Same molecular formula but different arrangement of their atoms CHAIN ISOMERISM POSITIONAL ISOMERISM FUNCTIONAL GROUP ISOMERISM GEOMETRIC ISOMERISM OPTICAL ISOMERISM Atoms are bonded in a different order ID: 580701
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Slide1
Optical IsomerismSlide2Slide3
Same molecular formula but different arrangement of their atoms
.
CHAIN ISOMERISM
POSITIONAL ISOMERISM
FUNCTIONAL GROUP ISOMERISM
GEOMETRIC ISOMERISM
OPTICAL ISOMERISM
Atoms are
bonded in a different order
.
Atoms are bonded in the same order but
arranged differently in space
.
Rotation prevented by double bond.
Non- superimposable mirror images.Slide4
E-Z
vs
cis
-trans
- Draw
cis and trans 1,2-dichloroethaneSlide5
E-Z
vs
cis
-trans
- Draw
cis and trans 1,2-dichloroethaneSlide6
E-Z vs
cis
-trans
Now try and name these using the
cis
-trans systemSlide7
E-Z naming system
You
look at what is attached to each end of the double bond in turn, and give the two groups a "priority" according to a set of
rules.
The atoms with the higher atomic number take priority.Slide8
E-Z naming
system
If the two groups with the higher priorities are on the same side of the double bond, that is described as the (Z)- isomer. So you would write it as (Z)-name of compound. The symbol Z comes from a German word
which
means together.Slide9
E-Z naming system
If
the two groups with the higher priorities are on opposite sides of the double bond, then this is the (E)- isomer. E comes from the German
word which
means opposite.Slide10
E-Z Isomers
Since Br has a higher atomic number than H, it takes priority.Slide11
E-Z vs
cis
-trans
Now try and name these using the E-Z systemSlide12
E-Z vs
cis
-trans
Now try and name these using the
cis
-trans systemZ-1-bromo-2-chloro-1-fluoroethene E-1-bromo-2-chloro-1-fluoroetheneSlide13
HomeworkSlide14Slide15
Z
-pent-2-ene
(
cis
)
E
-pent-2-ene
(trans)Slide16
E
-2-bromobut-2-ene (
cis
)
Z
-2-bromobut-2-ene (
trans
)Slide17
E
-1-chloro-2-methylbut-1-ene
Z
-1-chloro-2-methylbut-1-ene
The
cis
–
trans
system breaks down for this pair of isomers.Slide18Slide19
Optical isomers are:
Mirror images;
Non superimposable;
Chiral*;
Exclusive to
asymmetrical
compounds;
No plane of symmetry;Simplest example has 4 different groups attached to a central carbon atom;This carbon atom is known as the chiral centre;
Referred to as enantimers;Optically active.* Chiral means hand in greek*Slide20
Achiral molecules
If two of the groups attached to the central carbon are the same then the molecule can be moved around and twisted to show that it has a plane of symmetry. We call this an
achiral molecule
.Slide21
Plane Polarised Light
ANALOGY:Slide22
Insert a vertical slit
plane polarised stringSlide23
Add a second sli
tSlide24
The real thing - plane polarised light
Light is also made up of vibrations - this time, electromagnetic.
Polaroid has the ability to screen out all the vibrations apart from those in one plane and so produce plane polarised light.
If you wear one pair of Polaroid sunglasses and hold another pair up in front of them so that the glasses are held vertically rather than horizontally, you'll find that no light gets through - you will just see darkness. This is equivalent to the two slits at right angles in the string analogy. The polaroids are described as being "crossed".Slide25
Chiral Molecules
Enantiomers:
are optically active;
have different effects on
plane polarised light
;
A solution of one enantiomer rotates the plane of polarisation in a clockwise direction named the (+) form.
The other enantiomer will rotate the plane of polarisation in the other direction, named the (-) form.
A
racemic mixture (
racemate
) has equal quantities of both the enantiomers. Slide26
How can you tell that the plane of polarisation has been rotated?Slide27
Optically active sample:
You can easily tell whether the plane of polarisation has been rotated clockwise or anti-clockwise, and by how much.