Bonds carbon-oxygen double bond

Atoms can form different types of covalent bonds. In a single bond, two atoms are held together by one shared electron pair. Many compounds are also held together by multiple bonds—that is, bonds formed when two atoms share two or more pairs of electrons. If two atoms share two pairs of electrons, the covalent bond is called a double bond. Carbon-oxygen double bonds are found in molecules of carbon dioxide (CO2), and carbon-carbon double bonds are found in ethylene (C2H4) ... 

Recall that the carbon atom of carbon dioxide bears a partial positive charge because of the electron attracting power of its attached oxygens When hydroxide ion (the Lewis base) bonds to this positively polarized carbon a pair of electrons in the carbon-oxygen double bond leaves carbon to become an unshared pair of oxygen... 

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... 

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... 

In these and numerous other simple cases the keto form is more stable than the enol by some 45-60 kJ/mol (11-14 kcal/mol) The chief reason for this difference is that a carbon-oxygen double bond is stronger than a carbon-carbon double bond... 

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... 

This makes a carbon-oxygen double bond Note If you cannot see which va lence is the double valence then rotate the model first... 

Cumulative carbon-carbon-oxygen double bonds H—C—C=C=0 108(1)... 

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. 

Both the carbon-carbon and carbon-oxygen double bonds of fluoroketenes can take part in [2+2] cycloadditions, but with cyclopentadiene, only cyclo butanones are produced via concerted [2 +2 ] additions [J34] (equation 58) Cycloadditions involving the carbon-oxygen double bonds to form oxetanes are discussed on page 855 Difluoroketene is veiy short lived and difficult to intercept but has been trapped successfully by very electron rich addends to give 2 2 di fluorocyclobutanones m moderate yields [/55] (equation 59)... 

Commonly used in biology as a tissue preservative, formaldehyde, CIDO, contains a carbon -oxygen double bond. Draw the line-bond structure of formaldehyde, and indicate the hybridization of the carbon atom. 

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. 

C O , that is, the normal covalent carbon-oxygen double bond,- the estimated bond energy 6.60 v.e., then the ketones would show a resonance energy of 1.11 v.e. arising from the + —... 

It has been found that a carbon-oxygen double bond decreases the single-bond radius of the carbon atom involved Pauling and Brockway, paper to be submitted to This Journal. 

The carbon-oxygen double bond in all ketones involves resonance of the. . +. ... 

Active Substrate. If a new stereogenic center is ereated in a molecule that is already optically active, the two diastereomers are not (except fortuitously) formed in equal amounts. The reason is that the direction of attack by the reagent is determined by the groups already there. For certain additions to the carbon-oxygen double bond of ketones containing an asymmetric a carbon. Cram s rule predicts which diastereomer will predominate (diastereo-selecti vity). ... 

The addition of a negative ion to a carbon-oxygen double bond does not give a carbanion, since the negative charge resides on the oxygen. 

No rate enhancement of the enantioselective hydrogenation pathway is expected, in the manner adduced for the Pt-catalysed reaction, because the process is not one of simple H-atom addition across a carbon-oxygen double bond. 

The reaction is reversible, the reverse being the perhaps better known acid-catalysed dehydration of alcohols (p. 247). Protonation can also occur on oxygen in a carbon-oxygen double bond,... 

The carbon-oxygen double bond consists of two electrons in a a bond and two electrons in a n bond. 

The description of the carbon-oxygen double bond is analogous, but in addition to the cr-bonds there are unshared pairs of electrons on oxygen so that two excited states are possible, n-n and n-n. For n-n excitation the resultant half-vacant orbital on oxygen should possess electrophilic reactivity, and the electron rich -system should have nucleophilic characteristics. 62>... 

Furthermore, the data from Table 2 allow us to draw several valuable conclusions regarding the mechanism of hydride addition to carbon-oxygen double bonds. 

Alternative mechanisms for carbon-oxygen double bond hydrogenation and methanol synthesis are shown in Schemes 4 and 5. 

Conjugated with a carbon-oxygen double bond —C=C—C=0 136(1)... 

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