Recent attention has focused, for example, on reports of biological (3,4) and abiotic (5) formation of volatile tetramethyllead in aquatic media with its apparent large-scale transport into the atmosphere (6). Tin's chemical similarities to lead also imply its widespread environmental formation and gaseous transport as hydrophobic tetramethyltin (Me4Sn). Biogenesis of this molecule, though not heretofore detected in the aquatic environment, seems reasonable on the basis of recent evidence for in vitro methylation of various inorganic tin and organotin compounds by microbes isolated from the Chesapeake Bay (7-9) and by viable sediments from San Francisco Bay (10) or Canadian freshwater lakes (11).fThis work was presented in part at the 15th Middle Atlantic

7) F. P. Lossing. personal communication. The value of 156 kcai mol-' for AHf(CH&H=N+HZ) was derived from the AP of m l e 44 in the mass spectrum of (CH3)zCHNHz. We thank Dr. Lossing for his assistance in performing this measurement. (8) Values of 154 for AHf (CH3CH=N+HZ and CH3N+H=CHz reported by B. H. Solka and M. E. Russell, J. Phys. Chem., 78, 1268 (1974). (9) Values obtained from the proton affinities of NH3 and &CHzNH (207 and 220 kcal mol-l, respectively): I . The values for the heais of foimation of protonated vinyiamine and protonated vinyl alcohol were obtained by estimating the heats of formation and the proton affinities of the unprotonated species. The former were deduced using a group equivalent method and are in satisfactory agreement with the values found by calculations: L. Radom, W. J. Hehre, and J. A. Pople, J. Am. Chem. Soc., 93, 289 (1971). The proton affinities were taken to be the same as those measured for the corresponding saturated analogues, ethylamine and ethanol, respectively. G. Glockler, J. Phys. Chem., 61, 31 (1957).Abstract: The C7H7+ fragment ions formed in toluene, and the chlorinated, brominated, and iodinated toluenes, as well as the C,H6F+ fragment ions in fluorinated toluenes have been studied in an ion cyclotron resonance spectrometer. In all these systems, it is seen that there are two populations of C7H7+ ions, one of which reacts with the parent compound and other compounds, and one of which is totally unreactive. Because the reactive C7H7+ ions from the different precursors all undergo the same reactions and at the same rate as the C7H7+ ions in toluene and benzyl chloride, which have previously been shown to have the benzyl structure, this structure is assigned to the reactive C7H7+ populations; the unreactive C,H,+ ions are assigned the tropylium structure. The relative abundance of the unreactive tropylium ion is low ( < I 5%) in the chloro-, bromo-, and iodotoluenes, and decreases with decreasing energy of the ionizing electrons. This is interpreted to mean that the rearrangement to the seven-membered ring structure occurs after the fragment ion is formed. In toluene and fluorotoluenes, the unreactive component comprises 30-60% of the C7H6X' (X = H, F) ions, and decreases with increasing energy of the ionizing electrons, indicating that rearrangement occurs prior to the fragmentation of the parent ion. Rate constants for the hydride transfer to the benzyl ion from cyclopentane, cyclohexane, 3-methylpentane, and 3-methylhexane are reported. An estimate that LHr

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The relative ionization energies and proton affinities of AJV-dimethyl-, AyV-diethyl-, and AyV-di-n-propylaniline, and metaand para-methyl-substituted analogues (as well as AfJV,3,5-tetramethylaniline and 4-chloro-AT,Ardiethylaniline) have been determined in the gas phase through measurements of the equilibrium constants of charge-transfer and proton-transfer reactions in an ion cyclotron resonance spectrometer. Absolute values are assigned to the ionization energies and proton affinities generated in these experiments. Comparison standards were the ionization potential (7.12 eV) and proton affinity (223.4 kcal/mol) for A7JV-dimethylaniline taken from the literature. The heats of formation of the parent radical cations, M+, and the corresponding protonated molecules, MH+, vary in the same way, differing from one another by 21 ± 2 kcal/mol over the entire set; that is, the radical cations of these compounds display a constant hydrogen affinity of 74 ± 2 kcal/mol. This is interpreted to mean that all the compounds protonate at the nitrogen atom; previous work had suggested that meta-substituted isomers protonate on the ring. Further, it is demonstrated that variations in both the ionization energy and the proton affinity values upon changes in ring substitution can be predicted from the appropriate Hammett values, but not from the corresponding + values; changes brought about by differing N-substituents correlate with a* values.

Environmental tin, widely dispersed at low concentrations in waters, sediments, and biota, is now perceived to be a bioactive element susceptible to methylation and even hydridization by marine bacteria. Nonetheless, the redox cycle of tin in natural waters is poorly understood and recent advances in tin-specific molecular characterization fail to speciate Sn(II) and Sn(IV) reliably. On the other hand, such rapid developments in speciation methodology now permit growing numbers of studies of organotin distributions in aquatic systems, raising the question of the Lnatural? biogeochemical flux of methylstannanes in relation to increased anthropogenic organotin influx from industry and shipping. New methods for direct speciation of aquated or involatile organotins by liquid chromatography are compared with advances in purge-and-trap sampling of volatile or hydrophobic organotins speciated by gas chromatography. The work in our laboratory indicates that effective models for estuarine formation and transport may ultimately be developed, but that basic roadblocks to progress stem from inadequate descriptive aqueous organometallic chemistry and knowledge of critical kinetic parameters for the lifetimes of key organotin species in sea water.

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Ultratrace levels of organotin species and an organosulfur compound were detected in a National Bureau of Standards (NBS) human urine Standard Reference Material, SRM 2670, and a previously certified urine SRM 2672, using a purge and trap system coupled to a gas chromatograph equipped with a flame photometric detector. samples of the SRM were treated with sodium borohydride to form volatile tin hydrides. Species detected included dimethyltin (1.04 ng/ml), butyltin (0.03 ng/ml), and dimethyl-disulfide (2.73 ng/ml) in the new stock of freeze dried human urine SRM 2670 being prepared for issue by NBS and methyltin (1.0 ng/ml), butyltin (1.5 ng/ml), and inorganic tin (28.1 ng/ml) in the old stock of SRM 2672. This analytical technique should have useful applications in studies that are needed to develop a toxicological data base and monitoring programs for human organotin exposure.

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