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18217 Alkyl Halides and AminesMechanism:The attack of nucleophile on carbon and the departure of the halide ion take placesimultaneously in single step.This is rate-determining stepbecause the bond breakingand bond making processesoccur simultaneously. Sincetwo molecules are undergoingchange in covalency in ratedetermining step. It is a bimolecular nucleophilic substitution reaction which is taking place inone step. This mechanistic picture is based upon the following evidences.1) Kinetic Evidence:The rate of an SN2 reaction depends upon the concentration of nucleophile as well as theconcentration of alky halide. The rate expression for the reaction can be written asRate = [Nu][R-X]Where k = specific rate constant.This means that the rate of reaction will be double if the concentration of any of the two is doublee.g., the rate of increases when Cone of either ŌH or CH3-Br is increased.2) Stereo Chemical Evidence:A bimolecular nucleophilic substitution always occurs with inversion of configuration. Thecarbon atom in transition state is sp 2 -hybridized and is planar. The attacking nucleophile ad theleaving groups are present in the transition state on opposite sides of electrophilic carbon atom.Comparison of SN1 and SN2 MechanismSr. No. SN1 Sr. No. SN2(1)(2)(1)(2)(3)(4)It is a two step mechanism.First step is slow one andsecond is fast.It is a unimolecularreaction.It is favoured in polarsolvents.(3)(4)It is a single step mechanism.It has only one step and thatis slow.It is a bimolecular reaction.It is favoured in non-polarsolvents.
17 Alkyl Halides and Amines(5)(6)(7)Mostly tertiary alkyl halidesgive this reaction.50 % is inversion and 50%retension of configurationtakes place.Rate = K[R-X)(5)(6)(7)Mostly primary alkyl halidesgive this reaction.100% inversion ofconfiguration takes place.Rate = [Nu][R-X]17.1.7 1,2 Elimination ReactionsDefinition of Elimination Reaction:“The chemical reaction in which two groups are eliminated from two adjacent atoms iscalled elimination reaction”. Since β-hydrogen is necessary for eliminations, it is also called β-elimination.Explanation:β-hydrogen atom in alkyl halides is slightly acidic due to electron with drawing effect ofhalogen.183The attacking nucleophile can either attack α-carbon to give substitution product or β-hydrogen to give elimination reaction. Strong bases such as OH OR, NH2 cause elimination in preferences to substitution.Highly polarizable nucleophile and weak bases such as I - , RS - etc. give substitution reactions.E1 mechanism“It is unimolecular two step elimination reactions.”
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Textbook ofChemistryGrade 12
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OUR MOTTOStandards Outcomes Access
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CONTENTSNo. Chapter Name P. No.1314
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13 s and p - Block ElementsP [Ne] 3
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913 s and p - Block Elements(b) Phy
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13 s and p - Block ElementsArgonArg
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13 s and p - Block ElementsSulphurS
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13 s and p - Block ElementsThose ox
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13 s and p - Block Elements17Fig 13
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13 s and p - Block ElementsWith hot
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13 s and p - Block ElementsChlorine
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13 s and p - Block ElementsThe alum
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13 s and p - Block Elements13.1.6 H
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13 s and p - Block ElementsNotice t
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13 s and p - Block ElementsRb red (
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I2I1 + I213 s and p - Block Element
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13 s and p - Block ElementsCalcium,
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13 s and p - Block ElementsThis is
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13 s and p - Block Elements9. Behav
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13 s and p - Block Elements13.4.2 T
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13 s and p - Block ElementsThis fir
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13 s and p - Block ElementsWe know
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13 s and p - Block ElementsCarbon a
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13 s and p - Block Elements51Quick
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13 s and p - Block ElementsIt has b
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13 s and p - Block Elements55Quick
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13 s and p - Block Elementstoxicity
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13 s and p - Block Elementsviii. Wh
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v14 d and f - block elements transi
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15 Organic Compounds15.1 SOURCES OF
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15 Organic Compounds1053. Melting a
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15 Organic Compounds107Quick Quiz1.
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15 Organic CompoundsNitrileMethyle
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15 Organic Compounds6. There is a g
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15 Organic Compounds113C) Detection
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15 Organic Compounds115iii. Which o
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16 Hydrocarbons11716.1 TYPES OF HYD
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16 Hydrocarbons119orororQuick Quiz1
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16 Hydrocarbons1213-Ethyl-2,3,5-tri
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16 Hydrocarbons123(b) Alkanes are n
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16 Hydrocarbons125II. CycloalkanesA
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16 Hydrocarbons127shown again below
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16 Hydrocarbons129Activity1. Name t
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Page 135 and 136: 16 Hydrocarbons133HydrationAddition
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Page 139 and 140: 16 Hydrocarbons137benzeneconjugated
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Page 145 and 146: 16 Hydrocarbons143No geometrical is
Page 147 and 148: 16 Hydrocarbons1451) MetamerismThis
Page 149 and 150: 16 Hydrocarbons147(b)(c)(d)(e)16.7.
Page 151 and 152: 16 Hydrocarbons149terminal alkyne p
Page 153 and 154: 16 Hydrocarbons151BrominationChlori
Page 155 and 156: 16 Hydrocarbons153CumeneDisubstitut
Page 157 and 158: 16 Hydrocarbons155These are two equ
Page 159 and 160: 16 Hydrocarbons157Thus molecule of
Page 161 and 162: 16 Hydrocarbons159(c) Addition of H
Page 163 and 164: 16 Hydrocarbons161Explanation and E
Page 165 and 166: 16 Hydrocarbons163SulfonationThe in
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Page 169 and 170: 16 Hydrocarbons167On the other hand
Page 171 and 172: 16 Hydrocarbons169SOCIETY, TECHNOLO
Page 173 and 174: 16 Hydrocarbons171Exercise1. The mo
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Page 191 and 192: 17 Alkyl Halides and Amines189CH 3I
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Page 199 and 200: 17 Alkyl Halides and Amines197Key P
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