This document provides an overview of isomerism for students. It begins by outlining the prior knowledge needed to understand isomerism and then defines the main types: structural isomerism, stereoisomerism, geometrical isomerism, and optical isomerism. For each type, examples are given to illustrate key concepts like different arrangements of carbon skeletons or functional groups (structural), restricted double bond rotation causing cis/trans forms (geometrical), and chiral centers producing non-superimposable mirror images (optical). Checklists are provided to identify isomerism possibilities in different molecules. The document aims to clearly define and differentiate the various isomerism types through detailed explanations, diagrams, and molecular
Basic concepts of organic chemistry such as structural formulas, different kinds of representation, types of isomerism, examples, alkanes, alkenes, alkynes etc.
Isomers are molecules with the same molecular formula, but different structural or spatial arrangements of the atoms within the molecule. The reason there are such a colossal number of organic compounds which is more than 10 million is partly due to isomerism.
Isomerism - Structural Isomerisms in Organic compoundsDr Venkatesh P
Structural Isomerism in Organic compounds - Chain Isomerism, Positional Isomerism, Functional Isomerism, Metamerism and Tautomerism explained with suitable examples. In Introduction, Definition of Isomerism and Stereoisomerism given simply to understand the difference between Structural and Stereo isomerism.
https://youtu.be/a0snq_oz50A
…….. “DRUGS” do something in our body as a result of their molecular structure, which determines:
1. Physicochemical properties
2. Chemical / biochemical reactivity
3. Shape
4. STEREO-CHEMISTRY
I hope You all like it. I hope It is very beneficial for you all. I really thought that you all get enough knowledge from this presentation. This presentation is about materials and their classifications. After you read this presentation you knowledge is not as before.
Basic concepts of organic chemistry such as structural formulas, different kinds of representation, types of isomerism, examples, alkanes, alkenes, alkynes etc.
Isomers are molecules with the same molecular formula, but different structural or spatial arrangements of the atoms within the molecule. The reason there are such a colossal number of organic compounds which is more than 10 million is partly due to isomerism.
Isomerism - Structural Isomerisms in Organic compoundsDr Venkatesh P
Structural Isomerism in Organic compounds - Chain Isomerism, Positional Isomerism, Functional Isomerism, Metamerism and Tautomerism explained with suitable examples. In Introduction, Definition of Isomerism and Stereoisomerism given simply to understand the difference between Structural and Stereo isomerism.
https://youtu.be/a0snq_oz50A
…….. “DRUGS” do something in our body as a result of their molecular structure, which determines:
1. Physicochemical properties
2. Chemical / biochemical reactivity
3. Shape
4. STEREO-CHEMISTRY
I hope You all like it. I hope It is very beneficial for you all. I really thought that you all get enough knowledge from this presentation. This presentation is about materials and their classifications. After you read this presentation you knowledge is not as before.
Catalytic Reactions in Catalytic Reforming
Catalytic Reforming Reactions
Sulfur Related Problems
Effects of Sulfur in Catalytic Reforming
Reactions in Catalytic Reforming
Catalytic Reforming Catalysts
Effect of Sulfur on Catalytic Reforming Catalysts
Catalytic Reformer Efficiency
VULCAN Sulfur Guards
VULCAN Sulfur Guards for Catalytic Reformers
VULCAN Guard Installation Protects Isomerization Catalysts
Liquid Phase vs Gas Phase: Relative Advantages
Liquid Phase Treating
Which active metal is best?
Thiophenes and Nickel Sulfur Guards
Sulfiding mechanisms with reduced metals
Thiophene adsorption on nickel
Advantages of Cu/Zn Over Nickel Sulfur Guards
Copper oxide vs Nickel
Nickel Sulfur Guards
Manganese Sulfur Guards
Naphtha Steam Reforming Catalyst Reduction with MethanolGerard B. Hawkins
Procedure for Naphtha Steam Reforming Catalyst Reduction with Methanol
Scope
This procedure applies to the in situ reduction of VULCAN Series steam reforming catalysts using methanol cracking to form hydrogen over the catalyst in the steam reformer.
