A bromine ± alkyne p complex (l max 294 nm) of 1:1 stoichiometry has been observed for the first time in the course of the bromination of 1-phenylpropyne by means of a diode-array stopped-flow technique. ); this demonstrates that the complex is actually an essential intermediate on the reaction coordinate. The bromination of a series of nine alkynes has been studied. Bromination reactions with negative apparent activation parameters lead to mixtures of E and Z vinyl dibromides, whereas reactions with positive activation energy yield the E isomers exclusively. The reason for the difference in reactivity of these alkynes compared with structurally similar alkenes most likely lies in the stability of these 1:1 charge-transfer complexes. Usually open arylvinyl cations correspond to the energetically favored product-determining intermediates; bridged bromirenium ions are formed from deactivated alkynes and react to give E isomers. The kinetic effect of alkyl groups and of p-OCH 3 , p-CN, and p-NO 2 substituents at the aryl group on the bromination of arylalkylacetylenes is discussed. Density functional calculations provide insight into the geometries, energies, and bonding of the intermediate 1:1 and 2:1 Br 2 ± acetylene complexes involved. These theoretical investigations demonstrate that the most stable trimolecular Br 2 ± Br 2 ± acetylene adduct possesses a structure very similar to a crystallographically characterized Br 2 ± Br 2 ± alkene species, which can directly yield the ionic products, Br À 3 and vinyl cation, driven by the heterolytic action of a solvent.

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The results include the analysis of water, glycerine and mineral oil as well as aqueous solutions of thickeners such as Acrylates/C10-30 Alkyl Acrylate Crosspolymer (Ultrez-20 obtained from Noveon) and carbomer. Solutions of common surfactants and complex surfactant formulations such as shampoos have also been investigated. The results, in the form plots of force as a function of time or distance, resulting from slow bidirectional probe movement (submergence and desubmergence) in the analysed fluid, were interpreted by considering buoyancy, drag and viscous drag force given by Stokes equation. The data can be used to correlate with tactile evaluations of products by trained panel evaluations.

The reaction of guanosine with 3,4-epoxy-1-butene in acetic acid gives two main products of N-7 alkylation. After acidic hydrolysis the two aglycones have been isolated by h.p.l.c. and shown to be the regioisomeric 7-(2-hydroxy-3-buten-1-yl) guanine (I) and 7-(1-hydroxy-3-buten-2-yl) guanine (II), arising through nucleophilic attack by N-7 of the purine at the two oxirane carbons of 3,4-epoxy-1-butene. Spectral characteristics of both compounds are presented, including u.v., 1H-n.m.r. and mass spectra. Deoxyguanosine reacts with 3,4-epoxy-1-butene in 50% methanol-water at 37 degrees C to give the N-7 alkylated deoxynucleosides corresponding to I and II in a 59:41 ratio. The reaction rate depends on the nucleoside concentration, with second order rate constants at 37 degrees C of 1.6 X 10(-2) and 1.1 X 10(-2) h-1 M-1 for the formation of the two deoxynucleoside adduct corresponding to I and II, respectively. The same two compounds I and II in a similar (54:46) ratio have been identified after acidic or thermal hydrolysis of DNA which had been reacted with 3,4-epoxy-1-butene under similar conditions. The half life for the spontaneous depurination of I and II in the adducted DNA under physiological conditions (37 degrees C, pH 7.2) is 50 h.

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