Anions azide

The selectivity relationship merely expresses the proportionality between intermolecular and intramolecular selectivities in electrophilic substitution, and it is not surprising that these quantities should be related. There are examples of related reactions in which connections between selectivity and reactivity have been demonstrated. For example, the ratio of the rates of reaction with the azide anion and water of the triphenylmethyl, diphenylmethyl and tert-butyl carbonium ions were 2-8x10 , 2-4x10 and 3-9 respectively the selectivities of the ions decrease as the reactivities increase. The existence, under very restricted and closely related conditions, of a relationship between reactivity and selectivity in the reactions mentioned above, does not permit the assumption that a similar relationship holds over the wide range of different electrophilic aromatic substitutions. In these substitution reactions a difficulty arises in defining the concept of reactivity it is not sufficient to assume that the reactivity of an electrophile is related... 

The azide anion, often in hydiazoic acid, adds in good yield and, when strong electron-withdrawing groups are present, shows the normal 2,3-orientation (58) (49). The intermediates, useful for further synthetic goals, can, for example, be converted to heterocychc products, eg (59). The yields for various R groups are as follows ... 

Studies of the solvolysis of 1-phenylethyl chloride and its p-substituted derivatives in aqueous trifluorethanol containing azide anion as a potential nucleophile provide details relative to the mechanism of nucleophilic substitution in this system. 

Is azide anion linear or bent Name a common neutral organic molecule that is isoelectronic (same number of valence electrons) with azide anion. Is this molecule linear or bent ... 

According to the resonance picture, where is the excess negative charge in azide anion Will the center nitrogen or a terminal nitrogen act as the nucleophilic site Examine atomic charges and the electrostatic potential map. Do they substantiate your conclusion Explain. 

Electrostatic potential map for azide anion shows most negatively-charged regions (in red) and less negatively-charged regions (in blue). 

An investigation of the reactions of cis- and tra 5-2-methyl-4-phenyloxazoline-5-methylcarboxylate 31 with an azide anion shows that the transition state of the... 

Substitution of a protonated imidazole group by an azide anion permits an azido-carboxylic ester to be obtained in good yield [137]... 

A kinetic distinction between the operation of the SN1 and SN2 modes can often be made by observing the effect on the overall reaction rate of adding a competing nucleophile, e.g. azide anion, N3e. The total nucleophile concentration is thus increased, and for the SN2 mode where [Nu ] appears in the rate equation, this will result in an increased reaction rate due to the increased [Nut]. By contrast, for the Stfl mode [Nut] does not appear in the rate equation, i.e. is not involved in the rate-limiting step, and addition of N3e will thus be without significant effect on the observed reaction rate, though it will naturally influence the composition of the product. 

Tetranitro derivative 94 (y-TACOT Section 12.10.15.5) treated with sodium azide in DMSO gives 83% yield of a single symmetrical diazido dinitro derivative 81 resulting from nucleophilic substitution of an equivalent pair of nitro groups by the azide anion (Equation 5) <1996JOC5801>. 

Other approaches to tetrazoles were also recently published. Primary and secondary amines 195 were reacted with isothiocyanates to afford thioureas 196, which underwent mercury(II)-promoted attack of azide anion, to provide 5-aminotetrazoles 197 . A modified Ugi reaction of substituted methylisocyanoacetates 198, ketones, primary amines, and trimethylsilyldiazomethane afforded the one-pot solution phase preparation of fused tetrazole-ketopiperazines 200 via intermediate 199 <00TL8729>. Microwave-assisted preparation of aryl cyanides, prepared from aryl bromides 201, with sodium azide afforded aryl tetrazoles 202 . 

Ar-Acyl oxy- A -a 1 k oxyamides have been found to undergo SN2 reactions with a number of organic and inorganic nucleophiles including anilines, thiols, hydroxide and azide anions. Reaction products from all of these processes are themselves reactive anomeric amides and outcomes have uncovered novel chemistry of this unusual class of compounds. 

The nucleophilic attack of azide on 76b was also modeled at the pBP/DN //HF/ 6-31G level (Table 10, Fig. 23).44 In the gas phase the transition state is preceded by an ion-molecule complex (Fig. 23a) which is at a minimum on the reaction coordinate and in which the azide anion is 3.7 A from the amide nitrogen, and approaching the axis of the formyloxy-nitrogen (Nl-09) bond but in which the azide possesses all the anionic charge. 

Fig. 23 HF/6-31G geometries for (a) the ground state complex and (b) the transition state in the reaction of azide anion with iV-formyloxy-iV-methoxyformamidc 76b.

