rameters, thermal parameters, interatomic distances, interatomic angles, dihedral angles, and least-squares planes for 3-TNB (13 pages); listing of observed and calculated structure factors for 3-TNB (10 pages). Ordering information is given on any current masthead page.

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The enthalpies of reaction of the ‚Cr(CO) 3 C 5 Me 5 and disulfides (RSSR) forming RS-Cr(CO) 3 C 5 Me 5 have been measured by solution calorimetry, ∆H ) -13.3 + 1.5 kcal/mol (R ) Ph) and -11.2 + 1.2 kcal/mol (R ) Me). These data lead to Cr-SR bond strength estimates of 35 and 43 kcal/mol, respectively. The rates of oxidative addition have been investigated by FTIR spectroscopy. Phenyl disulfide reacts by a second-order mechanism whose rate-determining step is the attack of the chromium radical on the sulfur-sulfur bond, yielding chromium thiolate and a thiyl radical [k(298 K) ) 1.3 M -1 s -1 , ∆H Φ ) +10.2 kcal/mol, ∆S Φ ) -24.4 cal/(mol deg)]. Methyl disulfide reacts by a third-order mechanism going through a termolecular transition state in which the stronger sulfur-sulfur bond in the alkyl disulfide is attacked simultaneously by two chromium radicals [k(298 KThe rates of reaction of MeSSMe and PhSSPh with the hydride H-Cr(CO) 3 C 5 Me 5 have also been investigated in the presence of varying amounts of added ‚Cr(CO) 3 C 5 Me 5 radical. MeSSMe shows no apparent reaction with HCr(CO) 3 C 5 Me 5 , even in the presence of added ‚Cr(CO) 3 C 5 Me 5 . PhSSPh reacts with HCr(CO) 3 C 5 Me 5 primarily by a radical chain process involving ‚Cr(CO) 3 C 5 Me 5 and PhS‚ radicals. The upper limit to the rate of reaction by nonradical concerted addition is k obs < 4 × 10 -4 M -1 s -1 .

The heat capacity of sodium amide has been determined from 15 to 300°K. in an adiabatically operated calorimeter. At 298.15°K. the heat capacity, entropy and enthalpy were found to be 15.81 cal. deg.-1 mole-1, 18.38 cal. deg.-1 mole-1 and 2841.6 cal. mole-1, respectively.At 240°K. the standard free energy of formation of ammonous amide ion in the h}rpothetical 1 molal ammonia solution is 30.5 kcal. and the partial molal entropy of amide ion is -19.3 cal. deg.-1 mole-1 relative to 5240 [H+(am)[ = 0.0. In comparison with other negative ions the observed entropy of the amide ion in liquid ammonia appears qualitatively correct for a freely rotating ion. For the reaction: XH3(1) = H-(am) + NH»-] = -14.7 cal. deg.-1 mole 1 and K = 2.2 X 10 28 for the ionization of liquid ammonia.