John T.S. Andrews

Vapor pressure and third-law entropy of ferrocene

Subsequent to Edwards and Kington’s’ use of a third-law entropy ‘;check to show that the rings in the ferrocene (dicyclopentadienyliron) molecule rotate essentially freely about the ring-to-metal bond, new data relevant to the statistical calculation ofthe entropy have appeared and imply the desirability ofperforming the entropy check anew. The frequency assignments of Lippincott and Nelson’ used in evaluating the vibrational entropy of%he moIecule have been superceded by the assignment of Stammreich (reported by Fritz3), and the structural parameters affecting rotational entropies are now available from the electron-diffraction study of Bohn and Haaland4

Heat capacity and vapor pressure of crystalline bis(benzene)chromium. Third-law entropy comparison and thermodynamic evidence concerning the structure of bis(benzene)chromium☆

Abstract Heat capacity measurements from 5 to 350° K and vapor pressure measurements on bis(benzene)chromium together with the published frequency assignments permit a correlation between the third-law and spectroscopic entropies. Neither thermal anomalies nor zero point entropy were found. The agreement is consistent with free rotation about the ring to metal bonds and D6h symmetry for the molecule as proposed by Cotton. The thermodynamic functions for the crystal at 298.15°K are 53.52, 54.07, 26.77, and −27.30 cal · mole−1 °K−1 for the heat capacity, entropy, enthalpy function, and Gibbs function, respectively. The vapor pressure over the range 310 to 365°K is represented by log10p (mm) = 27.42−5451/T−5.535 log10T, (T in °K).

. The enthalpies of combustion and formation of (2.2)-paracyclophane and triptycene

The enthalpies of combustion, ΔHoc, for crystalline [2.2]-paracyclophane (C16H16) and triptycene (C20H14) have been measured by oxygen combustion calorimetry. The derived standard enthalpies of formation at 298.15 K in the crystalline state are (34.59±0.19) and (51.87±0.20) kcalth mol−1. The strain present in these molecular systems is discussed.

The heat capacity and thermodynamic functions of crystalline and liquid triptycene

Abstract The heat capacity of the propeller-shaped molecule triptycene (C 20 H 14 ) was measured from 5 to 550 K. No anomaly other than melting was apparent, and the sample (99.999 per cent pure, as determined by analysis of the melting curve) melted at 527.18 K ( Δ m S = 13.73 cal mol −1 K −1 ). The crystal density, determined from X-ray measurements, was 1.227 g cm −3 . A comparison of the heat capacity of triptycene with that of bicyclo[2.2.2]octane showed that the two were simply related at low temperatures, but that the comparison was not valid beyond 164.25 K where bicyclo-octane has a transition to a restricted-rotor phase. The values of C p , S o (H o − H 0 o ) T , and − (G o − H 0 o ) T for triptycene at 298.15 K were found to be 67.56, 65.48, 33.23, and −32.25 cal mol −1 K −1 .