haloalkanes-and-haloarenes.pdf - cloudfront.net

CBSENCERTSolutionsforClass12chemistryChapter1

Exercises

Q.1. NamethefollowinghalideaccordingtoIUPACsystemandclassifyitasalkyl,allyl,benzyl(primary,secondary,tertiary),vinylorarylhalide:CH32CHCHClCH3

Solution:

Substituents=-CH3(Methyl)and-Cl(Chloro)(Wordroot)Parentcarbonchain=4(but)Primarysuffix=aneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+SecondarysuffixIUPACnameis2-Chloro-3-methylbutane(secondaryalkylhalide).

Q.2. NamethefollowinghalideaccordingtoIUPACsystemandclassifyitasalkyl,allyl,benzyl(primary,secondary,tertiary),vinylorarylhalide:

CH3CH2CHCH3CHC2H5Cl

Solution:

Substituents=-CH3(Methyl)and-Cl(Chloro)(Wordroot)Parentcarbonchain=6(hex)PrimarySuffix=aneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+SecondarysuffixIUPACnameis3-chloro-4-methylhexane(secondaryalkylhalide).

Q.3. NamethefollowinghalideaccordingtoIUPACsystemandclassifythemasalkyl,allyl,benzyl(primary,secondary,tertiary),vinylorarylhalides:

CH3CH2CCH32CH2I

Solution:

Substituents=-CH3(Methyl)and-I(Iodo)(Wordroot)ParentCarbonchain=4(but)Primarysuffix=aneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+SecondarysuffixIUPACnameis1-Iodo-2,2-dimethylbutane(primaryalkylhalide).


CH33CCH2CHBrC6H5

Solution:

Substituents=-CH3(Twomethylgroups)and-Br(Bromo)(Wordroot)Parentcarbonchain=4(but)PrimarySuffix=aneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix1-Bromo-3,3-dimethyl-1-phenylbutane(secondarybenzylhalide)


CH3CHCH3CHBrCH3

Solution:

Substituents=-CH3(Methyl)and-Br(Bromo)(Wordroot)Parentcarbonchain=4(but)Primarysuffix=aneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix2-Bromo-3-methylbutane(secondaryalkylhalide)


CH3CC2H52CH2Br

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Solution:

Substituent=-C2H5(ethyl)Secondaryprefix=-Br(Bromo)(Wordroot)Parentcarbonchain=4(but)Primarysuffix=aneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix1-Bromo-2-ethyl-2-methylbutane(primaryalkylhalide)


CH3CClC2H5CH2CH3

Solution:

Substituents=-CH3(Methyl)and-Cl(Chloro)(Wordroot)Parentcarbonchain=5(pent)Primarysuffix=aneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix3-Chloro-3-methylpentane(Tertiaryalkylhalide)


CH3CH=CHCBrCH32

Solution:

Substitute=-CH3(Methyl)Secondaryprefix=Br(Bromo)(Wordroot)Parentcarbonchain=5(pent)Primarysuffix=eneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix4-Bromo-4-methylpent-2-ene(Allylhalide)


CH3CH=C(Cl)CH2CHCH32

Solution:

Substituent=-CH3(Methyl)Secondaryprefix=-Cl(Chloro)(Wordroot)Parentcarbonchain=6(hex)Primarysuffix=eneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix3-Chloro-5-methylhex-2-ene(Vinylhalide)

Q.10. NamethefollowinghalideaccordingtoIUPACsystemandclassifyitasalkyl,allyl,benzyl(primary,secondary,tertiary),vinylorarylhalide:p-ClC6H4CH2CHCH32

Solution:

Substituent=CH32CHCH2-(Methylpropyl)Secondaryprefix=-Cl(Chloro)(Wordroot)Parentcarbonchain=benzeneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix1-Chloro-4-(2-methylpropyl)benzene(Arylhalide)


m-ClCH2C6H4CH2CCH33




Solution:

Substituent=CH33CCH2-(Neopentyl)and-CH2Cl(Chloromethyl)(Wordroot)Parentcarbonchain=benzeneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix1-chloromethyl-3-(2,2-dimethylpropyl)benzene(Primarybenzylhalide)


o-Br-C6H4CHCH3CH2CH3

Solution:

Substituent=

(methylpropyl)Secondaryprefix=-Br(Bromo)(Wordroot)Parentcarbonchain=benzeneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix1-Bromo-2-(1-methylpropyl)benzene(Arylhalide)

Q.13. Predictallthealkenesthatwouldbeformedbydehydrohalogenationof1-Bromo-1-methylcyclohexanewithsodiumethoxideinethanolandidentifythemajoralkene.

Solution: 1-bromo-1-methylcyclohexane

Inthegivencompound,allβ-hydrogenatomsareequivalent.Thus,thedehydrohalogenationofthiscompoundgivesonlyonealkene.

Q.14. Predictallthealkenesthatwouldbeformedbydehydrohalogenationofthefollowinghalideswithsodiumethoxideinethanolandidentifythemajoralkene:2-Chloro-2-methylbutane

Solution:

Inthegivencompound,therearetwodifferentsetsofequivalentβ-hydrogenatomslabelledas'a'and'b'.Thus,dehydrohalogenationofthecompoundyieldstwoalkenes.

Saytzeff’sruleimpliesthatindehydrohalogenationreactions,thealkenehavingagreaternumberofalkylgroupsattachedtoadoublybondedcarbonatomsispreferablyproducedi.e.morestablealkeneisformedasthemajorproductTherefore,alkene(I)i.e.,2-methylbut-2-eneisthemajorproductinthisreaction.

Q.15. Predictallthealkenesthatwouldbeformedbydehydrohalogenationof2,2,3-Trimethyl-3-bromopentanewithsodiumethoxideinethanolandidentifythemajoralkene:




Solution: 2,2,3-Trimethyl-3-bromopentanehastwodifferentsetsofβ-hydrogenatomsandhence,inprinciple,cangivetwoalkenes(IandII).ButaccordingtoSaytzeff'srule,morehighlysubstitutedalkene(II),beingmorestable,isthemajorproduct.

Q.16. Howwillyoubringaboutthefollowingconversion?Ethanoltobut-1-yne

Solution: TheconversionofEthanoltoBut-1-yneisasfollows:

CH3CH2OHEthanol→SOCl2,PyridineCH3CH2ClChloroethane+SO2+HCl

HC≡CHEthyne+NaNH2→Liq.NH3HC≡CNa-+SodiumacetylideCH3CH2-ClChloroethane+HC≡CNa-+→CH3CH2C≡CHBut-1-yne+NaClInthisconversion,ethanolreactswithSOCl2inthepresenceofpyridinethroughnucleophilicsubstitutionreactionandgetsconvertintochloroethane.Onfurtherreactionofchloroethanewithsodiumacetylide,but-1-yneisformed.

