No abstract

9-[l-(Methylthio)ethylidene]bicyclo[4.2.1]nonane (41).This compound is prepared and isolated as described for 15; yield 68%. Extremely pure product was obtained with the aid of high-performance LC (hexane): MS, m/e 196; 1H NMR (CDC13) 3.30 (m, 1), 3.03 (m, 1), 2.20 (s, 3), 1.97 (s, 3), 2.0-1.2 (m, 12). syn -9-Acetyl-9-chlorobicyclo[4.2.1]nona-2,4,7-triene (44). To a solution of vinyl ether 13 in S02 at -78 °C was added an excess (3 equiv) of S02C1F. The reaction was instantaneous. The reaction mixture was poured onto saturated aqueous NaHC03 and extracted into Et20. After the extract was dried (MgS04) and concentrated, hydrolysis of the intermediate ester was effected by passing the reaction mixture through a column of Si02 (CHC13 as eluent): NMR (CDC13) 6.0-5.7 (m, 4), 5.30 (d, 2), 3.53 (d, 2), 2.27 (s, 3); MS, m/e 194, 196. Carbocation Generation. NMR samples were prepared by condensing S02 from a gas cylinder into an NMR tube containing the substrate and cooled in a dry ice/acetone bath. The concentration of the samples was about 100-200 mg/0.3 mL of solvent. To the cooled solution, was carefully added freshly prepared HFS03/SbF5 (5:1) via the wall of the tube. In the case of the unsaturated substrates 13, 15, and 19,1 equiv of acid was used; the cations 47a-c were generated with a twofold excess of acid. Mixing was effected by shaking the samples vigorously with the aid of a vibromixer. Samples were checked with 60-MHz NMR spectroscopy. Spectroscopic investigations were performed in the temperature range of -100 to -30 °C. Quenching was effected by pouring the samples onto saturated aqueous NaHC03. AppendixTables IV and V contain collections of various and 13C NMR spectral data, respectively.

The crystal structure of the heterocyclic mole-from N-methylimidazole by conversion into the appropriate cule 1,3-dimethyl-2( 3H)-imidazolethione and its lH n.m.r. dialkylimidazolium iodide and treatment with sulphur in spectrum have been interpreted as showing partial methanolic K,CO,. An X-ray structure determination was double-bond character in the N-C-N system, but no undertaken to decide which of the three structures (a), (b), aromaticity.or (c) (Figure 1) best described the molecule.AN investigation of the molecular structure of 1,3-dimethyl- S S-. s-2(3H)-imidazolethione, (I), was undertaken when it was Me, ) , Me Me, ; &Me N N' s s L=L/ LJ found that the compound had an unusually high melting Crystals suitable for X-ray investigation were grown from point (181-1 82") compared with its 1-methyl-3-ethyl water : orthorhombic, a 8.475 A, b 6.826 A, G 11.306 A, homologue, (11) (51"). Both compounds were synthesized Systematic absences show the

lSN NMR spectra of a number of 2-mercaptoazoles were obtained and the position of the iminothiol-thioamide prototropic tautomeric equilibrium was determined. Because of the large chemical shift difference of cu 100 ppm between the iminothiol and thioamide nitrogen atoms, the I5N chemical shifts of the S-methyl and N-methyl analogs of each tautomer provided reasonable chemical shift models for the same nitrogen atom in the tantomers. Only a small correction for an N-methyl effect was required.

Abstract-The m a s spectra of tetrazole, al1 isomers of mononiethyl-and dimethyltetrazole, several trifluoromethyl substituted tetrazoles, as well as deuterated analogs, were recorded. Loss of N, was the important fragmentation of the molecular ions of tetrazole and 2-niethyl substituted tetrazoles; however, HN2 loss was more important for 1-methyl substituted tetrazoles. The l-methyltetrazoles showed molecular ion peaks while the 2-methyltetrazoles exhibited an unprecedented [M + 11 peak with no molecular ion.NUMEROUS papers have recently appeared on the mass spectral fragmentation of various azoles including pyrroles,l imidazoles2 and pyrazoles? A brief report4 on the metastable transitions of s-triazole has appeared, but no detailed study of substituted triazoles has been reported. A study of the tetrazoles was missing untii the recent work of Fraser and H a g~e ,~ who reported the primary fragmentations of several 1-and 2-methyl-5-aryltetrazoles. They showed that the position of N-methyl substitution of 5-aryltetrazoles could be differentiated by mass spectrometry. With 1-methyl substitution the loss of a fragment of m/e 42 (N3 or CH,N,) was important while loss of N, was only 6 % of the base peak. In contrast, with 2-methyl substitution [M -N,] was the base peak.It is desired to report here a thorough study of the mass spectral fragmentation of tetrazole (1), 1-methyl-(11), 2-methyl-(III), 5-methyl-(IV), 1 ,5-dimethyl-(V), 2,5-dimethyl-(VI), 5-trifluoromethyl-(VII), 1 -methyl-5-trifluoromethyl-(VIII), 2-methyl-5-trifluoromethyitetrazole (IX), and several deuterated analogs (X) to (XIV).For the purposes of discussing the fragmentations observed, the tetrazoles studied fa11 into three structural categories, i.e. 2-methyl substitution, 1-methyl substitution, and those unsubstituted on nitrogen. The cleavages of the molecular ion [MI can be represented schematically for this discussion by a wiggly line bisecting the molecular ion into two fragments with the charge being retained on the portion * National Rescarch Council Postdoctoral Research Associate.