17.1.3 - Optical activity and reaction mechanisms Flashcards
In an SN1 pathway, what is formed when a halogenoalkane reacts with a hydroxide ion?
A racemic mixture
Why is a racemic mixture formed in a reaction between a hydroxide ion and a tertiary halogenoalkane?
The hydroxide ion can attack the planar intermediate from either side resulting in equal amounts of both enantiomers.
What is formed for a short duration when a primary halogenoalkane reacts with a hydroxide ion?
A transition state
Where C-OH and C-halogen bonds are partially attached.
What happens to the arrangement of groups after a substitution reaction?
The groups are inverted
What do dashed lines represent in a transition state?
Partial bonds.
What happens to the optical activity of the product due to the inversion of the groups in an SN2 reaction?
The optical activity of the product is different to that of the reactant as the groups have been inverted.
e.g If reactant is dextrorotary the product will be laevorotary
Why will the product of an SN1 reaction between a tertiary halogenoalkane and a hydroxide ion not be optically active?
A racemic mixture is formed.
Both enantiomers rotate plane polarised light by the same amount in different directions.
So there is no optical activity
What reaction pathway to primary and tertiary halogenoalkanes undergo?
Primary = SN2
Tertiary = SN1