Q.17. Howwillyoubringaboutthefollowingconversion?

Ethanetobromoethene

Solution: Thebrominationofethane(Br2inthepresenceoflightat520-670K)givesbromoethanewhichonfurthertreatmentwithalcoholicKOHresultsinthealkenecalledethene.

ThisagainonbrominationwithBr2/CCl4givesdibromide(vicinalbromide)called1,2-dibromoethanewhichontreatmentwithalcoholicKOHgivesbromoetheneasthefinalproduct.


Propeneto1-nitropropane

Solution: Thepreparationof1-nitropropanefrompropeneisasfollows:

Inthisconversion,firstAnti-Markovnikoff'sadditionreactiontakesplace.Duetothis,hydrogenofHBrattachtodoublebondedcarbon,wherelessnumberofhydrogensarepresent.Andbromideisattachtothatcarbon,wheremorenumberofhydrogensarepresent.ThereactionofAgNO2with1-bromopropaneresultsintheformationof1-nitropropane.


Toluenetobenzylalcohol

Solution: ThereactionfortheconversionofToluenetobenzylalcoholisasfollows:

Inthisconversion,toluenereactswithchlorineinthepresenceofUV-lightorheattoformbenzylchloride.BenzylchloridefurtherreactwithabaselikeaqueousKOHandheatingformsbenzylalcohol.


Propenetopropyne




Solution: Thereactionthattakeplaceduringconversionofpropenetopropyneisasfollows:

CH3-CH=CH2→E+additionBr2/CCl4CH3-CHBr-CH2Br→Liq.NH32NaNH2CH3-C≡CH

Inthisconversion,firstlyelectrophilicadditiontakesplaceinthepresenceofbrominetoform1,2-dibromopropane.1,2-dibromopropaneonfurtherreactionwithNaNH2formspropyne.


Ethanoltoethylfluoride

Solution: TheconversionofEthanoltoethylfluorideisasfollows:

Inthisconversion,firstlyethanolreactswithPCl5toformchloroethane.Further,chloroethanereactswithAgFandformsethylfluoride.ThisisknownasSwartsreaction.


Bromomethanetopropanone

Solution: TheconversionofBromomethanetopropanoneisasfollows:

Inthisconversion,firstlyBromomethanereactswithKCNaccordingtoSN2reactiontoformacetonitrile.AcetonitrileisfurthertreatedwithGrignardreagenttoformanadduct,whichonhydrolysisformspropanone.


But-1-enetobut-2-ene

Solution: TheconversionofBut-1-enetoBut-2-eneisasfollows:

Inthisconversion,firstlyMarkovnikov'sadditiontakesplace.Further,theeliminationofHBrtakesplaceinthepresenceofalcoholicKOHandfinallywegetBut-2-ene.


1-Chlorobutaneton-octane

Solution: Theconversionof1-chlorobutaneton-octaneinthepresenceofsodiummetalanddryetheriscalledWurtzreaction.TwoequivalentChlorobutanereactstogiven-octaneasafinalproductandsodiumchlorideastheby-product.

2CH3CH2CH2CH2-Cl1-Chlorobutane+2Na→-2NaClEtherCH3CH2CH2CH2CH2CH2CH2CH3n-octane


Benzenetobiphenyl

Solution: TheconversionofbenzenetobiphenylusingNaanddryetheriscalledFittigreaction.

Firstly,thebenzeneistreatedwithBr2/FeBr3resultsintheformationofbromobenzene.Itisanelectrophilicsubstitutionreaction.Further,thebromobenzeneistreatedwithsodiummetalinthepresenceofdryethertoformbiphenylasthefinalproductandsodiumbromideastheby-product.

Q.26. Explainwhythedipolemomentofchlorobenzeneislowerthanthatofcyclohexylchloride?




Solution:

sp2-hybridcarboninchlorobenzeneismoreelectronegativethanasp3-hybridcarbonincyclohexylchloride,duetogreaters-character.Thus,CatomofchlorobenzenehaslesstendencytoreleaseelectronstoClthancarbonatomofcyclohexylchloride.

Also,inchlorobenzene,thelonepairofelectronontheClatomisinresonancewithabenzenering.ThisgivespartialdoublebondcharactertoC-ClbondandthereisadecreaseinthemagnitudeofpartialnegativechargeonClatom.However,incyclohexylchloride,thereisaC-Clsinglebond.Thedipolemomentisaproductofchargeanddistance.AlsoC-ClbondwithpartialdoublebondcharacterhaslowerbondlengththanwithC-Clsinglebond.Hence,chlorobenzenehaslowerdipolemomentthancyclohexylchloride.

Q.27. Explainwhyalkylhalides,thoughpolar,areimmisciblewithwater?

Solution: Tobemisciblewithwater,thesolute-waterforceofattractionmustbestrongerthanthesolute-soluteandwater-waterforcesofattraction.Alkylhalidesarepolarmoleculesandsoheldtogetherbydipole-dipoleinteractions.Similarly,strongH-bondsexistbetweenthewatermolecules.Thenewforceofattractionbetweenthealkylhalidesandwatermoleculesisweakerthanthealkylhalide-alkylhalideandwater-waterforcesofattraction.Hence,alkylhalides(thoughpolar)areimmisciblewithwater.

Q.28. ExplainwhyGrignardreagentsshouldbepreparedunderanhydrousconditions?

Solution: Grignardreagentsareveryreactive.Inthepresenceofwater,theyreactandgivealkanesbecausealkylgroupactsasabaseandwaterhasacidichydrogen.

Q.29. Givetheusesoffreon12,DDT,carbontetrachloride,andiodoform.

Solution: UsesofFreon-12:-Freon-12(dichlorodifluoromethane,CF2Cl2)iscommonlyknownasCFC.Itisusedasarefrigerantinrefrigeratorsandairconditioners.Itisalsousedinaerosolspraypropellantssuchasbodysprays,hairsprays,etc.However,itdamagestheozonelayer.Hence,itsmanufacturewasbannedintheUnitedStatesandmanyothercountriesin1994.

UsesofDDT:-DDT(p,p-dichlorodiphenyltrichloroethane)isoneofthebest-knowninsecticides.Itisveryeffectiveagainstmosquitoesandlice.Butdueitsharmfuleffects,itwasbannedintheUnitedStatesin1973.

UsesofcarbontetrachlorideCCl4(i)Itisusedformanufacturingrefrigerantsandpropellantsforaerosolcans.(ii)Itisusedasfeedstockinthesynthesisofchlorofluorocarbonsandotherchemicals.(iii)Itisusedasasolventinthemanufactureofpharmaceuticalproducts.(iv)Untilthemid1960’s,carbontetrachloridewaswidelyusedasacleaningfluid,adegreasingagentinindustries,aspotreamerinhomes,andafireextinguisher.

