Now that we know quite a bit about alcohols and ethers and phenols, how many of you know about the physical properties of alcohol? You may ask why it is important? Well, we need to the know the physical properties of these organic compounds to be able to use them for our benefit. Imagine how would it be if alcohol weren’t miscible in water?
Therefore, in this chapter, we will look at the concept of physical properties of alcohols, phenols and ethers, one after the other. By the end of this chapter, you will be in a better position to know about the basic properties of these compounds.
Physical Properties of Alcohol
Alcohols are organic compounds where a hydroxyl group replaces the hydrogen atom of an aliphatic carbon. Thus, an alcohol molecule consists of two parts. The first one has the alkyl group and the other has the hydroxyl group.
They have a sweet odour and exhibit a unique set of physical and chemical properties. The presence of hydroxyl group is the main factor in determining the properties of alcohol. Let us now look at some of the prominent physical properties of alcohol.
Browse more Topics under Alcohols Phenols And Ethers
- Chemical Reactions of Alcohols, Phenols & Ethers
- Chemical Reactions of Ethers
- Introduction and Classification of Alcohols, Phenols & Ethers
- Preparation of Alcohols
- Physical Properties of Ethers
- Preparation of Ethers
- Preparation of Phenols
- Some Commercially Important Alcohols
1) The Boiling Point of Alcohols
Alcohols generally have higher boiling points as compared to other hydrocarbons having equal molecular masses. We can attribute this to the presence of intermolecular hydrogen bonding between hydroxyl groups of alcohol molecules. In addition to this, the boiling point of alcohols increases with increase in the number of carbon atoms in the aliphatic carbon chain.
2) The Solubility of Alcohols
The hydroxyl group decides the solubility of alcohol in water. The hydroxyl group in alcohol takes part in the formation of intermolecular hydrogen bonding. Thus, hydrogen bonds between water and alcohol molecules make alcohol soluble in water. The solubility of alcohol decreases with the increase in the size of the alkyl group because of the hydrophobic nature of the alkyl group.
3) The Acidity of Alcohols
Alcohols react with active metals such as sodium, potassium etc. and form the corresponding alkoxide. These reactions of alcohols are indicative of 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. This is due to the fact that it increases the electron density of the oxygen atom. Thus, primary alcohols are generally more acidic.
Phenols and Their Physical Properties
Phenols are the organic compounds that have a benzene ring bonded to a hydroxyl group. We also name them as carbolic acids. They exhibit unique physical and chemical properties that are mainly due to the presence of a hydroxyl group. Let us discuss some of the important physical properties of phenols in the section below.
1) The Boiling Point of Phenols
Phenols generally have higher boiling points in comparison to other hydrocarbons with equal molecular masses. The main reason behind this is the presence of intermolecular hydrogen bonding between hydroxyl groups of phenol molecules. In general, the boiling point of phenols increases with increase in the number of carbon atoms.
2) The Solubility of Phenols
The hydroxyl group determines the solubility of phenol in water. The hydroxyl group in phenol is responsible for the formation of intermolecular hydrogen bonding. Thus, hydrogen bonds form between water and phenol molecules which make phenol soluble in water.
3) The Acidity of Phenols
Phenols react with active metals such as sodium, potassium etc. and give the corresponding phenoxide. These reactions of phenols indicate its acidic nature. In phenol, the sp2 hybridized carbon of the benzene ring attached directly to the hydroxyl group acts as an electron withdrawing group.
Thus, it decreases the electron density of oxygen. Due to the delocalization of negative charge in the benzene ring, phenoxide ions are more stable than alkoxide ions. Therefore, we can say phenols are more acidic than alcohols.
Ethers and Their Physical Properties
Ether is an organic compound that has an oxygen atom bonded to two similar or different alkyl or aryl groups. The general formula for ethers can be R-O-R, R-O-Ar or Ar-O-Ar. Here, the term R points towards an alkyl group and Ar stands for an aryl group. Ethers exhibit a wide range of physical and chemical properties. physical properties of ethers are:
- An ether molecule has a net dipole moment. This dipole moment is mainly due to the polarity of C-O bonds.
- The boiling point of ethers is comparable to the alkanes. However, it is much lower than that of alcohols of comparable molecular mass despite the polarity of the C-O bond. The miscibility of ethers with water is on the same lines as that of alcohols.
- Ether molecules are miscible in water.
Solved Example for You
Q: Why are ethers soluble or miscible in water?
Ans: Like alcohols, the oxygen atom of ethers is capable of forming hydrogen bonds with a water molecule. Therefore, ethers are soluble in water.