Stable carbocations. CLXXXVI. Relation of carbon-13 NMR shifts to the effect of methyl substitution on electronic charge distribution at trigonal carbons

Novel aromatic systems. 4. Cyclobutadiene dications

“…1,2-dimethyl-3,3,4,4-tetrafluorocyclobutene,16b c/s-3,4-dichlorocyclobutene,50 3-cyclobutene-a'í-1,2dicarboxylic anhydride (30),46 and the cyclic carbonate of 3-cyclobutene-cw-l,2-diol (31 )47 were prepared according to literature procedures. tra/ii-3,4-Dibromocyclobutene (28) and c/s-3,4-diiodocyclobutene (29) were kindly provided by Professor R. Pettit (University of Texas).…”

“…Heating 26 in SbFs-SO2CIF to 75 °C only resulted in the decomposition of this species with no indication for the formation of 1. Similarly, attempted preparation of 1 from irans-3,4-dibromocyclobutene (28),44-45 m-3,4-diiodocyclobutene (29),45 3-cyclobutene-c/s-1,2-dicarboxylic anhydride (30),46 and the cyclic carbonate of 3-cyclobutene-m-1,2-diol (31)47 precursors in a variety of superacid systems gave no evidence for the formation of 1. 30 31 6.…”

Stable carbocations. 215. Carbon-13 nuclear magnetic resonance spectroscopic study of the benzenium, naphthalenium, and anthracenium ions

“…Comparison of the 13C NMR shieldings of C3 in 1 (5i3c3178.1) with that of the significantly more shielded corresponding position in the ethylenebenzenium ion 16 (5i3c3 155.4),24 however, indicates that the hyperconjugative donation of electron density into the electron-deficient pentadienyl fragment from the methylene's exocyclic bonds is not as important in the former as it is in the latter case. 2.13C NMR Spectroscopic Study of the Parent, 1-Methyl-, and 3-Methylnaphthalenium Ions, The parent (2), 3-methyl- (17), and 1 -methylnaphthalenium ions (18) were prepared by…”

Oxidation of polycyclic arenes in antimony(V) fluoride/sulfuryl chloride fluoride. Formation of arene dications and observation of electron exchange with radical cations based on carbon-13 nuclear magnetic resonance studies

“…17 The deshielding amounts to 244.7 ppm/e-, which is an unusually large proportionality factor for the relation between 13C chemical shifts and charge, but the ring deshielding is also affected by the methyl groups, which produce greater deshielding at positively charged carbons than at neutral carbon atoms. 18 Steric interactions undoubtedly also influence chemical shifts in this crowded system. 19 The most interesting behavior is observed in the borderline region between compounds which are fully oxidized to dications and those described above which are apparently oxidized only to the monopositive stage.…”