Does Addition of NO₂ to Carbon-Centered Radicals Yield RONO or RNO₂? An Investigation Using Distonic Radical Ions

Abstract

Nitrogen dioxide is used as a "radical scavenger" to probe the position of carbon-centered radicals within complex radical ions in the gas phase. As with analogous neutral radical reactions, this addition results in formation of an [M + NO2](+) adduct, but the structural identity of this species remains ambiguous. Specifically, the question remains: do such adducts have a nitro-(RNO2) or nitrosoxy-(RONO) moiety, or are both isomers present in the adduct population? In order to elucidate the products of such reactions, we have prepared and isolated three distonic phenyl radical cations and observed their reactions with nitrogen dioxide in the gas phase by ion-trap mass spectrometry. In each case, stabilized [M + NO2](+) adduct ions are observed and isolated. The structure of these adducts is probed by collision-induced dissociation and ultraviolet photodissociation action spectroscopy and a comparison made to the analogous spectra of authentic nitro-and nitrosoxy-benzenes. We demonstrate unequivocally that for the phenyl radical cations studied here, all stabilized [M + NO2](+) adducts are exclusively nitrobenzenes. Electronic structure calculations support these mass spectrometric observations and suggest that, under low-pressure conditions, the nitrosoxy-isomer is unlikely to be isolated from the reaction of an alkyl or aryl radical with NO2. The combined experimental and theoretical results lead to the prediction that stabilization of the nitrosoxy-isomer will only be possible for systems wherein the energy required for dissociation of the RO-NO bond (or other low energy fragmentation channels) rises close to, or above, the energy of the separated reactants. AbstractNitrogen dioxide is used as a "radical scavenger" to probe the position of carbon--centered radicals within complex radical ions in the gas phase. As with analogous neutral radical reactions, this addition results in formation of an [M+NO2] + adduct, but the structural identity of this species remains ambiguous. Specifically, the question remains: do such adducts have a nitro--(RNO2) or nitrosoxy--(RONO) moiety, or are both isomers present in the adduct population? In order to elucidate the products of such reactions, we have prepared and isolated three distonic phenyl radical cations and observed their reactions with nitrogen dioxide in the gas phase by ion--trap mass spectrometry. In each case, stabilized [M + NO2] + adduct ions are observed and isolated. The structure of these adducts is probed by collision--induced dissociation and ultraviolet photodissociation action spectroscopy and a comparison made to the analogous spectra of authentic nitro--and nitrosoxy--benzenes. We demonstrate unequivocally that, for the phenyl radical cations studied here, all stabilized [M + NO2] + adducts are exclusively nitrobenzenes. Electronic structure calculations support these mass spectrometric observations and suggest that, under low--pressure conditions, the nitrosoxy--isomer is unlikely to be isolated from the reaction of an alkyl or aryl radical ...

Ion‐molecule reactions of mass‐selected ions

“…Gas‐phase reaction of NO 2 with 4‐( N , N , N ‐trimethylammonium)‐phenyl radical cation. (from reference: Kirk et al, 2013). …”

“…Gas‐phase synthesis of N , N , N ‐trimethyl‐4‐nitrosoxybenzaminium (A‐ONO) cation. (from reference: Kirk et al, 2013). …”

“…Kirk et al (2013) described an elegant example of utilization of IMR to distinguish between potential isomeric products. To determine whether the [M + 46] product from the reaction of 4-(N,N,N-trimethylammonium)-phenyl radical cation (A) with NO 2 (Scheme 6) is a nitro (A-NO 2 ) or nitrosoxy (A-ONO) species, they compared fragmentation spectra of commercially available ANO 2 + cation and the A-ONO + species which they synthesized via IMR (Scheme 7): Both CID and UVPD action spectra unequivocally confirmed that the [M + 46] product in Equation (…”

Synthetic Diversity from a Versatile and Radical Nitrating Reagent

“…The spin-trapped DEPMPO-NO 2 adduct can be clearly observed at 243 Ka nd is consistentw ith previousr eports by Astolfi for an oxygen centered adduct (see Supporting Information). [24] Additionale vi-Scheme1.Traditionally,nitroalkenes have been accessed through avariety of strategies (A, B), we have developedanew nitratingr eagent-strategy based on aS ET redox active scaffold (C, D). dence of an ostensibly,l ess-stable nitrogen centered NO 2 adduct is also observed.…”

Visible-light-promoted tandem radical difunctionalization of olefinic amides: a direct access to NO2-containing benzoxazines and oxazolines

“…When Ru(bpy) 3 (PF 6 ) 2 and N -nitrosuccinimide in acetonitrile were irradiated with blue LEDs in the presence of 5-diethoxyphosphoryl-5-methyl-1-pyrroline- n -oxide (DEPMPO), a signal corresponding to NO 2 -DEPMPO radical adduct ( g = 2.0095, a P = 46.797 G, a N = 12.216 G, a H = 9.587 G, a H = 0.466 G, a H = 0.196 G) was clearly recorded by EPR and is consistent with previous literature reports. 7,17 However, in the absence of visible-light irradiation, the same reaction mixture of Ru(bpy) 3 (PF 6 ) 2 , DEPMPO, and N -nitrosuccinimide was found to be EPR silent. These experimental results confirmed that the NO 2 -radical was involved in the reaction system.…”