Nucleophilic addition reaction mechanism

A water-soluble Cj-symmetrical trisadduct of Cjq showed excellent radical scavenging properties in vitro and in vivo and exhibits remarkable neuro-pro tective properties [7,8]. It is a drug candidate for the prevention of ALS and Parldnsoris disease. Concerning the reaction mechanism, nucleophilic additions and radical additions are closely related and in some cases it is difficult to decide which mechanism actually operates [92]. For example, the first step in the reaction of f-eo with amines is a single electron transfer (SET) from the amine to the fullerene. The resulting amines are finally formed via a complex sequence of radical recombinations, deprotonations and redox reactions [36]. 

Both in the laboratory and in living organisms, the reactions of carbonyl compounds take place by one of four general mechanisms nucleophilic addition, nucleophilic acyl substitution, alpha substitution, and carbonyl condensation. These... 

A theoretical study of the reaction mechanism for addition of organozincate complexes to aldehydes was recently performed using density functional theory.298 It has been suggested that the addition takes place through formation of a four-centered transition state and, therefore, it can be considered a typical nucleophilic reaction. 

The versatility of 5-nitrosopyrimidines in pteridine syntheses was noticed by Pachter (64MI21603) during modification of the Timmis condensation between (262) and benzyl methyl ketone simple condensation leads to 4-amino-7-methyl-2,6-diphenylpteridine (264) but in the presence of cyanide ion 4,7-diamino-2,6-diphenylpteridine (265) is formed (equation 90). The mechanism of this reaction is still uncertain (63JOC1187) it may involve an oxidation of an intermediate hydroxylamine derivative, nitrone formation similar to the Krohnke reaction, or nucleophilic addition of the cyanide ion to the Schiff s base function (266) followed by cyclization to a 7-amino-5,6-dihydropteridine derivative (267), oxidation to a quinonoid-type product (268) and loss of the acyl group (equation 91). Extension of these principles to a-aryl- and a-alkyl-acetoacetonitriles omits the oxidation step and gives higher yields, and forms 6-alkyl-7-aminopteridines, which cannot be obtained directly from simple aliphatic ketones. 

In contrast to the above intramolecular reactions, Yamamoto and coworkers have demonstrated that aromatic halo-ketones having an alkyl substituent at their a-position are transformed to cyclized products at the carbonyl carbon (Eq. 21) [60]. This suggests that a new mechanism, nucleophilic addition of the arylpalladium moiety in the key intermediate to the carbonyl group (Scheme 2), can occur. Addition of an alcohol such as 1-hexanol is essential for the reaction. A possible role of it might be to facilitate the reduction of Pd(II) to Pd(0). 

The first part of the reaction is formation of a protonated Schiff base r)f sedoheptulose 7-phosphate with a lysine residue in the enzyme followed by a retro-aldol cleavage to give an enamine plus erythrose 4-j>hosphatc. Show the structure of the enamine and the mechanism by which it is formed. Hie second part of the reaction is nucleophilic addition of the enamine to glyceraldehyde 3-iihosphate followed by hydrolysis of the Sch ff base to give fructose 6-phosphate. Show the mechanism. 

The mechanism of both reactions involves nucleophilic addition of hydride (H ) to the polarized C - N triple bond. With LiAlHj, two equivalents of hydride are sequentially added to yield a dianion (Steps [l]-[2]), which is then protonated with HgO to form the amine in Step [3], as shown in Mechanism 22.12. 

Most reactions of carbonyl groups occur by one of four general mechanisms nucleophilic addition, nucleophilic acyl substitution, alpha substitution, am carbonyl condensation. These mechanisms have many variations, just a alkene electrophilic addition reactions and 8 2 reactions do, but the varia tions are much easier to learn when the fundamental features of the mechanisms are understood. Let s see what the four mechanisms are and what kinds of chemistry carbonyl groups undergo. 

Mechanism of the Crignard reaction. The nucleophilic addition of a carbanion to a ketone or aldehyde yields an alcohol. 

The mechanism classification and the overall transformation classification are orthogonal to each other. For example, substitution reactions can occur by a polar acidic, polar basic, free-radical, pericyclic, or metal-catalyzed mechanism, and a reaction under polar basic conditions can produce an addition, a substitution, an elimination, or a rearrangement. Both classification schemes are important for determining the mechanism of a reaction, because knowing the class of mechanism and the overall transformation rales out certain mechanisms and suggests others. For example, under basic conditions, aromatic substitution reactions take place by one of three mechanisms nucleophilic addition-elimination, elimination-addition, or SrnL If you know the class of the overall transformation and the class of mechanism, your choices are narrowed considerably. 

C. Reaction Mechanisms — Nucleophilic displacements and addition, nucleophilic aromatic substitution, electrophilic additions, electrophilic aromatic substitutions, eliminations, Diels-Alder and other cycloadditions... 

The key step in a basealdol reaction is nucleophilic addition of the enolate anion from one carbonyl-containing molecule to the carbonyl group of another carbonyl-containing molecule to form a tetrahedral carbonyl addition intermediate. This mechanism is illustrated by the aldol reaction between two molecules of acetaldehyde. Notice that OH is a true catalyst An OH is used in Step 1, but another OH is generated in Step 3. Notice also the parallel between Step 2 of the aldol reaction and the reaction of Grignard reagents with aldehydes and ketones (Section 12.5) and the first step of their reaction with esters (Section 14.7). Each type of reaction involves the addition of a carbon nucleophile to the carbonyl carbon of another molecule. 

In some cases an alternative mechanism is involved in what has been called a pseudo-Favorskii rearrangement (Eq. 11.61). The reaction involves nucleophilic addition to the carbonyl, followed by breakdown of the tetrahedral intermediate with concomitant migration... 

Using curved arrows to indicate the movement of electrons, draw the mechanism for each of the following reactions (a) nucleophilic addition of CN to CHjCHO and (b) electrophihc substimtion of benzene with SOjH. (Draw all resonance structures for the carbocation intermediate.)... 

The mechanism of both reactions involves nucleophilic addition of hydride (H ) to the polar-... 

General Mechanism—Nucleophilic Addition 786 General Mechanism—Acid-Catalyzed Nucleophilic Addition 787 Nucleophilic Addition of CN—Cyanohydrin Formation 791 The Wittig Reaction 794... 

This chapter reviews mechanistic studies on the stoichiometric reactions of coordinated hydrocarbons with nucleophiles and electrophiles, together with some related processes. Kinetic investigations of such reactions, especially nucleophilic additions, have increased considerably in recent years, greatly increasing our knowledge of the intimate mechanisms involved and of the factors important in controlling ligand reactivity. 

The base-promoted cleavage of C-C bond of non-enolizable ketones to form a carboxylic acid derivative and a neutral fragment is known as Haller-Bauer (HB) reaction [18, 19]. Sodium amide 2 is always used as the base and the corresponding amide products are produced. The generally mechanism for HB reaction involves nucleophilic addition of the amide to generate a tetrahedral intermediate 3, which could rearrange to form a carboxamide 4 and a carbanion. Then inter-molecular proton transfer leads to a hydrocarbon product (Scheme 3.1). 

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