Question

(a) Write molecular formula of benzene.
(b) Draw structure formula of benzene and write number of triple bonds present in it.
(c) Which is ethane in the following? Write a number of co-operative bonds present in it.
(i) \[{C_2}{H_2}\]
(ii) \[{C_2}{H_4}\]
(iii) \[{C_2}{H_6}\]

Answer 1

Hint: Try to recall that the molecular formula describes the exact number of atoms in a molecule and in the molecular formula of benzene, there are 6 carbon atoms and it forms a ring -like structure. Also, ethane is the second member of alkane series. Now, by using this you can easily answer the given question.

Complete step by step solution:
- It is known to you that there are 6 carbon atoms and 6 hydrogen atoms in the structure of benzene. So, the molecular formula of benzene is \[{C_6}{H_6}\].
- All six carbon atoms of benzene are \[s{p^2}\] hybridized and each carbon atom is arranged in a six membered ring and is bonded to only one hydrogen atom. It undergoes electrophilic substitution reactions easily.
- Benzene has delocalised pi electron clouds.
- Since, the molecular formula of benzene is \[{C_6}{H_6}\], it seemed clear that the molecule must be highly unsaturated.
- It is a highly unsaturated compound as it has four degrees of saturation. It has four double bonds and zero triple bonds in it. So, the structural formula of benzene is:
- We know that ethane is the second member of the alkane series and it has two carbon atoms and six hydrogen atoms. So, the molecular formula of ethane is \[{C_2}{H_6}\].
- There are seven sigma bonds in ethane so the number of co-operative bonds present in it is 7.

Note:
- It should be remembered that benzene is an aromatic compound and when ethyne gas is passed through a red hot tube then benzene is formed.
- Also, you should remember that benzene can be used as a non-polar solvent for large aromatic/organic compounds or organometallic complexes.