Question

Answer the following

(1) Draw chain and ring structures of organic compound having six carbon atoms in them.

(2) Which organic compounds are named as Alkanol in IUPAC system?

(3) Explain : What do you understand by substitution reaction?

(4) Which organic compounds readily undergo addition reactions? Why?

(5) State two examples of (organic) compound having covalent bond and two examples having ionic bond.

(6) State and explain how alkanes are further classified.

(7) What are alkynes? Name the first member of alkyne family.

Answer 1

1. (a) Chain structure:

b) Ring structure:

2. The alcohols are named as alkanols in IUPAC method. In naming the alcohols by IUPAC method, the last ‘e’ of the parent alkane is replaced by ‘ol’ to indicate the presence of OH group.

3. Substitution reaction: The reaction in which one atom of any other element substitutes or replaces one of the hydrogen atoms of a given hydrocarbon is known as substitution reaction. Substitution reaction does not add any atom to the hydrocarbon because it takes place only in saturated hydrocarbons (containing only single bonds). For example, in substitution reaction of methane with chlorine, methane reacts with chlorine in the presence of sunlight to form methyl chloride and hydrogen chloride.

4. Unsaturated hydrocarbons that include all the alkenes and alkynes, readily undergo addition reactions. Unsaturated compounds undergo addition reactions due to the presence of pi bond.

In unsaturated compounds, the electron charge cloud of the pi bond is placed above and below the plane of the bonding atom, which results in the easy availability of the electrons. However, in saturated compounds, two atoms are bonded by the sigma bond that is formed at the internuclear axis in between the two bonded atoms. This sigma bond is very strong as compared to pi bond. Hence, pi electrons provide a better site for the attacking species.

5. (i) Hydrocarbons such as methane and ethane have covalent bonds.

(ii) The compounds such as NaCl and KMnO₄ have ionic bonds.

6. Alkanes are saturated hydrocarbons with single bonds. Alkanes are further classified as follows:

• Cyclic alkanes: These are the alkanes in which the carbon atoms combine with each other to form a ring−like structure. For example, cyclohexane

• Straight chain alkanes: The alkanes in which all the carbon atoms are attached by covalent bonds in a continuous chain are called straight chain alkanes or normal alkanes. For example,

CH₃ − CH₂ − CH₂ − CH₃ is normal butane or n−butane.

• Branched chain alkanes: The alkanes in which all the carbon atoms are not in a continuous chain and some of them are linked to other carbon atoms to make the branch−like structure are called branched chain alkanes. For example, isobutane.

7. Alkynes: The hydrocarbons containing triple bonds between carbon atoms are called alkynes. Thegeneral formula of alkynes is C_nH_2n. The first member of alkyne family is ethyne or acetylene.