Physical and Chemical Properties of Alcohols

This topic educates about the physical and chemical properties of alcohols. Alcohols are organic compounds in which a hydrogen atom of an aliphatic carbon is replaced with a hydroxyl group. Thus an alcohol molecule consists of two parts; one containing the alkyl group and the other containing hydroxyl group.They have a sweet odor. They exhibit a unique set of physical and chemical properties. These physical and chemical properties of alcohols are mainly due to the presence of hydroxyl group. Some prominent physical and chemical properties of alcohols are given below:

Physical properties of alcohol:

  • The boiling point of alcohols:

    Alcohols generally have higher boiling points in comparison to other hydrocarbons having equal molecular masses. This is due to the presence of intermolecular hydrogen bonding between hydroxyl groups of alcohol molecules. In general, the boiling point of alcohols increases with increase in the number of carbon atoms in the aliphatic carbon chain. On the other hand, the boiling point decreases with increase in branching in aliphatic carbon chains the Van der Waals forces decreases with a decrease in surface area. Thus primary alcohols have a higher boiling point.

Solubility of Alcohols

  • The solubility of alcohol in water is governed by the hydroxyl group present. The hydroxyl group in alcohol is involved in the formation of intermolecular hydrogen bonding. Thus, hydrogen bonds are formed between water and alcohol molecules which make alcohol soluble in water. However, the alkyl group attached to the hydroxyl group is hydrophobic in nature. Thus, the solubility of alcohol decreases with the increase in the size of the alkyl group.

The Acidity of alcohols

  • Alcohols react with active metals such as sodium, potassium etc. to form the corresponding alkoxide. These reactions of alcohols indicate their acidic nature. The acidic nature of alcohol is due to the polarity of –OH bond. The acidity of alcohols decreases when an electron donating group is attached to the hydroxyl group as it increases the electron density on the oxygen atom. Thus, primary alcohols are generally more acidic than secondary and tertiary alcohols. Due to the presence of unshared electrons on the oxygen atom, alcohols act as Bronsted bases too.

Chemical properties of alcohols:

Alcohols exhibit a wide range of spontaneous chemical reactions due to the cleavage of C-O bond and O-H bond. Some prominent chemical reactions of alcohols are:

Oxidation of alcohol

  • Alcohols undergo oxidation in the presence of an oxidizing agent to produce aldehydes and ketones which upon further oxidation give carboxylic acids.

chemical properties of alcohols

Alcohols: Physical and Chemical Properties

Dehydration of alcohol

  • Upon treatment with protic acids, alcohols undergo dehydration (removal of a molecule of water) to form alkenes. Dehydration of alcohol

chemical properties of alcohols

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Practise This Question

Which of the following statements is correct regarding case of dehydration in alcohols  [CPMT 1980, 85; MP PMT 2001; BHU 2002]

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