The procedure is likely to be applied to plants using only heavier feeds (e.g.: LPG and/or naphtha) and some combination of VULCAN Series catalysts.
Introduction
A small number of steam reforming plants do not have an available source of the commonly used reducing media (e.g.: hydrogen, hydrogen-rich off-gas, natural gas). These plants will usually operate on LPG and/or naphtha feed only where cracking of this hydrocarbon is not usually advised for reduction of the steam reforming catalyst ...
Catalytic Reforming technology - Infographics
IFP Fixed-bed Semi-regenerative Unit Revamps, Troubleshooting
IFP (CCR) Technology Optimization
In trying to determine the potential benefits from revamping a Fixed-bed Semi-Regenerative catalytic reformer, a refiner must evaluate several areas of operation:
— What is the unit operating objective?
— What degrees of freedom are available for revamp /optimization?
— Can refinery margins, and the discretionary capital budgeting program support the revamp / optimization?
Refiners must select the catalytic reformer operating point that will maximize profit within the following:
1) the mechanical constraints of the unit and
2) the short term unit operating objectives.
projects that improve operating profit are compared with the required capital investment.
This is done using discounted cash flow, or one of a number of other capital budgeting analysis tools, and those projects with the greatest return are put at the top of the capital budget list.
Revamp objectives
Revamp Philosophy
Revamp options
Semi-Regenerative Reforming Unit
Typical Flow Scheme
Continuous Reforming Unit
Typical Flow Scheme
Revamp to Hybrid Operation
What may be achieved?
Typical C5+ Yield at Decreasing Pressure
Changes Required for Full Conversion
Typical Benefits of Full Conversion
Revamping of Existing Continuous Reforming Units
Fired Heaters Revamp
Burners
Reactor Options
Regeneration Section
Summary
The petroleum industry uses Reforming as a primary process for quality improvement to meet final fuel specifications as well as hydrogen and LPG production for many intermediate processing units. This course covers the core elements of Reforming technology. Key variables that affect product yields and properties are described and their impact on the optimisation of the unit operation discussed. A framework is presented for troubleshooting operating problems and, throughout this discussion, participants are encouraged to describe their specific challenges.
Catalytic Reforming Process is one of the most important processes in the petroleum and petrochemical industries which produce high octane number gasoline.
Unit II-Geometric isomerism and conformational isomer as PCI Syllabus of POC-IIIGanesh Mote
It Includes Cis-Trans Isomer, E& Z Nomenclature, Syn and Anti isomer, Determination of geometrical isomer, Conformations of ethane, Butane, Cyclohexane, Stereospecific and stereoselective addition reactions.
Model Attribute Check Company Auto PropertyCeline George
In Odoo, the multi-company feature allows you to manage multiple companies within a single Odoo database instance. Each company can have its own configurations while still sharing common resources such as products, customers, and suppliers.
The Art Pastor's Guide to Sabbath | Steve ThomasonSteve Thomason
What is the purpose of the Sabbath Law in the Torah. It is interesting to compare how the context of the law shifts from Exodus to Deuteronomy. Who gets to rest, and why?
This is a presentation by Dada Robert in a Your Skill Boost masterclass organised by the Excellence Foundation for South Sudan (EFSS) on Saturday, the 25th and Sunday, the 26th of May 2024.
He discussed the concept of quality improvement, emphasizing its applicability to various aspects of life, including personal, project, and program improvements. He defined quality as doing the right thing at the right time in the right way to achieve the best possible results and discussed the concept of the "gap" between what we know and what we do, and how this gap represents the areas we need to improve. He explained the scientific approach to quality improvement, which involves systematic performance analysis, testing and learning, and implementing change ideas. He also highlighted the importance of client focus and a team approach to quality improvement.
Read| The latest issue of The Challenger is here! We are thrilled to announce that our school paper has qualified for the NATIONAL SCHOOLS PRESS CONFERENCE (NSPC) 2024. Thank you for your unwavering support and trust. Dive into the stories that made us stand out!
