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Mixtures of bromotrichloromethane and the alkanes at circa 60 mm pressure have been irradiated in a Pyrex vessel with light from a medium pressure mercury lamp. The products, which consist solely of chloroform and monobromoalkanes, have been analysed. The reaction has been shown to be a chain process involving attack on the alkane by trichloromethyl radicals which abstract hydrogen atoms from the primary, secondary and tertiary positions in the order 1 : 80 : 2,300 at 190°.kk2/kp2 = 2.68 ± 1.48 exp (3.08 ± 0.46 k. cal/RT); kt2/k82 ≈ 5.25 × exp (5.5 k. cal/RT).

The synthesis of a novel series of smooth muscle relaxants which have been shown to act via the opening or activation of potassium channels is described. Compounds have been evaluated for their ability to inhibit spontaneous tone in guinea pig isolated trachealis and structure-activity relationships are discussed. One compound in particular, 1,1-dimethyl-5-nitro-3-(2-pyridon-1-yl)indan-2-ol, (16) was identified as a potent relaxant of airways smooth muscle in vitro with IC50 = 0.15 microM and was found to significantly inhibit histamine-induced dyspnoea in conscious guinea pigs when given orally 30-45 min prior to challenge.

The photolysis of carbon tetrachloride in the presence of a number of alkanes has been investigated in the gas phase. The products obtained from the photolysis experiments were those expected from a chain reaction in which trichloromethyl radicals abstract hydrogen atoms from the alkane. The data have been used to determine Arrhenius parameters for hydrogen abstraction from the series of alkanes CH4, C2H6, C3H8, and i-C4H10 by trichloromethyl radicals, The rate data obtained are used to explain why termination reactions involving alkyl radicals become less significant as the alkane becomes more complex.

The construction of a two-stage ion beam mass spectrometer is described. Ions formed by electron impact are focused into a beam which enters a reaction vessel containing neutral molecules at a relatively high pressure. Secondary ions formed by reaction between the primary ion beam and neutral molecules are repelled out at right angles to the primary beam into a conventional magnetic analyser. The instrument was calibrated using the known Ar + + Ar → Ar + Ar + electron transfer reaction. It was then used to study the reaction of acetylium (CH 3 CO + ) and nitronium (NO + 2 ) ions with aromatic compounds. The principal secondary ions were those involving electron transfer from the aromatic nucleus, but in addition ions of the type C 6 H 6 NO + 2 formed by addition of the primary ion to the aromatic compound were detected. However, the relative ‘yield’ of adduct ion from different aromatic compounds showed little correlation with the reactivity of these compounds towards acylation or nitration in solution.

The effect of the addition of hydrogen chloride on the photolysis of carbon tetrachloride in the presence of cyclohexane has been investigated in a companion paper. The data enable the rate constant ratio k8/(k5)1/2 to be determined. Since k−8 is well established, k5 can be estimated from known thermochemical data. The validity of the thermochemical derivation is checked by applying it to trifluoromethyl radicals. The photolysis of bromotrichloromethane and carbon tetrachloride in the presence of hydrogen chloride has been investigated over a range of temperatures. From these results and assuming reaction (5) has no activation energy, Arrhenius parameters for reaction (8) have been determined: The activation energies for the reaction of methyl, trichloromethyl, and trifluoromethyl radicals with hydrogen chloride are compared, and at first sight surprising results are rationalized in terms of relative electronegativity.

The paper describes an investigation of the gas chromatographic properties of tetrafluoroethylene telomers of general formula F(CF2)nI, Br(CF2)nBr, Br(CF2)nI, I(CF2)nI and (CF3)2CF(CF2)nI. The telomers are well resolved on columns with squalene, silicone oil or tritolyl phosphate stationary phases, and relative retention volumes are given for these three columns. The temperature dependence of the relative retention volumes of F(CF2)nI and Br(CF2)nBr telomers has been investigated. The relative retention volumes are correlated with the telomer boiling points, and with structural features of the telomers.

The photolysis of azocyclohexane, carbon tetrachloride, and cyclohexane at 360 nm has been investigated over a wide temperature range. At moderate temperatures a chain reaction ensues from which the following approximate rate constants could be determined assuming 2CCl3. C2Cl6, k5 = 109.7 (303–673K): The really striking feature of the results is that they show that termination in bicyclohexyl [reaction (7)] is extremely slow: The root-mean-square rule for estimating the cross-combination rate is also followed. The photolysis of carbon tetrachloride and cyclohexane at 250 nm has also been investigated. The reaction is complicated by the occurrence of two concurrent photolytic processes, the main one yielding trichloromethyl radicals and chlorine atoms, and the subsidiary one yielding dichlorocarbene and molecular chlorine. Nonetheless the results from this reaction can be interpreted in the medium temperature range 360–430K, where long chains are present, in terms of the rate constants derived from the azocyclohexane system.