Usesofiodoform(CHI3):-Iodoformwasusedearlierasanantiseptic,butnowithasbeenreplacedbyotherformulations-containingiodine-duetoitsobjectionablesmell.Theantisepticpropertyofiodoformisonlyduetotheliberationoffreeiodinewhenitcomesincontactwiththeskin.

Q.30. Writethestructureofthemajororganicproductineachofthefollowingreaction:

Solution:

Alkyliodidesareoftenpreparedbythereactionofalkylchlorides/bromideswithNaIindryacetone.ThisreactionisknownastheFinkelsteinreaction.Inthegivenequationthemajororganicproductis1-Iodopropane.

ThisisoneoftheHalogenexchangereaction.


Solution:

Inthisreaction,dehyrdrohalogenationtakesplacewhichresultsintheformationof2-methylpropene.


Solution:

Inthisreactionunimolecularnucleophilicsubstitutionreactiontakesplaceresultingintheformationofbutan-2-ol.

Q.33. Writethestructureofthemajororganicproductinthefollowingreaction:

CH3CH2Br+KCN→aq.ethanol




Solution: CH3CH2BrBromoethane+KCN→aq.ethanolCH3CH2CNCyanoethane+KBr

Inthisreactionnucleophilicsubstitutionreactiontakesplacewherenucleophileattackonthecarbonwhichisattachedtoleavinggroup.Here,bondbreakingandbondmakingactionoccursimultaneously.

Q.34. Writethestructureofthemajororganicproductinthefollowingreaction:C6H5ONa+C2H5Cl→

Solution: C6H5ONaSodiumphenoxide+C2H5ClChloroethane→WilliamsonsynthesisC6H5-O-C2H5Ethoxybenzene+NaCl

Inthismethod,analkylhalide(Ethylchloride)isallowedtoreactwithsodiumphenoxideandproduceEthoxybenzeneasamajorproduct.ThisreactionisalsoknownasWilliamsonsynthesis.ThereactioninvolvesSN2attackofanalkoxideiononprimaryalkylhalide.


Solution:

Inthisreaction,nucleophilicsubstitutionmechanismtakesplace.Thehydroxylgroupofanalcoholisreplacedbyhalogenonreactionwiththionylchloride.ThionylchlorideispreferredbecauseinthisreactionalkylhalideisformedalongwithgasesSO2andHCl.Thetwogaseousproductsareescapable,hence,thereactiongivespurealkylhalides.

Q.36. Writethestructureofthemajororganicproductinthefollowingreaction:CH3CH2CH=CH2+HBr→Peroxide

Solution: CH3CH2CH=CH2But-1-ene+HBr→PeroxideCH3CH2CH2CH2-Br1-BromobutaneAccordingtoAnti-Markovnikov’srule,hydrogenwilladdtothatcarbonwhichhavelessnumberofhydrogenatomsandBr-(Nu-)attachtothatcarbonwhichhavemorenumberofhydrogenatoms.


Solution:

AccordingtoMarkovnikov'sruleHatomwilladdtothatcarbonwhichhavemoreHatomsandBr-(Nucleophile)attackonthatcarbonwhichhavelessHatoms.

Q.38. Writethemechanismofthefollowingreaction:nBuBr+KCN→EtOH-H2OnBuCN

Solution: Thegivenreactionis:nBuBr+KCN→EtOH-H2OnBuCN,givenreactionisaSN2reaction.InthisreactionCN-ionactsasthenucleophileandattackonthecarbonatomatwhichBrleavinggroupisattachedandlesshinderendCN-ionisanambidentnucleophileandcanattackthroughbothCandN.Inthiscase,itattacksthroughtheCatom.

Q.39. ArrangethecompoundsofeachsetinorderofreactivitytowardsSN2displacement:

2-Bromo-2-methylbutane,1-Bromopentane,2-Bromopentane.

Solution: AnSN2reactioninvolvestheapproachingofthenucleophiletothecarbonatomtowhichtheleavinggroup(-Br)isattached.Whenthenucleophileisstericallyhindered,thenthereactivitytowardsSN2displacementdecreases.

CH3CH2CH2CH2-Br1-Bromopentane1oCH3CH2CH2CHBrCH32-Bromopentane2oCH3CH2CBrCH322-Bromo-2-methylbutane3o

Duetothepresenceofsubstituents,hindrancetotheapproachingnucleophiledecreasesSN2order1°>2°>3°(alkylhalide).1-Bromopentane>2-bromopentane>2-Bromo-2-methylbutane(nu-approachtendency).Hence,theincreasingorderofreactivitytowardsSN2displacementis:2-Bromo-2-methylbutane<2-Bromopentane<1-Bromopentane.

Q.40. ArrangethecompoundsofeachsetinorderofreactivitytowardsSN2displacement:1-Bromo-3-methylbutane,2-Bromo-2-methylbutane,3-Bromo-2-methylbutane

Solution:

RateofSN2reactionisinverselyproportionaltosterichindrance.Sincesterichindranceinalkylhalidesincreasesintheorderof1°<2°<3°,theincreasingorderofreactivitytowardsSN2displacementis3°<2°<1°,Hence,thegivensetofcompoundscanbearrangedintheincreasingorderoftheirreactivitytowardsSN2displacementas:2-Bromo-2-methylbutane<2-Bromo-3-methylbutane<l-Bromo-3-methylbutane

Q.41. ArrangethecompoundsofeachsetinorderofreactivitytowardsSN2displacement:

1-Bromobutane,1-Bromo-2,2-dimethylpropane,1-Bromo-2-methylbutane,1-Bromo-3-methylbutane




Solution: Thestructuresofthegivencompoundsareasfollows:

ThesterichindrancetothenucleophileintheSN2reactionincreaseswithadecreaseinthedistanceofthesubstituentfromtheatomcontainingtheleavinggroup.Further,thesterichindranceincreaseswithanincreaseinthenumberofthesubstituent.Therefore,theincreasingorderofsterichindrancesinthegivencompoundsisasfollows:1-Bromobutane<1-Bromo-3-methylbutane<1-Bromo-2-methylbutane<1-Bromo-2,2-dimethylpropaneHence,theincreasingorderofreactivityofthegivencompoundstowardsSN2displacementis:1-Bromo-2,2-dimethylpropane<1-Bromo-2-methylbutane<1-Bromo-3-methylbutane<1-Bromobutane

Q.42. OutofC6H5CH2CIandC6H5CHClC6H5,whichismoreeasilyhydrolysedbyaqueousKOH?

Solution:

HydrolysisbyaqueousKOHproceedsthroughSN1andbytheformationofcarbocation.Ifcarbocationisstable,thenthecompoundiseasilyhydrolysedbyaqueousKOH.(polarproticsolvent)Now,C6H5CH2Clforms1°-carbocation,whileC6H5CHClC6H5forms2°-carbocationwhichismorestablethan1°-carbocationaspositivechargeismoredelocalised.

