1. Online Counseling Resource YCMOU ELearning Drive…
15-Apr-17
Online Counseling Resource YCMOU ELearning Drive…
School of Architecture, Science and Technology
Yashwantrao Chavan Maharashtra Open University, Nashik – , India
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2. OC-SBT/ SBI/ SGS031-U01-03 Introduction
15-Apr-17
OC-SBT/ SBI/ SGS031-U01-03 Introduction
Programmes and Courses
SEP – SBT031 – Unit 01
SEP – SBI031 – Unit 01
SEP – SGS031 – Unit 01
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15-Apr-17
Credits
Academic Inputs by
Mrs. Rasika Bhore
M.sc ( Microbiology)
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4. How to Use This Resource
15-Apr-17
How to Use This Resource
Counselor at each study center should use this presentation to deliver lecture of minutes during Face-To-Face counseling.
Discussion about students difficulties or tutorial with assignments should follow the lecture for about minutes.
Handouts (with 6 slides on each A4 size page) of this presentation should be provided to each student.
Each student should discuss on the discussion forum all the terms which could not be understood. This will improve his writing skills and enhance knowledge level about topics, which shall be immensely useful for end exam.
Appear several times, for all the Self-Tests, available for this course.
Student can use handouts for last minutes preparation just before end exam.
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Learning Objectives
After studying this module, you should be able to:
Discuss Isomerism & various types of isomerism.
Describe anomerism, epimerism.
Describe mutarotation.
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Introduction
Isomerism was first noticed in 1827, when Friedrich Woehler prepared cyanic acid and noted that although its elemental composition was identical to fulminic acid, its properties were quite different.
Jons Jakob Berzelius introduced the term isomerism to describe the phenomenon.
In 1849, Louis Pasteur separated tiny crystals of tartaric acid into their two mirror-image forms.
Isomerism occurs when there are two or more compounds (called isomers) with the same molecular formula but different arrangements of their atoms.
Isomers have different physical and chemical properties but the differences may be great or small depending on the type of isomerism.
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Isomerism
Isomers are molecules having same molecular formula, but have a different arrangement of the atoms in space & existence of such isomers is called isomerism.
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Structural Isomerism
In structural isomerism, the atoms are arranged in a completely different order. There are 3 types of structural isomerism.
Chain Isomerism
Positional Isomerism
Functional group Isomerism
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1.Chain Isomerism
Isomers arise because of the possibility of branching in carbon chains.
For example, there are two isomers of butane, C4H10. In one of them, the carbon atoms lie in a straight chain whereas in the other the chain is branched.
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2. Positional Isomerism
The basic carbon skeleton remains unchanged, but important groups are moved around on that skeleton.
For example, there are two structural isomers with the molecular formula C3H7Br. In one of them the bromine atom is on the end of the chain, whereas in the other it's attached in the middle.
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11. 3. Functional Group Isomerism
Isomers contain different functional groups that is, they belong to different families of compounds.
For example molecular formula C3H6O2. Amongst the several structural isomers of this are propanoic acid (a carboxylic acid) and methyl ethanoate (an ester).
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Stereoisomerism
Isomers have same molecular formula & same structure also but they differ in the configuration, that is the arrangement of their atoms in space.
The presence of asymmetric carbon atoms allow the formation of stereoisomers.
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13. Geometric (cis-trans) Isomerism
Geometric isomerism can arise when there is lack of free rotation around a bond, often a C=C bond.
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E-Z Isomerism
Cis-trans isomers are also called as E-Z isomers
E- : the higher priority groups are on opposite sides of the double bond.
Z- : the higher priority groups are on the same side of the double bond.
The melting point of Cis isomers is lower than trans isomers.
The boiling point of Cis isomers is higher than the trans isomers.
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Optical Isomerism
Optical isomers are named like this because of their effect on plane polarized light.
Simple substances which show optical isomerism exist as two isomers known as enantiomers.
D & L forms
A enantiomer which rotates the plane of polarization in a clockwise direction is known as dextrorotatory or (+) form.
The other enantiomer which rotates the plane of polarization in an anti-clockwise direction is known as levorotatory or (-) form.
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D & L Sugars
D & L sugars are mirror images of each other. They have same name, e.g.- D-glucose & L-glucose.
Almost all the properties of the two members of an enantiomeric pairs (D & L) are identical, they have same boiling point, the same melting point & the same solubility but they exhibit different optical activity.
When the equal amount of D & L isomers are present, the resulting mixture has no optical activity because activity of each isomer cancel one another.
Such a mixture is said to be a Racemic or dl mixture.
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Epimerism
Epimerism is the stereoisomerism in respect of groups of a single asymmetric carbon of a molecule.
D-glucose L-glucose
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Another Epimers are……..
D - xylose
D- ribose
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Anomerism
The predominant form of sugars like glucose & fructose in a solution cyclize into rings.
During the conversion from straight-chain form to cyclic form, the
C-1 of glucose becomes a chiral center which can form two possible configurations.
These are α & ß .The C-1 carbon is called the anomeric carbon & so are α & ß forms are anomers.
In the α anomer, the hydroxyl (-OH) group attached to C-1 is below the plane of the ring & in ß anomer, it is above the plane of the ring.
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Some Anomers are………..
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Mutarotation
Mutarotation is the change in the specific optical rotation by the interconversion of α & ß forms to an equilibrium mixture.
In water, α-D glucopyranose & ß-D glucopyranose interconvert through the open chain form of sugar. This interconversion was detected by optical rotation.
The specific rotation [α]D of the α & ß anomers of D-glucose are +112° & +18.7°. When crystalline sample of either anomers is dissolved in water, [α]D changes with time until an equilibrium value of +52.7° is attained. This change called mutarotation.
Enzymes called mutarotase catalyze the interconversion of anomeric sugars in vivo.
Non-reducing sugar cannot show mutarotation due to the absence of the free anomeric OH group.
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What we learn…………
Isomerism exist between the molecules having same molecular formula but different structures or orientations.
Isomerism mainly are of 2 types: structural isomerism & stereoisomerism.
Structural isomers having different structures or different positions.
Stereoisomerism divides into geometric & optical isomerism.
Geometric isomerism arises when free rotation around C=C is absent.
Optical isomers depend on d & l forms of sugars.
Alpha & beta are anomers.
In mutarotation, the alpha & beta forms interconvert.
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23. Critical Thinking Questions
15-Apr-17
Critical Thinking Questions
Why the boiling point of cis isomers is greater than that of the trans isomers?
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24. Hints to Critical Thinking Question
Cis isomer is polar.
Both groups in same side develop negative charge.
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15-Apr-17
Study Tips
For more clear idea of isomerism, observe your hands in mirror & see they are mirror images of each other, but non super-imposable.
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15-Apr-17
Study Tips
Microsoft Encarta Encyclopedia
Structural isomerism
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27. End of the Presentation
15-Apr-17
End of the Presentation
Thank You !
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