Protonated carbon atoms

This is a hydrolysis reaction where a hydroxide anion adds to a nitrile. As illustrated below, the hydroxide anion adds to the nitrile carbon atom. Proton... 

Proton b is on a carbon atom bonded to oxygen it should absorb around 8 3 to 8 4. Protons a are less deshielded by the oxygen, probably around 81 to 8 2. Protons c are on a carbon bonded to a carbonyl group they should absorb around 52.1 to 52.5. Protons d, one carbon removed from a carbonyl, will be deshielded less than protons c and also less than protons a, which are next to a more strongly deshielded carbon atom. Protons d should absorb around 51.0. 

When considering the proton NMR spectra of ketones and aldehydes, we are interested primarily in the protons bonded to the carbonyl group (aldehyde protons) and the protons bonded to the adjacent carbon atom (the a carbon atom). Aldehyde protons normally appear at chemical shifts between 8 9 and 8 10. The aldehyde proton s absorption may be split (/ = 1 to 5 Hz) if there are protons on the a carbon atom. Protons on the a carbon atom of a ketone or aldehyde usually appear at a chemical shift between 8 2.1 and 8 2.4 if there are no other electron-withdrawing groups nearby. Methyl ketones are characterized by a singlet at about 8 2.1. 

Reduction of benzophenone in liquid ammonia gives both alcohol and pinacol products. The ketyl intermediate in this reaction is stabilized by phenyl substituents, and competitive carbon atom protonation and dimerization generate alkoxide salts that remain in solution until hydrolyzed prior to product isolation. Benzophenone (diphenyl ketone) forms a deep blue ketyl which is stable in solvents that lack acidic hydrogens such as hydrocarbons and ethers. It is widely used as an indicator of oxidizing or acidic impurities during the purification of such solvents. 

As carbon atoms with sp and sp2 configurations are more electronegative than sp3 carbon atoms, proton abstraction by bases from acetylenic, ethylenic, or aromatic CH bonds occurs more readily than from saturated aliphatic CH bonds. 

The mechanism proceeds by nucleophilic attack of the nitrogen lone pair at the electron-deficient carbonyl carbon atom protonation and elimination of water complete the reaction (Scheme 6.10). 

A calculation (see p. 163) indicates that although acrolein has a larger coefficient in the LUMO at the -position than at the carbonyl carbon atom, protonated acrolein has the larger coefficient at the carbonyl carbon atom. Thus, the more electrophilic the carbonyl group, the more likely it is that all nucleophiles will attack at the carbonyl carbon atom. In contrast to its behaviour with acrylic ester, ammonia does react86 with acryloyl chloride (101), which has a very electrophilic carbonyl group, at the carbonyl carbon atom. 

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