Phenylnitrenium ion

In a seminal theoretical paper, we showed that, at the Modified Neglect of Differential Overlap (MNDO) level, phenylnitrenium ions 17 as well as NH2, PH2,... 

For phenylnitrenium ions, we85 and others 72,78,102 104 have computed that there is extensive positive charge delocalisation into the aromatic ring and arylnitrenium ions are best described as 4-imino-2,5-cyclohexadienyl-l-yl carbenium ions 18. 

X = C6H4Y) have lifetimes of 0.6 ms (Y = 4-OMe) to 26 ns (Y = 4-CF3). They are quenched by azide ion at the diffusion limit. The Yukawa-Tsuno r+ value for these is 2.8, also consistent with a large amount of resonance delocalization. Photolysis of (52) results in the A -methyl-iV-phenylnitrenium ion (53), which presumably gives the observed products (54), aniline and iV-methylaniline as shown. ... 

Figure 13.17. The DFT calculations show singlet phenylnitrenium ion is planar and the triplet is perpendicular.

TABLE 13.2. Singlet-Triplet Energy Gaps in 4-Snbstitnted Phenylnitrenium Ions (X—C6H4NH ) ... 

One general, and as yet unsolved problem, is understanding and predicting the regiochemistry of arylnitrenium ion addition to DNA bases. This reaction is complicated because phenylnitrenium ion has four potential sites of addition (Fig. 13.21) the nitrenium center as well as the ortho and para ring carbons. Likewise, DNA has numerous sites for electrophilic addition. In guanine bases alone, there is a possibility for addition to N7, 06, N2, or C8. 

Falvey examined the reactions of A-methyl-A-phenylnitrenium ion 65 (Fig. 13.37) in the presence and absence of chloride. It was found the yield of aniline (resulting from hydrolysis of the product iminium ion) was unaffected by added base. This finding ruled out a deprotonation process and led to the conclusion that a 1,2-hydride shift had occurred. Cramer et al. modeled this process using ab initio methods. 

The next development in direct detection of nitrenium ions came from McClelland et al. ° who applied the azide method to LFP measurements. This permitted the direct detection of those arylnitrenium ions implicated in carcinogenic DNA damage. McClelland s approach proved to be particularly useful in the study of 4-aryl and 4-alkoxy substituted phenylnitrenium ions. Apparently, the corresponding singlet nitrenes are sufficiently long lived to allow for protonation in aqueous solution. Several arylnitrenium ions studied by this route are described in Table 13.6. 

Hanway, P. J. Winter, A. H. Phenyloxenium ions more like phenylnitrenium ions than isoelectronic phenylnitrenes , J. Am. Chem. Soc. 2011,133, 5086-5093. 

Nitrenium ions have been observed following flash photolysis of 4-ethoxy- and 4-methoxyphenyl azides in aqueous solution and a series of polyfluorinated phenyl azides in acidic media, such as acetonitrile containing sulfuric acid. Measured lifetimes of the phenylnitrenium ions varied from 1 ps up to milliseconds. 

Fishbein, J. C., McClelland, R. A., Halide Ion Trapping of Nitrenium Ions Formed in the Bamberger Rearrangement of N Arylhydroxylamines. Lifetime of the Parent Phenylnitrenium Ion in Water, Can. J. Chem. 1996, 74, 1321 1328. 

Irradiation of the N-(2-cyclopropenylcarbonyloxy)phthalimide (249) in the presence of N-phenylcarbazole and a radical donor such as tributylstannane results in smooth decarboxylation to yield N-(2-cyclopropenyl)phthalimide (250) in high yield. In contrast the N-(cyclopropylcarbonyloxy)phthalimide (251) underwent complete decarboxylation to the corresponding cyclopropane (252). Irradiation of the diazide (253) in methanol provides access to the new isoxazolo-[4,5-d]- and -[4,5-e]-diazepine systems, (254) and (255) respectively. Photolysis of N-(methylphenylamino)-2,4,6-trimethylpyridinium tetrafluoroborate yields the singlet N-methyl-N-phenylnitrenium ion which reacts with methanol and tetra-... 

Phenyloxenium ions (Ar-O ) have been computationally compared with their iso-electronic phenylniticnes (Ar-N ) and phenylnitrenium ions (Ar-NH ) at the mul-... 

Figure 4 Bond lengths (A), obtained from DFT calculations on phenylcarbene and phenylnitrenium ion ...

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