane of the ring. 

Problem 9.4 You have two bonks labeled 1.2-Cyclopentanediol, one containing a compound of ni.p. 30, the t lhcr a compound of m.p. 55 both compounds arc opncally inactive. How could you decide, beyond any doubt, which bottle should be labeled <7v and which nv///. ... 

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