Carbon-oxygen electronegativity

I. . negative charge near the highly electronegative oxygen atom. The carbon-oxygen electronegativity differ-... 

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. 

The dipole moment of a molecule is the vectorial sum of the individual dipoles within it. Bond dipoles are usually represented using the symbol /x and are expressed in units of Debye. The dipoles result from charge separation. The carbon-carbon bond in ethane, H3C—CH3 is symmetrical and not expected to have a dipole moment. The carbon-oxygen bond of methanol (CH3OH), on the other hand, links two elements of differing electronegativity and is expected to have a significant molecular dipole. Methanol s molecular dipole is 1.7 whereas, for ethane, it is 0. 

Oxygen is considerably more electronegative than either sulfur or carbon. Each sulfur-oxygen and carbon-oxygen bond should be polar with a net negative charge resides on the oxygen. 

Carbon-oxygen double bonds are polarized because of the high electronegativity of oxygen relative to carbon. Thus, all types of carbonyl compounds have substantial dipole moments, as listed in Tabic 2. 

Hence, the elctron density is somewhat reduced at the hydrogen attached to the teriary carbon. Oxygen, being more electronegative than carbon or hydrogen, will... 

The electronegative oxygen polarizes the carbon-oxygen bond, rendering the carbon electron deficient and hence subject to nucleophilic substitution. 

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