Relative Arrhenius parameters have been determined for the addition of trifluoromethyl radicals to vinyl chloride (XCl), vinyl bromide (XBr), acrylonitrile (XCN), methyl vinyl ketone (XCOCH3), 2-methylbut-2-ene, and to iso-butene, taking the rate of addition to ethylene as standard. Addition occurred virtually exclusively at the unsubstituted end of all the olefins. The relative rates of addition at 164°C show very little variation. The preexponential terms for addition to the CH2 ends are constant within experimental error, and the small variations in rate are due principally to the activation energy term. The present results are put on an absolute scale using the previously determined Arrhenius parameters for addition to ethylene and are compared with data for other similar monomers determined previously.

The reaction of hydrogen atoms with chloroform, deuterochloroform and bromodichloromethane has been investigated. The mechanisms of the reactions are similar to those discussed in parts 1 and 2 only the reactions are complicated by the occurrence of hydrogen (or deuterium) abstraction as well as halogen-atom abstraction. The initially formed trihalogenomethyl and dihalogenomethyl radicals combine with hydrogen atoms to form vibrationally excited halogenomethanes. From the results it has been possible to compare the relative rates of abstraction of hydrogen and halogen and to deduce the fate of the different vibrationally excited molecules. The results of parts 1 and 2 together with the results from the present paper are combined and the following relative rates of the initial abstraction steps are deduced: (i) the relative rates of abstraction of chlorine from different halogenomethanes CCl2Br—Cl, 1; CDCl2—Cl, 1.2; CCl3—Cl, 1.3; CCl2F—Cl, 2.0; (ii) the relative rates of halogen (or hydrogen) abstraction from the same molecule kBr/kCl, 1.5–1.6; kH(D)/kCl, 3.3–3.4; kCl/kF, 4.7. In a similar way the stabilization/decomposition ratios of the various vibrationally excited molecules are compared.

The photochemical reaction of CF2Br2 with CHFCF2 and CH2CH2 has been examined in a series of gas-phase experiments. A mechanism for the radical chain addition which takes place is proposed. The variation in the rate of formation of the termination products, CF2BrCF2Br and CF2BrCHFCF2Br, with reactant concentration is explained if five important termination reactions are taken into account and a long-lived excited state of the CF2Br2 is accepted. Arrhenius parameters for the addition of CF2Br· radicals to the olefins have been derived : CF2Br·+ E → CF2BrE·(2), CF2Br·+ CF2Br·→ CF2BrCF2Br (4), k2/k½4(addition to CHF)=(1.2 ± 0.3)× 102 exp (–3300 ± 200/RT), k2/k½4(addition to CF2)=(2.0 ± 0.3)× 102 exp (–4400 ± 200/RT), k2/k½4(addition to CH2)=(2.5 ± 0.5) exp (–1000/RT). A factors are in 1.½ mol–½ s–½; activation energies in kcal/mol; R= 1.99 cal deg.–1 mol–1; 1 cal = 4.184 J.

The light-induced addition of SF5Cl to fluoro-olefins (E) has been studied in a large series of experiments in which light intensity, temperature and relative concentrations have been varied. The reaction mechanism is the same as that established for ethylene with the following principal chain carrying steps : [graphic ommitted] and the combination of two SF5· radicals (k6) the main chain termination step. The addition to tetrafluoro-, trifluoro- and 1,1-difluoro-ethylene has been investigated and from studies on the latter two compounds the following rate expressions were obtained. [graphic ommitted] *R the gas constant taken to be 1.9872 cal deg.–1 mol–1 and subsequent energies expressed in cal mol–1(1 cal = 4.1855 J).

The reaction of hydrogen atoms with bromotrichloromethane and with fluorotrichloromethane has been investigated. The main course of both reactions is shown to be the same as that established in part 1 for the reaction of hydrogen atoms with carbon tetrachloride. Both reactions involve initial halogen abstraction followed by combination of the resultant trihalogenomethyl radical with a hydrogen atom to form a vibrationally excited trihalogenomethane molecule. From the experimental results it has been possible to compare the relative rates of abstraction of the different halogens and to study the fate of the different vibrationally excited trihalogenomethanes.

The light-induced reaction between bromotrichloromethane and n-butane has been studied in a series of gas-phase experiments. Taking a literature value for the recombination of trichloromethyl radicals, the value k2= 7.6 × 106 exp (–7530/RT) l. mole–1 sec–1 was determined: CCl3˙+ RH→CCl3H + R˙.(2) The difference in the rates of abstraction of primary and secondary hydrogen atoms is given by ks2/kp2= 0.67 exp(3640/RT). From experiments in which hydrogen bromide was added a value of k46305= 108.44±0.63 was determined: CCl3˙+ HBr→CCl3H+Br. (5)

Arrhenius parameters have been measured for the addition and hydrogen abstraction reactions of trichloromethyl radicals with propene, 2-fluoropropene, and hexafluoropropene.

