Nitrosonium ion, and

Ridd - has reinterpreted the results concerning the anticatalysis of the first-order nitration of nitrobenzene in pure and in partly aqueous nitric acid brought about by the addition of dinitrogen tetroxide. In these media this solute is almost fully ionised to nitrosonium ion and nitrate ion. The latter is responsible for the anticatalysis, because it reduces the concentration of nitronium ion formed in the following equilibrium ... 

The kinetics of aromatic nitrosation at ring carbon have received little attention. The first attempt to determine the nature of the electrophile was made by Ingold et a/.117, who measured the rates of the nitrous acid-catalysed nitration of 4-chloroanisole by nitric acid in acetic acid which proceeds via initial nitrosation of the aromatic ring. Assuming that the electrophiles are the nitrosonium ion and... 

Lewis dot diagrams of nitric oxide compared to the nitrosonium ion and molecular nitrogen. Each bond contains one electron from each atom. These simple diagrams fail to properly account for the effective bond order of 2.5 predicted by molecular orbital theory and must be only considered as illustrative. The dimer of two nitric oxide molecules has five bonds, which is the same as two individual molecules. Thus, nitric oxide remains dissociated at room temperatures. 

The chemistry of nitrite at acidic pH is closely related to that of nitrosonium ion described earlier. The pfC, of nitrous acid is around 3.4-3.6, though precise measurement is difficult because of its rapid secondary reactions. Acidification of nitrite produces nitrous acid, which is in reversible equilibrium with nitrosonium ion and hydroxide ion (Turney and Wright, 1959), although in aqueous solu-... 

Acidic nitrite solutions readily donate nitrosonium ion and are important synthetic reactions to form diazonium salts. 

Similar [3 + 2] annulations of allenylsilanes 86 and propargylsilanes 87 with a, /i-unsaturated ketones, ketones, 7V-acyliminium ions, nitrosonium ions and tropylium cations giving the corresponding cyclopentenes (cyclohexenes), dihydrofurans, 3-pyrrolines, isoxazoles and azulene derivatives, respectively, have been reported (equations 60 and 6i)142.t54,i68-t72>... 

The mechanism for this reaction consists of many steps. It begins with nucleophilic attack of the amine on the nitrosonium ion, and it can conceptually be divided into two parts formation of an A-nitrosamine, followed by loss of H2O, as shown in Mechanism 25.2. 

In 2000, Hubig and Kochi claimed to have made the first observation of a true Wheland intermediate of an S Ar when studying nitrosation of methyl-substituted benzenes by time-resolved spectroscopy [49]. Irradiation of a suspension of NOBF " in dichloromethane containing mesitylene with a laser pulse of 355 nm generated a transient species, which was identified as the radical ion pair. This species rapidly converted to another transient, which was assigned as the Wheland intermediate. However, theoretical studies have indicated that the reaction does not proceed via a radical ion pair and that the Wheland structure is a transition state rather than an intermediate of the nitrosation reaction [50]. This interpretation also found support in the analysis of the x-complex of nitrosonium ion and henzene hy IRMPD [44]. 

The yellow species formed in the reaction between sodium nitrite and thiosulfate in acidic, aqueous solution has been identified as the 5-nitrosated thiosulfate (03SSN0) , which is suggested to be formed by parallel pathways involving the nitrosonium ion and dinitrogen trioxide. The much studied reaction between nitrite and sulfite to give hydroxylamine disulfonate has received further attention and some apparent discrepancies have been clarified. For the pH range 4.5 to 7 the rate equation is given by (11). 

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