Positive protons, indicating

OH elimination from ortho substituted aldoximes 179 (X = CH2, NH, O) may be at least partially the result of a hydrogen migration/cyclization/elimination process, whereby the heterocycles 182 are formed72 (46). A metastable peak shape analysis, the investigation of 2H-labelled derivatives and the study of positional isomers indicate that in addition to 182 the protonated isocyanide 183 is formed via a mechanism which is not fully understood. However, it is known that the generation of 183 occurs without any detectable interaction with the XH ortho substituent. 

The HREIMS of 2,7-dibromocarbazole (388) was identical to that of 3,6-dibromocarbazole (386). Differences were identified in the chemical shifts and splitting pattern of the H-NMR spectrum. Thus, a deshielded, two-proton doublet at 7.87 with ortho-coupling (/=8.3 Hz), assignable to the C-4 and C-5 protons, indicated the location of two bromine atoms at the C-2 and C-7 positions of the carbazole nucleus. This was also evident from the shielded ortho- and meto-coupled (/=8.3, 1.5 Hz) two-proton double doublet at S 7.36, assignable to the C-3 and C-6 protons. Further, a mutually meto-coupled (/= . 5 Hz) two-proton doublet at S 7.57, assignable to the C-1 and C-9 protons, supported the location of the two bromine atoms ortho to these carbons. Based on these spectral analyses and the HREIMS identical to that of... 

Methoxy-5-nitropyrimidine is also attacked at a CH position, as indicated by the relatively high upheld shift of one of the ring protons.14,41 The formation of the gem-dimethoxy adduct is thus ruled out. Of the two possible isomeric adducts only the one resulting from attack at the 2-position (17) is formed, as unequivocally shown by the singlet at <5 5.75, which is observed starting from 4-methoxy-5-nitropyrimidine-6-rf.41... 

Dipole-moment measurements in benzene solution on 1,4-dimethylpiper-azine and on a series of 1 -alkyl-4-tm-butylpiperazines120 show clearly that the N-alkyl groups exist predominantly in the expected position and indicate a value of 1.8 kcal mol-1 for the N-methyl group. This must now be considered a minimum value, and kinetic protonation of 1,4-dimethylpiperazine with 13C-NMR analysis of the products326 gives 2.96 + 0.05 kcal mol". An attempt312 to apply the line-broadening method failed.313... 

For both species the unpaired spin density resides in four equivalent carbons nuclei attached to these centers (N0, Q0) have sizeable hfcs due to the familiar n, a spin polarization (cf. Fig. 4a). The CIDNP effects of the bridgehead (p) protons indicate major differences a sizeable positive hfc of Q-+ can be ascribed to hyperconjugation (it, cr spin delocalization cf. Fig. 4b) in contrast, N-+ shows only very weak and negative ( ) hfcs. Since the p protons of N,+ lie in the nodal plane of its SOMO, the hyperconjugative interaction is inefficient the observed sign of the p protons was therefore ascribed to residual ic, a polarization [324], This type of interaction is usually obscured by the typically much stronger hyperconjugative interaction. 

More recently, the radical cation of the parent system has been characterized by ESR/ENDOR spectroscopy [340], These experiments revealed medium-sized hfcs for both the bridgehead (—11.4 G) and the equatorial protons (+11.4G) and large positive hfcs (+ 77 G) for the axial protons (which in 75 are replaced by the trimethylene bridge). The large difference between the couplings of the axial and equatorial protons indicates a nonplanar, puckered geometry of the radical cation. No evidence for interconversion is apparent up to 160 K this finding requires an inversion barrier of at least 12 kJ mol-1. 

Fig. 4.—(a) Overall, 500-MHz, H-N.m.r. Spectrum of Compound 4. (b) Expanded, Structural-reporter-group Regions of the Resolution-enhanced, 500-MHz, H-N.m.r. Spectrum of Compound 4. [The bold numbers in the spectra refer to the corresponding residues in the structure. The relative-intensity scale of the expanded, N-acetyl-proton region differs from that of the other parts of die spectrum, as indicated. The HOD resonance has been omitted from the expanded spectrum its position is indicated by an arrow.]... 

If the symbols p and e are used without indication of charge, they refer to positive proton and negative electron, respectively. 

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