The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
Ethnobotany and Ethnopharmacology:
Ethnobotany in herbal drug evaluation,
Impact of Ethnobotany in traditional medicine,
New development in herbals,
Bio-prospecting tools for drug discovery,
Role of Ethnopharmacology in drug evaluation,
Reverse Pharmacology.
3. ISOMERISM
Before you start it would be helpful to…
• know the functional groups found in organic chemistry
• know the arrangement of bonds around carbon atoms
• know what affects the boiling point of organic molecules
4. TYPES OF ISOMERISM
CHAIN ISOMERISM
STRUCTURAL ISOMERISM
Same molecular formula but
different structural formulae
POSITION ISOMERISM
FUNCTIONAL GROUP
ISOMERISM
GEOMETRICAL ISOMERISM
STEREOISOMERISM
Same molecular
formula but atoms
occupy different
positions in space.
Occurs due to the restricted
rotation of C=C double bonds...
two forms… E and Z (CIS and
TRANS)
OPTICAL ISOMERISM
Occurs when molecules have a
chiral centre. Get two nonsuperimposable mirror images.
5. STRUCTURAL ISOMERISM - INTRODUCTION
COMPOUNDS HAVE THE SAME MOLECULAR FORMULA
BUT DIFFERENT STRUCTURAL FORMULA
Chain
different arrangements of the carbon skeleton
similar chemical properties
slightly different physical properties
more branching = lower boiling point
6. STRUCTURAL ISOMERISM - INTRODUCTION
COMPOUNDS HAVE THE SAME MOLECULAR FORMULA
BUT DIFFERENT STRUCTURAL FORMULA
Chain
different arrangements of the carbon skeleton
similar chemical properties
slightly different physical properties
more branching = lower boiling point
Positional
same carbon skeleton
same functional group
functional group is in a different position
similar chemical properties - slightly different physical properties
7. STRUCTURAL ISOMERISM - INTRODUCTION
COMPOUNDS HAVE THE SAME MOLECULAR FORMULA
BUT DIFFERENT STRUCTURAL FORMULA
Chain
different arrangements of the carbon skeleton
similar chemical properties
slightly different physical properties
more branching = lower boiling point
Positional
same carbon skeleton
same functional group
functional group is in a different position
similar chemical properties - slightly different physical properties
Functional Group different functional group
different chemical properties
different physical properties
• Sometimes more than one type of isomerism occurs in the same molecule.
• The more carbon atoms there are, the greater the number of possible isomers
8. STRUCTURAL ISOMERISM - CHAIN
caused by different arrangements of the carbon skeleton
similar chemical properties
slightly different physical properties
more branching = lower boiling point
There are two structural isomers of C4H10. One is a straight chain molecule where all
the carbon atoms are in a single row. The other is a branched molecule where three
carbon atoms are in a row and one carbon atom sticks out of the main chain.
BUTANE
straight chain
2-METHYLPROPANE
branched
C4H10
9. STRUCTURAL ISOMERISM - CHAIN
DIFFERENCES BETWEEN CHAIN ISOMERS
Chemical
Isomers show similar chemical properties because
the same functional group is present.
Physical
Properties such as density and boiling point show trends according
to the of the degree of branching
Boiling Point
“straight” chain isomers have higher values than branched ones
the greater the degree of branching the lower the boiling point
branching decreases the effectiveness of intermolecular forces
less energy has to be put in to separate the molecules
- 0.5°C
straight chain
- 11.7°C
branched
greater branching
= lower boiling point
10. STRUCTURAL ISOMERISM - POSITIONAL
molecule has the same carbon skeleton
molecule has the same same functional group... BUT
the functional group is in a different position
have similar chemical properties / different physical properties
Example 1
POSITION OF A DOUBLE BOND IN ALKENES
1
2
PENT-1-ENE
double bond between
carbons 1 and 2
2
3
PENT-2-ENE
double bond between
carbons 2 and 3
There are no other isomers with five C’s in the longest chain but there are three
other structural isomers with a chain of four carbons plus one in a branch.
