The electron as a protecting group. 3. Generation of acenaphthyne radical anion and the determination of the heat of formation of a strained cycloalkyne.

Acenaphthyne dicarboxylate (12) was transferred into the gas phase from solution via electrospray ionization and subsequently was sequentially fragmented in a Fourier transform mass spectrometer to afford acenaphthyne radical anion (9). Structural confirmation of 9 was achieved by converting it to acenaphthenone enolate (13) and demonstrating that this species is identical to the ion produced upon deprotonation of acenaphthenone (5). The reactivity of 9 was explored, and since an electron can serve as a protecting group, we were able to measure the heat of hydrogenation (98 +/- 4 kcal mol(-1)) and the heat of formation (160 +/- 4 kcal mol(-1)) of acenaphthyne (1) via the application of a thermodynamic cycle. Its strain energy (68 kcal mol(-1)) and acenaphthylene's (10H) first and second C-H bond dissociation energies (117 +/- 4 and 84 +/- 2 kcal mol(-1)) also were obtained. Ab initio and density functional theory calculations were carried out on the species of interest to explore their geometries and energetics. Our results were interpreted in comparison to cyclopentyne, and its predicted heat of formation (98 kcal mol(-1)) and strain energy (59 kcal mol(-1)) are reported.

Rearrangements of 3-aryl-substituted cyclopropenyl anions and the gas-phase acidity of 3-(4-methylphenyl)cyclopropene.

3-(4-Methylphenyl)-3-trimethylsilylcyclopropene and 3-(4-trifluoromethylphenyl)-3-trimethylsilylcyclopropene react with fluoride ion in the gas phase to afford 6-substituted 3-indenyl anions via a spontaneous rearrangement of their corresponding cyclopropenyl anions. These isomerizations led us to reinvestigate the reported gas-phase generation of 1,2,3-triphenylcyclopropenyl anion, and contrary to the previous study, a similar rearrangement to 1,2-diphenyl-1-indenyl anion is observed. Despite the instability of 3-aryl-3-cyclopropenyl anions, we were able to measure the acidity of 3-(4-methylphenyl)cyclopropene at the allylic position (delta H(o)acid = 398.6 +/- 1.4 kcal/mol) by the DePuy kinetic method. Ab initio calculations on the structures and energies of mono- and triaryl-substituted cyclopropenyl anions also are presented.

Effect of background interference on accelerant detection by canines.

Additional studies were performed with respect to examining the lower limits at which canines can reliably detect products commonly used as accelerants and distinguish them from pyrolysis products or background hydrocarbons. As part of a testing exercise performed in conjunction with a national conference of the Canine Accelerant Detection Association (CADA), 34 canines were subjected to a series of tests, some of them were a recertification proficiency. In one of the tests, the dogs were nearly unanimously successful in locating one can (out of five) containing 50% evaporated gasoline at the 5 microL level on a burnt carpet matrix, and pinpointing the 6-in. square sector on a piece of plain carpeting where the same amount of gasoline (5 microL) was applied. However, only half were able to detect a second doped sample containing a lesser amount (0.05, 0.1, or 0.2 microL) of gasoline, and registered a number of alerts on samples containing only burnt carpeting material. The dogs were also tested on measured amounts (2 or 5 microL) of a variety of other light, medium, and heavy petroleum products applied to a variety of substances containing significant pyrolysis products. As a group, the canines were much less successful in pinpointing these products than they were with gasoline at this same level, and again registered a number of alerts on cans containing only pyrolysis products. The significant number of alerts by canines on samples not containing gasoline or other products points out the importance of obtaining laboratory confirmation on samples on which dogs alert, and on keeping accurate field and training records of canines to establish their credibility.

Evaluation of canines for accelerant detection at fire scenes.

In recent years, canines have been successfully used in fire investigations to detect accelerant residues. We set out to determine the lower limits at which canines could reliably detect potential accelerants. Measured amounts ranging from 10 to as little as 0.01 microL of gasoline, kerosene, and isopars were applied to preselected spots along a continuous sample path (25 to 40 feet long) made out of burned and unburned wood or nylon carpeting strips at the testing site. Two canines were led past this sample path at least three times and positive alerts and negative responses were recorded. Both dogs were generally able to alert on spots containing 0.01 microL or more of all three accelerants, at or beyond the purge and trap recovery and gas chromatographic detection method employed. The canines did alert occasionally on background, especially that containing traces of styrene residues, either purposely added in specific amounts or formed upon partial pyrolysis of carpeting material. The dogs alerted on sites containing 0.1 to 1.0 microL of freshly applied gasoline or kerosene placed at actual heavily damaged fire scenes, but were less successful on samples containing smaller amounts.