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Secondary Alcohol

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Specific groups of atoms in an organic molecule can determine its physical and chemical properties. These groups are referred to as functional groups. Organic compounds that contain the functional group -OH, the hydroxyl group is called alcohols.

Alcohols are important commercially and include uses as solvents, drugs and disinfectants.

Definition

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"Secondary alcohol is defined as the hydroxyl bearing carbon atom is bonded to two other carbon atoms."

In terms of hydrogen, secondary alcohol is defined as the carbon with the OH group, there is only one hydrogen.

Structure

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Secondary alcohols are obtained by treating a Grignard reagent with aldehydes other than formaldehyde. The secondary alcohol has two carbons attached to the hydroxyl group.

 Secondary Alcohol

The structure of some of the secondary alcohols is given below. 

Secondary Alcohol Examples

Oxidation

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Secondary alcohols are oxidized to ketones by chromic acid.

R2CHOH $\overset{Cr_{2}O_{7}}{\rightarrow}$ R2C=O

Ketones resist the further oxidation but under vigorous conditions they are oxidized to a mixture of carboxylic acids. For example,

Oxidation of Secondary Alcohol

Thus the ketones the first stage oxidation products of secondary alcohols, contain the same number of carbon atoms as original alcohol, but carboxylic acids contain fewer carbon atoms than the parent alcohol.

Dehydration

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The dehydration of alcohols provides examples of all elimination reactions. Dehydration of secondary alcohols under acidic conditions follows the E1 pathway. Dehydration is facilitated by acid because protonation of the hydroxyl group effectively converts this leaving group from hydroxide ion to water.

Because H3O+ is a stronger acid than H2O the conjugate base of the former is a better leaving group than that of the later. Whenever a relatively stable carbocation is produced by dehydration of a protonated alcohol.

Dehydration of Secondary Alcohol

Dehydration of secondary alcohol gives an alkene which is most highly substituted (Saytzeff rule). Further if the major product is also capable of showing cis-trans isomerism, the the trans isomer always predominates.

Examples

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Some of the examples of secondary alcohols are listed below.
  1. Propan-2-ol
  2. Butan-2-ol
  3. Pentan3-ol
  4. Cyclohexanol
  5. Cyclopentanol
  6. Cyclobutanol