Hence,C6H5CHCIC6H5ishydrolysedmoreeasilythanC6H5CH2ClbyaqueousKOH.

Q.43. p-Dichlorobenzenehashighermeltingpointandlowersolubilitythanthoseofo-andm-isomers.Discuss.

Solution:

p-Dichlorobenzeneismoresymmetricalthano-andm-isomers.Forthisreason,itfitsmorecloselythano-andm-isomersinthecrystallattice.Sinceduringmeltingordissolution,thecrystallatticebreaks,therefore,moreenergyisrequiredtomeltordissolvethep-isomerthanthecorrespondingo-andm-isomers.Asaresult,p-dichlorobenzenehasahighermeltingpointandlowersolubilitythano-andm-isomers.

Q.44. Howthefollowingconversioncanbecarriedout?

PropenetoPropan-1-ol

Solution:

Inthisconversionfirstpropeneundergoanti-markovnikovadditionduetowhichhydrogenofHBrattachtothatcarbonwherelessnumberofhydrogensarepresentandbromideattachtothatcarbonwheremorenumberofcarbonarepresentandconvertintobromopropanethenitwillundergowithnucleophilicsubstitutionreactioninthepresenceofaqueousKOHandheatandfinallyconvertintopropan-1-ol.


Ethanoltobut-1-yne

Solution: TheconversionofEthanoltobut-1-yneiscarriedoutinthefollowingsteps:

CH3CH2OHEthanol→SOCl2,PyridineCH3CH2ClChloroethane+SO2+HCl

HC≡CHEthyne+NaNH2→Liq.NH3HC≡C-Na+SodiumacetylideCH3CH2-ClChloroethane+HC≡C-Na+→CH3CH2C≡CHBut-1-yne+NaClIntheabovereaction,ethanolisreactedwiththionylchloridetoformethylchloride.Inthesecondreaction,ethyneistreatedwithsodamidetoformsodiumacetylide.ThissodiumacetylideistreatedwithchloroethanetoformBut-1-yne.


1-Bromopropaneto2-bromopropane




Solution:

Inthegivenconversion,firstdehydrohalogenationreactiontakesplaceinthepresenceofalcoholicKOHthenMarkovnikovadditiontakesplace.

Q.47. Howthefollowingconversionscanbecarriedout?

2-Methyl-1-propeneto2-chloro-2-methylpropane

Solution:

InthisconversionMarkovnikovadditiontakesplaceasaresultofwhichhydrogenattachtothatcarbonwhichhasmorenumberofhydrogensandchlorineattachtothatcarbonwhichhaslessnumberofhydrogen.


Ethylchloridetopropanoicacid.

Solution: Theconversionofethylchloridetopropanoicacidisasfollows:

CH3CH2ClEthylchloride+KCN→aqueousethanolCH3CH2CNPropanenitrile+KClCH3CH2CNPropanenitrile→H+/H2OCH3CH2COOHPropanoicacid

Inthisconversion,firstlyethylchloridereactswithKCNinaqueousethanol(Nucleophilicsubstitution)andformspropanenitrile.Thiswillundergohydrolysisinacidmediumandfinallyconvertintopropanoicacid.


But-1-eneton-butyliodide.

Solution: TheconversionofBut-1-eneton-butyliodideisasfollows:

CH3-CH2-CH=CH2But-1-ene→Anti-MarkovnikovadditionHBr/PeroxideCH3-CH2-CH2-CH2-Br1-BromobutaneCH3-CH2-CH2-CH2-Br1-Bromobutane→FinkelsteinreactionNaI,dryactoneCH

Inthisconversion,firstbut-1-enereactswithHBraccordingtoAnti-Markovnikov'saddition.Asaresultofwhichhydrogenwillattachtothatcarbonwhichhaslesshydrogenatomsandbrominewillattachtothatcarbonwhichhasmorehydrogenatomstoform1-Bromobutane.1-Bromobutanereactswithsodiumiodideinpresenceofacetonegivesn-Butyliodide.ThisreactionisknownasFinkelsteinreaction.


2-Chloropropaneto1-propanol.

Solution: Theconversionof2-Chloropropaneto1-propanolisasfollows:

Inthisconversion,firstlydehydrohalogenationtakesplaceinthepresenceofalcoholicKOHtoformpropene.ThenAnti-Markovnikov'sadditiontakesplaceinthepresenceofHBrandperoxide.Thehydrogenfromthehydrogenhalideattachestothatcarbonwhichhavelessnumberofhydrogenatoms.Thebromineatomattachestothatcarbonwhichhavemorenumberofhydrogenatomsandforms1-bromopropane.

1-bromopropanewillreactinaqueousKOH(nucleophilicsubstitution)andforms1-propanol.


Isopropylalcoholtoiodoform

Solution: Theconversionofisopropylalcoholtoiodoformisasfollows:

Inthisconversion,firstlyisopropylalcoholundergoesoxidationtoformacetoneinpresenceofchromicacidwhichisagoodoxidisingagent.FurtherreactionoftheketonewithNaOI,resultsintheformationofiodoform.


Chlorobenzenetop-nitrophenol




Solution: TheconversionofChlorobenzenetop-nitrophenolisasfollows:

Inthisconversion,firstlychlorobenzeneundergoesanitrationreactiontoformp-chloronitrobenzeneasthemajorproduct.

Thep-chloronitrobenzeneundergoesanaromaticnucleophilicsubstitutionreactioninthepresenceofsodiumhydroxideathightemperatureandpressureandfinally,p-nitrophenolisobtained.


2-Bromopropaneto1-Bromopropane

Solution: Theconversionof2-bromopropaneto1-bromopropaneisasfollows:

Inthisconversion,2-bromopropaneundergodehydrohalogenationinpresenceofalcoholicKOHandformspropene,whichreactswithhydrogenbromidefinallyconvertsinto1-bromopropanebyAnti-Markovnikovaddition.


Chloroethanetobutane

Solution: TheconversionofChloroethanetobutaneisasfollows:

2CH3-CH2-Cl→Wurtzreaction2Na/dryetherCH3-CH2-CH2-CH3+2NaCl

Inthisconversion,twomolesofchloroethanereactwithsodiuminpresenceofdryethertoformbutane.ThisreactionisknownasWurtzreaction.


Benzenetodiphenyl

Solution: TheconversionofBenzenetodiphenylisasfollows:

Inthisconversion,first,thebenzeneundergoesbrominationandformsbromobenzene.

FurthertwomolesofbromobenzeneundergoFittigreactioninpresenceofsodiummetalanddryethertoformbiphenyl.


