John M. Tedder

Directive Effects in Gas-Phase Radical Addition Reactions

Publisher Summary The solvent plays a major part in determining the course of most reactions in solution. The electron displacements accounted for by the electronic theory may be more important in the effect they have on the solvation of the transition state than any supposed “resonance stabilization.” In this context, the chapter investigates the reactions in the gas phase, free from the complications of the solvent, and determines the the extent to which the substituent effects established in solution and rationalized by the electronic theory, are effective in the gas phase. These activation parameters are in principle capable of complete interpretation using existing theory, whereas activation parameters determined in solution are very difficult to interpret because the extent of solvation, and the very structure of the solvent, changes with changing temperature. It is anticipated that kinetic study of radical reactions in the gas phase would provide the vital bridge connecting the qualitative pictorial theories of the organic chemist with semi-quantitative models of the theoretical chemist.

C-trifluoroacylation - a convenient route to carboxylic acids

Abstract Trifluoroacetic anhydride will trifluoroacylate reactive aromatic and heterocylic nuclei without the aid of a Friedel-Crafts catalyst. The resulting trifluoromethyl ketone undergoes hydrolysis to yield the corresponding carboxylic acid. This provides a very simple route to aromatic and heterocyclic carboxylic acids.

The preparation, spectra and tautomerism of some 4(n-arylamino)-1,2-naphthoquinones

Abstract Twelve 4(N-arylamino)-1,2-naphthoquinones ( 1 ) have been prepared by the direct addition of substituted anilines to 1,2-naphthoquinone, and their spectra have been studied. In the solid and in ethanol solution the 1,2-naphthoquinone tautomer ( 1a ) predominates, but in trifluoroacetic acid the 2-hydroxy-1,4-naphthoquinone-4-aryliminium ( 2a ) is the major species.

Free radical addition to olefins. Part 14.—Addition to trifluoromethyl radicals to fluoroethylenes

A competitive method has been used to determine the relative Arrhenius parameters for the addition of trifluoromethyl radicals to specific sites in fluoroethylenes taking the addition to one end of ethylene as standard.[graphic omitted]The relative activation energies correlate well with those for the addition of other halogenoalkyl radicals to the same olefins. The A-factors have been calculated from absolute rate theory using two models of the transition state, one resembling the products and the other resembling the reactants. Comparison of the calculated and experimental A-factors suggests that formation of the bond between the trifluoro-methyl radical and the alkene has proceeded sufficiently far, in the transition state, to cause significant breaking of the alkene double bond.

Synthesis of BRL 55834 - a novel, potent airways-selective potassium channel activator

Abstract An efficient synthesis of the potassium channel activator, BRL 55834 (2), is described and its absolute stereochemistry established as 3S,4R by X-ray crystallographic analysis of the corresponding (S)-α-methylbenzyl carbamate 12. BRL 55834 is the first compound of this pharmacological class to demonstrate selectivity for the smooth muscle of the airways compared with that of the vasculature.

The reactions of trifluoromethyl and trichloromethyl radicals with conjugated and methylene-interrupted dienes and enynes

Abstract The photochemical addition of CF 3 I to buta-1,3-diene and vinylacetylene in the gas phase gave 1,4-adducts as the main products. In gas phase reactions only products derived from hydrogen abstraction were detected in the CF 3 I/penta-1,3-diene system, but the 1,4-adducts again predominated in the liquid phase. CCl 3 Br similarly gave a mixture of 1,2- and 1,4-adducts, the latter predominating, on photochemical reaction with penta-1,3-diene. The 1,2-adduct was the main product from the CCl 3 Br/pent-1-en-4-yn reaction, but some hydrogen abstraction was observed. The preference shown by conjugated dienes to give 1,4-adducts in the trans - configuration is interpreted in terms of steric factors and the propensity of dienes to adopt the s - trans conformation.

Free radical addition to olefins. Part 23. The addition of pentafluoroethyl radicals to fluoro-olefins

Abstract Relative Arrhenius parameters have been determined for the addition of pentafluoroethyl radicals to each end of vinyl fluoride, vinylidene fluoride, trifluoroethylene and to tetrafluoroethylene taking ethylene as standard. The results compare very well with our earlier data for trifluoromethyl radicals. The pentafluoroethyl radicals are more selective and this selectivity can be attributed to changes in the activation energy term. The combined data are used to produce “revised” data for heptafluoropropyl radicals.

The study of ion–molecule reactions in the gas phase using a triple quadrupole mass spectrometer. Part 1. The reactions of CH3+, CD3+, and C2H5+ with simple olefins

A triple quadrupole mass spectrometer has been used to study the reactions of simple carbocations with low molecular weight olefins in the gas phase at relatively high pressures (10–3–10–4 Torr). In each case a high energy ‘addition complex’ is formed which fragments spontaneously to give daughter ions, the extent of fragmentation depending to some extent on the pressure and on the translational energy of the primary ions. Also formed are ‘second generation’ ions due to reactions of the predominant daughter ions with the olefin. Ions with the same mass as the high energy ‘addition complexes’ have been fragmented by collision (C.I.D.) with inert molecules (N2) to yield similar daughter ions to those found from the ‘addition complexes’. In the reactions, involving CD3+ ions, deuterium is widely, but not completely randomly, distributed among the daughter ions.

Free radical addition to olefins. Part 19.—Trifluoromethyl radical addition to fluoro-substituted propenes and its absolute rate of addition to ethylene

The rates of addition of trifluoromethyl radicals to each end of propene, 1,1,1-trifluoropropene and hexafluoropropene have been determined using a competitive technique, taking as a standard the rate of addition to ethylene. The rate of addition of trifluoromethyl radicals to ethylene (2) has been compared with the rate of combination of trifluoromethyl radicals (6), and a value of k2/k½6=(1.6 ± 0.2)× 103 exp (–2 900 ± 500 cal mol–1/RT) dm½ mol–½ s–½ was determined (1 cal = 4.184 J). [graphic omitted] Since the value of k6 is now well established, a new value of the absolute rate of addition of trifluoromethyl radicals to ethylene and to the other olefins can be computed.

Gas chromatographic properties of tetrafluoroethylene telomers

Abstract 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.