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The positive hyperfine coupling constants of the geminal 1H nuclei in cis-1,2-dimethyl- and cis-1,2-diphenylcyclopropane radical cations show a significant stereoelectronic effect: the 1H nuclei trans (anti) to the substituents are coupled much more strongly than the corresponding nuclei cis (syn) to them. Theoretical calculations on these radical cations and on bismethano[2,2]paracylophane as well as new 1H-CIDNP experiments at 200 Mz elucidate the general features of these systems. Copyright © 2014 John Wiley & Sons, Ltd.

Examining the structures presented by Loschmidt in 1861 shows that he portrayed organic structures in a visually appealing way, but the structures do not support several claims and accolades of Loschmidt's modern-day champions. There is serious doubt that Loschmidt viewed benzene as a planar cyclic array of six carbon atoms; he did not understand positional isomerism of benzene derivatives or the essence of geometric isomerism. He did not recognize that carbons of the C6 nucleus could only be singly bonded to a substituent. Concerning his “prediction” of cyclopropane, Loschmidt may have been the first to consider a “circular” array of three atoms; this achievement must be viewed in the light of similar predictions for a cyclic dinitrogen oxide, tetracyclohexane, heptacyclononane, and a [1,1]-metacyclophane. His structures worked well for strings of sp2-hybridized carbons or for molecules with chains of tri-substituted carbons. Loschmidt did not differentiate between the bond lengths of double and triple bonds, as claimed. Copyright © 2013 John Wiley & Sons, Ltd.

Photo-induced electron donor–acceptor reactions between 1-cyanonaphthalene (CNN) and norbornadiene (N) generate products of several structure types. Methanol adducts (1–3) formed in polar solvents are rationalized via the radical cation, N+·, and stereospecific (exo-) nucleophilic attack by methanol. In less polar solvents, CNN and N form [2 + 2]-cycloadducts, exclusively on the exo-face of N. In non-polar solvents containing methanol, CNN, N and methanol combine to form 1:1:1 adducts, containing the sensitizer on the endo- and the methoxy groups on the exo-face. The formation of these products is rationalized via the trapping of encounter complexes of different geometries. Any rearrangement of the norbornenyl system can be eliminated, since neither tricyclyl nor 7-methoxynorbornenyl structures are formed. Apparently, the alcohol captures an endo-encounter complex of CNN and N by attack from the exo-face, similar to the attack of methanol on N+·. © 1998 John Wiley & Sons, Ltd.

The enhancement factors of the 1H polarization induced in radical pairs generated by α-cleavage of 12CO- and CO-labelled ketones deviate from the ratios expected on the basis of the relative abundances of the respective carbon isotopomers. For dibenzyl ketone, the ratio of absolute CIDNP intensities of the 1H(13C) doublet (90% 13CO) to the 1H(12C) singlet (10% 12CO) was found to be >9:1 at 58·3 kG and

Nuclear spin polarization effects observed during the electron transfer-induced cleavage of the trans head-to-head dimer of 3,3-dimethylindene are incompatible with the intermediacy of a single dimer radical cation. Instead, they are compatible with the ‘cooperative’ involvement of a localized, doubly linked and a delocalized, singly linked dimer radical cation. The mechanistic consequences for the cycloaddition and cycloreversion of radical cations are discussed.

Gas phase ion/molecule reactions have been used to probe the structure of ions obtained by electron impact upon 1-(diphenylmethylene)cyclopropane and 2,2-diphenyl-1-methylenecyclopropane. The resulting ions of molecular composition C16H14 (m/z 206+) were reacted with charge transfer reagents (6·9 < IP < 8·8eV), giving evidence for the presence of isomeric ions with different reactivities. The less reactive ion is identified as a trimethylenemethane species (TMM+) in which one cyclopropane bond is broken; the more reactive ions are assigned as vertical ions in which the cyclopropane ring is unaffected. The vertical ions have recombination energies of 8·44 ± 0·05eV, whereas TMM+ has one of 7·41±0·05eV. The TMM+ fraction is not constant; it increases with increasing IP of the reagent. This is attributed to a reagent-catalyzed isomerization of the vertical ion to TMM+. In addition, the reagent ions are observed to undergo a unique reaction with the neutral methylenecyclopropane derivatives: electron transfer and ring opening to yield TMM+. These findings limit the application of the customary equilibrium measurements as a method to determine the substrate IP.