✅17 - Organic Chemistry II
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What type of isomerism is optical isomerism?
Stereoisomerism
What are structural isomers?
Compounds with the same molecular formula but with different structural formula
What are functional group isomers?
They differ because they have different functional groups
What are chain isomers?
Differ because they have different patterns of branching in their carbon chains
What are positional isomers?
Differ because the same functional group is attached to different carbon atoms in the chain
What are stereoisomers?
Have the same structural formula but differ because their atoms or groups are arranged differently in three dimensions
What are geometric isomers?
Differ because their atoms or groups are attached at different positions on opposite sides of a C-C double bond
What is chirality?
Two or more molecules that appear identical but cannot be superimposed onto one another.
What are chiral centres?
Carbons with four different atoms or groups attached
What is plane polarised light?
Light in which oscillations exist in planes at right angles to the direction of travel.
What can be used to convert unpolarised light into plane polarised light?
Materials such as Polaroid, which absorb all of the oscillations expect those in a single plane
What is polarimetry?
The use of a polarimeter to measure the amount of optical activity, if any, of a substance.
What is a monochromatic light source?
One of only one colour or frequency
What is a polariser?
A polarising filter that converts unpolarised light into plane polarised light
What happens in a polarimeter if a substance is optically active?
The plane of polarisation will be rotated so it is no longer vertical - Clockwise = dextrorotatory, Anticockwise = laevorotatory
What is the second polarising filter in a polarimeter called?
The analyser
What does the analyser do?
It is rotated to a position here the maximum light intensity can be seen. The angle of rotation is measured and quoted.
Do enantiomers have identical physical properties?
Yes - apart from the direction in which they rotate plane polarised light.
Do enantiomers have identical chemical properties?
Yes - apart from the way they react with enantiomers of other substances
What is a racemic mixture?
One containing equal amounts of two enantiomers.
What does SN2 indicate?
S = substitution N= nucleophillic 2=bimolecular and second order
What does SN1 indicate?
S = Substitution N = Nicleophillic 1 = unimolecular and first order
How can optical activity be used as evidence for SN2?
Because of the inversion that occurs in the SN2 mechanism, the optical activity of the product is different to that of the reactant. If the reactant is dextrorotatory, the product will be laevorotatory and vice versa.
How can optical activity be used as evidence for SN1 mechanisms?
If the reaction is via SN1, there will be no optical activity in the product.