Chirality

What is meant by the term stereoisomerism

Molecules with the same structural formula but different spacial arrangement of atoms

What are the types of stereoisomerism

Geometric or optical

How do optimal isomers occur

When two compounds have the same molecular formula but are not superimposible on each other

What are enantiomers

When a compound contains a carbon atom bonded to four different groups or atoms, existing in two forms which are non-superimposable mirror images of each other

What is a carbon atom with four different groups bonded to it called

A chiral centre

How do two chiral isomers affect plane polarised light

By rotating the plane in opposite directions

What is an optically inactive mixture containing enantiomers and how does it affect plane polarised light

• An equimolar or racemic mixture/racemate when enantiomers are in 1:1

• Does not rotate light as equal and opposite rotations cancel

How is plane polarised light made

By passing light through a polarising filter (a polaroid) and oscillates in only one plane

What are polarimeters used for

To determine whether a sample interacts with plane polarised light

What are the 6 parts of the polarising process to determine the enantiomers

Lamp → monochromator filter → polarising filter → sample cell → analysing filter → detector

What is an Sn1 reaction

When there is only one species in the rate determining step

What is a Sn2 reaction

Where there are two species involved in the rate determining step

Which out of 1˚2˚3˚ has the fastest rate of reaction in a Sn2 nucleophilic substitution reactiob

1˚>2˚>>3˚

Explain how the concept of steric hinderance explains the rate 1˚>2˚>>3˚in a Sn2 reaction

A tertiary haloalkane is surrounded by 3 alkyl groups which inhibit the attack from a nucleophile (steric hinderance) so nucleophile is unable to attack the carbon in C-X bond as readily as it could for primary

Outline the Sn2 mechanism for the reaction between 2-bromopropane and NaOH

Outline the Sn2 mechanism for the reaction between 2-bromobutane and NaOH

Outline the Sn1 mechanism for the reaction between 2-bromopropane and NaOH

Which out of 1˚2˚3˚ has the fastest rate of reaction in a Sn2 nucleophilic substitution reactiob

3˚>>2˚>1˚

Explain how the stability of carbocations explains the rates 3˚>>2˚>1˚ In a Sn1 reaction

Reaction proceeds through a carbocation intermediate. Tertiary carbocations are most stable than primary or secondary due to three alkyl groups resulting in positive inductive effects

Outline the Sn1 mechanism for the reaction between 2-bromobutane and NaOH