SOLVED INCONQ NCERT UESTIONS or CLASS 12 HALOALKANES & HALOARENES
10.5 A hydrocarbon CsH1o does not react with chlorine in dark but gives a single monochloro compound C,HgCl in bright sunlight. Identify the hydrocarbon. Ans. The hydrocarbon with molecular formula CsH, 0 can either a cycloalkane or an alkene. Since the compound does not react with Cl2 in the dark, therefore it cannot be an alkene but must be a cycloalkane. Since the cycloalkane reacts with Cl2 in the presence of bright sunlight to give a single monochloro compound, CsHgCI, therefore, all the ten hydrogen atoms of the cycloalkanes must be equivalent. Thus, the cycloalkane is cyclopentane. cloulikanes must be equivalent. Thus CI No reaction 2 dark Cyclopentane (CsH1o Cl Sunlight Monochloro-cyclopentane
10.6 Write the isomers of the compound having formula C4HgBr. Ans. Double bond equivalent (DBE) for C H Br 4 (4-2) 9 1-2)1CI-2) 2 So none of the isomer has a ring or unsaturation, so the isomers are position or chain isomers CH CH2 CH2 CH2 Br 1-Bromo butane CH 3 C CH 3 CH CH. Br 1-Bromo-2-mcthyipropane (ii) CH3 --CH2-- CHCH 3 Br 2-Bromo butane 3 (v) CH Br CH, 2-Bromo-2-methylpropane
10.7 Write the equations for the preparation of 1-iodoobutanefrom (i)1-butanol (ii)1-chlorobutane (iii) but-l-ene. Ans. D CH3 CH2 CH2 CH2OH+KIH3PO4 (ii CH3 CH2 CH2 CH2CI+KI Acetone CH,CH,CH,CH21 + H2O + KH2PO4 CH CH2CH2CH2I+KCI (ii) CHj CH2-CH - CH2+HBr Aacke CH3CH2CH2CH2Br J Nall Acetone
10.8 What are ambident nucleophiles? Explain with an example. Ans. Nucleophiles which can attack through two different sites are called ambident nucleophiles. for example, cvanide ion is a resonance hybrid of the following two structures: It can attack through carbon to form cyanide and through N to form is O cyanide. 10.9 Which compound in each of the following-pairs. will react faster in SN2 reaction with ? (i)CH,Br or CH2l (ii)(CH3)3CCI or CH3CI Ans.()Since I- ion is a better leaving group than Br-ion, therefore, CH3l reacts faster CH3Br in SN2 reaction with OH-ion (ii)On steric grounds, 1 alkyl halides are more reactive than tert-alkyl halides in SN2 reactions. Therefore, CH3CI will react at a faster rate than (CH3) CCl in a SN2 reaction with OHion.
10.10 Predict all the alkenes that would be formed by dehydrohalogenationof the following halides with sodium ethoxide in ethdnol and identify the major alkene: (i)1-Bromo-I-methylcyclohexane (ii)2-Chloro-2-methylbutane. ill) 2,2,3-Trimethyl-3-bromopentane. CH CH 3 CH2H Major Minor rH H-CH, (in CH, CH CH C-CH3+CHCH2 (Major) (Minor) CI H CH, CH2TH s CH2 (Minor) CH3 Br H CH3 Ha CH (Major)
10.13 Give the uses of freon 12, DDT, carbon tetrachloride and iodoform. Ans. lodoform: It was earlier used as an antiseptic but the antiseptic properties are due to the liberation of free iodine and not due to iodoform itsdf. Due to its objectionable smell, it has been replaced by other formulations containing iodine. Carbon tetrachloride: Uses: (i)As an industrial solvent for oil, fats, resins etc.and also in dry cleaning. (ii)CCI4 vapours are highly non inflammable, thus CCl4 is used as a fire extinguisher under the name pyrene. (ili)Used in the manufacture of refrigerants and propellants for aerosol cans. Freons: Freon-12 (CC2F2) is most common freons in industrial use. Uses: For aerosol propellants, refrigeration and air conditioning purposes
DDT (p -p'- Dichloro diphenyl trichloro ethane): (i)The use of DDT increased enormously on a world wide basis after World War Il, primarily because of its effectiveness against the mosquitoes that spreads malaria and other insects which damages crops.. (ii) However, problems related to extensive use of DDT began to appear in the late 1940 s. Many species of insects developed resistance to DDT, it was also discovered to have a high toxicity towards fishes. DDT is not metabolised very rapidly by animals, instead it is deposited and stored in the fatty tissues. If the ingestion continues at a steady rate, DDT builds up within the animals overtime.
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