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The quantitative kinetics of pyrolysis of some cyclic and polycyclic compounds are examined from the point of view of biradical intermediates. Transition state methods for estimating the Arrhenius parameters of the lowest free energy biradical pathway to products in cyclic and polycyclic compound reactions are described and illustrated. A large number of the polycyclic reactions are found to have Arrhenius parameters consistent with the biradical mechanism estimates. Other reactions are found to have much faster experimental rates and must therefore be concerted. The value of activation energy and activation entropy estimates as discriminatory tests of mechanism, i.e., single step (concertedness) or consecutive step processes, is discussed.

1. A new method has been developed for the preparation of ethynylmagnesium bromide under pressure, and it has been condensed with aromatic and hydrogenated azomatic ketanes. In this way the synthesis has been effected in 30–46% yield of 1-methyl-1-phenyl-2-propyn-1-ol, 1-p-methoxyphenyl-1-methyl-2-propyn-1-ol, and 4-ethynyl-l,2-dihydro-7-methoxynaphthalene. 2. The last compound has been selectively hydrogenated to 1,2-dihydro-7-methoxy-4-vinylnaphthalene (I), which has been condensed with 2-cyclopenten-1-one (II), 2-methyl-2-cyclopenten-l-one (IX), 2,4-dimethyl-2-cylopenten-1-one (XII) and 2-cyclohexen-1-one (XVII). In this way a number of tetraeyclic ketanes related to estrone have been synthesized, and in two cases their structures have been proved.

Use of the integrated ion—current technique offers great advantages over conventional mass spectrometry. It provides a most sensitive method of analysis with limits of detection in the subpicogram region. Furthermore it can be frequently used to resolve isomeric compounds. In conjunction with other techniques it offers a great potential in the detection and estimation of air pollutants. INTRODUCTION The identification and estimation of polycyclic aromatic hydrocarbons in the atmosphere has become increasingly important following demonstration of the carcinogenic properties of some of these compounds. The presence of benzo(a)pyrene and benzfluoranthene in the atmosphere in particular has received the greatest attention in the last few years although it should be remembered that dibenzanthracene' is just as carcinogenic whilst many of the other polycyclic compounds are also moderately active. It is, therefore, highly desirable that methods for the rapid analysis of the individual hydrocarbons be developed. Several of the analytical methods available have been reviewed by Sawicki2. Primarily they consist of isolation of the polycyclic group of compounds followed by estimation of the individual species. Column, paper and thin layer chromatography have all been used in the initial separation followed by UV absorption or fluorimetric examination2. The limits of polycyclic estimation by these methods range from the microgram region for the column chromatography/UV method to the nanogram region for the thin layer! fluorescence method. The application of gas chromatography to the analysis of polycyclic compounds has also been developed over the last few years35. To some extent it has been criticized for its lack of sensitivity in that the detection limit for benzo(a)pyrene using a flame ionization detector is only approximately 5g, which is very much poorer than any of the fluorimetric methods. Furthermore peaks arising from benzo(a) and benzo(e)pyrene are hardly resolved at all using conventional analytical columns6. Chromatographic methods however, have the advantage that a simultaneous analysis can be carried out for many of the more volatile polycyclic compounds. More recently, particularly with the use of capillary columns and electron 685 J. R. MAJER AND R. PERRY capture detectors7 the sensitivity has been increased and gas chromatography is being more frequently used as a routine method of analysis. In a recent study involving the mechanism of formation of polycyclic compounds, during the incomplete combustion of ethylene, the advantages of using high resolution mass spectrometry in the identification and estimation of polycyclic compounds became apparent. Use of an integrated-ion current technique enabled the assay of polycyclic compounds to be made in the subpicogram range. Furthermore the shape of the ion-current curve was found to be dependent upon isomers present in the sample used. I propose therefore to confine further remarks to a description of this method and its potential application in conjunction with other techniques. DISCUSSION In quantitative mass spectrometry, it is usual, on vaporization of a sample into the source, to maintain a reservoir of sample vapour at a constant pressure while the mass spectrum is being measured or recorded. This is achieved by allowing the vapour to leak slowly into the mass spectrometer ion source so that no perceptible change in the reservoir pressure is caused. The ion current at a specific m/e value is then directly related to the partial pressure of the appropriate component in the reservoir. Absolute concentrations can then be determined by calibrating the instrument with pure samples of each component of the mixture. Such a technique is wasteful, however, in that only a small fraction of the sample is used (

The photodynamic activities of 157 polycyclic compounds of wide structural range were determined, with the use of Paramecium caudatum. High photodynamic activity was largely confined to polycyclic compounds, either homocyclic or heterocyclic, with four or five fused rings. Significant absorption of light was shown to be prerequisite but not sufficient for high photodynamic activity. A significant statistical association between photodynamic activity and carcinogenicity was demonstrated. It was shown that compounds with high photodynamic activity had 4 times greater odds of being carcinogenic than compounds with low activity. However, the photodynamic assay cannot identify a particular polycyclic compound as being carcinogenic or noncarcinogenic.

A new polycyclic compound, namely tetramethyltetraphenylcyclooctasilsesquioxane, was obtained by the reaction of cis-1,3,5,7-tetrahydroxy-1,3,5,7-tetraphenylcyclotetrasiloxane with tetramethylcyclotetrasiloxane.