Carbonyl groups reactivity

The mechanisms of the Fischer esterification and the reactions of alcohols with acyl chlorides and acid anhydrides will be discussed m detail m Chapters 19 and 20 after some fundamental principles of carbonyl group reactivity have been developed For the present it is sufficient to point out that most of the reactions that convert alcohols to esters leave the C—O bond of the alcohol intact... 

The carbonyl group reactivities in thiophenes and benzenes are very similar, as shown by the similar rates of alkaline hydrolysis of esters and by the great similarity of the thiophenealdehydes to benzaldehyde in numerous carbonyl group reactions. This has been ascribed to the counteracting —I- -M effects of the thienyl group in this kind of reactions. ... 

The DiTOX system has been shown to induce high levels of stereoselectivity for a range of reaction types based on carbonyl group reactivity. 

One problem with the reactions of C6H5N with organic carbonyl containing molecules was that the carbonyl group reactivity scale could not be extended past the simple esters HC02CH3 and CH3C02CH3 because their rates were already at the lower limit of determination in the FA. To get around this limitation, we examined other hypovalent species such as... 

An tdternative mcchtinism involving an epoxide imermediate appears to operate in some cases (eq. 2.22) 120], When the carbonyl group reactivity is effectively decreased by sicric hindrance, a reductive enoli/ation is observed (cq. 2. 2,7) 1121 ]. 

Seebach has reviewed methods of reactivity umpolung, the principle whereby the polarity of a reactive grouping may be reversed to give a complementary set of reactions (see discussion above). A majority of the applications of this principle still refer to carbonyl group reactivity, along the lines shown in (32). 

Acid chlorides, on the other hand, are more reactive toward addition than ketones since the inductive effect of the chlorine substituent increases carbonyl group reactivity and more than compensates for the small tt-donor effect of the chlorine. 

The aldol condensation highlights the two most important facets of carbonyl group reactivity enolate formation and attack of nucleophiles at a carbonyl carbon. The base (hydroxide) is not strong enough to convert all of the starting aldehyde into the corresponding enolate ion, but it does bring about an equilibrium between the aldehyde and a small... 

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