Nucleophilic substitution properties

Features Can undergo electrophilic and nucleophilic substitution Properties Water-wh. liq., char, odor > 99.5% assay 2-Pyrol [ISP]... 

Chemical Properties. The presence of both a carbocycHc and a heterocycHc ring faciUtates a broad range of chemical reactions for (1) and (2). Quaternary alkylation on nitrogen takes place readily, but unlike pyridine both quinoline and isoquinoline show addition by subsequent reaction with nucleophiles. Nucleophilic substitution is promoted by the heterocycHc nitrogen. ElectrophiHc substitution takes place much more easily than in pyridine, and the substituents are generally located in the carbocycHc ring. 

SuIfona.tlon, The sulfonic acid group is used extensively in the dyes industry for its water-solubilizing properties, and for its ability to act as a good leaving group in nucleophilic substitutions. It is used almost exclusively for these purposes since it has only a minor effect on the color of a dye. 

Ring substituents show enhanced reactivity towards nucleophilic substitution, relative to the unoxidized systems, with substituents a to the fV-oxide showing greater reactivity than those in the /3-position. In the case of quinoxalines and phenazines the degree of labilization of a given substituent is dependent on whether the intermediate addition complex is stabilized by mesomeric interactions and this is easily predicted from valence bond considerations. 2-Chloropyrazine 1-oxide is readily converted into 2-hydroxypyrazine 1-oxide (l-hydroxy-2(l//)-pyrazinone) (55) on treatment with dilute aqueous sodium hydroxide (63G339), whereas both 2,3-dichloropyrazine and 3-chloropyrazine 1-oxide are stable under these conditions. This reaction is of particular importance in the preparation of pyrazine-based hydroxamic acids which have antibiotic properties. 

H-Dibenz[6,/]azepine-5-carboxamide pharmacological properties, 7, 546 Dibenz[6,e]azepine-6,11-dione, 10-amino-reactions, 7, 526 Dibenz[6,e]azepinediones intramolecular nucleophilic substitution, 7, 516 synthesis, 7, 531 Dibenz[6,e]azepine-5,11-diones epoxides, 7, 515 reduction, 7, 525... 

Pterin, 4-amino — see Folic acid, 4-amino-4-deoxy-Pterin, 6-amino-structure, 3, 276 Pterin, 7-amino-structure, 3, 276 Pterin, 6-arylthio-reactivity, 3, 299 Pterin, 6-(l-carboxyethoxy)-synthesis, 3, 309 Pterin, 6-carboxy-7-hydroxy-properties, 3, 277 Pterin, 7-carboxy-6-hydroxy-properties, 3, 277 Pterin, 6-chloro-nucleophilic substitution, 3, 292 synthesis, 3, 290... 

Pyrido[3,4-d]pyrimidine-2,4-dione synthesis, 3, 215 Pyridopyrimidines, 3, 201 iV-alkylations, 3, 206 biological activity, 3, 260-261 1-electron reductions, 3, 207 IR spectra, 3, 204 mass spectra, 3, 204 MO calculations, 3, 204 NMR, 3, 202, 203 nucleophilic substitution, 3, 213 8-nucleosides synthesis, 3, 206 physical properties, 3, 201-205 protonation, 3, 206 radical reactions, 3, 215 reactions with water, 3, 207 reduced... 

Because carbocations are key intermediates in many nucleophilic substitution reactions, it is important to develop a grasp of their structural properties and the effect substituents have on stability. The critical step in the ionization mechanism of nucleophilic substitution is the generation of the tricoordinate carbocation intermediate. For this mechanism to operate, it is essential that this species not be prohibitively high in energy. Carbocations are inherently high-energy species. The ionization of r-butyl chloride is endothermic by 153kcal/mol in the gas phase. ... 

Unlike most ethers, epoxides (compounds in which the C—O—C unit forms a three-membered ring) are very reactive substances. The principles of nucleophilic substitution are important in understanding the preparation and properties of epoxides. 

Additional control of the nucleophilic substitution pathways a and b should be possible by varying the properties of the heteroarylium moiety in 33 as well as the substituent R and, to a minor extent, by the nature of the C-bonded halogen. Tire cation of 7a appeared to be an especially useful model compound and was thus selected in order to systematically study these influences and to define a standard situation. Structure 7a is easily accessible in excellent yield, and its molecular size allowed high-level MO calculations. 

Ab initio calculations suggested that the oxygen-substituted compounds 40 and 41 should be much better candidates for nucleophilic substitution reactions that follow pathway b than the halo salts belonging to the 7a-7i family (Scheme 9). Tire properties of the CCls-substituted cation of 43 should reveal more similarities with those of 7a than with those of 40 and 41. 

Another class of silicon-containing polymers that have great potential to be extremely useful precursor materials are poly(chlorocarbosilanes).14f 46 Poly (chlorocarbosilanes) are not useful without modification because of the rapid hydrolysis of Si—Cl bonds, forming HC1 and an insoluble crosslinked polymer network. However, nucleophilic substitution of these Si—Cl bonds with various reagents produces materials widi a broad range of properties that are determined by the nature of the nucleophile used.47 Poly(chlorocarbosilanes) can be easily synthesized by ADMET (Fig. 8.18) without any detrimental side reactions, since the Si—Cl bond is inert to both catalysts 12 and 14. Early studies produced a polymer with Mn = 3000.14f... 