Tert-butylbromidetoisobutylbromide

Solution: Theconversionoftert-butylbromidetoisobutylbromideisasfollows:

Inthisconversion,firstlytert-butylbromideundergoesdehydrohalogenationinpresenceofalcoholicKOHresultingintheformationof2-methylpropene,thenAnti-Markovnikovadditiontakesplaceinpresenceofhydrogenbromidetoformisobutylbromide.


Anilinetophenylisocyanide




Solution:

Incarbylaminereaction,anilineconvertsintophenylisocyanide.WhenanilinereactswithCHCl3andKOHinthepresenceofheat,itformsphenylisocyanide.Inthisreaction,theelectrophilicdichlorocarbeneattacksthenucleophilicnitrogenofaniline.


Toluenetobenzylalcohol

Solution:

InthisconversionfirsttoluenereactswithchlorineinthepresenceofultravioletlightandgetsconvertedintobenzylchloridethenitwillreacttoaqueousKOH(nucleophilicsubstitution)andconvertintobenzylalcohol.


Benzeneto4-bromonitrobenzene

Solution:

Inthisconversionfirstbenzenereactswithbromine(bromination)toformbromobenzenethenitundergonitrationinthepresenceofconc.nitricacid/conc.sulphuricacidandfinallyitgetsconvertedintop-bromonitrobezene(4-bromonitrobenzene)asthemajorproduct.


Benzylalcoholto2-phenylethanoicacid

Solution:

InthisconversionfirstbenzylalcoholreactswithPCl5accordingtoSN2reactionthenconvertintobenzylchloride.ItthenreactswithKCNandaqueousethanolaccordingtoSN1reactionandconvertintobenzylcyanidethenhydrolysistakesplaceandfinallyconvertinto2-phenylethanoicacid.


Ethanoltopropanenitrile

Solution: CH3-CH2-OH→SN2redP/Br2CH3-CH2-Br→SN2KCN,Aq.ethanolCH3-CH2-CN

Inthisconversionfirstethanolreactswithbromineinpresenceofredphosphorus,thecompoundformedisethylbromidethenitwillreactswithKCNandaqueousethanolandfinallyconvertintopropanenitrile.


Anilinetochlorobenzene

Solution:

Inthisconversion,firstdiazotisationtakesplacewithanilineandanilinewillconvertintobenzenediazoniumchloridethenitwillreactwithCu2Cl2(Gattermannreaction)andformschlorobenzene.


2-Chlorobutaneto3,4-dimethylhexane




Solution: Wurtz’sreactionisanorganicchemicalcouplingreactioninwhichalkylhalidesreactswithsodiummetalinpresenceofdryetherandformahigheralkane.

InthisconversionWurtzreactiontakesplacewhichresultsintheformationof3,4-dimethylhexane.

Q.64. GivetheIUPACnameofthefollowingcompound:CH3CHClCHBrCH3

Solution:

Secondaryprefix=-Br(Bromo),-Cl(Chloro)(Wordroot)ParentCarbonchain=4(but)Primarysuffix=aneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix2-Bromo-3-chlorobutane

Q.65. GivetheIUPACnameofthefollowingcompound:

CHF2CBrClF

Solution:

Secondaryprefix=-Br(Bromo),-Cl(Chloro),-F(Fluoro)(Wordroot)ParentCarbonchain=2(eth)Primarysuffix=aneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix1-Bromo-1-chloro-1,2,2-trifluoroethane


ClCH2C≡CCH2Br

Solution:

Secondaryprefix=-Br(Bromo),-Cl(Chloro)(Wordroot)ParentCarbonchain=4(but)Primarysuffix=yneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix1-Bromo-4-chlorobut-2-yne


CCl33CCl

Solution:

Secondaryprefix=-Cl(Chloro)and-CCl3(trichloromethyl)(Wordroot)ParentCarbonchain=3(prop)Primarysuffix=aneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix2-(trichloromethyl)-1,1,1,2,3,3,3-heptachloropropane


CH3Cp-ClC6H42CHBrCH3

Solution:

Secondaryprefix=-Br(Bromo)andpara-phCl(4-chlorophenyl)(Wordroot)ParentCarbonchain=4(but)Primarysuffix=aneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix2-Bromo-3,3-bis(4-chlorophenyl)butane


CH33CCH=CClC6H4I-p




Solution:

Secondaryprefix=-Cl(Chloro)andpara-phI(iodophenyl)(Wordroot)ParentCarbonchain=4(but)Primarysuffix=eneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix1-chloro-1-(4-iodophenyl)-3,3-dimethylbut-1-ene

Q.70. ThetreatmentofalkylchlorideswithaqueousKOHleadstotheformationofalcoholsbutinthepresenceofalcoholicKOH,alkenesaremajorproducts.Explain.

Solution: Inanaqueoussolution,KOHalmostcompletelyionisestogiveOH-ion,whichisastrongnucleophile,whichleadsthealkylchloridetoundergoasubstitutionreactiontoformalcohol.R-Cl+KOH(aq)→R-OH+KCl

Ontheotherhand,analcoholicsolutionofKOHcontainsalkoxideRO-ionaswell,whichisanucleophileaswellasstrongbase.Thus,itcanabstractahydrogenfromtheβ-carbonofthealkylchloridefavouringaneliminationreactionandformsanalkene.

Thus,itdependsontheconditionaswell,tofavouraneliminationandasubstitutionreaction.

Q.71. PrimaryalkylhalideC4H9Br(a)reactedwithalcoholicKOHtogivecompound(b),Compound(b)isreactedwithHBrtogive(c)whichisanisomerof(a).When(a)isreactedwithsodiummetalitgivescompound(d),C8H18whichisdifferentfromthecompoundformedwhenn-butylbromideisreactedwithsodium.Givethestructuralformulaof(a)andwritetheequationsforallthereactions.

Solution: Thetwoprimaryalkylhalideshavingtheformula,C4H9Braren-butylbromideandisobutylbromide.

Therefore,compound(a)iseithern-butylbromideorisobutylbromide.Now,compound(a)reactswithNametaltogivecompound(d)ofmolecularformula,C8H18,whichisdifferentfromthecompoundformedwhenn-butylbromidereactswithNametal.Hence,compound(a)mustbeisobutylbromide.

Thus,compound(d)is2,5-dimethylhexane.

Whenahaloalkanewithβ-hydrogenatomisheatedwithalcoholicsolutionofpotassiumhydroxide,thereiseliminationofhydrogenatomfromβ-carbonandahalogenatomfromtheα-carbonatom.Itisgiventhatcompound(a)reactswithalcoholicKOHtogivecompound(b).Hence,compound(b)is 2-methylpropene.

Also,compound(b)reactswithHBrtogivecompound(c)whichisanisomerof(a).Hence,compound(c)is 2-bromo-2-methylpropane,

Q.72. Whathappenswhenn-butylchlorideistreatedwithalcoholicKOH.

