Isomers that have the same molecular formula but a different structural formula.
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Define 'positional isomer'.
Isomers that have the same molecular formula and chain length, but differ by the position of their functional group.
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Define 'functional isomer'.
Isomers that contain different functional groups.
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Define 'chain branching isomer'.
Isomers that have the same molecular formula but a different chain length.
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Define 'stereo isomer'.
Isomers that have the same molecular formula but a different arrangement of atoms in space.
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Define 'geometric isomer'.
These occur in alkenes only due to restriction of rotation about the double bond, as a result of the pi bond.
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Define 'optical isomer'.
Isomers that have the same molecular formula, but differ in how they interact with plane polarised light.
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Conditions for being a geometric isomer?
1. C=C bond. 2. Must have two different atoms on the LHS and two different atoms on the RHS. It doesnt matter whether the left hand groups are the same as the right hand groups.
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If a geometric isomer has an E before its name, this means that...
The highest priority groups are on the opposite sides.
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If a geometric isomer has an Z before its name, this means that...
The highest priority groups are on the same side.
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How can you tell if an atom has a higher priority?
It will have a larger Mr value.
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Shapes of molecules: if a molecule has 3 bond pairs and one lone pair...
It has a pyramidal shape and a bond angle of 107.5 degrees.
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Shapes of molecules: if a molecule has 5 bond pairs...
It has a trigonal bipyramid shape and has bond angles of 120 and 90 degrees.
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Define 'chiral centre'.
An atom within a molecule that is bonded to four different atoms/groups.
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Define 'enantiomers'.
Non-superimposable mirror image forms of each other that rotate the plane of polarised light in opposite directions.
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Define 'racemic mixture'.
An equimolar mixture of both enantiomers that has no overall effect on the plane of polarised light.
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It is possible to have enantiomers with two chiral centres. What are these called?
Diastereoisomers. They cannot be mirror image forms of each other.
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What affects the extent to which the plane of polarised light is rotated?
1. The enantiomer. 2. The conc of the enantiomer in the solution. 3. The length of the tube containing the solution through which light is passed. 4. The frequency of the light. 5. Temperature.
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What represents a rotation of plane polarised light to the right?
An R, + or D (clockwise).
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What represents a rotation of plane polarised light to the left?
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