1286
G. H. PAULI, F. A. MOMANY, A N D R. A. BONHAM
VOl. 86
centage yields of labeled parent molecule measured a t 1 atmosphere gas pressure. We conclude that the average ease of substitution of T for H does not change greatly among these molecules, and, as a corollary conclusion, that steric interference with the substitution TABLE VI reaction is not very important for either chlorine atoms RELATIVE PROBABILITY OF T-FOR-HSUBSTITUTIOX REACTION PER or alkyl radicals. If there is a variation in the last C-H BONDI N THE MOLECULE column of Table VI, it may be a decrease in the direcRatio tion CH4-CH3Cl-CH3F and indicates an influence for R T alonea not of atomic size of H , C1, and F, but probably of inUS. Relative creasing electronegativity. Experiments with liquid cycloprobaCH3F seen necessary to determine whether any apTarget CiHiT bility + -Decomposition productof molecule, preciable decomposition of CHzTF has taken place if a RH CtHaT Ref. Identity Yield Ref. reacn. more accurate estimate of these relative T for H subCH, 0.83 4 CHiT 0 . 1 2 X R T 20 0 93 stitution probabilities is described. n-CiHia .82 4,23 CZHIT(?) .. 3 82* CHIF .61 14 ? 3 .61b The Abstraction of H by Energetic T Atoms.--A large 41 Present work CHxT T h i s work 78 CHaCl fraction of the recoil tritium atoms formed in the Cyclo-CiHs 60 4 CzHaT 0.40 4 1.00 presence of CHaCl react by abstracting an H atom to Possible decomposition a Measured a t about 1 atmosphere. form H T . Comparison of the results in scavenged and products not included in the absence of experiments in the liquid unscavenged samples indicates that essentially all of phase. this H T yield is obtained from a hot reaction. The The data of Table V I include gas phase comparisons magnitude of this yield has been definitely correlated only for the molecules CH3F and n-CdHlo and are with the bond strength of the C-H bonds in the target consequently subject to possible increase if some of the molecule, and results with CH3Cl are in reasonable originally produced labeled molecules have decomposed agreement with those obtained for hydrocarbons.26 a t this pressure. No gas pressure-dependent yields If CH?TCl molecules decomposed partially by dewere observed with CH4 or CHsF, but labeled radicals hydrohalogenation, a pressure-dependent yield of H T have been caught with I2 scavenger in each case.10s20 could arise from eq. 10a. The constancy of the H T Liquid phase scavenger experiments have not yet been yield relative to the total gaseous activity indicates no run because of the very high vapor pressures a t ambient appreciable contribution from such methylenic dereactor t e m p e r a t ~ r e . ~ ,The ' ~ yield of n-C4HSTfrom compositions. n-C4Hlodoes show a gas phase pressure d e p e n d e n ~ e , ~ ~ CH?TCI* +CHCl + HT (loa) but liquid phase studies indicate that decomposition + CTCl + Hz (lob) in the 1-atmosphere gas phase work is not Acknowledgment.-The cooperation of the operatThe relative figures in the final column of Table VI ing personnel of the Omaha VA Hospital reactor is indicate that the variations in T-for-H substitution gratefully acknowledged. are much less than the factors of 3 suggested by the perferent from 0.78. The comparison of relative probabilities of T for H substitution can be extended through other binary comparisons to CH4, CH3F, and n-C4Hlo, giving the ratios shown in Table VI.4.5,'4
(21) :E K C 1,ee. P h I ) Thesis, University o f K a n s a s , 1983 (2.5) I< K n o b a n d F S l i a w l a n d , unpublished resulta
[CONTRIBUTIOS S o 1l i 3
(26) LV Rreckenridge, J W. R o o t , and F S Rowland. J . Chrm P h y s , S9, 2871 (1963).
FROM 'ri
