Most stable carbanion

In the same way, the addition of monomer yields the radical ions which possess the most stable carbanion ends and the most stable radical ends, e.g.,... 

Stable conformation for CHjSOH and CH3SOCH3 may be illustrated by the Newman projections of 32 and 33, while those of the carbanions are given by 34 and 35. This means that the a-sulfinyl carbanion is nonplanar and the Hj proton on the opposite side of the S—O bond is removed preferentially. The same calculation also indicated that conformer 32 is 16.5kcalmol and 17.2kcalmol" more stable than conformers 29 and 31, respectively . This new MO calculation thus contradicts the earlier suggestion that the most stable carbanionic conformer is 29 but emphasizes the importance of the contribution of 3d-orbitals for the stabilization of a-sulfinyl carbanions. 

Reductive ring opening of cyclic -alkyl andinium salts happens regioselectively at the Al-aryl bond to form an N, -dialkyl amine. A 2e reduction has been proposed, followed by cleavage to the most stable carbanion (Fig. 23) [122]. 

Which of the following, C CR, CH2Ph, CH(C=N)2, is the most stable carbanion Which is the least ... 

Answer The most stable carbanion will be the weakest base and have the lowest P abH- This means that CH(C=N)2, with a pATabH of 11 -2, is the most stable. The next... 

The most stable carbanion will be the weakest base and have the lowest pATabH-Electron-Withdrawing Group Trends... 

In the presence of nucleophiles, cyclopropylideneamines 12 undergo smooth nucleophilic addition to afford adducts 13, that very often suffer from ring opening to ketimines 14 (see Section 5.2.3.4.) such ring opening gives rise to the most stable carbanion [i.e. the least substituted or a benzylic carbanion (R = Ph)]. The use of alkoxides leads to imidates. e.g. 15, while the use of hydroxide (or water during aqueous workup) affords amides, e.g. 16. 

It should be stressed that several cyclopropylideneamines 28 have been generated in situ from a-haloimines 3 under basic Favorskii conditions and that nucleophilic addition of the bases used (e.g. alkoxides, hydroxide) led to adducts 29 which, in most cases, were not isolable. Instead, they readily open to give the most stable carbanions (30 or 31). This feature accounts for the formation of branched amides 33 from aliphatic a-halo ketimines and of linear imidates 32 (Nu = OR) or amides 32 (Nu = OH) from a-chloro-a-phenyl ketimines. ... 

A noteworthy example of an unexpected result in this area is the cyanation of l-chloro-3-phenyl-propan-2-one (15) with sodium or potassium cyanide in aqueous acetone which yielded the condensation product 16 in 55% yield.It is proposed that the reaction occurs via a Favorskii-type 1,3-dehydrochlorination, followed by trapping of the intermediate cyclopropanone 18 by cyanide to give cyanohydrin 19, which is not isolable. Instead, it adds across the intermediate cyclopropanone 18 to give adduct 20, which opens in the so-called normal way to afford the most stable carbanion 21, the benzylic carbanion. On protonation, the final cyclopropanecar-bonitrile 16 is formed and isolated as one stereoisomer, resulting from stereospecific addition of cyanide to the intermediate cyclopropanone. As expected, the isomeric 1-chloro-l-phenyl-propan-2-one (17) reacted in similar manner with aqueous cyanide to afford adduct 16, albeit in a lower yield. 

Single P C bond cleavage has been described. For example, phosphonium salts 2.56 are reduced to phosphines by LAH in THF under reflux the cleaved bond corresponds to reduction of the most stable carbanion [H2] (Figure 2.28). The P—C bonds of allylic phosphonates 2.57 or phosphonium salts can also be cleaved by... 

The alkaline hydrolysis of phosphonium salts gives phosphine oxides and hydrocarbons resulting from the most stable carbanions in each case. O Benzyl tris(2-pyridyl)phosphonium bromide (17) undergoes rapid alkaline hydrolysis at room temperature to give good yields of benzylbis(2-pyridyl) phosphine oxide and pyridine. ... 

Anionic polymerisation employs nucleophiles such as alkyllithiums, alkoxides or hydroxide as the initiator. Hydroxide, for example, adds to an electron-deficient alkene to form the most stable carbanion (in a Michael-type reaction). The carbanion then adds to another electron-deficient alkene to build the polymer chain. The polymerisation is terminated by, for example, protonation. 

Solution Sodium cyanide (Na CN) is a strong nucleophile. In the a,3-unsaturated ketone, there are three possible sites for nucleophilic attacks, at carbon 2, carbon 3, and carbon 4. The CI will add to the conjugated system so as to form the most stable carbanion. The stability of an anion depends upon the ability of its atoms to share the negative charge. 

Hydrolysis of the phosphonium salt residues (3) was, as ej ected, a side reaction, the group cleaved being that which formed the most stable carbanion (see Scheme 3). For example, reactions with the phosphonium salt derived from 2-bromomethylnaphthalene gave... 

In the ElcB reaction, the regiochemistry is entirely dependent on the ease of formation of the carbanion. Which hydrogen is the most acidic, and which one, when removed, gives the most stable carbanion We should briefly review carbanion stability. Because alkyl groups are electron donors, primary carbanions are the most stable, and tertiary ones the least ... 

Anionic polymerization is initiated by BuLi or another anion and proceeds via the most stable carbanion to give a regioregular polymer. The process is terminated by exposure to oxygen, water, or COj. The process requires very pure, dry monomers, and solvents. 

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