Extra energy is needed to break the hydrogen bond before it boils. Because of hydrogen bonding in alcohol the boiling point rises up. But the boiling point of alcohols is much higher than ether of similar molecular weight. This can be explained in terms of hydrogen bonds. The boiling point of ether and alkane of similar molecular weight are not far apart. It is expected that the boiling point of substances with same or similar molecular weight should have same or similar boiling point. Here intramolecular hydrogen bonding occurs between the hydrogen atom of alcohol group and the oxygen atom of carboxylic acid group.Įffects of hydrogen bonding On boiling point For example salicylic acid has two functional groups alcohol and carboxylic acid. This occurs when two functional groups are present in same molecule and they are in such way that can attract each other to form hydrogen bond. When hydrogen bonding occurs between two partially charged atoms of same molecule that is called intramolecular hydrogen bonding. As for example, hydrogen bonding between aldehyde and water molecule has given below: 2. For such bonding one molecule should have a partially positive hydrogen as acceptor atom and another should have a partially negative or donor atom. When hydrogen bonding occurs between to atoms of different molecule then it is called intermolecular hydrogen bonding. Depending on that hydrogen bonding are of two types: Hydrogen bonding can occur between two atoms of same molecule or between two atoms of different molecule.
The partially positive charged hydrogen is then attracted by the other partially negative charged oxygen or nitrogen is known as hydrogen bond. This unequal distribution of electron pair leads to the formation of two partial dipole. For example hydrogen bond between two molecules of water is shown below:īecause of the presence of very electronegative atom like oxygen or nitrogen, the shared electron pair between oxygen and hydrogen are pulled towards the more electronegative atom. Hydrogen bonds are usually showed as dotted lines between two atoms. This is a very weak bond and strength of hydrogen bond (5-10 Kcal per bond) is much less than the strength of covalent bond. Hydrogen bond is an attractive force between a partially positive charged hydrogen and a partially negative charged atom (oxygen and nitrogen).