Cyclopentane stability

Cyclopentane has two nonplanar- confor-mations that are of similar- stability the envelope and the half-chair. 

Biradical I would yield cyclopentene plus ethylene, biradical II the hepta-1,6-diene. Process I may have a lower energy of activation because of the stabilization of the free electron by the secondary carbon atom and also because less energy is required to compress the appropriate carbon-carbon bond, in the cyclopentane ring to yield the cyclopentene, than to rupture the ring to give the diene. 

Spherical polar coordinates are used for conformational representation of pyranose rings in the C-P system. Unlike the free pseudorotation of cyclopentane, the stable conformations of cyclohexane conformers are in deeper energy wells. Even simong the (less stable) equatorial (6 = 90 ) forms, pseudorotation is somewhat hindered. Substitutions of heteroatoms in the ring and additions of hydroxylic or other exocyclic substituents further stabilize or destabilize other conformers compared to cyclohexane. A conformational analysis of an iduronate ring has been reported based on variation of < ) and 0 (28), and a study of the glucopyranose ring... 

The preceding differences and similarities indicate a considerable difference in the stabilities of cis and trans cyclopentane-fused heterocycles as compared with those of the higher homologs. Such differences are especially striking when the formation of the heterocycles proceeds through an equilibrium reaction. 

Hydroxylating 3-phenylisoxazoline is enthalpicly the same as for cyclopentane, with an added 39 kJmol for anomeric stabilization (equation 46) °. 

Problem 9.5 (a) Calculate AH of combustion per CHj unit for the first four cycloalkanes, given the following AH s of combustion, in kJ/mol cyclopropane, -2091 cyclobutane, -2744 cyclopentane, -3320 cyclohexane, -3952. (b) Write (i) the thermochemical equation for the combustion of cyclopropane and (ii) the theoretical equation for the combustion of a CH unit of any given ring, (c) How do ring stability and ring size correlate for the first four cycloalkanes ... 

Organometallic methods, with the possible exception of those involving the stoichiometric generation of enolates and other stabilized carbanionic species 140], have seldom been used in carbohydrate chemistry for the synthesis of cyclohexane and cyclopentane derivatives. The present discussion will not cover these areas. The earliest of the examples using a catalytic transition metal appears in the work of Trost and Runge [41], who reported the Pd-catalyzed transformation of the mannose-derived intermediate 22 to the functionalized cyclopentane 23 in 98% yield (Scheme 10). Under a different set of conditions, the same substrate gives a cycloheptenone 24. Other related reactions are the catalytic versions of the Ferrier protocol for the conversion of methylene sugars to cyclohexanones (see Chap. 26) [40,42,43]. 

Exists in two, forms crysts (from acet), mp 104-05° (dec) readily sol in acet si sol in chlf, ale eth acetate insol in eth, CS2, Benz gasoline was prepd from cyclopentene N2Oa in eth petr eth under strong cooling and crysts, mp 69 70°. of low stability was prepd by passing nitrous gas in an ethereal soln of cyclopentane with strong cooling (Ref 1)... 

The photo-oxidation of n-butane has been modelled by ab initio and DFT computational methods, in which the key role of 1- and 2-butoxyl radicals was confirmed.52 These radicals, formed from the reaction of the corresponding butyl radicals with molecular oxygen, account for the formation of the major oxidation products including hydrocarbons, peroxides, aldehydes, and peroxyaldehydes. The differing behaviour of n-pentane and cyclopentane towards autoignition at 873 K has been found to depend on the relative concentrations of resonance-stabilized radicals in the reaction medium.53 The manganese-mediated oxidation of dihydroanthracene to anthracene has been reported via hydrogen atom abstraction.54 The oxidation reactions of hydrocarbon radicals and their OH adducts are reported.55... 

Example Isopentane (IC5), normal pentane (NC5), and cyclopentane (CC5) are to be separated by means of distillation. A 5000-bpd rich feed with these components is received. The mixed feed containing these and many other components—including ethane, propane, butane, through benzene—is received as a liquid. A three-column distillation train, in series, will be installed to produce IC5, NC5, and CC5 spec product liquid streams. Methane, ethane, propane, and butane have been removed in an upstream stabilizer column. Only trace ethane and propane are remaining in the feed stream feeding the first column, IC5. 

Vinyltins were used for synthetic purposes in radical addition-elimination sequences. The main limitation comes from the necessity to functionalize the olefin by groups such as esters able to stabilize the transient carbon-centred radical573. Phenyl-substituted systems proved to be reactive as well, whereas methyl- and cyclohexenyl-substituted ones failed to react574. An intramolecular version was developed giving access to methylene cyclopentane units (equation 44)575. 

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