Carbonyl basicity

Experiments show that both alkenes and ketones undergo acid-catalyzed reactions. Alkene reactions usually require use of a very strong acid, H2SO4 or HX, while ketone reactions occur under milder conditions. This suggests that ketones are stronger bases, and that their conjugate acids enjoy special stabilization. 

Consider protonation of 2-methylpropene (X = CH2) versus protonation of acetone (X = O). 

Experimental reactivity patterns are based on solution behavior which are influenced by interactions between solvent and reacting molecules (especially ions). Compare electrostatic potential maps of 2-methyl-2-propyl cation and dimethylhydroxy cation. Identify sites that might form strong hydrogen bonds with water. Which ion will be better stabilized by its interaction with water  

Electrostatic potential map for 2-methyl-2-propyl cation shows most positively-charged regions (in blue) and less positively-charged regions (in red). 

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Properties of the carbonyl group of ferrocenyl germyl ketones (15) were studied by IR, NMR and XRD. The carbonyl basicity was assessed based on hydrogen bonding with phenol in carbon tetrachloride solution (see also Tables 2 and 3). The spectra were compared with those of the analogous Si compounds and those of acetyl- and benzoylgermanes54. 

Relative stability of the respective parent carbocations estimated from proton-transfer equilibria, in kcal mol po values in log unit of log(KIKo) for the gas-phase carbonyl basicity are obtained by multiplying the p values of the gas-phase basicities AAG(co) by a factor of 1000/2.303 7. ... 

Table 19 Yukawa-Tsuno correlations for the stability of benzylic cations, from the carbonyl basicities in the gas and solution phases.

On the other hand, there is no simple linear relationship in the PhC (OH)R system between the Tq values and the carbonyl-basicity values AG(co>h+ of the unsubstituted derivatives (Table 18). It is likely that the effect of stabilities of the conjugate bases is more important in the carbonyl-basicity equilibria than in the C=C basicity equilibria. In fact, the Tq value obtained from the basicity of acetophenones can be correlated using (34) with the AG(cc)h+ value... 

In Part III we cover that broad category of organic compounds called the carbonyls. First we give you an overview of carbonyl basics, including structure, reactivity, and spectroscopy. Then we go into more detail on aldehydes and ketones, enols and enolates, and carboxylic acids and their derivatives. 

For similar compounds, the order of carbonyl basicity is face-bridging CO > edge-bridging CO > terminal CO (Section II). These trends in carbonyl basicity reflect the degree of delocalization of electron density onto the CO ligand. Carbonyl stretching frequencies provide a guide to the extent... 

Numerous papers have appeared recently about Rh dispersed on oxide systems both via salt impregnation ° " ° ° " and via heterogenization of Rh carbonyls [basically Rh6(CO)i6 and Rh4(CO)i2] In the follow-... 

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