A theoretical study at a HF/3-21G level of stationary structures in view of modeling the kinetic and thermodynamic controls by solvent effects was carried out by Andres and coworkers [294], The reaction mechanism for the addition of azide anion to methyl 2,3-dideaoxy-2,3-epimino-oeL-eiythrofuranoside, methyl 2,3-anhydro-a-L-ciythrofuranoside and methyl 2,3-anhydro-P-L-eiythrofuranoside were investigated. The reaction mechanism presents alternative pathways (with two saddle points of index 1) which act in a kinetically competitive way. The results indicate that the inclusion of solvent effects changes the order of stability of products and saddle points. From the structural point of view, the solvent affects the energy of the saddles but not their geometric parameters. Other stationary points geometries are also stable. 

Andres, J., Bohm, S., Moliner, V., Silla, E. and Tunon, I. Atheoretical study of stationary structures for the addition of azide anion to tetrafuranosides modeling the kinetic and thermodynamic controls by solvent effects, J. Phys. Chem., 98 (1994), 6955-6960... 

A special, isotope-labeled case of the azide-tetrazole equilibrium was studied by Cmoch et al. <2000JP0480>, and the results are shown in Scheme 23. 2-Chloro-3-nitropyridine 86 was treated with potassium azide containing a doubly labeled (15NN15N) azide anion. The authors detected formation of two differently labeled tetrazolopyridines the 2,4- 87 and the 1,3-labeled 88 derivatives. 

Novak et al. <1998JA1643> devised a novel approach to amino-substituted tctrazolo[ 1,5-tf Jpyridine which provides a really unique pathway (Scheme 34). These authors studied the possibility of formation of nitrenium ions from the pivaloylhydroxylamine 143 and found that if azide anion is present in the main reaction route is the formation of tetrazolo[l,5-tf]pyridine 146. The authors concluded that the first intermediate is the formation of the carbonium cation 144 which captures the azide anion to yield 2-azidopyridine 145, that is, the valence bond isomer of the product 146. 

Table 6 Tetrazolopyridazines, -pyrimidines, and -pyrazines prepared by nucleophilic substitution of haloazines by azide anion...

Noelting and Michel, as well as A. R. Hantzsch, had observed around 1900 that benzenediazonium cations evolved dinitrogen on treatment with azide anions, but only R. Huisgen and I. Ugi s kinetic reinvestigation of this reaction at low temperature revealed in 1956—1957 the formation of 1-phenyl-pentazole, and allowed later the isolation of stable arylpentazoles when the phenyl group had electron-donating substituents.39... 

Further interestingly, azide anion (N ), rather weak nucleophile, could easily react with PVC in DA-solvents to give the azide derivatives (equivalent NaN, 60°C, DS (degree of substitution) 64% (hexamethyiphosphortriamide, HMPA), 33% (DMF) and 0%... 

Fig. 1 for stepwise solvolysis of R-X is due to the increase in ks (s ), with decreasing stability of the carbocation intermediate, relative to the constant value of az (M s ) for the diffusion-limited addition of azide anion. The lifetime for the carbocation intermediate eventually becomes so short that essentially no azide ion adduct forms by diffusion-controlled trapping, because addition of solvent to R occurs faster than escape of the carbocation from the solvent cage followed by addition of azide ion (k Now, the nucleophile adduct must form through a... 

Azide ion is a modest leaving group in An + Dn nucleophilic substitution reactions, and at the same time a potent nucleophile for addition to the carbocation reaction intermediate. Consequently, ring-substituted benzaldehyde g m-diazides (X-2-N3) undergo solvolysis in water in reactions that are subject to strong common-ion inhibition by added azide ion from reversible trapping of an o -azido carbocation intermediate (X-2 ) by diffusion controlled addition of azide anion (Scheme... 

The visible spectra of oxyHr and metIh N3 are dominated by ligand-to-metal charge transfer bands from the hydroperoxide or azide anions, but otherwise they are similar to those of the synthetic complexes (Rgure 2) (38). The d-d transitions observed at 700 and KXX) nm are more intense than usually observed for high-spin iron(llI) complexes, probably due to the strong antiferromagnetic coupling interaction (38,40). 

The tetraazapentalene ring system forms the core of the thermally insensitive explosive TACOT (Section 7.10) and so its fusion with the furoxan ring would be expected to enhance thermal stability and lead to energetic compounds with a high density, y-DBBD (95) is prepared from the nitration of tetraazapentalene (91), nucleophilic displacement of the o-nitro groups with azide anion, further nitration to (94), followed by furoxan formation on heating in o-dichlorobenzene at reflux. The isomeric explosive z-DBBD (96) has been prepared via a similar route. ... 

Several other azido esters has been reported, including (7), (8) and (9), which are synthesized along similar routes of ester formation followed by substitution of halogen with azide anion or in the reverse order. 

The second synthetically useful general transformation of any of the chloro esters 1,2 consists of an intra- or intermolecular nucleophilic substitution of the chlorine atom in any of the Michael adducts. Several examples of such reactions have been mentioned above (Table 1 and Scheme 26), and substitutions of any specific importance (for example, with hydride or azide anion [9,10,62]) as well as subsequent transformations of such substitution products will be discussed in the corresponding Sections [66]. 

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