Isomerism Fall 2024-25 PDF

COLLEGE OF ENGINEERING Department of Mechanical and Industrial Engineering Isomerism All In one Pic  Isomerism Isomers are molecules that have the same molecular formula, but have a different arrangement of the atoms in space. T...

COLLEGE OF ENGINEERING Department of Mechanical and Industrial Engineering Isomerism All In one Pic  Isomerism Isomers are molecules that have the same molecular formula, but have a different arrangement of the atoms in space. This concept is called Isomerism. Two types Structural Isomerism Stereo Isomerism Structural Isomerism: compounds have same molecular formula but different structure. Example is bromopropane.  Stereo Isomerism Stereo Isomers: compounds have same molecular formula but different arrangement of atoms in space. This idea is called Stereo Isomerism. Two types: Geometrical Isomerism Optical Isomerism  Geometrical isomerism Geometrical Isomerism is also called as cis-trans isomerism, It results from no rotation about double bonds. It also arises in cyclic compounds because of restriction in rotation about single bonds. No free rotation around this bond, because of ring formation.  Geometrical Isomerism in Alkenes Carbon atoms of the C=C in alkenes are sp2 hybridized. The two carbon atoms of C=C and four atoms attached to them are in same plane and their position are fixed. C=C can not rotate because of pi bond present in it. Because of this restriction cis-trans isomerism results.  Geometrical Isomerism in Alkenes There are two types of isomers because there are two positions. When two similar groups are on the same side of double bond it is a cis isomer. When two similar groups are on the opposite side of double bond it is a trans isomer.  Exercise What is the difference between these two isomers?  Geometrical Isomerism in Cyclic Compounds GI is possible in cyclic compounds. Because there is no rotation around C-C single bond due to ring. If we have to rotate C-C single bond in cyclic compounds we have to break the ring. Example is cis and trans decaline.  Exercise Draw the geometrical isomers for the following Compound  Optical Isomerism A molecule will show optical isomerism, only if it is optically active. It should have Chiral carbon. A molecule which rotates the plane of polarized light in right or left direction is called optically active. This idea is called Optical Activity. An optically active molecule is found in two isomeric forms. These are called Optical isomers. Optical isomers have same physical properties: MP, BP, Density etc. Video_ Optical Isomerism- https://www.youtube.com/watch?v=RBtgAz70_JY  Rotate in right side, so Dextrorotatory Polarized Light Optical Isomers Simple Light Rotate in left side, so Leavorotatory  Optical Isomerism Optical Isomers: are two compounds which have same molecular formula, but different arrangement of atoms in space. They rotate the plane of polarized light in opposite direction. This idea is called optical isomerism. One isomer rotate the plane of polarized light clockwise (right side). It is called Dextrorotatory. It is indicated by + sign.  Optical Isomerism Other isomer rotate the plane of polarized light anticlockwise (left side). It is called Leavorotatory. It is indicated by (-) sign. The optical rotatory power of both the isomers are equal in magnitude but opposite in direction. An equimolar mixture of two isomers is called Racemic Mixture. It will not rotate the plane of polarized light.  Terminologies Plane of Symmetry: A plane which divides an object in two equal halves is called plane of symmetry. Chiral / Dissymmetric: An object which is not having any plane of symmetry is called Chiral / Dissymmetric. Example? Video https://www.youtube.com/watch?v=71GjsRnsoL8  Terminologies Chiral carbon: A carbon atom which is bonded to four different atoms or groups, is called an asymmetric or chiral carbon. Chiral carbons are optically active and show optical isomerism. Mirror images of chiral carbon do not superimpose. Non superimposable mirror images are called Enantiomers. Optical Isomers which are not mirror images are called Diastereomers. Lactic Acid (II and III) and (I and IV) are diastereomers  Optical Isomerism in Lactic Acid Lactic acid is an example of optical isomerism. It has one chiral carbon. There are three forms of lactic acid. In this two are optically active. These are non superimposable mirror images of each other. They are called Enantiomers. And one is optically inactive. It is racemic mixture of both enantiomers.  Optical Isomerism in Lactic Acid (+) Lactic Acid: It rotates the plane of polarized light towards right. (-) Lactic Acid: It rotates the plane of polarized light towards left. (±) Lactic Acid: It does not rotate the plane. It is racemic mixture of (+) and (-) forms of lactic acid.  Exercise What is the reason for Optical isomerism in the above molecule? What are the different forms? How do you experimentally determine different enantiomers?  Tutorial Questions Which molecule will show geometrical isomerism? a. Propene b. 3-Hexene c. Butene-1 d. Butene-2