Chemistry of carbynes: reaction of CF, CCl, and CBr with alkenes

Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction

“…5 To our knowledge, kinetic data on the reactions of brominated radical species with pyrrole are unavailable. But, the reaction rate coefficients of the bromomethylidyne radical (CBr) with alkenes and alkynes at room temperature have been measured and found to be much smaller (< 10 -12 cm 3 molecule -1 s -1 ) [31][32][33] than for analogous reactions with CH radical (~10 -10 cm 3 molecule -1 s -1 ). 34,35 Based on these observations, it is reasonable to assume that the reaction of CBr with pyrrole is at least 100 times slower than the CH with pyrrole reaction.…”

Theoretical study on reaction mechanism of the CF radical with nitrogen dioxide

“…Second, the very strong electron back-donation from one of the 2pπ orbitals of F to the vacant 2pπ orbital of C takes place. The back-donation effect is confirmed by the fact: (1) there is an inverse C − F + dipole moment [the magnitude is 0.70 Debye at the B3LYP/6-311G(d) level]; (2) the C-F bond is very strong and has partial π character, i.e., at the B3LYP/6-311G(d) level, the CF bond length is 1.278 Å, and the bond order is 1.2567 (the bond order of CH is 1.0853 at the same level). Such strong back-donation breaks down the combination of the vacant 2pπ orbital with the lone pair on C-atom as in CH.…”

“…It was suggested that Path (1a) to FCO + NO is a major route, while Path (1b) and Path (2) may be responsible for the observed slight pressure effect. In our calculations, an isomer 10 with formal FCO (1) NO (2) structure is located as an energy minimum lying 68.3 kcal/mol below the reactant R. Yet, it has short CO (1) and NO (2) bond lengths as 1.280 and 1.212 Å, respectively, and the internal O (1) N bond is long as 1.720 Å. Then, isomer 10 is more like an adduct species between FCO and NO rather than one between FC and NO 2 at the terminal O-end.…”

Formation and Characterization of a BeOBeC Multiple Radical Featuring a Quartet Carbyne Moiety

“…Theobservation of aquartet ground state carbyne is quite unusual, as the previously reported carbyne radicals have doublet ground state. [2,[9][10][11][12][13][14][15][16] Thep reference of ad oublet ground state for carbyne radicals can be understood from the bonding of the methylidyne HC radical, which has ad oublet 2 P ground state with aq uartet state lying 17.1 kcal mol À1 higher in energy. [31] Theg round state HC radical has an electron configuration of (1s) 2 (2s) 2 (3s) 2 (1p) 1 .…”

“…[10][11][12][13][14][15][16] Such radicals in the doublet state with one unpaired electron and one electron pair on carbon are found to be very reactive toward alkenes and they can even insert into the well-known inert C À Hb onds.Byc ontrast, the quartet state radicals with three unpaired electrons prefer to react with radicals and are prone to H-abstraction reactions.T he experimentally known carbynes predominately have doublet electronic ground states. [2,[9][10][11][12][13][14][15][16] Thep ossibility of tuning the ground state electronic spin from the low-spin doublet to high spin quartet for carbynes has been theoretically discussed and predicted. [17][18][19] Chemical substitutions with greater electropositivity (s-donation) and p-acceptance of the single substituent were predicted to favor the high-spin state.S ome carbynes with quartet ground spin state were predicted.…”