11. STRUCTURAL ISOMERISM - POSITIONAL
molecule has the same carbon skeleton
molecule has the same same functional group... BUT
the functional group is in a different position
have similar chemical properties / different physical properties
Example 2
POSITION OF A HALOGEN IN A HALOALKANE
1
1-CHLOROBUTANE
halogen on carbon 1
2
2-CHLOROBUTANE
halogen on carbon 2
BUT
2
is NOT
3-CHLOROBUTANE
Moving the chlorine along the chain makes new isomers; the position is measured from
the end nearest the functional group... the third example is 2- NOT 3-chlorobutane.
There are 2 more structural isomers of C4H9Cl but they have a longest chain of 3
12. STRUCTURAL ISOMERISM - POSITIONAL
molecule has the same carbon skeleton
molecule has the same same functional group... BUT
the functional group is in a different position
have similar chemical properties / different physical properties
Example 3
RELATIVE POSITIONS ON A BENZENE RING
1,2-DICHLOROBENZENE
ortho dichlorobenzene
1,3-DICHLOROBENZENE
meta dichlorobenzene
1,4-DICHLOROBENZENE
para dichlorobenzene
13. STRUCTURAL ISOMERISM – FUNCTIONAL GROUP
molecules have same molecular formula
molecules have different functional groups
molecules have different chemical properties
molecules have different physical properties
ALCOHOLS and ETHERS
ALDEHYDES and KETONES
ACIDS and ESTERS
14. STRUCTURAL ISOMERISM – FUNCTIONAL GROUP
ALCOHOLS and ETHERS
Name
ETHANOL
METHOXYMETHANE
Classification
ALCOHOL
ETHER
Functional Group
R-OH
Physical properties
polar O-H bond gives rise
to hydrogen bonding.
get higher boiling point
and solubility in water
Chemical properties
Lewis base
Wide range of reactions
R-O-R
No hydrogen bonding
low boiling point
insoluble in water
Inert
15. STRUCTURAL ISOMERISM – FUNCTIONAL GROUP
ALDEHYDES and KETONES
Name
PROPANAL
Classification
ALDEHYDE
KETONE
R-CHO
R-CO-R
Functional Group
PROPANONE
Physical properties
polar C=O bond gives
dipole-dipole interaction
polar C=O bond gives
dipole-dipole interaction
Chemical properties
easily oxidised to acids of
same number of carbons
undergo oxidation under
extreme conditions only
reduced to 1° alcohols
reduced to 2° alcohols
16. STRUCTURAL ISOMERISM – FUNCTIONAL GROUP
CARBOXYLIC ACIDS and ESTERS
Name
PROPANOIC ACID
Classification
CARBOXYLIC ACID
Functional Group
R-COOH
METHYL ETHANOATE
ESTER
R-COOR
Physical properties
O-H bond gives rise
to hydrogen bonding.
get higher boiling point
and solubility in water
No hydrogen bonding
insoluble in water
Chemical properties
acidic
react with alcohols
fairly unreactive
hydrolysed to acids
17. STEREOISOMERISM
Molecules have the SAME MOLECULAR FORMULA but the atoms are
joined to each other in a DIFFERENT SPACIAL ARRANGEMENT - they
occupy a different position in 3-dimensional space.
There are two types...
• GEOMETRICAL ISOMERISM
• OPTICAL ISOMERISM
18. GEOMETRICAL ISOMERISM IN ALKENES
Introduction
•
•
•
•
an example of stereoisomerism
found in some, but not all, alkenes
occurs due to the RESTRICTED ROTATION OF C=C bonds
get two forms...
19. GEOMETRICAL ISOMERISM IN ALKENES
Introduction
•
•
•
•
an example of stereoisomerism
found in some, but not all, alkenes
occurs due to the RESTRICTED ROTATION OF C=C bonds
get two forms...
