Optical Isomerism And Reaction Mechanisms
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Which halogenoalkanes can do Sn2
Primary
Process of Sn2 mechanism
-Nucleophile approaches from opposite side of molecule to halogen as like charges repel -forms transition state with overall negative charge with nucleophile and halogen both bonded -halogen leaves
What is produced by Sn2
Optically active product if optically active halogenoalkane
How many steps in Sn2
One as nucleophile attacks and leaving group depart simultaneously
Which halogenoalkanes do Sn1 and why
Secondary and tertiary as presence of methyl groups prevents the nucleophile from attacking from the other side of the halogen
Why is it possible for carbocation to be produced by secondary/tertiary
Due to positive inductive effect of the surrounding alkyl groups which stabilise positive charge
What is process of Sn1 mechanism
Halogen leaves forming carbocation -forms trigonal planar intermediate which can be attacked from above or below with equal probability by nucleophile -forms two forms of chiral alcohol in racemic mixture so in equal proportions (optically inactive)
Which step slow and which fast in Sn1
First step slow (forming carbocation) second fast (attack by nucleophile)
Rate equation for Sn1 reactions
Rate= k [halogenoalkane]
Rate equation for Sn2 reaction
Rate = k [halogenoalkane] [nucleophile]
What reacts more quickly tertiary, secondary or primary halogenoalkanes
Tertiary