Ch-13. Hydrocarbons (Exercise) Page 396

Question 1:	How do you account for the formation of ethane during chlorination of methane?
Answer :	Chlorination of methane proceeds via a free radical chain mechanism. The whole reaction takes place in the given three steps. Step 1: Initiation: The reaction begins with the homolytic cleavage of Cl – Cl bond as: Step 2: Propagation: In the second step, chlorine free radicals attack methane molecules and break down the C–H bond to generate methyl radicals as: These methyl radicals react with other chlorine free radicals to form methyl chloride along with the liberation of a chlorine free radical. Hence, methyl free radicals and chlorine free radicals set up a chain reaction. While HCl and CH3Cl are the major products formed, other higher halogenated compounds are also formed as: Step 3: Termination: Formation of ethane is a result of the termination of chain reactions taking place as a result of the consumption of reactants as: Hence, by this process, ethane is obtained as a by-product of chlorination of methane.
Question 2:	Write IUPAC names of the following compounds: a. b. c. d. e. f. g.
Answer :	(a) IUPAC name: 2-Methylbut-2-ene (b) IUPAC name: Pen-1-ene-3-yne (c)  can be written as: IUPAC name: 1, 3-Butadiene or Buta-1,3-diene (d) IUPAC name: 4-Phenyl but-1-ene (e) IUPAC name: 2-Methyl phenol (f) IUPAC name: 5-(2-Methylpropyl)-decane (g) IUPAC name: 4-Ethyldeca-1, 5, 8-triene
Question 3:	For the following compounds, write structural formulas and IUPAC names for all possible isomers having the number of double or triple bond as indicated: (a) C4H8 (one double bond) (b) C5H8 (one triple bond)
Answer :	(a) The following structural isomers are possible for C4H8 with one double bond: The IUPAC name of Compound (I) is But-1-ene, Compound (II) is But-2-ene, and Compound (III) is 2-Methylprop-1-ene. (b) The following structural isomers are possible for C5C8 with one triple bond: The IUPAC name of Compound (I) is Pent-1-yne, Compound (II) is Pent-2-yne, and Compound (III) is 3-Methylbut-1-ene.
Question 4:	Write IUPAC names of the products obtained by the ozonolysis of the following compounds: (i) Pent-2-ene (ii) 3,4-Dimethyl-hept-3-ene (iii) 2-Ethylbut-1-ene (iv) 1-Phenylbut-1-ene
Answer :	(i) Pent-2-ene undergoes ozonolysis as: The IUPAC name of Product (I) is ethanal and Product (II)is propanal. (ii) 3, 4-Dimethylhept-3-ene undergoes ozonolysis as: The IUPAC name of Product (I)is butan-2-one and Product (II)is Pentan-2-one. (iii) 2-Ethylbut-1-ene undergoes ozonolysis as: The IUPAC name of Product (I)is pentan-3-one and Product (II)is methanal. (iv) 1-Phenylbut-1-ene undergoes ozonolysis as: The IUPAC name of Product (I)is benzaldehyde and Product (II)is propanal.