CIS (Z)
Groups/atoms are on the
SAME SIDE of the double bond
TRANS (E)
Groups/atoms are on OPPOSITE
SIDES across the double bond
20. GEOMETRICAL ISOMERISM
RESTRICTED ROTATION OF C=C BONDS
Single covalent bonds can easily rotate. What appears to be a different structure is
not. It looks like it but, due to the way structures are written out, they are the same.
ALL THESE STRUCTURES ARE THE SAME BECAUSE C-C BONDS HAVE ‘FREE’ ROTATION
Animation doesn’t
work in old
versions of
Powerpoint
21. GEOMETRICAL ISOMERISM
RESTRICTED ROTATION OF C=C BONDS
C=C bonds have restricted rotation so the groups on either end of the bond are
‘frozen’ in one position; it isn’t easy to flip between the two.
Animation doesn’t
work in old
versions of
Powerpoint
This produces two possibilities. The two structures cannot interchange easily
so the atoms in the two molecules occupy different positions in space.
22. GEOMETRICAL ISOMERISM IN ALKENES
E/Z or CIS-TRANS
E/Z
Z (zusammen)
higher priority groups / atoms on
the SAME side of C=C bond
E (entgegen)
higher priority groups / atoms on
OPPOSITE sides of C=C bond
23. GEOMETRICAL ISOMERISM IN ALKENES
E/Z or CIS-TRANS
E/Z
Z (zusammen)
higher priority groups / atoms on
the SAME side of C=C bond
E (entgegen)
higher priority groups / atoms on
OPPOSITE sides of C=C bond
To determine priority, the Cahn, Ingold and Prelog convention is used.
eg
C2H5 > CH3 > H
and
I > Br > Cl > F > C > H
24. GEOMETRICAL ISOMERISM IN ALKENES
E/Z or CIS-TRANS
E/Z
Z (zusammen)
higher priority groups / atoms on
the SAME side of C=C bond
E (entgegen)
higher priority groups / atoms on
OPPOSITE sides of C=C bond
To determine priority, the Cahn, Ingold and Prelog convention is used.
eg
C2H5 > CH3 > H
and
I > Br > Cl > F > C > H
25. GEOMETRICAL ISOMERISM IN ALKENES
E/Z or CIS-TRANS
Z (zusammen)
higher priority groups / atoms on
the SAME side of C=C bond
E (entgegen)
E/Z
higher priority groups / atoms on
OPPOSITE sides of C=C bond
To determine priority, the Cahn, Ingold and Prelog convention is used.
eg
E
C2H5 > CH3 > H
Z
and
I > Br > Cl > F > C > H
Z
E
26. GEOMETRICAL ISOMERISM IN ALKENES
E/Z or CIS-TRANS
CIS /
TRANS
Should only be used when there are two H’s and two
non-hydrogen groups attached to each carbon.
cis
non-hydrogen groups / atoms on the
SAME side of C=C bond
trans
non-hydrogen groups / atoms on
OPPOSITE sides of C=C bond
27. GEOMETRICAL ISOMERISM IN ALKENES
E/Z or CIS-TRANS
CIS /
TRANS
Should only be used when there are two H’s and two
non-hydrogen groups attached to each carbon.
cis
non-hydrogen groups / atoms on the
SAME side of C=C bond
trans
non-hydrogen groups / atoms on
OPPOSITE sides of C=C bond
28. GEOMETRICAL ISOMERISM IN ALKENES
E/Z or CIS-TRANS
CIS /
TRANS
Should only be used when there are two H’s and two
non-hydrogen groups attached to each carbon.
cis
non-hydrogen groups / atoms on the
SAME side of C=C bond
trans
non-hydrogen groups / atoms on
OPPOSITE sides of C=C bond
cis
trans
cis
trans
29. GEOMETRICAL ISOMERISM
GEOMETRICAL ISOMERISM
Isomerism in butene
There are 3 structural isomers of C4H8 that are alkenes*. Of these ONLY
ONE exhibits geometrical isomerism.
