Cations phenyl diazonium

Examine the geometries (in particular, CN bond distances) of methyl diazonium, tert-butyl diazonium and phenyl diazonium ions. Which, if any, of these ions is best described as a weak complex between a cation and N2 Which is furthest away from this description Is your result consistent with the observed reactivity patterns Explain. 

The same strategy has recently been used in the quite challenging determination of the standard potentials for the reduction of phenyl and substituted phenyl radicals.48 In this case the radical is so easy to reduce that starting from iodides was not sufficient. One had to go to the very reducible phenyl diazonium cations to see the wave of the radical appear beyond the radical-producing wave. 

It is of interest to mention some detailed mass spectrometric results that were obtained by performing distinct experiments (a) ion-molecule reactions in mixtures of haloben-zenes and ammonia under chemical ionization conditions (b) ion-molecule reactions of mass-selected ionized halobenzenes toward ammonia in a quadrupole collision cell of a hybrid tandem mass spectrometer (c) ion-molecule reactions of phenyl diazonium cations with ammonia in the same quadrupole collision cell and, finally, (d) electrospray ionization of anilines in a hybrid quadrupole-time of flight mass spectrometer (QTof). Characterization of the product ions relies on collisional activation experiments in the low or high kinetic energy regime98. 

FIGURE 11. Reactions of phenyl diazonium cation with ammonia (a) mass spectrum of the ions produced within the quadrupole collision cell and (b) high energy (8 keV, nitrogen collision gas) of the so-produced m/z 94 ions. Spectrum (c) corresponds to the reactions of the m/z 77 phenyl cation formed in the ion source with ammonia... 

In the phenyl-substituted fulvene (117), reaction with isoamyl nitrite or the phenyl diazonium cation gives the corresponding substitution products (116) and (118) <88JOC3529>. The reaction with diazonium salts has also been used for the preparation of polymethin-type azo-dyes (119) in high yield (Scheme 26) <90JPR43>. 

Phenyl cations are formed by thermal decomposition of aryl diazonium ions. The cation is so extremely reactive that under some circumstances it can recrqrture the nitrogen... 

Whereas reaction of hydrazones disubstituted in the 4,5-position of the selenazole rings with diazotized arylamines only gives formazans, compounds unsubstituted in the 5-position can be attacked there by the diazonium cation. In fact, the azo coupling in this position is decidedly quicker reaction of 5-benzylidenehydrazino-4-phenyl-... 

Scaiano and Kim-Thuan (1983) searched without success for the electronic spectrum of the phenyl cation using laser techniques. Ambroz et al. (1980) photolysed solutions of three arenediazonium salts in a glass matrix of 3 M LiCl in 1 1 (v/v) water/acetone at 77 K. With 2,4,5-trimethoxybenzenediazonium hexafluorophos-phate Ambroz et al. observed two relatively weak absorption bands at 415 and 442 nm (no e-values given) and a reduction in the intensity of the 370 nm band of the diazonium ion. The absence of any ESR signals indicates that these new bands are not due to aryl radicals, but to the aryl cation in its triplet ground state. 

The wide utility of aryl diazonium ions as synthetic intermediates results from the excellence of N2 as a leaving group. There are several general mechanisms by which substitution can occur. One involves unimolecular thermal decomposition of the diazonium ion, followed by capture of the resulting aryl cation by a nucleophile. The phenyl cation is very unstable (see Part A, Section 3.4.1.1) and therefore highly unselective.86 Either the solvent or an anion can act as the nucleophile. 

Phenols from Diazonium Ion Intermediates. Aryl diazonium ions can be converted to phenols by heating in water. Under these conditions, there is probably formation of a phenyl cation. 

When 4-/-butylcyclohex-1 -enyl(phenyl)iodonium tetrafluoroborate (3) is heated at 60 °C in chloroform, 1-fluorocyclohexene 4, 1-chlorocyclohexene 5 and l-(o-iodophenyl)cyclohexene 6 are formed with accompanying iodobenzene leaving group (eq 2).3 These three substitution products are best accounted for by formation of an ion pair involving cyclohexenyl cation 7. The cyclohexenyl cation 7 formed picks up fluoride from tetrafluoroborate and chloride from chloroform solvent, and recombines with the iodobenzene generated (eq 3). This kind of reactions with a counteranion and solvent are characteristic of unstable carbocations and are known in the case of phenyl cation generated from the diazonium salt in the Schiemann-type reaction.4... 

The mechanism by which a nucleophile displaces the diazonium group depends on the nucleophile. While some displacements involve phenyl cations, others involve radicals. Nucleophiles, e.g. CN , Cl and Br , replace the diazonium group if the appropriate cuprous salt is added to the solution containing the arene diazonium salt. The reaction of an arene diazonium salt with cuprous salt is known as a Sandmeyer reaction. 

The phenyl cation (134) firstpostulated by Waters335 is a highly reactive species oflow stability and plays a fundamental role in organic chemistry—for example, in the chemistry of diazonium ions. According to gas-phase studies and calculations, its stability is between that of the ethyl cation and the vinyl cation.336 Since it is an extremely electrophilic and short-lived species, it could not be isolated or observed directly in the condensed phase. For example, solvolytic and dediazoniation studies under superacidic conditions by Faali et al.337,338 failed to find evidence of the intermediacy of the phenyl cation. Hyperconjugative stabilization via orf/zo-Me3Si or... 

Sun et al. extended the diazo-carboxylate covalent bonding to the assembly between diazo-resins and gold nanoparticles.19 The ionic LbL assembly was first achieved by using diazo resins (DAR) and citrate-capped gold nanoparticles. Under UV irradiation, diazonium groups decomposed to phenyl cations that reacted with the nucleophilic carboxylate groups on the gold nanoparticles via an SN1 reaction. 

Sensitized) photolysis of diazonium salts as a mild general method for the generation of aryl cations, chemoselectivity of the singlet and triplet 4-substituted phenyl cations. Journal of Organic Chemistry, 70, 603-610. 

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