The relative rates of hydrogen and deuterium abstraction by chlorine atoms from H2–D2, CH4–CD4, and C2H6–C2D6 in direct competition have been studied by a mass spectrometer technique permitting direct determinations of rates. The pair CHCl3–CDCl3 was investigated by a substitution—addition competition with C2Cl4. Data were obtained between 300° and 475°K, and values of kH/kD ranged between 3.64 and 10.9 for CH4/CD4, 2.37 to 2.69 for C2H6/C2D6, 1.58 to 2.26 for CHCl3/CDCl3, and 4.7 to 8.9 for H2/D2. For the family of reactions involving C–H–Cl, an extensive series of model calculations were made by the ``bond-energy—bond-order'' method. The expected variation of activation energy with heat of reaction was computed and compared with experiment. The expected variation of kinetic isotope effect with both temperature and heat of reaction was computed for a range of conditions much wider than these experiments. Simple activated complex theory predicts several strong trends of kinetic isotope effect with heat of reaction. The data, in a general semiquantitative way, follow these predicted trends, but in terms of fine details the data do not fit the theoretical lines. In view of the known simplifications in activated complex theory, this agreement with broad trends is all that anyone should expect.

The chlorine-photosensitized oxidation of trichloroethylene in the gas phase has been investigated at 363 and 403°K. Dichloroacetyl chloride is the main reaction product and its rate of formation is given by d[CnHCl@]/dt = L[O2l/(k + k'[021).

Herrn Professor Dr. R i c h a r d Kuhn zurn 60. Geburtstag gewidrnetDie Photochlorierung von Gemischen aus C2CI4 einerseits und CH4, CH3C1, CHzC12 oder CHCI, anderseits, sowie die Photochlorierung von CH4, CH3CI und CH2Cl2 wurden untersucht; die drei letztgenannten Reaktionen sind ebenfalls einer Untersuchung von Gemischen aquivalent, da die Reaktionsprodukte einen starken EinfluB auf den Redktionsverlauf haben. Es werden kinetische Gleichungen abgeleitet; ferner wird eine Reaktionszeit definiert (im wesentlichen das Inverse einer Reaktionsgeschwindigkeitskonstanten) : die Reaktionszeit in einem Gemisch ist gleich der Summe der Reaktionszeiten der Komponenten. Diese kinetischen Betrachtungen gestatten es, den komplizierten Verlauf der Photochlorierung von CH4, CH3CI und CHzClz zu klaren. Unter Zuhilfenahrne einiger Literaturangdben werden so zuverllssige Werte fur etwa 40 Geschwindigkeitskonstanten elementarer Atom-und Radikalreaktionen erhalten. * ) Boursier de I'IRSIA (Institut pour I'Encouragcment de la Recherche Scientifique dans I'Industric et I'Agriculture, Bruxelles).

The inhibitory eflfect of oxygen on the photochlorination of ethane has been studied between 253 and 423°K. It can be explained by the removal of ethyl radicab by molecular oxygea : C2H5 + 02^C2H502 k9. The value kg = 063 x 10' molei sec~i is in good agreement with literature data. The dependence of the rate on concentrations and light intensity is discussed and permits one to discard an alter native «iplanation involving the reaction CI+O2->C102. * We wish to thank the référée for valuable suggestions. 1 Huybrechts, Martens, Meyers, Olbregts and Thomas, to be published. 2 Goldfinger, Huybrechts and Olbregts, to be published. 3 Dingledy and Calvert, /.