Unit 4.1 Stereoisomerism (og)

Question 1

What are the 2 types of isomerism?

Answer 1

• Structural isomerism
• Stereoisomerism

Question 2

Define structural isomerism

Answer 2

Same molecular formula but different structural formulae

Question 3

Define stereoisomerism

Answer 3

Same molecular formula but atoms occupy different positions in space

Atoms arranged in 3D space

Question 4

What are the 3 types of structural isomerism?

Answer 4

1. Chain isomerism (CH₃ above or below or summin)
2. Position isomerism (Functional group different places)
3. Functional group isomerism (Functional group within, also in diff places)

Question 5

What are the 2 types of stereoisomerism?

Answer 5

1. Geometrical isomerism
2. Optical isomerism

Question 6

What is geometrical isomerism

Answer 6

• Occurs due to the restricted rotation of C=C double bonds
• 2 forms
• E and Z (CIS and TRANS)

Question 7

What is optical isomerism

Answer 7

• Occurs when molecules have a chiral centre
• Get two non-superimposable mirror images

4 different groups of atoms attached

Question 8

So u obviously, should know how to tell what isomerism is taking place.
However, how to actually name them, yano?

Answer 8

I’ll look at book…. right???

Question 9

What molecules can have geometrical isomerism?

Answer 9

The ones with the pi-bond (C=C double bond)
Cuz like, restricted rotation
And so 2 different forms: CIS (Z) & TRANS (E)

Question 10

How do u tell if geometrical isomerism exist?

Answer 10

1. Pi-bond n shi
2. Two different atoms/groups attached

Question 11

What molecules can have optical isomerism?

Answer 11

Appears to be 4 different groups attached… so….?

Question 12

What are the 2 different forms of optical isomerism?

Answer 12

• Optical isomers
• Enantiomers

Question 13

When does optical isomerism occur?

Answer 13

• When molecules have a chiral centre

Question 14

What consists of a chiral centre?

Answer 14

• Asymmetric carbon atom
  (4 different atoms/groups arranged tetrahedrally around)

Question 15

Explain thalidomide scandal (ADHD edition)

Answer 15

1. Thalidomide marketed as mild sleeping pill
2. Unfortunately caused babies born with malformed limbs D:
3. Pair of thalidomide enantiomers: 50:50 ratio (equimolar ratio)
4. Turns out it had teratogenic deformities despite only one of them causing it
5. That’s cuz molecule interconverts between isomers
6. Pure sample of only one isomer = IMPOSSIBLE

Question 16

Define equimolar ratio?

Answer 16

• 50:50 mixture
• of enantiomers
• aka racemic mixture

Question 17

How would u spot chiral centres?

Answer 17

Remember:
- 4 different atoms/groups arranged tetrahedrally around it
So, 4 different atoms/groups around a single atom.
Can be found in like an alkane or summin
Skeletal formulas too

Question 18

Explain molecules containing chiral carbons having two forms?

Answer 18

• They are non-superimposable mirror images of each other
  (Can’t stack the molecules on top of each other)

Question 19

U might have to:
1. Draw a displayed formula of such
2. Spot a chiral molecules
3. Re-draw the molecule in 3D
4. And its mirror image

Answer 19

Okay?

Question 20

How do u get differences in optical isomers?

Answer 20

• Differ in their reaction to plane-polarised light
• Polarimeter type shi
• Rotation = differences for sure = cuz of brightness

Question 21

State the model answer of polarimeter outcomes (optical isomers differences)

Answer 21

• A single enantiomer will rotate plane polarised light in a single direction
• Either to the left or the right
• The other enantiomer would rotate the light in the opposite direction

Question 22

What it means if the light appears to have turned to the right?

Answer 22

It’s DEXTROROTATORY
(d) or (+) form

Question 23

What it means if the light appears to have turned to the left?

Answer 23

It’s LAEVOROTATORY
(l) or (-) form

Question 24

Why is there no net effect on the rotation of plane polarised light?

Answer 24

The 2 directions they rotate the light is cancelled out

Question 25

You made flash cards, that’s great. U only have like 1 day to revise all this tho. Plus do u even have time for questions?

Answer 25

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