A comprehensive investigation of subsurface vapor intrusion into buildings in the Village of Endicott in upstate New York provided an unusually rich data set for studying the relationship between subslab soil gas and indoor air concentrations. The study concludes that vapor intrusion into buildings with basement foundations and concrete floors generally results in ratios of subslab soil gas to indoor air concentrations greater than 100:1 at this site. The data set also shows that ambient background‐ and indoor‐contaminant vapor sources can result in measured indoor air concentrations that could be mistakenly ascribed to subsurface‐contaminant vapor sources and erroneous conclusions regarding the relationship between subslab soil gas and indoor air concentrations. By separating the measured subslab soil gas concentrations of tetrachloroethene, trichloroethene, and 1,1,1‐trichloroethane into low‐ and high‐range data subsets, the influence of background and indoor sources of these compounds was more easily discerned.

The presence of methyl-^s ubstituents in the 3 or 4 position of the pyridine nucleus results in insignificant effects on the rates of reaction with methyl iodide over the corresponding 3-and 4-methylpyridines. However, the presence of methyl-c/3 substituents in the 2 position results in enhanced reactivity of the pyridine bases with methyl, ethyl, and isopropyl iodide. The failure to observe any significant difference in the rates of reaction of the 3-and 4methyl-if3-pyridines compared to the corresponding methyl-^) derivatives indicates that the electronic effects of the methykf3 substituent are not significantly different from those of the methyl substituent. On the other hand, the observation that the presence of the methyl-c/3 group in the 2 position brings about a significant increase in the rate of reaction with the alkyl iodides is consistent with the postulated smaller steric requirements of deuterium compared to hydrogen. umerous examples of secondary isotope effects which have been observed in organic reactions have been interpreted variously in terms of the classical effects which have long been attributed to the more usual substituents.5

The introduction of methyl-^groups in the 3 or 4 position of pyridine results in no observable change in the heats of reaction of these bases with boron trifluoride over the normal derivatives. On the other hand, in the 2 position, there is observed a significant increase in the heat of reaction for the deuterium derivatives, corresponding to the smaller steric requirements of methyl-rf3 over methyl-^groups. Use of a reference acid of smaller steric requirements, BH3, causes the difference to disappear, consistent with the predictions of the steric interpretation, but contrary to the predictions of either of the two electronic interpretations, inductive or hyperconjugative, now under consideration. These results support the conclusion that the secondary isotope effects of deuterium arise predominantly from its smaller steric requirements. Deuterium labeling of the methyl groups in 3-and 4-picoline has no observable effect on the rates (1) Chemical Effects of Steric Strains. XX.(2) Based in part on theses submitted by John G. Koelling and Gerald J. McDonald in partial fulfillment of the requirements for the degree of

Notesrestricted in PhS02• radical. Our entropy of activation (AS *) of -7 eu is in good accord with Bartlett's6 observation of lowering of AS* in ¿erí-butyl perester decomposition.Experimental Section Kinetics.-The sulfur dioxide was expelled from the melted reaction mixture (243-297°) by a stream of nitrogen which was purified by passing through alkaline alcoholic solution of pyrogallol. The S02 was then absorbed in aqueous sodium hydroxide and titrated in the presence of 1% H2O2. The reaction mixture consisted of 0.0025 mol of phenyl sulfone and 0.05 g-atom of sulfur.Mass Spectrometry.-A Nier-type double collector mass spectrometer, MS-6, produced at the Institute Jo£ef Stefan, Ljubljana, Yugoslavia, was used. For the isotope effect determination natural abundance of sulfur-34 was utilized. Samples of SO2 gas from the reaction carried out to about 2% completion, and to complete decomposition of phenyl sulfone, respectively, were collected in a liquid air trap and purified in a vacuum line, and the 32S/34S mass ratios were determined as previously described.6

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