Question

What is meant by sn1,sn2,sn3 reactions explain briefly and give difference between them and state 10 examples each

Question is for 7 marks

So please keep it somewhat big

Answer 1

Characteristics of SN¹ reactions: -


Two step reaction.
Rate of reaction = K [R — L]
It is a first order reaction.
Carbocation intermediate is formed. rearrangement of carbocation is possible.
Rate is dependent on stability of carbocation. [3°>2°>1°]
Rate of reaction also depends on stability of cation and anion.
Polar Protic Solvent favours SN¹ reaction. (As PPS dissolves both cation and anion in it)
Leaving group should be strong i.e. weak base (same as SN²).
Weak nucleophile performs SN¹ reaction. (Strong nucleophile will directly attack substrate resulting in E¹ reaction)
Rate of reaction is independent of concentration and strength of nucleophile.
Products formed will be both R- and S- form i.e. mirror image.
Low temperature favours SN¹ reactions.
Characteristics of SN² reactions: -


Single step reaction.
Rate of reaction = K [R — L] [Nu(:)]
It is a second order reaction.
Rate is dependent on concentration and strength of Nucleophile.
Transition state is formed which is sp² hybridized, planar structure. (Not sp³d as Carbon doesn't have d orbital.)
No carbocation intermediate formation.
Leaving group should be strong i.e. weak base.
Rate of reaction is inversely proportional to bulkiness of groups attached to C atom. [CH3Cl > CH3CH2Cl > CH3CH(CH3)Cl > CH3C(CH3)²Cl]
Rate of reaction 1° > 2° > 3° substrates.
Strong nucleophile performs SN² reactions. Nucleophile attacks substrate directly from backside.
Polar Aprotic Solvent like DMSO, DMF, DMA favours SN² reactions. (Because PAS doesn't dissolves/solvent cations and it dissolves only anions in solution, so by taking PAS cations are removed and only Nu(:) is only anion present to attack substrate.]
Walden inversion occurs.
Reaction is favored by low temperature. High temperature leads to E² reaction.
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