Solution: Whenn-butylchlorideistreatedwithalcoholicKOH,theformationofbut-1-enetakesplace.Thisreactionisadehydrohalogenationreaction.

Q.73. WhathappenswhenbromobenzeneistreatedwithMginthepresenceofdryether?

Solution: WhenBromobenzeneistreatedwithMginthepresenceofdryether,Phenylmagnesiumbromide(Grignardreagent)isformed.




Q.74. Whathappenswhenchlorobenzeneissubjectedtohydrolysis?

Solution: Chlorobenzenedoesnotundergohydrolysisundernormalconditions.However,itundergoeshydrolysiswhenheatedwithsodiumhydroxidesolutionatatemperatureof623Kandapressureof300atmtoformphenol.

Q.75. WhathappenswhenethylchlorideistreatedwithaqueousKOH?

Solution: WhenethylchlorideistreatedwithaqueousKOH,itundergoeshydrolysistoformethanol.Inthisreaction,nucleophilicsubstitutiontakesplace.

Q.76. Whathappenswhenmethylbromideistreatedwithsodiuminthepresenceofdryether?

Solution: Whenmethylbromideistreatedwithsodiuminthepresenceofdryether,ethaneisformed.ThisreactionisknownastheWurtzreaction.Thisisatypeofcouplingreaction,inwhichtwoalkylgroupscombinewitheachother.

Q.77. WhathappenswhenmethylchlorideistreatedwithKCN?

Solution: WhenmethylchlorideistreatedwithKCN,itundergoesanucleophilicsubstitutionreactiontogivemethylcyanide.CH3Cl+KCN→nucleophilicsubstitutionCH3CN+KCl

Q.78. Writethestructureofthefollowingorganichalogencompound:2-chloro-3-methylpentane

Solution:

Secondaryprefix=-Cl(Chloro)and-CH3(methyl)(Wordroot)ParentCarbonchain=5(pent)Primarysuffix=aneIUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix2-chloro-3-methylpentane

Q.79. Writethestructureofthefollowingorganichalogencompound:p-Bromochlorobenzene

Solution:

Secondaryprefix=-Cl(Chloro),-Br(Bromo)(Wordroot)ParentCarbonchain=6(benzene)IUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffixp-Bromochlorobenzene

Q.80. Writethestructureofthefollowingorganichalogencompound:1-Chloro-4-ethylcyclohexane

Solution:

Secondaryprefix=-Cl(Chloro)and-C2H5(ethyl)

Primaryprefix=Cyclo

(Wordroot)ParentCarbonchain=6(benzene)IUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix1-Chloro-4-ethylcyclohexane

Q.81. Writethestructureofthefollowingorganichalogencompound:2-(2-Chlorophenyl)-1-iodooctane




Solution:

Secondaryprefix=-I(iodo)andPh-Cl(Chlorophenyl)(Wordroot)ParentCarbonchain=8(oct)IUPACname=secondaryprefix+primaryprefix+wordroot+primarysuffix+secondarysuffix2-(2-Chlorophenyl)-1-iodooctane.

Q.82. Writethestructureofthefollowingorganichalogencompound:2-Bromobutane

Solution:

Secondaryprefix=-Br(Bromo)(Wordroot)ParentCarbonchain=4(but)IUPACname=secondaryprefix+primaryprefix+wordroot+primarysuffix+secondarysuffix2-bromobutane.

Q.83. Writethestructureofthefollowingorganichalogencompound:

4-tert-Butyl-3-iodoheptane

Solution:

Secondaryprefix=-I(iodo)and-(CH3)3C(tert-Butyl)(Wordroot)ParentCarbonchain=7(hept)IUPACname=Secondaryprefix+Primaryprefix+Wordroot+Primarysuffix+Secondarysuffix4-tert-Butyl-3-iodoheptane.

Q.84. Writethestructureofthefollowingorganichalogencompound:1-Bromo-4-sec-butyl-2-methylbenzene

Solution:

Secondaryprefix=-Br(Bromo),(sec-butyl)and-CH3(methyl)(Wordroot)ParentCarbonchain=6(benzene)IUPACname=secondaryprefix+primaryprefix+wordroot+primarysuffix+secondarysuffix1-Bromo-4-sec-butyl-2-methylbenzene.

Q.85. Writethestructureofthefollowingorganichalogencompound:1,4-Dibromobut-2-ene

Solution:

Secondaryprefix=-Br(Bromo)(Wordroot)ParentCarbonchain=4(but)Primarysuffix=eneIUPACname=secondaryprefix+primaryprefix+wordroot+primarysuffix+secondarysuffix1,4-Dibromobut-2-ene

Q.86. Whichofthefollowinghasthehighestdipolemoment?

iCH2Cl2iiCHCl3iiiCCl4




Solution: Dipolemoment=Charge×Distanceμ=q×dItisavectorquantity.

DichloromethaneCH2Cl2μ=1.60 DInCH2Cl2,theresultantofthedipolemomentsoftwobondsisstrengthenedbytheresultantofthedipolemomentsoftwoC-Hbonds.Asaresult,CH2Cl2hasahigherdipolemomentof1.60DthanCHCl3.CH2Cl2hasthehighestdipolemoment.

ChloroformCHCl3μ=1.08DInCHCl3,theresultantofdipolemomentsoftwoC-ClbondsisopposedbytheresultantofdipolemomentsofoneC-HbondandoneC-Clbond.SincetheresultantofoneC-HbondandoneC-ClbonddipolemomentsissmallerthantwoC-Clbonds,theoppositionistoasmallextentandCHCl3moleculeisasymmetrical.Asaresult,CHCl3hasasmalldipolemomentof1.08D.

CarbontetrachlorideCCl4μ=0D

CCl4moleculeissymmetrical.Therefore,thedipolemomentsofallfourC-Clbondscanceleachother.So,itsresultantdipolemomentiszero.Hence,thegivencompoundscanbearrangedintheincreasingorderoftheirdipolemomentsas:CCl4<CHCl3<CH2Cl2.

Q.87. AhydrocarbonC5H10doesnotreactwithchlorineindarkbutgivesasinglemonochlorocompoundC5H9Clinbrightsunlight.Identifythehydrocarbon.

Solution: Ahydrocarbonwiththemolecularformula,C5H10hasthegeneralmolecularformulaCnH2n.Therefore,itcanbeeitherbeanalkeneoracycloalkane.Itisacycloalkanebecausehydrocarbonsdonotreactwithchlorineinthedark;itcannotbeanalkene.

Also,thehydrocarbongivesasinglemonochlorocompound,C5H9Clbyreactingwithchlorineinbrightsunlight.Asinglemonochlorocompoundmeansthatthehydrocarbonmustcontainhydrogenatomsthatareallequivalent.Andasallhydrogenatomsofacycloalkaneareequivalent,thehydrocarbonmustbeacycloalkane.Hence,thecompoundiscyclopentane.Thereactionsinvolvedare:

Q.88. WritetheisomersofthecompoundhavingformulaC4H9Br.

