Butyl ions, generated by the y irradiation of neopentane, undergo hydride transfer reactions with alkanes having tertiary hydrogen atoms (/-C4H9+ + RH z'-C4Hio + R+) to form isobutane and a tertiary carbonium ion as products. By irradiating neopentane in the presence of mixtures of two reactant molecules, one deuterated and one nondeuterated, the relative rates of the hydride transfer reaction for 22 C5-C8 alkanes were determined with an unusually high accuracy, from the observed ratios of z'-C4H9D to z'-C4Hi0. Absolute rate constants for the reactions, based on a determination of the rate of depletion of the isobutane yield when ammonia is added, are given. The rate constants are generally very low [10-u-10-10 cm3/(molecule sec)], but are shown to depend on the heat of reaction and steric factors involving van der Waals interactions between the approaching ion and hydrogen atoms or methyl groups on the carbon atom ß to the tertiary carbon. The evidence indicates that the hydride transfer reactions of the /-butyl ion have an activation energy, E*.t < 0.15 eV. In another series of experiments, unsaturated hydrocarbons were added to neopentane-isopentane mixtures, and the rates of the condensation reaction of these additives with /-butyl ions were determined by measuring the rate of depletion of the isobutane yield. The rate constants for the condensation reactions are in the range 10~10-10~9 cm3/(molecule sec). Some insight into processes occurring in the radiolysis of neopentane can be gained from these results. It is shown, for example, that in the absence of reactive additives, not more than about 14% of the /-butyl ions undergoes processes resulting in the formation of isobutene.(1) This research was supported by the Atomic Energy Commission.(2) (a) F. W.

364 1 but the differences are greatly attenuated. This observation might be attributed to a substantial amount of diffuse character in these negative ion states which is greatly diminished in condensed phase^.'^,'^ Summary. The key findings of the present investigation are (a) that significant through-space methyl-?r interactions exist in the +' * and G4* negative ion states of 4 and 5, (b) the this interaction in fi4*, and probably also in &*, primarily involves the hydrogen 1s (T) rather than the carbon p (~) orbital of the methyl group, and (c) that conformations with interior out-of-plane methyl hydrogens make a significant (but as yet unspecified) contribution to the distribution of conformations in 4. Similar considerations also apply to 5. We believe that the electron-transmission technique may prove to be quite powerful in probing certain conformational questions. This will serve to greatly expand its already recognized importance in providing electron affinities and attachment energies of complex molecules. Acknowledgment.We thank the National Science Foundation (Grant No. CHE77-14930) for support of this work and the Gillette Research Foundation for a fellowship to J.C.G. must be directed toward Cz of the diene system (Le., must be an interior methyl H). This would result in a through-space interaction of the C3 P(T) orbital and, more importantly, the C2 p(?r) orbital with a hydrogen 1s orbital (or orbitals) which would account for the observed destabilization of +4*. The major interaction is illustrated in Figure 6 for conformation 4b, although there are clearly an infinite number of conformations with interior out-of-plane methyl hydrogens which would account for this observation. (The occurrence of such conformations can be rationalized on the basis of an interaction between the eclipsed methyl hydrogen and H2 in conformation 4a.) A similar through-space interaction accounts for the relative stabilization of J.s* in 4 and 5 compared to 2 and 3, respectively. Indeed the agreement of the relative trans-cis shifts of both q3* and q4* with the foregoing through-space interaction is an important factor in support of this analysis.The long-wavelength electronic-absorption band for the negative ions of 1, 3, and 4, prepared by y-irradiation in methyltetrahydrofuran glasses at -196 "C, has been attributed to a transition between IC3* and +4*.14 The energies of these transitions (2.18, 2.16, and 2.20 eV, respectively) are in the same relative order as are the values of Abstract Rate constants have been measured for reactions of the type AD2+ + MH -MD + ADH+, where AD: is CD' CND' , CD3CDOD+, (CD3COCD3)D+, or (C2D5)20D+ and the MH molecules are alcohols, acids, mercaptans, H2S, AsH3, PH3, or aromatic molecules. Rate constants are also presented for the reactions ArHD+ + D20 -ArDD+ + HDO, where k H D + is a deuteronated aromatic molecule and ArDD+ is the same species with a D atom incorporated on the ring. In all but two cases, the competing deuteron transfer is sufficiently endothermic that it cannot be observ...

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Irradi a tion of CC I4 , CFCI3 , a nd CF2C1 2 in the prese nce of C2 H6 in vesse ls co ntaining s ilica sa nd or fused qua rt z tubing results in th e formati on of chl orine-cont aining produ cts. The form ation of these compounds occurs at wavelength s ex tending up to a pproximately 400 nm, that is, at wavele ngths wel l beyond the a bsorpti on threshold of the ch lo romethanes in the gas p hase . It is s uggested that CCI, adsorbed on silica surfaces ph otod issociates to yield CCI" and CCl2 s pec ies. The poo r mate ri a l ba la nce obtained in these experim ents ind ica tes that several of the chl orine -co ntaining fragme nts are strongly adsorbed o n the su rface. At a CCI, pressure of 13 Pa (0.1 torr), ph otolys is with 366 nm light in th e prese nce of sa nd resu lt s in the decomposit ion of one mo lec ule for every 10' photo ns stri king th e sudace. Under oth erw ise id e nt ical co ndit ions, the photon-induced breakdown of CFC I3 and CF2CI2 is res pectively o nl y JO pe rce nt ur 3 pe rc e nt as effi c ie nt.Key words: Chl oron1etha nes, photoche mist ry; q ua ntum yields; q ua rtz; sa nd; surface reacti ons; tropospheri c s ink. . IntroductionIn a recent study [1 r from this laboratory, it was shown th a t in th e gas phase, the photodecompositi on c ross secti on of CC14 at 313 nm was ~ 3 .7 ± 0 .4 X 10-26 cm 2 mo lec ul e-I at 300 K. Because sun l ight reach ing sea level consists mainly of wa velengths a bove 320 nm , thi s laboratory result suggests tha t in th e troposphe re gaseous CC14 will not be di ssociated by light. Th e p hotodi ssoc iation cross section of f1u orines ubst ituted meth a nes a t th e wavele ngth s whi ch reach the ear th's surface s hou ld be eve n smalle r th a n th at [or CC14 , s ince th e abso rpti on s pec tra of th e f1u orin e-substituted compounds are shifted to shorter wavele ngth s [2]. The refore, c hloromethanes and fluorochloromethanes released to the a tmospher e would be expected to diffuse to the stratosph ere, unless s ome mec hanism for their re moval other th an p hotodecomposition exists. As Molina and Rowland [2] suggested , th ese compounds in the stratosphere would absorb h igh ene rgy ph otons and undergo photodissociation to produ ce chlorin e atoms , which in turn would be expected to unde rgo a c ha in re ac tion resulting in the re moval of ozone molec ules .Howe ve r, the re were available two pi eces of evide nce whi ch ind icated that possibly CCl4 wh en adsorbed on cel·tain sltl-faces d oes undergo photodecomposition at wavelength s as long as th ose wh ich reach the earth's surface . Th e first such observa ti o n was that the cross section for ph otodeco mpos iti on of CC I4 showed a n appare nt increase by a facto r of fi ve wh e n the measure ments were made in quartz ra th er th an Pyrex 2 vessels. Second ly, measurements of the co ncentra ti on of CCl4 in th e tro pos phere in the e astern he mis ph ere as a functi on of la titude fro m 50 N to 3 0 S have shown th at there is a pro nou nced minimum in the CC14 concentrati on in the...