but-1-ene
cis but-2-ene
(Z) but-2-ene
trans but-2-ene
(E) but-2-ene
2-methylpropene
* YOU CAN GET ALKANES WITH FORMULA C4H8 IF THE CARBON ATOMS ARE IN A RING
30. GEOMETRICAL ISOMERISM
How to tell if it exists
Two different
atoms/groups
attached
Two different
atoms/groups
attached
Two similar
atoms/groups
attached
Two similar
atoms/groups
attached
Two similar
atoms/groups
attached
Two different
atoms/groups
attached
Two different
atoms/groups
attached
Two different
atoms/groups
attached
GEOMETRICAL ISOMERISM
Once you get two similar
atoms/groups attached to
one end of a C=C, you
cannot have geometrical
isomerism
GEOMETRICAL ISOMERISM
31. OPTICAL ISOMERISM
Occurrence
another form of stereoisomerism
occurs when compounds have non-superimposable mirror images
Isomers
the two different forms are known as optical isomers or enantiomers
they occur when molecules have a chiral centre
a chiral centre contains an asymmetric carbon atom
an asymmetric carbon has four different atoms (or groups)
arranged tetrahedrally around it.
32. OPTICAL ISOMERISM
Occurrence
another form of stereoisomerism
occurs when compounds have non-superimposable mirror images
Isomers
the two different forms are known as optical isomers or enantiomers
they occur when molecules have a chiral centre
a chiral centre contains an asymmetric carbon atom
an asymmetric carbon has four different atoms (or groups)
arranged tetrahedrally around it.
CHIRAL CENTRES
There are four different colours
arranged tetrahedrally about
the carbon atom
2-chlorobutane exhibits optical isomerism
because the second carbon atom has four
different atoms/groups attached
33. OPTICAL ISOMERISM
SPOTTING CHIRAL CENTRES
Look at each carbon atom in the chain and see what is attached to it. For a chiral centre
you need an asymmetric carbon with four different atoms/groups) arranged tetrahedrally around it.
IF A CARBON HAS MORE THAN ONE OF ANY ATOM/GROUP ATTACHED, IT CAN’T BE CHIRAL
CH3CH2CH2CH2Cl
1-chlorobutane
C
C
C
C
3 H’s around it
2 H’s around it
2 H’s around it
2 H’s around it
NOT chiral
NOT chiral
NOT chiral
NOT chiral
34. OPTICAL ISOMERISM
SPOTTING CHIRAL CENTRES
Look at each carbon atom in the chain and see what is attached to it. For a chiral centre
you need an asymmetric carbon with four different atoms/groups) arranged tetrahedrally around it.
IF A CARBON HAS MORE THAN ONE OF ANY ATOM/GROUP ATTACHED, IT CAN’T BE CHIRAL
CH3CH2CH2CH2Cl
1-chlorobutane
CH3CH2CHClCH3
2-chlorobutane
C
C
C
C
3 H’s around it
2 H’s around it
2 H’s around it
2 H’s around it
NOT chiral
NOT chiral
NOT chiral
NOT chiral
C
C
C
C
3 H’s around it
2 H’s around it
H, CH3, Cl,C2H5 around it
3 H’s around it
NOT chiral
NOT chiral
CHIRAL
NOT chiral
35. OPTICAL ISOMERISM
SPOTTING CHIRAL CENTRES
Look at each carbon atom in the chain and see what is attached to it. For a chiral centre
you need an asymmetric carbon with four different atoms/groups) arranged tetrahedrally around it.
