Ionized cyclopropane

Finally, A -pyrazolines lose N2 (73KGS64) but it is possible that this takes place thermally before ionization, since thermolysis of A -pyrazolines usually gives cyclopropanes (Section 4.04.2.2.2(iv)). 

The ionization potentials of substituted cyclopropanes also show a significant correlation with eq. (2). The value of pr obtained is comparable to that observed for substituted ethylenes and 1-substituted propenes (section II.A.2.) and is considerably above that found for substituted benzenes (for which a value of Pr = 59 is obtained). This result confirms the existence of a large resonance interaction between the cyclopropane ring and substituents. The magnitude of a is considerably greater for substituted cyclopropanes than it is for substituted ethylenes or benzenes. 

Electron impact ionization of both disubstituted cyclopropanes 145 and 146 lead to the elimination of the Br radical. From the CA spectra of the resulting [M—Br]+ ions and those of C4H+ ions generated from other suitable precursors it must be concluded that both cyclopropane derivatives give only the 1-methylallyl cation 147. There is no experimental evidence for the generation of the isomeric 2-methylallyl cation 148. Moreover, it was shown that 147 and 148 do not interconvert under the experimental conditions used (36). 

Many other ion-molecule reactions involving highly unsaturated hydrocarbon ions and neutral olefins or the equivalent strained cycloalkanes have been studied by mass spectrometry98. For example, we may mention here the addition of ionized cyclopropane and cyclobutane to benzene radical cations giving the respective n-alkylbenzene ions but also isomeric cyclodiene ions such as ionized 8,9-dihydroindane and 9,10-dihydrotetralin, respectively. Extensive studies have been performed on the dimerization product of charged and neutral styrene4. 

Artemisyl, Santolinyl, Lavandulyl, and Chrysanthemyl Derivatives.— The presence of (41) in lavender oil has been reported earlier. Poulter has published the full details of his work (Vol. 5, p. 14) on synthetic and stereochemical aspects of chrysanthemyl ester and alkoxypyridinium salt solvolyses (Vol. 3, pp. 20—22) and discussed its biosynthetic implications. Over 98% of the solvolysis products are now reported to be artemisyl derivatives which are formed from the primary cyclopropylcarbinyl ion (93) which results from predominant (86%) ionization of the antiperiplanar conformation of (21)-)V-methyl-4-pyridinium iodide the tail-to-tail product (96 0.01%) may then result from the suprafacial migration of the cyclopropane ring bond as shown stereochemically in Scheme 3. This is consistent with earlier work (Vol. 7, p. 20, ref, 214) reporting the efficient rearrangement of the cyclobutyl cation (94) to (96) and its allylic isomer, via the tertiary cyclopropylcarbinyl cation (95). ... 

Cyclopropane (D3 , symmetry) has a degenerate pair of in-plane e orbitals (S, A). Vertical ionization leads to a doubly degenerate E state, and JT distortion results in two nondegenerate electronic states, A and 82 (Cav symmetry), corresponding to two different molecular structures. The Ai state (orbital S singly occupied) corresponds to a structure with one lengthened C—C bond it is lowest in energy for many cyclopropane radical cations (Fig. 6.10). 

For radical cations of norcaradiene and derivatives, the interaction of the cyclopropane in-plane e orbitals with the butadiene frontier MO favors the type B structure. The assignments are based on ab-initio calculations, CIDNP results, and the ET photochemistry. The norcaradiene radical cation (lla ) has a electronic ground state (Cj symmetry). The Cl—C6 bond is shortened on ionization (—3.4 pm) while the lateral bonds are lengthened (+2.8 pm). The delocalization of spin density to C7 (py = 0.246 py 5 = 0.359) and the hyperfine coupling constants of the cyclopropane moiety a e = 1.36 mT oysyn = —0.057 mT flvanti = —0.063 mT) support a type B structure. 

The two species of 202 amu are taken to be the initially formed Franck-Condon structure and the parent species giving coherent resonance motion loss of a bromine atom gives BrCH2CH2CH2, which is detected after ionization by the probe pulse as C3H5, at 41 amu. The decay of BrCH2CH2CH2 leads to cyclopropane, a product not ionized by the probe pulse, and hence not seen through mass spectrometry. 

The pump-probe-detect arrangements for the femtosecond experiments was similar to those described above. When cyclobutanone was pumped with two photons of a X = 307-nm femtosecond pulse, two consecutive C—CO bond cleavages led to the formation of the trimethylene diradical, detected as an easily ionized transient at 42 amu, with buildup and decay times of 120 20 fs. The decay presumably involves isomerizations to cyclopropane and to propylene— structures not ionized by the probe pulse and thus undetected during the experiment. 

TABLE 4. Orbital energies and ionization potentials of cyclopropane ... 

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