Solution: Therearefourisomersofthecompoundhavingtheformula C4H9Br.Theseisomersaregivenbelow.(a)1-Bromobutane

(b)2-Bromobutane

(c)1-Bromo-2-methylpropane

(d)2-Bromo-2-methylpropane

Q.89. Writetheequationforthepreparationof1-iodobutanefrom1-butanol.

Solution: CH3-CH2-CH2-CH2-OH+HI→(ZnCl2)CH3-CH2-CH2-CH2-I+H2OInpresenceofZnCl2,alcoholreactswithHIandformsalkyliodideandwater.Thisisasubstitutionreaction.

Q.90. Writetheequationforthepreparationof1-iodobutanefrom1-chlorobutane




Solution:

ThisreactionisknownasFinkelsteinreaction,wherehalogenexchangetakesplace.

Q.91. Writetheequationforthepreparationof1-iodobutanefrombut-1-ene.

Solution:

Analkeneisconvertedtocorrespondingalkylhalidebyreactionwithhydrogenbromide.Alkyliodidearepreparedbythereactionwithofalkylchlorides/bromideswithNaIindryacetone.

Q.92. Whatareambidentnucleophiles?Explainwithanexample.

Solution: Nucleophileshavingtwonucleophilicsitesareambidentnucleophiles.Hence,ambidentnucleophileshavetwositesthroughwhichtheycanattack.

Nitriteionisanexampleofanambidentnucleophile.Itcaneitherattackthroughoxygenresultingintheformationofalkylnitritesoritcanattackthroughnitrogenresultingintheformationofnitroalkanes.

Q.93. WhichcompoundineachofthefollowingpairswillreactfasterinSN2reactionwithOH-?CH3BrorCH3I

Solution: InSN2mechanism,thereactivityofhalidesforthesamealkylgroupincreasesintheorderR-F<<R-Cl<R-Br<R-I.Asthesizeoftheionincreases,itbecomesabetterleavinggroup.Therefore,CH3IwillreactfasterthanCH3BrinSN2reactionwithOH-.

Q.94. WhichcompoundineachofthefollowingpairwillreactfasterinSN2reactionwithOH-?

(CH3)3CClorCH3Cl

Solution: TheSN2mechanisminvolvestheattackofthenucleophileattheatombearingtheleavinggroup.TheorderofreactivityofalkylhalidestowardsSN2reaction,tertiaryhalide,secondaryhalideprimaryhalideandmethylhalide.But,inthecaseof(CH3)3CCl,theattackofthenucleophileatthecarbonatomishinderedbecauseofthepresenceofbulkysubstituentsonthatcarbonatombearingtheleavinggroup.Ontheotherhand,therearenobulkysubstituentsonthecarbonatombearingtheleavinggroupinCH3Cl.Hence,CH3Clreactsfasterthan(CH3)3CClinSN2reactionwithOH-.




Intextquestion

Q.1. Writethestructureofthefollowingcompound:2-chloro-3-methylpentane

Solution: Inthegivenmolecule,therootwordis"pent".Soithasfivecarbonatomsintheparentchain.Twosubstituentsi.e.,chlorineandmethylgrouppresentatsecondandthirdcarbon.Thesuffixis"-ane".Soallcarbonatomsbondedeachotherwithsingle(sigma)bond.Hence,thestructureis

Q.2. Writethestructureofthefollowingcompound:1-chloro-4-ethylcyclohexane

Solution: Inthegivenmolecule,therootwordis"hex".Soithassixcarbonatomsintheparentchain.Twosubstituentsi.e.,chlorineClandethyl-C2H5grouppresentat1stand4thcarbonrespectively.Thesuffixis"-ane".Soallcarbonatomsbondedeachotherwithsingle(sigma)bond.Theword"cyclo"indicatesallsixcarbonatomsformaringorclosedstructure.Hence,thestructureis

Q.3. Writethestructureofthefollowingcompound:4-tert.Butyl-3-iodoheptane

Solution: Inthegivenmolecule,therootwordis"hept".Soithassevencarbonatomsintheparentchain.Twosubstituents(writteninprefixpart)i.e.,iodoandtert.Butylgrouppresentat 3rdand4thcarbon.Thesuffixis"-ane".Soallcarbonatomsbondedeachotherwithsingle(sigma)bond.Hence,thestructureis

Q.4. Writethestructureofthefollowingcompound:1,4-Dibromobut-2-ene

Solution: Inthegivenmolecule,therootwordis"But".So,ithasfourcarbonatomsintheparentchain.Twobrominegroupsareattachedat 1stand4thcarbon.So,theprefix"dibromo"isused.Thesuffixis"-ene"whichindicatesthepresenceofadoublebondwhichislocatedatsecondcarbon.Hence,thestructureis

Q.5. Writethestructureofthefollowingcompound:1-Bromo-4-sec.butyl-2-methylbenzene

Solution: 1-Bromo-4-sec.butyl-2-methylbenzene

Primaryprefix=-Br(Bromo)Substituents=-CH3(methyl)and

CH3-CH|-CH2-CH3(Secondarybutyl)Parenthydrocarbon=Benzene

Q.6. WhyissulphuricacidnotusedduringthereactionofalcoholswithKI?

Solution: InthepresenceofsulphuricacidH2SO4,KIproducesHI.2KI(s)Potassiumiodide+H2SO4(l)Sulphuricacid→2KHSO4(s)Potassiumhydrogensulphate+2HI(g)Hydrogeniodide

SinceH2SO4isanoxidisingagent,itoxidisesHI(producedinthereactiontoI2).2HI(g)Hydrogeniodide+H2SO4(l)Sulphuricacid→SO2(g)Sulphurdioxide+I2(s)Iodine+H2O(l)Water

Thus,thereactionbetweenalcoholandHItoformanalkyliodidecannotoccur.Hence,sulphuricacidisnotusedduringthereactionofalcoholswithKI.Instead,anon-oxidisingacidsuchasH3PO4isused.

CH3OH(l)Methanol+KI(s)Potassiumiodide+H3PO4(l)Phosphoricacid→∆CH3-I(l)Iodomethane+KH2PO4(s)Potassiumdihydrogenphosphate+H2O(l)Water

Q.7. Writestructuresofdifferentdihalogenderivativesofpropane.




Solution: Therearefourdifferentdihalogenderivativesofpropane.Thestructuresofthesederivativesareshownbelow:

Note:Chemicalcompoundsthathaveidenticalchemicalformulaebutdifferinpropertiesandthearrangementofatomsinthemoleculearecalledisomers.

Q.8. AmongtheisomericalkanesofmolecularformulaC5H12,identifytheonethatonphotochemicalchlorinationyieldsfourisomericmonochlorides.