Arrhenius parameters have been determined for the addition of trichloromethyl radicals to fluoroethylenes; for the unsymmetric olefins the parameters have been determined for each end of the double bond. [graphic omitted] The determined activation energies are compared with localization energies, and with free valence as calculated from simple Huckel theory.

Dichloromethane, chlorofluoromethane, and dichlorofluoromethane have been brominated competitively with each other and with chloroform and methyl chloride. Using the literature values for the rates of bromination of these latter two compounds, the rate constants for the three former compounds have been determined: where R is taken to be 1.987 cal deg−1 mol−1 (1 cal = 4.186 J).

Hydrogen atoms, generated in a Wood's tube, have been allowed to react with carbon tetrachloride vapour. The products of the reaction have been analyzed and found to be hydrogen chloride, chloroform, methylene dichloride and traces of methyl chloride. The effect of the relative concentrations of the reactants, of an inert gas and of added hydrogen chloride on the ratio of the principal products has been investigated. From these data it is possible to build up a complete picture of the reaction sequences. The initial step is chlorine abstraction by a hydrogen atom; the trichloromethyl radical so produced reacts with a further hydrogen atom to yield an excited chloroform molecule which either undergoes collisional deactivation or loses hydrogen chloride to yield dichlorocarbene.

The light-induced chlorination of butane and 2-methylpropane by t-butyl hypochlorite has been been studied from 10 to 70°C in the gas phase. Light intensity, pressure, reactant concentration and temperature have been varied and the results have been rationalized in terms of chlorination proceeding by way of a t-butoxy radical chain carrier. The relative rates of hydrogen abstraction by the t-butoxy radical, [graphic ommitted] have been obtained per H atom for the primary, secondary and tertiary positions of the two hydrocarbons studied. kS2/kP2= 1.63±0.01 exp (3.81±0.1 kJ/RT); kT2/kP2= 1.73±0.01 exp (4.94±0.1 kJ/RT). It was also possible to relate the rate of hydrogen abstraction k2 to the rate of decomposition of the t-butoxy radical (k4), [graphic ommitted] kP2/k4= 2.7±1.1 × 10–5 exp (38.1±1.7 kJ)/RT. These results are consistent with earlier results for alkyl and alkoxy radicals.

Mixtures of isomeric dihalo- and halomethylcyclopentanes and of dihalo-, halo-methyl- and halocyanocyclobutanes have been separated by gas chromatography on a tritolylphosphate column. The order of elution is the same for each set of isomeric disubstituted cycloalkanes. The relative retention volumes can be used to determine rapidly the structure of a given isomer and distringuish it from other stereoisomers. An attempt is made to rationalise the retention volume data in terms of the structural properties of the cycloalkanes.

The light-induced addition of SF5Cl to ethylene (E) has been studied in a series of gas-phase experiments in which concentration, relative light intensity and temperature have been varied. The results can be rationalized by the following chain mechanism in which the addition step (2) is appreciably reversible in the temperature range studied: SF5Cl +hv → SF5·+ Cl·(1) SF5·+ E ⇌ SF5E·(2), (–2) SF3E·+ SF5Cl → SF5ECl + SF5·(3) Cl·+ E → ECl·(4) ECl·+ SF5Cl → ECl2+SF5·(5) SF5·+ SF5·→ S2F10(6) From a series of experiments in which both pressure and temperature were varied the following rate expressions were obtained. k2/k½6=(3.9 ± 0.6) exp (–1,900 ± 200/RT)1.½mole–½ sec–½,‡k–2/k3=(118 ± 20) exp (–6,660 ± 300/RT)1.–1 mole.

Mixtures of dichlorocyclobutane, -cyclopentane, -cyclohexane and -cycloheptane isomers, and of chlorofluoro-, bromofluoro-, bromochloro- and dibromocyclohexane isomers have been separated by gas chromatography on a tritolyl phosphate column. The order of elution of the isomers is the same for each set of dihalocyclo alkanes except for the fluoro compounds, and individual isomers can be quickly identified from their retention times.

Trichloromethyl radicals have been allowed to react with 1-fluorobutane and 1,1,1-trifluoropentane in the gas phase. Arrhenius parameters have been obtained for the attack at each individual site in these molecules.

The reaction of C1 ions with ethene and propene has been studied in the gas phase using a triple quadrupole mass spectrometer.

Hydrogen bromide is shown to have a pronounced effect on atomic brominations in the gas phase; this is due to two effects, (i) a possible reversible reaction of alkyl radicals with hydrogen bromide, and (ii) the direct reaction between hydrogen bromide and alkyl bromides leading to olefins.

The paper is concerned with reactions involving radical cations in the gas phase. Three separate systems have been studied. These are: alkane radical cations with alkanes (e.g. CH4 +. + C4 H10 →); alkene radical cations with alkenes (e.g. C2 H4 +. C2 H4) and the formation of aromatic radical cations (e.g. C6 H6 +) in the reactions of alkyl cations with aromatic nuclei.