Isomerism and Stereochemistry

Question 1

Stereochemistry: chemistry of molecules in 3D

Answer 1

Organic molecules
> structural isomers + stereoisomers
> conformational + configurational
> optical + geometrical

Question 2

Structural isomers

Answer 2

same molecular formula
atoms bonded in different orders
Different properties

Question 3

Conformational

Answer 3

rotation around σ bonds and 3D shape of sp3 centre

Question 4

Stereoisomers

Answer 4

same molecular formula
atoms bonded in same order
different 3D arrangement

Question 5

Configurational

Answer 5

No conversion by rotation of single bond

Question 6

Geometrical

Answer 6

cis/trans
E/Z

stereoisomers that arise due to restricted rotation
within a molecule

Question 7

Optical

Answer 7

D/L
S/R

Question 8

how many structural isomers?

Answer 8

7

Question 9

Montelukast:

Answer 9

Symptomatic relief of seasonal allergic rhinitis in patients with asthma and prophylaxis of asthma in children (note: oral formulation)

Question 10

conformational isomers (CI)

Answer 10

configurational isomers: optical isomers (OI)
configurational isomers: geometrical isomers (GI)

Question 11

tetrahedral angle, degree?

Answer 11

109.5 degree

Question 12

All single bonds are ____to rotate
Although might be restricted by nearby ______ groups

Answer 12

free
bulky

Question 13

cis

Answer 13

same side

Question 14

trans

Answer 14

opposite side

Question 15

highest priority?

Answer 15

biggest atomic number

Question 16

geometric can happen only when…

Answer 16

two different groups at each end of double bond

Question 17

use E/Z for when…

Answer 17

you have multiple functional groups and there are different priorities dependent on the Ar

Question 18

carbon has _____ priority than hygrogen

Answer 18

higher

Question 19

e.g. 1-bromo-1-chloro-2-methylbut-1-ene:
search diagram

Answer 19

Bromine is higher priority than chlorine
1. Carbon is same priority as carbon
2. Carbon is higher priority than hydrogen

For linear carbon chains, the longest one is always highest priority

Question 20

double bond - rotation?

Answer 20

cannot rotate

Question 21

when c attached to 4 diff groups;

Answer 21

When a carbon is attached to 4 different groups/ arms present, none of which are the same

Question 22

Configurational Isomers: chirality
think of left and right hand…

Answer 22

cannot be superimposed

Question 23

What is the Achiral carbon?

Answer 23

At least 2 same groups/atoms present
Yes plan of symmetry

compound and its mirror image are the same, can be superimposed

Question 24

Define Enantiomers:

Answer 24

Same physical/chemical properties
Differ in activities with plan polarised light that gives rise to optical isomerism, and also in their pharmacological actions

non-superimposable

Question 25

Chiral centre

Answer 25

the C in the middle functional groups attaches to it

Question 26

Chiral molecules ______ plane-polarised light: this is called ______ activity

Answer 26

rotate

optical

Question 27

Racemic Mixture

Answer 27

A mixture that contains more of one enantiomer than the other is optically active

Question 28

rotation - naming:
clockwise / anti-clockwise

Answer 28

Rotation clockwise direction: dextrorotatory, (+)
Anticlockwise rotation: levorotatory, (−)

Question 29

Examples of drugs that are racemic mixtures

Answer 29

atenolol
warfarin

Question 30

Configurational Isomers: D and L system are…

Answer 30

Fisher: (+)-glyceraldehyde enantiomer=D-glyceraldehyde,
(-)-glyceraldehyde enantiomer=L-glyceraldehyde

Question 31

How to assign R & S system?

Answer 31

1) Priority: from 1 to 4 = assigned on basis of atomic number.
Higher atomic number gets higher priority

2) Substituents: if no priority, the next set of atoms in the unassigned groups is examined

3) Double or triple bonds: assigned priorities as if both atoms were duplicated or triplicated

4) Arrange (rotate) the molecule: group 4 is pointing away from the viewer

Question 32

learn the different lines

Answer 32

thick black - pointing towards you
faint lines - pointing away from you

Question 33

Lowest-priority group always pointing ____ from us

Answer 33

away

Question 34

Each additional chiral centre generates ________ isomers

Answer 34

additional

Question 35

Labetalol

Answer 35

a member of the beta-blocker family (drugs that bind to beta-adrenergic receptors). It is used to treat hypertension, especially hypertension in pregnancy