Aldehydes carbon-oxygen double bond

The most obvious way to reduce an aldehyde or a ketone to an alcohol is by hydro genation of the carbon-oxygen double bond Like the hydrogenation of alkenes the reac tion IS exothermic but exceedingly slow m the absence of a catalyst Finely divided metals such as platinum palladium nickel and ruthenium are effective catalysts for the hydrogenation of aldehydes and ketones Aldehydes yield primary alcohols... 

Aldol condensation offers an effective route to a p unsaturated aldehydes and ketones These compounds have some interesting properties that result from conjugation of the carbon-carbon double bond with the carbonyl group As shown m Figure 18 6 the rr systems of the carbon-carbon and carbon-oxygen double bonds overlap to form an extended rr system that permits increased electron delocalization... 

FIGURE 18 7 Nucleophilic addition to a p unsaturated aldehydes and ketones may take place either in a 1 2 or 1 4 manner Direct addition (1 2) occurs faster than conjugate addition (1 4) but gives a less stable product The product of 1 4 addition retains the carbon-oxygen double bond which is in general stronger than a carbon-carbon double bond... 

This suggests sp hybridization at carbon and a ct + tt carbon-oxygen double bond analogous to that of aldehydes and ketones... 

The carbon-nitrogen triple bond of nitriles is much less reactive toward nucleophilic addition than is the carbon-oxygen double bond of aldehydes and ketones Strongly basic nucleophiles such as Gngnard reagents however do react with nitriles in a reaction that IS of synthetic value... 

The carbon-oxygen double bond of the carbonyl group is opened, and the hydrogen sulfite radical is added. An increase in temperature reverses the reaction more easily for ketones than for aldehydes. 

The most common reaction of aldehydes and ketones is the nucleophilic addition reaction, in which a nucleophile, Nu , adds to the electrophilic carbon of the carbonyl group. Since the nucleophile uses an electron pair to form a new bond to carbon, two electrons from the carbon-oxygen double bond must move toward the electronegative oxygen atom to give an alkoxide anion. The carbonyl carbon rehybridizes from sp2 to sp3 during the reaction, and the alkoxide ion product therefore has tetrahedral geometry. 

C—Organic bases are, in general, amines (contain N). An ether would have an oxygen single-bonded to two carbons (R groups). An aldehyde has oxygen double-bonded to a carbon at the end of a chain. Aldehydes (RCHO) and... 

The carbon-carbon double bond in vinyl monomers and the carbon-oxygen double bond in aldehydes and ketones are the two main types of linkages that undergo chain... 

Addition reactions occur in compounds having n electrons in carbon-carbon double (alkenes) or triple bonds (alkynes) or carbon-oxygen double bonds (aldehydes and ketones). Addition reactions are of two types electrophilic addition to alkenes and alkynes, and nucleophilic addition to aldehydes and ketones. In an addition reaction, the product contains all of the elements of the two reacting species. 

The carbon-oxygen double bond in aldehydes and ketones is similar and can be described in either of these two ways. If we adopt the iocalised-orbital description, formaldehyde will have two directed lone pairs in place of two of the C-H bonds in ethylene. In this case the axes of these hybrid orbitals will be in the molecular plane (unlike the oxygen lone pairs in water). Either the components of the double bond or the lone pairs can be transformed back into symmetry forms. The alternative description of the lone pairs would he one er-type along the 0-0 direction and one jr-type with axis perpendicular to the 0-0 bond hut in the molecular plane. It is the latter orbital which has the highest energy, so that an electron is removed from it in. ionisation or excitation to the lowest excited state. 

Reduction of aldehydes and ketones usually occurs by the addition of hydrogen across the carbon-oxygen double bond to yield alcohols, but reductive conversion of a carbonyl group to a methylene group requires complete removal of the oxygen, and is called deoxygenation. 

The most important functional groups that participate in chain-growth polymerizations are the carbon-carbon double bond in alkenes and the carbon-oxygen double bond in aldehydes and ketones. In such polymerizations the active species A adds to one atom of the double bond and produces a new active species on the other atom ... 

The related reaction between carbon-carbon and carbon-oxygen double bonds is just beginning to be developed. This Wittig analog provides new routes for carbonyl alkylidenation of aldehydes, ketones and members of the carboxylic acid family. 

The Grignard reagent adds to the carbon- oxygen double bond just as in the reaction with aldehydes and ketones (Sec. 15.12). The product is the magnesium salt of the carboxylic acid, from which the free acid is liberated by treatment with mineral acid. 

Catalytic hydrogenation of a,jS-unsaturated aldehydes and ketones yields saturated alcohols, addition of hydrogen occurring both at carbon-carbon and at carbon-oxygen double bonds. It is for the purpose of ultimately preparing saturated alcohols that the aldol condensation is often carried out. For example, /i-butyl alcohol and 2-ethyl-1-hexanol are both prepared on an industrial scale in this way ... 

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