Water as a base

On the other hand, the catalytic effect of water as a base is stronger at the 2-position. This result can be explained if one assumes that the proton is transferred by a water molecule which solvates the O- group in the reagent 3-sulfo-l-naphth-oxide dianion. As can be seen in 12.148, the base is already in the optimum position when the stage of the o-complex is reached. This explanation is supported by a comparison of the entropies of activation for reaction at the 2- and 4-positions. 

Nucleophilic reactions with water 77 Reactions with water as a base 87 Reactions of nucleophiles other than water 90 Reactivity, selectivity, and transition state structure 105 Hard and soft nucleophiles 110 Summary and conclusions 112 Acknowledgments 114 References 114... 

Reactions of carbocations with water as a base removing a [3-proton to form an alkene or aromatic product have been less studied than nucleophilic reactions with water. Nevertheless, the correlations included in Fig. 1 (p. 43) represent a considerable range of measurements and these can be further extended to include loss of a proton a to a carbonyl group.116 Indeed, if one places these reactions in the wider context of proton transfers, it can be claimed that they constitute the largest of all groups of reactions for which correlations of rate and equilibrium constants have been studied.116,244,245... 

Acidity constant (/fE) (Section 4.2) An equilibrium constant for the reaction of an acid with water as a base used as a measure of the strength of an acid. For a general acid, HA, the equation for Ka is... 

On the other hand, the catalytic effect of water as a base is stronger at the... 

It seems surprising at first to refer to water as a base. This is probably due to the fact that we have always considered the hydrogen ion concentration in water identical with the hydroxonium concentration, and because the dissociation constant of water as well as of other solvents is exceedingly small. Alcohol is about five hundred times weaker than water as a base. Were we to add water to an alcoholic solution of an acid, the water would act qualitatively as does ammonia when it is added to an aqueous acid solution ... 

Sulfide ion, present in many ores, can react with water as a base (it cannot possibly be an acid because it contains no hydrogen) ... 

With two curved arrows, deprotonate the oxonium ion using water as a base. 

Water as a Base Calcium hydride, CaH2, reacts vigorously with water to produce hydrogen gas. Water acts as a base in this reaction because it is in a very strong acid. 

Since fCj,(HP04 ) is greater than fC3(HP04 ), the HP04 ion exhibits a greater tendency to react with water as a base than as an acid. Therefore, a solution of Na2HP04 is basic. 

NaOCHjCHa. White solid (Na in EtOH). Decomposed by water, gives ethers with alkyl halides reacts with esters. Used in organic syntheses particularly as a base to remove protons adjacent to carbonyl or sulphonyl groups to give resonance-stabilized anions. 

In the Br0nsted-Lowry view an acid doesn t dissociate in water it transfers a pro ton to water Water acts as a base... 

Step 3 in Figure 5 6 shows water as the base which ab stracts a proton from the car bocation Other Bronsted bases present in the reaction mixture that can function in the same way include tert butyl alcohol and hydrogen sulfate ion... 

Step 3 This step is a fast acid base reaction that follows the nucleophilic substitution Water acts as a base to remove a proton from the alkyloxonium ion to give the observed product of the reaction tert butyl alcohol... 

The proton transfer equilibrium that interconverts a carbonyl compound and its enol can be catalyzed by bases as well as by acids Figure 18 3 illustrates the roles of hydroxide ion and water m a base catalyzed enolization As m acid catalyzed enolization protons are transferred sequentially rather than m a single step First (step 1) the base abstracts a proton from the a carbon atom to yield an anion This anion is a resonance stabilized species Its negative charge is shared by the a carbon atom and the carbonyl oxygen... 

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