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Isomers (Chirality) Flashcards

1
Q

Define Isomers

A

Different compounds with the same molecular formula

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2
Q

Define Constitutional Isomers / Structural Isomers

A

Isomers whose atoms have a different connectivity.

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3
Q

Define Stereosiomers / optical / configurational

A

Isomers with the same molecular formula and same connectivity of atoms but different arrangement of atoms in space.

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4
Q

2 branches of Stereosiomerism:

A

Enantiomers (mirror images)

Diastereomers (not mirror images)

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5
Q

Geometric Isomerism

A

‘cis’ and ‘trans’

cis = same side (Z)
trans = opposite (E)
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6
Q

Optically inactive..

A

chiral

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7
Q

Racemic mixture

A

1:1 mixture of enantiomers, racemate

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8
Q

Geometric Isomerism

How do we assign priority group?

A

CIP rule

Based on highest atomic number = priority

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9
Q

Chiral means..

A

Assymetrical and mirror image are not superimposable.

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10
Q

In a chiral molecule, how do we differentiate them?

A

S or R rotation

S= anticlockwise 
R = clockwise
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11
Q

How do we assign S or R rotation?

A

Assign priority groups using CIP - number 1-4

and see the direction of priority groups

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12
Q

What should always be assigned priority group number 4?

A

Hydrogen - lowest priority.

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13
Q

What if Hydrogen is not on number 4?

A

Assign chirality then reverse

e.g. if its S with H at the front, answer becomes R.

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14
Q

What if Hydrogen is on a plane bond?

A

Rotate before assigning.

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15
Q

Do R and S enantiomers have the same physical and chemical properties? Why?

A

Yes because they have the same arrangement.

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16
Q

How do R and S enantiomers differ? (2)

A

Based on

rotation of plane polarised light

interaction with other chiral molecules

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17
Q

Is a racemic mixture optically active or inactive?

A

Inactive - equal amounts.

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18
Q

How to calculate light passing through a polarising filter? (equation)

A

a (Degrees) = measured rotation / C x L

c = conc g/ml

L = path length

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19
Q

What is enantiomeric excess?

A

When one enantiomer is present in higher concentration than the other.

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20
Q

Equation for enantiomeric excess

What if its in moles/grams?

A

observes rotation / rotation of pure. X 100

R - S / R+ S X100

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21
Q

Significance of Enantiomers in drugs
Ibuprofen

Whats it for?
Whats the significance here?

A

S enantiomer is responsible for the anti-inflammatory properties.

R = not harmful and there is an enzyme that converts R to S.

22
Q

Significance of Enantiomers in drugs
Fluoxetine

Whats it for?
Whats the significance here?

A

Depression

S = pharmacological activity

23
Q

Significance of Enantiomers in drugs
Warfarin

Whats it for?
Whats the significance here?

A

Reduce blood clots

S = more active than R

24
Q

Significance of Enantiomers in drugs
Thalidomide

Whats it for?
Whats the significance here?

A

Was for morning sickness but caused babies to be born without limbs.

Only one enantiomer had this effect.

25
Describe Enantiomers
A single chiral centre, can either be R or S. Optically Active
26
Describe Diastereisomers
Multiple chiral centres. Can be RR SR etc and can use 2 n to find out all the possibilities. where n is the number of chiral centres
27
Describe Meso-compounds
Can have multiple chiral centres but are symmetrical (unlike the rest) Optically INACTIVE.
28
Can Enantiomers be separated?
No because of their identical properties but they can be converted to diastereoisomers with different physical properties.
29
What is a classic method of 'separating' Enantiomers?
Resolution Through the preparation of appropriate diastereoisomeric derivates.
30
Can Diastereisomers be separated?
Yes because they have different physical properties and reactivity - melting point, boiling points, solubilities etc.
31
Give an example of how we can separate Diastereoisomers: (3)
Use a solvent in which one diastereoisomer is very soluble in and the other is less. Both will dissolve, less soluble one crystallises out and is filtered other is evaporated
32
Define Resolution
The separation of enantiomers from either racemic mixture or enantiomerically enriched mixture. Via converting into diastereoisomers.
33
Describe Chiral Chromatography
Racemic solution is passed over a chiral stationary phase giving rapid and reversible diastereotopic interaction.
34
Classic Resolution | involving Salts
R- acid + S-acid enantiomers converted into R,S salt and S,S salt diastereoisomers Crystalise and separate into ----- R, S salt and S,S salt Reacidify using HCL. S-baseH+ and S-baseH+ becomes R-acid and S-acid separated
35
Resolution by Esterification
Form covalent bond between chiral carboxylic acid and alcohol = diastereoisomers. Separate them by crystallisation and then recover the separate enantiomers by ester hydrolysis.
36
How many stereoisomer can Meso compounds have?
3 stereoisomers assuming 2 identical chiral carbon atoms with no other stereo centres
37
2 examples of pharmacological effects of chirality:
one may have strong binding to target, other may not one may be active with no adverse effects, other may be toxic
38
2 examples of biochemical effects of chirality:
if a chiral reactant is used, do the isomers form the same products or does each form a different product? Are some stereoisomers formed more than others?
39
Stereoselective reaction
Preferential formation of one stereoisomer over another No prevention of formation but one predominates
40
Stereospecific reaction
Each stereoisomeric reactant produces a different stereoisomeric product or a different set of products.
41
Stereoselectivity reaction can... (2)
- can show no stereoselectivity, results in racemisation | - can show by inverting stereochemistry, conserving it to preferentially reacting to form particular ones,
42
Stereochemical outcomes are important in: (3)
metabolism of drugs drug action at receptors toxicity through undesirable activity of stereoisomers
43
What is a concerted reaction?
Bond making and breaking happens in the same step. (SN2)
44
Stereochemistry is either ...... or ...... in concerted reactions
inverted or conserved
45
What is a non-concerted reaction?
Bond breaking and making occurs in different steps. (SN1) Intermediates allow changes to stereochemistry.
46
Do non-concerted reactions have stereoselectivity?
no stereoselectivity
47
In non concerted reactions, from where can the planar intermediate be attacked?
can attack planar intermediate from above or below the plane equally easily. Forms planar intermediate carbocation. Also planar radicals.
48
What is syn addition?
Two substituents added to the same side of the double bond similar to cis
49
What is anti addition?
Two substituents added to opposite sides of the double bonds similar to trans
50
Enzymes can react with pharmaceuticals to...
destroy stereochemistry or to form chiral products with alternative activities which is why its important a drug is administered to the right place.

Medicinal Chemistry (2 decks)

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