Deprotonation compounds

The phosphine oxide (-)-(5 )-[2-(dimethylamino)ethyl]methyloxophenylphosphorane85 was treated with butyllithium or LDA to give, via directed lithiation, the methylene-deprotonated compound regioselectively. Alkylation with bromomethylbenzene gave (S)-[l-benzyl-2-(di-methylamino)ethyl]methyloxophenylphosphorane with low diastereoselectivity (d.r. 55 45)86. 

The general expression for the concentration of the /th deprotonated compound is written as ... 

MALDI mass spectrometry has become a powerful analytical tool for both synthetic polymers and biopolymers [31], Typical MALDI spectra include mainly the monocharged molecular species by protonation in positive ion mode. More easily deprotonated compounds are usually detected in negative ion mode. Some multiply charged ions, some... 

For example, if the proton is attached to a highly electron-withdrawing atom, or an atom having an electronegative surrounding environment, the acidity is enhanced. Also, if the deprotonated compound is relatively stable, ionization is facilitated. 

Furthermore, there is extra resonance stabilization in the deprotonated compound. As the proton is ionized, the negative charge created can be shared by all the backbone carbon atoms, though the electron density will be highest at the oxygen atom. The ionized compound exists in the following forms ... 

As can be seen from the previous answers, conjugated double bonds are essential for charge delocalization, which is the essence of extra stabilization. From the structures shown, one can see that 2,4-dinitrophenol has one more conjugated double bond than p-nitrophenol. This implies that 2,4-dinitrophenol has more contributing structures than p-nitrophenol, therefore it is more acidic. The contributing structures for both deprotonated compounds are shown,... 

Any of the bases will deprotonate compounds above and to the left of them. So, to deprotonate the least acidic of these, the amine, you would choose to use butyllithium. To deprotonate the alkyne (a reaction which is commonly used to make C-C bonds) you could use BuLi, or alternatively sodium hydride (NaH). BuLi has to be handled under an inert atmosphere, while NaH, although it reacts with water, can be spooned out safely as a suspension in oil. 

When acetone was used as solvent, a significant change in reactivity occurs, as a deprotonated compound [Ir2(C=CPh)(CO)2(p-l,8-(NH)2naphtha)(P Pr3)2]... 

Recall that the equilibrium will favor the weaker acid (H2O). Accordingly, NaOH should be a sufficient base for deprotonating compound 1. This is true even if our estimate for the pk a of compound 1 was incorrect by several pk), units. 

Deprotonation of terminal acetylenes by organolithiurn compounds in organic solvents or by alkali metal amides is an extremely fast reaction, even at very... 

The large sulfur atom is a preferred reaction site in synthetic intermediates to introduce chirality into a carbon compound. Thermal equilibrations of chiral sulfoxides are slow, and parbanions with lithium or sodium as counterions on a chiral carbon atom adjacent to a sulfoxide group maintain their chirality. The benzylic proton of chiral sulfoxides is removed stereoselectively by strong bases. The largest groups prefer the anti conformation, e.g. phenyl and oxygen in the first example, phenyl and rert-butyl in the second. Deprotonation occurs at the methylene group on the least hindered site adjacent to the unshared electron pair of the sulfur atom (R.R. Fraser, 1972 F. Montanari, 1975). 

Dioxo compounds are deprotonated at C-2 and C-4 by two equivalents of strong bases (e.g. LDA or BuLi). Carbon atom C-4 of those dianions is much more nucleophilic than the less basic center C-2 (Hauser s rule C.R. Hauser, 1958 K.G. Hampton, 1965). The formation of some typical d -synthons and their pA values are given below. 

The TT-allylpalladium complexes 241 formed from the ally carbonates 240 bearing an anion-stabilizing EWG are converted into the Pd complexes of TMM (trimethylenemethane) as reactive, dipolar intermediates 242 by intramolecular deprotonation with the alkoxide anion, and undergo [3 + 2] cycloaddition to give five-membered ring compounds 244 by Michael addition to an electron-deficient double bond and subsequent intramolecular allylation of the generated carbanion 243. This cycloaddition proceeds under neutral conditions, yielding the functionalized methylenecyclopentanes 244[148], The syn-... 

As is broadly true for aromatic compounds, the a- or benzylic position of alkyl substituents exhibits special reactivity. This includes susceptibility to radical reactions, because of the. stabilization provided the radical intermediates. In indole derivatives, the reactivity of a-substituents towards nucleophilic substitution is greatly enhanced by participation of the indole nitrogen. This effect is strongest at C3, but is also present at C2 and to some extent in the carbocyclic ring. The effect is enhanced by N-deprotonation. 

Section 15 13 Thiols are compounds of the type RSH They are more acidic than alco hols and are readily deprotonated by reaction with aqueous base Thiols can be oxidized to sulfemc acids (RSOH) sulfimc acids (RSO2H) and sulfonic acids (RSO3H) The redox relationship between thiols and disul tides IS important m certain biochemical processes... 

Most of the reactions of ester enolates described so far have centered on stabilized eno lates derived from 1 3 dicarbonyl compounds such as diethyl malonate and ethyl ace toacetate Although the synthetic value of these and related stabilized enolates is clear chemists have long been interested m extending the usefulness of nonstabilized enolates derived from simple esters Consider the deprotonation of an ester as represented by the acid—base reaction... 

Indole is a neutral compound but can be protonated or deprotonated under strongly acidic or basic conditions, respectively. The piC of the conjugate acid is about —2.4 that of the neutral compound is about 16.7 (1). 

Potassium Amides. The strong, extremely soluble, stable, and nonnucleophilic potassium amide base (42), potassium hexamethyldisilazane [40949-94-8] (KHMDS), KN [Si(CH2]2, pX = 28, has been developed and commercialized. KHMDS, ideal for regio/stereospecific deprotonation and enolization reactions for less acidic compounds, is available in both THF and toluene solutions. It has demonstrated benefits for reactions involving kinetic enolates (43), alkylation and acylation (44), Wittig reaction (45), epoxidation (46), Ireland-Claison rearrangement (47,48), isomerization (49,50), Darzen reaction (51), Dieckmann condensation (52), cyclization (53), chain and ring expansion (54,55), and elimination (56). 

Further deprotonation, dehydration, and polymerization of monomers and dimers may yield ringlike stmctures of hydroxy—aluminum complexes (10). Coalescence of ring compounds into layers by further growth results in the formation of crystalline aluminum hydroxide at pH 6, the point of minimum aqueous solubiUty. 

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