A-Hydrogen acidity

Sulphonyl a-hydrogens, acidity of 402-405 Sulphonylisoxazolines, reactions of 791 Sulphonylmercuration 172 Sulphonylmethanes, acidities of 592 Sulphonyl migration 169 Sulphonyl nitrenes 810 2-Sulphonyloxaziridines 72 Sulphonyloxiranes 169 synthesis of 639... 

The effects of heteroatoms on autoxidation reactions are reviewed and discussed in terms of six phenomena (1) the effect on reactivity of a-hydrogens in the hydroperoxide chain mechanism in terms of electron supply and withdrawal (2) the effect on a-hydrogen acidity in base-catalyzed oxidation (3) the effect on radical ion stability in base-catalyzed redox chains (4) the possibility of heteroatom hydrogen bond attack and subsequent reactions of the resulting heteroradical (5) the possibility of radical attack on higher row elements via valence expansion (6) the possibility of radical addition to electron-deficient II and III group... 

The carbonyl group plays two roles in the aldol condensation. It not only provides the unsaturated linkage at which addition (step 2) occurs, but also makes the a-hydrogens acidic enough for carbanion formation (step 1) to take place. 

In this chapter wc shall continue with our study of carbanion chemistry, with emphasis on the attachment of alkyl groups to the a-carbons of carbonyl and acyl compounds. Such alkylation reactions owe their great importance to the special nature of the carbonyl group, and in two ways. First, the carbonyl group makes a-hydrogens acidic, so that alkylation can take place. Next, the products... 

Elimination of water is particularly favored from p-chlorophenyF and (p-trifluoromethyl)phenyl selenides, whereas elimination of seleninic acid is mainly observed from methylseleno derivatives. Here, two different effects work in the same direction. The arylseleno group, more than the methylseleno group, makes the a-hydrogen acidic, and has at the same time a lower tendency to stabilize a p-caib-enium ion via the formation of a seleniranium ion. 

We have seen in Chapter VI that the strength of a hydrogen acid can be fairly well estimated from its structure, so that effects of change of structure of A and C on the rate of the acidic and basic... 

The reaction of sodium with fiuorene is of considerable interest. Fluorene possesses a hydrogen acidic enough that it might be expected to react directly with sodium to form 9-fiuorenylsodium. Fluorene is aromatic enough to be expected to form the sodium addition compound in the presence of the specific ether solvents which promote addition compound formation. 

A neutral salt is a compound of 1 eq. of an oxygen acid, with 1 eq. of a base Or a compound of 1 eq. of a metal with 1 eq. of the radical of a hydrogen acid. Thus neutral sulphate of potash contains 1 eq. of Sulphuric acid, and 1 eq. of potash while common salt is composed of 1 eq. of sodium, and 1 eq. of chlorine. 

A hydrogen acid is, in almost every case, composed of 1 eq. of hydrogen, and 1 eq. of a radical, simple or compound. Thus hydrochloric acid is composed of 1 eq. of hydrogen, and 1 eq. of chlorine and hydrocyanic acid is formed of 1 eq. of hydrogen, and 1 eq. of the compound radical cyanogen. 

With bases, sulphuric acid forms salts, which are called sulphates. In the neutral sulphates, the water of the oil of vitriol is replaced by its equivalent of a metallic oxide or, if we regard oil of vitriol as a hydrogen acid, then in the neutral sulphates the hydrogen is replaced by its equivalent of a metal. Thus we have... 

That is, the basic oxide, and the hydrogen add, give rise to water and to chloride of potassium, both neutral substances. Neither have we any fficulty in adopting the same view in the ease of a hydrogen acid with a compound radical for example, hydrocyanic acid —... 

In this form we see that, assuming sulphuric acid to be a hydrogen acid, the whole of its relations admit of being expressed as simply as those of hydrochloric acid. These two acids, and all acids analogous to either of them, come into the same category, and the same is true of their salts, all of which are considered compounds of metals with radicals, simple or compound. In this simple way we get rid of the absurdity of two different explanations for the same phenomena, and we arrive at the following general definition of an acid and of a salt ... 

This is the only view that can be taken in the case of the acids and salts of simple radicals but in the case of compound radicals, we have already seen that another view is taken. For example, oil of vitriol is considered to be, not a hydrogen acid, but an oxygen acid united to water, and is called hydrated sulphuric acid, H0,S03 and in its salts the water is supposed to be replaced by metallic oxide, MOjSOj. 

Monobasic acids are those of which an equivalent forms a neutral salt with 1 eq. of base. The general formula of a monobasic acid, considered as a hydrogen acid, is HR, and its action on a protoxide is as follows—HR-fMO = HO-J-MR so that MR is the general formula for a monobasic salt. R stands here for the radical, which with hydrogen forms the acid. 

Some groups that increase a-hydrogen acidity... 

In a letter to Berzelius of 23 February 1836 Liebig objected to Lowig s theory that oil of spiraea, C12H5O4 + H (salicyl aldehyde) is a hydrogen acid... 

PROBLEM 7.86 If you were to add the methoxide base to propane, would propane have a hydrogen acidic enough to react with the base In other words, would you predict a reaction ... 

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