Solution: TheisomerofthemolecularformulaC5H12shouldcontainfourdifferenttypesofH-atomstohavefourisomericmonochlorides.Thus,theisomeris2-methylbutane.ThefourtypesofH-atomsarelabelledasa,b,candd.

Q.9. AmongtheisomericalkanesofmolecularformulaC5H12,identifytheonethatonphotochemicalchlorinationyieldsasinglemonochloride.

Solution: OnlyonetypeofhydrogenatomsintheisomerofthealkaneofthemolecularformulaC5H12shouldbetheretohaveasinglemonochloride.Thisisbecausethereplacementofanyhydrogenatomleadstotheformationofthesameproduct.Thus,theisomerisneopentane.

Neopentane

Q.10. AmongtheisomericalkanesofmolecularformulaC5H12,identifytheonethatonphotochemicalchlorinationyieldsthreeisomericmonochlorides.

Solution: TheisomerofthealkaneofthemolecularformulaC5H12shouldcontainthreedifferenttypesofH-atomstohavethreeisomericmonochlorides.Thus,theisomerisn-Pentane.ThethreetypesofHatomsarelabelledasa,bandc.

Q.11. Drawthestructureofmajormonohaloproductsinthefollowingreaction:

Solution:

Itisasubstitutionreaction.

NOTE:ThionylchlorideispreferredbecauseinthisreactionalkylhalideisformedalongwithgasesSO2andHCl.Thetwogaseousareescapable,hence,thereactiongivespurealkylhalides.


Solution:

Thisreactionisassociatedwithfreeradicalmechanismandbrominationdoesnottakeplaceonthebenzenering.





Solution:

Thehydroxylgroupofanalcoholisreplacedbyhalogenonreactionwithconcentratedhalogenacids.


Solution:

ItisatypeofadditionreactionwhereMarkovnikovproductisamajorproduct.Iodinewilladdtothecarbonatomhavinglessernumberofhydrogenatoms.

Q.15. Drawthestructureofmajormonohaloproductsinthefollowingreaction:CH3CH2Br+NaI→

Solution: CH3CH2Br(l)Ethylbromide+NaI(s)Sodiumiodide→CH3CH2I(s)Ethyliodide+NaBr(s)Sodiumbromide

Alkylhalideservesasleavinggroupatthereactivesp3hybridisedcarbon.Theiodidedisplacesthebromideleavinggroup,resultinginasubstitutedproduct(alkyliodide)andsodiumbromide.


Solution:

Thisreactionproceedsthroughfreeradicalmechanismandformallylproduct.

Q.17. Arrangethesetofcompoundsinorderofincreasingboilingpoints.Bromomethane,Bromoform,Chloromethane,Dibromomethane.

Solution:

Foralkylhalideshavingthesamealkylgroup,theboilingpointincreaseswithanincreaseintheatomicmassofthehalogenatom.Since,theatomicmassofBromineisgreaterthanthatofChlorine,theboilingpointofbromomethaneishigherthanthatofchloromethaneduetoVanderWaalforces.

Also,foralkylhalideshavingthesamealkylgroup,theboilingpointincreaseswithanincreaseinthenumberofhalides.Therefore,theboilingpointofdibromomethane(CH2Br2)ishigherthanthatofchloromethane(CH3Cl)andbromomethane(CH3Br),butlowerthanthatofbromoform(CHBr3).

Q.18. Arrangethesetofcompoundsinorderofincreasingboilingpoints.1-Chloropropane,Isopropylchloride,1-Chlorobutane.

Solution:

Foralkylhalideshavingthesamealkylgroup,theboilingpointincreaseswithanincreaseintheatomicmassofthehalogenatom.Sinceallhavechloride,so,alldependsonalkylchain.Butanehasoneextracarbonthanpropane.So,1-Chlorobutanehasahigherboilingpointthan1-Chloropropane.Also,theboilingpointdecreasesasbranchingincreases.

BoilingPointorder:Isopropylchloride<1-Chloropropane<1-Chlorobutane

Q.19. WhichalkylhalidefromthefollowingpairwouldyouexpecttoreactmorerapidlybyanSN2mechanism?Explainyouranswer.

Solution: 2-bromobutaneisa2°alkylhalide,whereas1-bromobutaneisa1°alkylhalide.Theapproachingofnucleophileismorehinderedin2-bromobutanethanin1-bromobutane.Therefore,1-bromobutanereactsmorerapidlythan2-bromobutanebySN2mechanism.





Solution: 2-bromobutaneis2°alkylhalide,whereas2-bromo-2-methylpropaneis3°alkylhalide.Thus,greaternumberofsubstituentsarepresentin3°alkylhalidethanin2°alkylhalideforhinderingtheapproachingnucleophile.Therefore,2-bromobutanereactsmorerapidlythan2-bromo-2-methylpropanebyanSN2mechanism.


Solution: Boththealkylhalidesareprimary.However,thesubstituent -CH3isatagreaterdistancetothecarbonatomlinkedtoBrin1-bromo-3-methylbutanethanin1-bromo-2methylbutane.Therefore,theapproachingnucleophileislesshinderedincaseoftheformerthanincaseofthelatter.Hence,1-Bromo-3-methylbutanereactsfasterthan1-bromo-2-methylbutanebySN2mechanism.

Q.22. Inthefollowingpairofhalogencompounds,whichcompoundundergoesfasterSN1reaction?(i)

and(ii)

Solution: Thealkylhalide(i)is3°while(ii)is2°.Therefore,(i)forms3°carbocationwhile(ii)forms2°carbocation.Greaterthestabilityofthecarbocation,fasteristherateof SN1reaction.3°carbocationismorestabledueto9hyperconjugationandmore+Ieffectof3-CH3groupswhile2°carbocationformedhas4hyperconjugationand2-C2H5(+Igroup)groups.So,itislessstable.

Q.23. Inthefollowingpairofhalogencompounds,whichcompoundundergoesfasterSN1reaction?(i)

and(ii)

Solution: Thealkylhalide(i)is2°while(ii)is1°.2°carbocationismorestablethan1°carbocationbecausein2°carbocation

,5hyperconjugationsaretakingplaceand+Ieffectoftwoalkylgroupswhilein

,2hyperconjugationsaretakingplaceand+Ieffectof-C5H11group.Therefore(i),2-chloroheptane,undergoesfasterSN1reactionthan(ii),1-chlorohexane.

Q.24. IdentifyA,B,C,D,E,RandR1inthefollowing:




Solution:

When an alkyl halide is treated with Na inthepresenceofdryether,hydrocarboncontainingdoublethenumberofcarbonatomsaspresentintheoriginalhalideisobtainedastheproduct.ThisreactionisknownasWurtzreaction.Therefore,thehalide R'-X is

R'XontreatmentwithMggivesDi.e.,

DontreatmentwithwatergivesE,







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