Oxidation and Reduction in Chemistry

An Experimentally Established Key Intermediate in Benzene Nitration with Mixed Acid

“…+ by either the sulfuric acid or the bisulfate anion, HSO 4 À ,w hich both act as ab ase.Asingle electron transfer (SET) mechanism, widely considered as an alternative reaction path, involves the transfer of an electron from the aromatic ring to the nitronium ion;r ecombination of the resulting radical pair produces the same Whelandintermediate (ArHNO 2 + ). [18][19][20][21][22][23] Early model gas-phase computations by Peluso and Del Re [21] on the interaction of benzene and NO 2 + established the possibility of ac onical intersection between the ground and the first excited singlet state,accompanied by charge-transfer,t hereby supporting the SET mechanism for the reaction. In 2010, Xu, Zilberg, and Haas [23] employed CASSCF computations with the cc-pVDZ basic set to investigate the interactions of benzene with several positively charged electrophiles,i ncluding NO 2 + .T he results suggested that benzene and the charged electrophile are in an electronically excited state in the gas phase initially,whereas the ratecontrolling step lies on the ground state potential energy surface.T he transition from excited to ground state is achieved by ac onical intersection.…”

An Experimentally Established Key Intermediate in Benzene Nitration with Mixed Acid

“…[13][14][15] Thereaction then gives nitrobenzene by removal of the ipso proton from ArHNO 2 + by either the sulfuric acid or the bisulfate anion, HSO 4 À ,w hich both act as ab ase.Asingle electron transfer (SET) mechanism, widely considered as an alternative reaction path, involves the transfer of an electron from the aromatic ring to the nitronium ion;r ecombination of the resulting radical pair produces the same Whelandintermediate (ArHNO 2 + ). [18][19][20][21][22][23] Early model gas-phase computations by Peluso and Del Re [21] on the interaction of benzene and NO 2 + established the possibility of ac onical intersection between the ground and the first excited singlet state,accompanied by charge-transfer,t hereby supporting the SET mechanism for the reaction. In 2010, Xu, Zilberg, and Haas [23] employed CASSCF computations with the cc-pVDZ basic set to investigate the interactions of benzene with several positively charged electrophiles,i ncluding NO 2 + .T he results suggested that benzene and the charged electrophile are in an electronically excited state in the gas phase initially,whereas the ratecontrolling step lies on the ground state potential energy surface.T he transition from excited to ground state is achieved by ac onical intersection.…”

“…[18][19][20][21][22][23] We estimated the electron transfer from the aromatic p-system to the nitronium unit by applying two alternative population analysis methods.F igure 1b compares computed atomic charges for the p-complex intermediates in isolation (gas phase), computed at B3LYP/6-311 + G(2d,2p) and within the stepwise route in mixed acid conditions.B oth the NBO method [41,42] and Hirshfeld population analysis [43] predict ar oughly 0.70 ec harge transfer from the aromatic ring to the NO 2 + ion for the complex in isolation. TheS ET mechanism of nitration is aw ell-established concept.…”

“…We also conducted natural bond orbital (NBO)41, 42 and Hirshfeld43 analyses for the charge shifts during the formation of the intermediate π‐complex. The single electron transfer (SET) S E Ar reaction mechanism18, 19 is based on the assumption that considerable electron donation from the aromatic species to the attacking electrophile takes place during π‐complex formation.…”

Nitração aromática: substituição eletrofílica ou reação com transferência de elétrons?

“…Um mecanismo alternativo foi apresentado pela primeira vez na década de 40 por Kenner e Weiss 32,33 . Estes autores propuseram que a reação de nitração aromática poderia ocorrer através da transferência de elétrons entre o anel aromático e o eletrófilo.…”