OXYGEN DERIVATIVES
I. Hydroxy derivatives - alcohols and phenols
The characteristic functional group is -OH (hydroxyl) - group. Hydroxyl groups can be found on all types of carbon chains. In the IUPAC system, the class suffix is -ol and the class prefix is hydroxy-.
1. Alcohols are hydroxy derivatives of aliphatic and alicyclic hydrocarbons.
a) Monohydric alcohols are classified as primary, secondary or tertiary alcohols depending on the position of hydroxyl functional group. Primary alcohols have the hydroxyl group attached to a carbon atom that is bonded at most to one other carbon atom. Secondary alcohols have the hydroxyl group attached to a carbon atom that is bonded to two other carbon atoms. Tertiary alcohols have the hydroxyl group attached to a carbon atom that is bonded to three other carbon atoms:
b) Dependingon thenature of the hydrocarbon residue (the group connectedto the -OH group), several types of alcohols can be distinguished:
- - If the residue derives from a saturated hydrocarbon (acyclic or cyclic), the respective alcohol is a saturated alcohol. For example:
- - If the residue has a double or triple bound, the respectivealcohol is an unsaturated alcohol. For example:
propenol (allyl alcohol) CH2 = CH-CH2-OH propynol CH ≡ C-CH2-OH
An organic compound that contains a hydroxyl group bonded to a carbon atom having a double bond and that is usually characterized by the grouping -C=C(OH)- is called enol. The enols are usually unstable, do not survive long, and change into carbonyl compounds (keto - enol tautomerism), e.g.:
- - If the residue contains an aromatic nucleus, the respective alcohol is an aromatic alcohol. Aromatic alcohols may be regarded as aryl derivatives of aliphatic alcohols. For example:
c) Alcohols are classified according tothe number ofhydroxyl groups present in it. Alcohols containing one hydroxyl group arecalled monohydric, while those containing two and three hydroxyl groups are termed dihydric and trihydric, respectively. Dihydric and trihydric alcohols come under the categoryof polyhydric alcohols.
Itis not possible to have more than one hydroxyl group attached to one andthe same carbon atom. These compounds are usually unstable and change intocarbonyl compounds.
2. Phenols are hydroxy compounds in whichthe -OH group is directly attached to an aromatic ring. The name phenol is formed from “phen” - old name of benzene and suffix –ol. The simplest phenol is hydroxybenzene, also called phenol, with formula C6H5OH.