With the iron atom in its most negative oxidation state of —2 this complex possesses nucleophilic properties and thus can be used in nucleophilic substitution reactions. As the iron atom in this complex formally has ten valence electrons, it is isoelectronic with Pd(0), which is a well-known catalyst in allylic substitution reactions [49]. 

The solvent dependence of the reaction rate is also consistent with this mechanistic scheme. Comparison of the rate constants for isomerizations of PCMT in chloroform and in nitrobenzene shows a small (ca. 40%) rate enhancement in the latter solvent. Simple electrostatic theory predicts that nucleophilic substitutions in which neutral reactants are converted to ionic products should be accelerated in polar solvents (23), so that a rate increase in nitrobenzene is to be expected. In fact, this effect is often very small (24). For example, Parker and co-workers (25) report that the S 2 reaction of methyl bromide and dimethyl sulfide is accelerated by only 50% on changing the solvent from 88% (w/w) methanol-water to N,N-dimethylacetamide (DMAc) at low ionic strength this is a far greater change in solvent properties than that investigated in the present work. Thus a small, positive dependence of reaction rate on solvent polarity is implicit in the sulfonium ion mechanism. 

A similar approach has been described by the same authors for the synthesis of related cyclic peptidomimetics [44]. A set often nucleophiles was employed for the substitution of the chlorine atom of the cyclic triazinyl-peptide bound to the cellulose membrane. By virtue of the aforementioned rate enhancement effects for nucleophilic substitution of the solid-supported monochlorotriazines, these reactions could be rapidly carried out by microwave heating. All products were obtained in high purity, enabling systematic modification of the molecular properties of the cyclic peptidomimetics. 

Although diselenonium-, ditelluronium- and mixed sulfonium-selenonium dications can exhibit either oxidative or electrophilic properties in reactions with nucleophiles, substitution at the onium chalcogen atom is more typical.96 Owing to the increased stability of heavier dichalcogenium-dications, they react only with highly activated substrates such as aniline and tV,A-dimethylaniline, while no reaction is observed with phenol and diphenylamine.113 Reactions of ditelluronium dications with activated aromatics are also not known (Scheme 44).114... 

Chiral sulfonium ylides have been known for some 30 years, and their stereochemistry and properties have been studied.15 Optically active selenonium ylides were obtained by reacting selenoxides with 1,3-cyclohexanedione under asymmetric conditions by Sakaki and Oae in 1976 for the first time,16 and also optically resolved by fractional recrystallization of the diastereomeric mixtures in the early 1990s.17 In 1995, optically active selenonium ylides 6 were obtained in over 99% de by nucleophilic substitution of optically active chloroselenurane or selenoxide with active methylene compounds with retention of configuration.18 The absolute configurations were determined by X-ray analysis of one... 

A similar but simpler 4-imino-hexahydropyrrolo[l,2-tf]pyrazin-l(277)-one 311 was prepared starting from the product obtained by nucleophilic substitution of a primary amine to the bromoacetamide of the L-prolylnitrile 310 (Scheme 40). The cyclization occurred directly in basic medium by refluxing for 96 h in EtOAc. This compound showed a potent activity as an orally bioavailable dipeptidyl peptidase IV inhibitor with anti-hyperglycemic properties <2003JME2774>. 

Spin traps can act as one-electron oxidizers. This property is even more pronounced in the interactions of traps with anion-radicals. Traps can block the ion-radical pathway. In other words, they inhibit the whole reaction, including the ion-radical step. This can be explained by both the oxidation of substrate anion-radical and chain termination due to oxidation of product anion-radical. An illustrative example is the inhibition of nucleophilic substitution of 2-chloroquinoxaline by the radical trap bis(tcrt-butyl)nitrone (Carver et al. 1982). 

The polarity of carbon-halogen bond of alkyl halides is responsible for their nucleophilic substitution, elimination and their reaction with metal atoms to form organometallic compounds. Nucleophilic substitution reactions are categorised into and on the basis of their kinetic properties. Chirality has a profound role in understanding the reaction mechanisms of Sj l and Sj 2 reactions. Sj 2 reactions of chiral all l halides are characterised by the inversion of configuration while Sj l reactions are characterised by racemisation. 

Thioesters are more reactive towards nucleophilic substitution than oxygen esters, and are widely employed in natural biochemical processes because of this property. Coenzyme A is a structurally complex thiol, and functions in the transfer of acetyl groups via its thioester acetyl coenzyme A (acetyl-CoA CH3CO-SC0A). 

In Part 11 we concentrate on aromatic systems, starting with the basics of structure and properties of benzene and then moving on to related ciromatic compounds. We even throw in a section of spectroscopy of aromatic compounds. Chapters 7 and 8 finish up this pcirt by going into detail about substitution reactions of aromatic compounds. You find out all you ever wanted to know (and maybe more) about electrophilic and nucleophilic substitutions, along with a little about elimination reactions. 

The parent polymer by itself is not a useful material owing to the extreme hydrolytic sensitivity of the P-Cl bond. However, this feature has been turned around and used as an advantage. Nucleophilic substitution of the chlorines in the polymer results in substituted polyphosphazenes which are hydrolytically stable. Also, using this method the polymer architecture and properties are readily fine-tuned by a subtle variation of the substituent. Over three hundred types of polyphosphazenes have been synthesised by this method. Assembly of organic polymers containing cyclo-phosphazenes as pendant groups is another approach that is gaining importance [6]. 

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