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Alcohols contain an –OH group attached to a saturated (sp 3 ) carbon atom. Phenols contain an –OH group attached to one of the carbons of a benzene ring (sp 2 ). Ethers contain an –O- atom bonded to two carbon atoms which can be either aliphatic or aromatic.
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Alcohols contain an –OH group attached to a saturated (sp3) carbon atom.
Alcohols are classified as primary (1°), secondary (2°), or tertiary (3°).
Simple alcohols are usually referred to by their common names which consist of the alkyl group name followed by a space and the word alcohol.
The difference in boiling points between hydrocarbons and the corresponding alcohols decreases as the chain length of the hydrocarbon increases.
Diols and triols have especially high boiling points compared to alkanes of similar size due to more extensive hydrogen bonding.
Alcohols are usually considered to be neutral compounds. Water solutions of alcohols have a pH of 7, the same as for water itself.
Alcohols can be dehydrated when heated with catalytic amounts of a strong acid. The reaction is called an intramolecular dehydration. An Hatom is lost from one carbon and an –OH group from an adjacent carbon:
Dehydration of secondary and tertiary alcohols may follow a more complicated course than that for primary alcohols.
In the dehydration of 2-butanol previously shown, the predominate 2-butene product formed is a mixture of cis and trans isomers. The trans isomer predominates because it is more stable than the cis isomer.
The weakest bonds in an alcohol are the O-H bond and the adjacent C-H bond. These bonds only are oxidized during selective oxidations.
The reaction does not stop at the aldehyde when permanganate or dichromate are used as the oxidizing agent. Aldehydes can be produced using milder oxidizing agents such as pyridinium chlorochromate (PCC).
Permanganate and dichromate can be used for simple chemical diagnostic tests for primary and secondary alcohols.
Phenols contain an –OH group bonded to one of the sp2 carbon atoms of a benzene ring. The phenol family includes the parent compound, phenol, as well as a wide variety of other compounds having additional substituents attached to the phenol ring.
The O-H bond in phenols is more polar than that in alcohols because the benzene ring has an electron withdrawing effect which further polarizes the O-H bond.
Phenols do not undergo dehydration, because that would form a triple bond within the benzene ring destroying its aromatic nature.
Ethers contain an oxygen atom bonded to two different carbon atoms. The carbon atoms can be either aliphatic or aromatic carbons.
The boiling point of dimethyl ether is higher than that of the corresponding alkane, propane, because the C-O-C bond is bent and the two carbon-oxygen bonds are polar.
When a primary alcohol is dehydrated, it produces an ether as well as an alkene:
• Thiols are easily oxidized to disulfides by many oxidizing agents:
The reactions to form disulfides and insoluble heavy metal salts are of physiological importance.