The effect of cyclohexene, a preservative in dichloromethane on the liquid-liquid extraction and analysis of chlorinated drinking water

Liquid-liquid extraction with dichloromethane is the Environmental Protection Agency's (EPA) method of choice for the analysis of acid or base neutral organic chemicals in water. Free radical chlorination and oxidation products of cyclohexene (the solvent preservative) in dichloromethane have been observed in extracts of chlorinated drinking water (after 10(5) fold concentration) by gas chromatography and gas chromatography-mass spectrometry. The chlorinated cyclohexene derivatives limit the quantitative and qualitative analysis of compounds eluting at Kovát's index less than 700-1000 and the use of these extracts for organoleptic and mutagenic studies. The effect of residual free chlorine in water on the cyclohexene present in the solvent was studied. Over ten cyclohexene derivatives were produced in every case when any residual free chlorine was present in the water. When chlorine is reduced to chloramine, the cyclohexene derivatives were greatly reduced in number and amount.     

Hydrogenation of

The course of the hydrogenation of [5]- and [6]metacyclophane (1b and 1c) and their thermochemistry is described. Both compounds are hydrogenated rapidly (within 10 s) to furnish the bridgehead olefins 13b and 12c. The accompanying hydrogenation enthalpies are -220 and -141 kJmol(-1), respectively. Strain energies (SE) and olefinic strains (OS) of a number of bridgehead olefins have been evaluated by DFT calculations; it was concluded that 13b belongs to the class of hyperstable olefins which correlates nicely with its reluctance to undergo hydrogenation. By combining experimental hydrogenation enthalpies and DFT calculations, SE of 187 and 121 kJmol(-1) were derived for 1b and 1c.     

Raman active lattice spectrum of single crystal 2,4,6-triphenyltriazine

The Raman spectra of single crystal 2,4,6-triphenyltriazine have been recorded in the lattice region at 300 and 30°K. The interpretation of the results was based on assuming that the molecular structure is D_3h (i.e. complete planarity) instead of the most probable non-planar conformation of C₁ symmetry. Assignment of the lattice vibrations was based on a rigid-body approximation. Considerable temperature effect was observed in the spectrum when the crystal was cooled to 30°K. This seemed to indicate large anisotropic thermal motions in the crystalline solid.     

Emission background in the Raman spectra of barbituric acid and azobenzene

The suggestion that two photon absorption and reemission may contribute to the emission background observed in the Raman spectra of barbituric acid and azobenzene has been tested by a study of the anti-Stokes fluorescence and of the dependence of the emission on the incident laser intensity of these molecules. Both tests indicate that the two photon process is an insignificant factor in the background emission.