Nucleophilic displacement with nitrate anion

Aryloxy groups are much easier to displace compared to primary and secondary alkox-ide anions and so, aryl ethers are generally more useful in displacement reactions. Amine nucleophiles react with unsymmetrical aryl ethers to form the amine of the heavier nitrated moiety.Accordingly, 2,4,6-trinitrodiphenyl ether reacts with ammonia to expel phenoxide... 

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. ... 

Formation of vinyl acetate by the reaction of ethylene with Pd(OAc)2 can be understood by the acetoxypalladation and )3-H elimination (path a). No hydride shift occurs because the acetoxy group is electron-attracting. In addition, ethylene glycol monoacetate (9) is formed as a nucleophilic addition product in the presence of nitrate anion (path b) [13]. Formation of glycol monoacetate is explained by the displacement of Pd-OAc with a nitrate anion, followed by hydrolysis of the nitrate ester. 

Nucleophilic anions, i.e. halides, pseudohalides, alkoxides, phenoxides, and thio-phenoxides, are particularly suitable for these reactions. Even anions of lower reactivity in nucleophilic displacements, i.e. carboxylates, nitrates, nitrites and hydroperoxides, find practical application under PTC conditions. Reactions are rigorously Sf,2 in mechanism primary substrates are thus most suitable, since secondary substrates afford elimination products in high yields, especially when reacted at high temperatures, and tertiary substrates only give rise to elimination. This behaviour is consistent with the low polarity of the organic phase, preventing unimolecular mechanisms and favouring elimination over substitution when the reaction center is not a primary carbon atom. 

Imidazole reactivity was fully covered in CHEC-I, and only a brief summary is included here. The neutral molecule is Jt-excessive, being subject to electrophilic attack at N-3, less readily at C-4(5), and seldom at C-2. In benzimidazole electrophiles preferentially attack N-3 and the benzene ring carbons. Nucleophilic substitution reactions usually require some form of electron withdrawal elsewhere in the system, with displacements of groups at C-2 often favored. Imidazolium species are naturally more susceptible to nucleophilic attack, and they only undergo electrophilic substitutions with difficulty (e.g. nitration, sulfonation). The corresponding imidazole anions, when they can form, are highly reactive towards electrophiles. 

---