IF A CARBON HAS MORE THAN ONE OF ANY ATOM/GROUP ATTACHED, IT CAN’T BE CHIRAL
CH3CH2CH2CH2Cl
1-chlorobutane
CH3CH2CHClCH3
2-chlorobutane
(CH3)2CHCH2Cl
1-chloro-2-methylpropanane
(CH3)3CCl
2-chloro-2-methylpropanane
C
C
C
C
3 H’s around it
2 H’s around it
2 H’s around it
2 H’s around it
NOT chiral
NOT chiral
NOT chiral
NOT chiral
C
C
C
C
3 H’s around it
2 H’s around it
H, CH3, Cl,C2H5 around it
3 H’s around it
NOT chiral
NOT chiral
CHIRAL
NOT chiral
C 3 H’s around it
C 2 CH3’s around it
C 2 H’s around it
NOT chiral
NOT chiral
NOT chiral
C 3 H’s around it
C 3 CH3’s around it
NOT chiral
NOT chiral
36. OPTICAL ISOMERISM
Spatial differences between isomers
• two forms exist which are NON-SUPERIMPOSABLE MIRROR IMAGES of each other
• non-superimposable means you you can’t stack one form exactly on top of the other
37. OPTICAL ISOMERISM
Spatial differences between isomers
• two forms exist which are NON-SUPERIMPOSABLE MIRROR IMAGES of each other
• non-superimposable means you you can’t stack one form exactly on top of the other
Some common objects are mirror images and superimposable
superimposable but not mirror images
non-superimposable mirror images
spoons
books
hands
38. OPTICAL ISOMERISM
Spatial differences between isomers
• two forms exist which are NON-SUPERIMPOSABLE MIRROR IMAGES of each other
• non-superimposable means you you can’t stack one form exactly on top of the other
Some common objects are mirror images and superimposable
superimposable but not mirror images
non-superimposable mirror images
NB
For optical isomerism in molecules, both conditions must apply...
they must be mirror images AND be non-superimposable
spoons
books
hands
39. OPTICAL ISOMERISM
What is a non-superimposable mirror image?
Animation doesn’t
work in old
versions of
Powerpoint
40. OPTICAL ISOMERS - DIFFERENCE
•
•
•
•
•
isomers differ in their reaction to plane-polarised light
plane polarised light vibrates in one direction only
one isomer rotates light to the right, the other to the left
rotation of light is measured using a polarimeter
rotation is measured by observing the polarised light coming out towards the observer
41. OPTICAL ISOMERS - DIFFERENCE
•
•
•
•
•
isomers differ in their reaction to plane-polarised light
plane polarised light vibrates in one direction only
one isomer rotates light to the right, the other to the left
rotation of light is measured using a polarimeter
rotation is measured by observing the polarised light coming out towards the observer
• If the light appears to have
turned to the right
DEXTROROTATORY
d or + form
turned to the left
LAEVOROTATORY
l or - form
42. OPTICAL ISOMERS - DIFFERENCE
•
•
•
•
•
isomers differ in their reaction to plane-polarised light
plane polarised light vibrates in one direction only
one isomer rotates light to the right, the other to the left
rotation of light is measured using a polarimeter
rotation is measured by observing the polarised light coming out towards the observer
• If the light appears to have
turned to the right
DEXTROROTATORY
d or + form
turned to the left
LAEVOROTATORY
l or - form
Racemate
a 50-50 mixture of the two enantiomers (dl) or (±) is a racemic mixture.
The opposite optical effects of each isomer cancel each other out
Examples
Optical activity is common in biochemistry and pharmaceuticals
• Most amino acids exhibit optical activity
• many drugs must be made of one optical isomer to be effective
- need smaller doses (safer and cost effective)
- get reduced side effects
- improved pharmacological activity
43. OPTICAL ISOMERISM
The polarimeter
A
B
C
D
E
F
A
B
C
D
E
F
Light source produces light vibrating in all directions
Polarising filter only allows through light vibrating in one direction
Plane polarised light passes through sample
If substance is optically active it rotates the plane polarised light
Analysing filter is turned so that light reaches a maximum
Direction of rotation is measured coming towards the observer
If the light appears to have
turned to the right
DEXTROROTATORY
turned to the left
LAEVOROTATORY
44. OPTICAL ISOMERISM
How optical isomers can be formed
Carbonyl compounds undergo nucleophilic addition. If there are two different
groups attached to the C=O bond, the possibility of forming optical isomers arises.
THE NUCLEOPHILIC ADDITION OF HCN TO ETHANAL
If the nucleophilic cyanide ion
attacks from above one
optical isomer is formed
45. OPTICAL ISOMERISM
How optical isomers can be formed
Carbonyl compounds undergo nucleophilic addition. If there are two different
groups attached to the C=O bond, the possibility of forming optical isomers arises.
