Carbonyl carbon/oxygen double bonds

In the above examples the polymerisation takes place by the opening of a carbon-carbon double bond. It is also possible to open carbonyl carbon-oxygen double bonds and nitrile carbon-nitrogen triple bonds. An example of the former is the polymerisation of formaldehyde to give polyformaldehyde (also known as polyoxymethylene and polyacetal) (Figure 2.3). 

The peptide bond between the carbon and nitrogen exhibits partial doublebond character due to the closeness of the carbonyl carbon-oxygen double-bond allowing the resonance structures in Fig. lb to exist. Because of this, the C-N... 

The titanium methylidene interacts with the carbonyl carbon-oxygen double bond in a sequence that is believed to resemble the metathesis process. With the metallacycle (4), a titanium oxametallacycle is believed to be formed, which then decomposes to generate the new carlxm-carbon double bond and a titanium-oxygen product. The driving force for the reaction has been attributed to the oxophilicity of titanium (equation 18). ... 

The carbon-oxygen double bond and, to a lesser degree, the carbon-carbon double bond are found in many organic compounds. The carbonyl (carbon-oxygen double bond) has a very sharp and intense band around 1,700 cm-1. 

To understand the effect of a carbonyl group attached directly to the ring consider Its polarization The electrons m the carbon-oxygen double bond are drawn toward oxy gen and away from carbon leaving the carbon attached to the nng with a partial posi tive charge Using benzaldehyde as an example... 

Neither sodium borohydride nor lithium aluminum hydride reduces isolated carbon-carbon double bonds This makes possible the selective reduction of a carbonyl group m a molecule that contains both carbon-carbon and carbon-oxygen double bonds... 

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... 

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 carbon-oxygen double bond of a carbonyl group is similar in many respects to the carbon-carbon double bond of an alkene. The carbonyl carbon atom is s/ 2-hybridized and forms three valence electron remains in a carbon p orbital and forms a tt bond to oxygen by overlap with an oxygen p orbital. The oxygen atom also has two nonbonding pairs of electrons, w hich occupy its remaining two orbitals. 

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. 

When a carbonyl group is bonded to a substituent group that can potentially depart as a Lewis base, addition of a nucleophile to the carbonyl carbon leads to elimination and the regeneration of a carbon-oxygen double bond. Esters undergo hydrolysis with alkali hydroxides to form alkali metal salts of carboxylic acids and alcohols. Amides undergo hydrolysis with mineral acids to form carboxylic acids and amine salts. Carbamates undergo alkaline hydrolysis to form amines, carbon dioxide, and alcohols. 

Although the high reactivity of metal-chalcogen double bonds of isolated heavy ketones is somewhat suppressed by the steric protecting groups, Tbt-substituted heavy ketones allow the examination of their intermolecular reactions with relatively small substrates. The most important feature in the reactivity of a carbonyl functionality is reversibility in reactions across its carbon-oxygen double bond (addition-elimination mechanism via a tetracoordinate intermediate) as is observed, for example, in reactions with water and alcohols. The energetic basis... 

Aromatic dicarboximides behave in a different way on irradiation with aikenes. Instead of cycloaddition to the carbon-oxygen double bond, the overall reaction gives a product in which the alkene is inserted between the nitrogen atom and one of the carbonyl groups (4.78). The reaction is stereospecific, and the mechanism may... 

When the carbonyl group bears as one substituent a group that can potentially depart as a Lewis base, the most common result of addition of a nucleophile to the carbonyl carbon is elimination to regenerate a carbon-oxygen double bond... 

Multiple bonds to an element count as multiple single bonds to that element. That is, the carbon-oxygen double bond of carbonyl group (C=0) is oxidatively equivalent to a carbon atom with two single bonds to oxygen originating from it (-O-C-O-). 

Carbonyl compounds will be taken in this chapter to mean any organic compound that contains at least one carbon-oxygen double bond where we limit the substitution to only saturated aliphatic, saturated alicyclic and aryl hydrocarbyl groups. Carbonyl compounds with a variety of unsaturated substituents have earlier been discussed within the context of enones4. Non-hydrocarbyl substituents, X , may be directly attached to the carbonyl and elsewhere in the molecule. The first type of species, RCOX, is alternatively identified as acyl derivatives such as carboxylic acids and their esters, halides and amides and have already been discussed in a recent Patai thermochemistry... 

Carbonyls, compounds with carbon-oxygen double bonds, also absorb light in the UV region. For instance, acetone has a broad absorption peak at 280 nm. In this example, the electron can be excited from an unshared pair into a nonbonding -orbital, (ji... 

---