Alcohol carbonyl nucleophilic addition reactions

Each of the following substances can be prepared by a nucleophilic addition reaction between an aldehyde or ketone and a nucleophile. Identify the reactants from which each was prepared. If the substance is an acetal, identify the carbonyl compound and the alcohol if it is an imine, identify the carbonyl compound and the amine and so forth. 

Nucleophilic addition reaction (Section 19.4) A reaction in which a nucleophile adds to the electrophilic carbonyl group of a ketone or aldehyde to give an alcohol. 

The carbonyl group of aldehydes and ketones may be reduced to an alcohol group by a nucleophilic addition reaction that appears to involve hydride as the nucleophile. The reduction of the carbonyl group may be interpreted as nucleophilic attack of hydride onto the carbonyl carbon, followed by abstraction of a proton from solvent, usually water. 

Just as addition of a Grignard reagent to an aldehyde or ketone yields an alcohol, so does addition of hydride ion, H (Section 17.4). Although the details of carbonyl-group reductions arc complex, LiAll-14 and N aBH4 act as if they were donors of hydride ion in a nucleophilic addition reaction (Figure 19.7).. Addition of water or aqueous acid after the hydride addition step protonates the tetrahedral alkoxide intermediate and gives the alcohol product. 

Aldehydes can undergo reactions with alcohols under acidic conditions. The product of this nucleophilic addition reaction is called hemiacetal. Hemiacetal is formed by the nucleophilic addition of alcohol to the carbonyl carbon. Hemiacetal can react with one more mole of alcohol to form an acetal. 

Nucleophilic addition reactions are mainly of technical interest in the context of further reactions at C=0 groups present in aldehydes or ketones. The electronic nature of a carbonyl group is characterized by the greater electronegativity of the oxygen atom compared to the carbon atom. Thus, the carbon atom is the preferred place of nucleophilic attack, that is, of reaction with an electron-rich reagent. Scheme 2.2.12 gives as an example the technically important cyanohydrin reaction. Other important nucleophilic additions are the reaction of carbonyl compounds with alcohols and water, bisulfite and metal hydrides. 

A nucleophilic addition reaction to an aldehyde or ketone. The nucleophile approaches the carbonyl group from an angle of approximately 75° to the plane ofthesp orbitals, the carbonyl carbon rehybridizes from sp to sp, and an alkoxide ion is formed. Protonation by addition of acid then gives an alcohol. 

The nucleophilic addition reaction is the most common general reaction type for aldehydes and ketones. Many different kinds of products can be prepared by nucleophilic additions. Aldehydes and ketones are reduced by NaBH4 or UAIH4 to yield primary and secondary alcohols, respectively. Addition of Grignard reagents to aldehydes and ketones also gives alcohols (secondary and tertiary, respectively), and addition of HCN delds cyanohydrins. Primary amines add to carbonyl compounds yielding imines, or Schiff bases, and secondary... 

Many of the most interesting and useful reactions of aldehydes and ketones involve trans formation of the initial product of nucleophilic addition to some other substance under the reaction conditions An example is the reaction of aldehydes with alcohols under con ditions of acid catalysis The expected product of nucleophilic addition of the alcohol to the carbonyl group is called a hemiacetal The product actually isolated however cor responds to reaction of one mole of the aldehyde with two moles of alcohol to give gem mal diethers known as acetals... 

---