Cyclopentane entropy

The k-values between —5 °C (85-100 s ) and —22 °C (3 1 s ) yielded the following values of the overall activation enthalpy AH and activation entropy AS for the fluxonial exchange rates of tetrameric tert-butyllithium in cyclopentane ... 

The activation energy of the dissociation of (MeLi)4 in diethyl ether is lower than that of (t-BuLi)4 in cyclopentane apparently because the solvation of the transition state of the former aggregates by the ether facilitates their dissociation. The reported values of the entropies of activation support this explanation. 

For larger molecules, we also consider how one part of a molecule moves relative to other parts. A long hydrocarbon chain can rotate and vibrate in more ways than a short one, so entropy increases with chain length. A ring compound, such as cyclopentane (CsHjo), has lower entropy than the corresponding chain compound, pentene (C5H10), because the ring structure restricts freedom of motion ... 

Cycloheptane and cyclooctane data on the thermal properties are also given in Table 3.1 They show little change from the cyclopentane and cyclohexane properties. Again, there is no indication of increasing amounts of conformational entropy in the transition entropies. For cyclooctane in solution H and NMR could prove ring-inversions and pseudorotation among the boat-chair conformations through the twist-boat-chair intermediate to very low temperatures (100 K). Only about 6% of the cydooctane could be found at about 300 K in the other three crown-family... 

Aston G, Fink HL, Schiunann SC (1943) The heat capacity and entropy, heats of transition, fusion and vaporization and the vapor pressure of cyclopentane. Evidence for a non-planar structure. J. Am. Chem. Soc. 65 341... 

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