THE NUCLEOPHILIC ADDITION OF HCN TO ETHANAL
If the nucleophilic cyanide ion
attacks from above one
optical isomer is formed
However, attack from below,
gives the non-superimposable
mirror image of the first
46. OPTICAL ISOMERISM
How optical isomers can be formed
Carbonyl compounds undergo nucleophilic addition. If there are two different
groups attached to the C=O bond, the possibility of forming optical isomers arises.
THE NUCLEOPHILIC ADDITION OF HCN TO ETHANAL
If the nucleophilic cyanide ion
attacks from above one
optical isomer is formed
However, attack from below,
gives the non-superimposable
mirror image of the first
The reaction produces a mixture of the two optical
isomers because both modes of attack are possible
47. OPTICAL ISOMERISM
How optical isomers can be formed
Carbonyl compounds undergo nucleophilic addition. If there are two different
groups attached to the C=O bond, the possibility of forming optical isomers arises.
THE NUCLEOPHILIC ADDITION OF HCN TO ETHANAL
ANIMATION
The reaction produces a mixture of the two optical
isomers because both modes of attack are possible
48. OPTICAL ISOMERISM
Synthesis of 2-hydroxypropanoic acid (lactic acid)
LACTIC ACID can be formed from ethanal in a two stage process.
1. Nucleophilic addition of hydrogen cyanide to ethanal
2 Hydrolysis of the nitrile group
HCN
H+ / H2O
49. OPTICAL ISOMERISM
Synthesis of 2-hydroxypropanoic acid (lactic acid)
LACTIC ACID can be formed from ethanal in a two stage process.
1. Nucleophilic addition of hydrogen cyanide to ethanal
2 Hydrolysis of the nitrile group
HCN
During the first stage, the nucleophilic CN- ion
can attack from below, or above, the aldehyde.
A mixture of the two enantiomers is formed.
H+ / H2O
50. OPTICAL ISOMERISM
Synthesis of 2-hydroxypropanoic acid (lactic acid)
LACTIC ACID can be formed from ethanal in a two stage process.
1. Nucleophilic addition of hydrogen cyanide to ethanal
2 Hydrolysis of the nitrile group
HCN
During the first stage, the nucleophilic CN- ion
can attack from below, or above, the aldehyde.
A mixture of the two enantiomers is formed.
Acid hydrolysis of the mixture provides a
mixture of the two lactic acid forms.
H+ / H2O
51. OPTICAL ISOMERISM - THALIDOMIDE
The one obvious difference between optical isomers is their response to plane
polarised light. However, some naturally occurring molecules or specifically
synthesised pharmaceuticals show different chemical reactivity.
The drug, THALIDOMIDE is a chiral molecule and can exist as two enantiomers. In the
1960’s it was used to treat anxiety and morning sickness in pregnant women.
Tragically, many gave birth to children with deformities and missing limbs.
It turned out that only one of the enantiomers (the structure on the right) was effective
and safe; its optically active counterpart was not. The major problem was that during
manufacture a mixture of the isomers was produced. The drug was banned worldwide, but not after tens of thousands of babies had been affected.
52. OPTICAL ISOMERISM – Other points
The following points are useful when discussing reactions producing optical isomers.
The formation of racemic mixtures is more likely in a laboratory reaction
than in a chemical process occurring naturally in the body.
If a compound can exist in more than one form, only one of the optical
isomers is usually effective.
The separation of isomers will make manufacture more expensive.
A drug made up of both isomers will require a larger dose and may cause
problems if the other isomer is ‘poisonous’ like thalidomide.
53. REVISION CHECK
What should you be able to do?
Recall the definitions of structural isomerism and stereoisomerism
Explain and understand how structural, geometrical and optical isomerism arise
Work out all the possible isomers for a given formula
Recall and understand the importance of optical activity in natural product chemistry
CAN YOU DO ALL OF THESE?
YES
NO