THERMODYNAMIC PROPERTIES OF CRYSTALLINE AND LIQUID CHLOROCYCLOHEXANE AND INVERSION OF RING

Heat capacity of crystalline and liquid chlorocyclohexane (c-C6H11Cl) at T = 5 K to 304 K was measured by vacuum adiabatic calorimetry. Two solid-to-solid transformations were found: at T = 120 K with DELTA(trs)H(m) = (50.5 +/- 0.5) J . mol-1 and at T = 220.4 K with DELTA(trs)H(m) = (8010.7 +/- 2.9) J . mol-1. Melting temperature of c-C6H11Cl is 229.34 K, and DELTA(fus)H(m) = (2042.8 +/- 4.4) J . mol-1. The enthalpy of vaporization was directly determined with a heat-conduction differential microcalorimeter: DELTA(vap)H(m)-degrees(298.15 K) = (42.92 +/- 0.62) kJ . mol-1. Values DELTA0(T)S(m)(1, 298.15 K) = (242.2 +/- 1.0) J . K-1 . mol-1, PHI(m)(1, 298.15) = (111.4 +/- 0.5) J . K-1 . mol-1, and DELTA0(T)S(m)-degrees(g, 298.15 K) = (348.0 +/- 2.3) J . K-1 . mol-1 were calculated on the base of these. The temperature dependence of DELTA(vap)H(m)-degrees in the temperature range from T = 296 K to 320 K was studied, and DELTAC(p)-degrees(1 to g) was estimated. By low-temperature i.r. spectroscopy it was established that the liquid and the crystal I consist of a mixture of the equatorial and axial-chair conformers, but crystals II and III (at T < 220.4 K) consist of only e-conformer. The conformational analysis of chlorocyclohexane was made by the molecular-mechanics method. Statistical calculations of standard thermodynamic properties of c-C6H11Cl in the gaseous state were carried out for T = 100 K to 1000 K, taking into account conformation composition. Calculated and experimental values of C(p,m)-degrees and S(m)-degrees-(g) at T = 298.15 K, and S(m)-degrees-(g) at T 353.15 K are in satisfactory agreement. The following thermodynamic functions of chlorocyclohexane were obtained: DELTA(f)H(m)-degrees-(g, 298.15 K) = -(164.2 +/- 2.0) kJ.mol-1; DELTA(f)H(m)-degrees-(1, 298.15 K) = -(206.9 +/- 2.1) kJ . mol-1; DELTA(f)G(m)-degrees-(g, 298.15 K) = kJ . mol-1; DELTA(f)G(m)-degrees-(1, 298.15 K) = -(21.3 +/- 2.6) kJ . mol-1.