Isomerism Ravi

8/3/2019 Isomerism Ravi

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A term paper submitted for the partial fulfillment of the course

CHE 101

Submitted to: Submitted by:

Mr. HARMINDER SINGH Name: Ravi Ranjan

Deptt. Of Chemistry Roll. RE6901A14

Reg.No:10900841

Section: E6901


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ACKNOWLEDGEMENT

I would like to express the deepest appreciation to my subject teacher

Mr. Harminder Sir, who gave me this term paper through which I was able to interact with

the mysterious chemistry world. Sir you are a complete genius. You continuously &

convincingly enriched our knowledge throughout the session. Without Your guidance

and persistent help this dissertation would not have been possible.

My friend Rana Pratap Singh needs special thanks as he gave me his laptop for the project.

Without you, I would not have imagined to do this project.Sorry for taking so much

time.

Google also deserves thanks. Seriously nothing is perfect in this world except Google. Had

there been not Google, what we would have done.

Last but not the least, my parents for their evergreen love, support and trust on me. You have

a special place in my heart for inspiring the talent in me.

Thanks.


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Table of contents:

S. No. Contents Page No.(From- To)

1. Introduction of isomerism 4

2. Isomerism in Organic Chemistry 4

3. Types of Isomerism in Organic Chemistry 4-16

4. Isomerism in Inorganic Chemistry 17

5. Types of Isomerism in Inorganic Chemistry 17-21

6. References 22


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1. Introduction

Isomerism

Similar molecular formula of different compounds having different chemical or physicalproperties due to change in the arrangement of atoms is called isomerism.

Different structures are called isomers of each other.

For the first time isomerism was noticed in 1827, when Friedrich Woehler prepared cyanic acid

and found that although its elemental composition was identical to fulminic acid its properties

were quite different. From this it was found that chemical compounds could be different only

when they had different elemental compositions.

2. Isomerism in Organic Chemistry

It is one of the most important characteristics shown by the organic compounds.

The concept of isomerism illustrates the fundamental importance of molecular structure

and shape in organic chemistry. Carbon is the seventeenth most abundant element found

on the earths crust. It forms compounds than any other element except hydrogen.

3. Types of Isomerism in Organic Chemistry

In organic chemistry, isomerism is divided into following types:

I. STRUCTURAL ISOMERISM: Similar molecular formula of different compounds

but different chemical or physical properties due to change in the connectivity of

atoms is known as Structural Isomerism.

It is sub-divided into:


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a) Chain Isomerism[1]: Similar molecular formula of different compounds but

different chemical or physical properties due to change in the length of carbon

chain. It is also called skeletal isomerism.

Example:

C5H12 :

C4H9Br:

pentane 2-methylbutane
http://www.creative-chemistry.org.uk/molecules/chain.htmhttp://www.creative-chemistry.org.uk/molecules/chain.htm


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C5H12:

&

b) Positional Isomerism: Similar molecular formula of different compounds but

different chemical or physical properties due to change in the position (locant

nos. of functional group, multiple bonds or side chain). In positionalisomerism, parent system always remains the same.

Example:

C4H8:

CH3-CH2-CH=CH2 & CH3-CH=CH-CH3


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c) Functional Group Isomerism [2]: Similar molecular formula of different

compounds but different chemical or physical properties due to change in the

functional group. A functional group isomer can be identified using infrared

spectroscopy.

Example:

Cyclo hexane & 1-hexene

&

C2H6O:

CH3-O-CH3 & CH3CH2-O-H

Di methyl ether Ethanol


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C4H8&C4H6:

d) Ring-Chain Isomerism: It is a type of functional group isomerism. This type

of isomerism is due to different modes of linking of carbon atoms, i.e., the

isomers possess either open chain or closed chain structures. For ring-chain

isomerism, the open structure must have at least one pi bond.

Examples:


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e) Metamerism: Similar molecular formula of different compounds but different

chemical or physical properties due to change in the molecular formula of

alkyl groups around polyvalent functional group. There is always same

functional group in all metamers.

Examples:

Diethyl ether & Methyl propyl ether

CH3-CH2-O-CH2-CH3 & CH3-O-C3H7

Diethyl amine & Methyl propyl amine


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C2H5-NH-C2H5 & CH3-NH-C3H7

Diethyl Ketone & Methyl Propyl ketone

f) Tautomerism: Phenomena in which any compound can exist into two

functional isomers are called tautomerism. Different isomers are called

tautomers of each other in which position of any one atom (generally H) may

be different. In other words we can say that when proton (H +) migrates from

one polyvalentatom to other polyvalent atom, the isomerism aroused is called

tautomerism.

The word tautomerism was proposed in 1886 to describe the mobile

equilibrium between two compounds having weakly bonded hydrogen atom.

It is basically of two types:

Keto-Enol tautomerism &


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Base Catalyzed tautomerism

Example:

Tetrahydronaphthalenedione:

2-aminopyrroles[3]:


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II. STEREO ISOMERISM: Isomerism aroused due to the change in the arrangement of

atoms in the space without changing the connectivity is known as Stereo Isomerism.

They differ only in the three-dimensional orientations of their atom in space.

It is further divided into:

a) Geometrical Isomerism: This isomerism arises due to the restricted rotation of

doubly bonded carbon. They can also arise from ring structures where rotation

of bond is restricted.

When the substituent groups are attached in the same direction, the

isomerism aroused is called cis-isomerism while when the

substituent groups are attached in the opposite direction, the isomerism

aroused is called trans-isomerism.

Generally Trans form is more stable than cis form due to less steric

repulsion.

When there are more than two different substituent groups on double

bond carbon than cis/trans form is not effective, and then E/Z system

is used. Z (zusammen) means together and is similar to cis form

whileE(entgegen) means opposite and is similar to Trans form.

A molecular configuration is assigned E/Z naming on the basis of

certain priority rule. The atom with higher atomic number is given

higher priority. If both the higher priority groups are on the same side,

the system is Z form & if on the opposite sides, it is E form.

Example:


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Cis-2-pentene & trans-2-pentene:

&

Trans-Fumaric Acid & Cis-Maleic Acid[4]:


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cis-1,2-dichloroethene & trans-1,2-dichloroethene:

&

(E)-But-2-ene & (Z)-But-2-ene

b) Optical Isomerism: Isomerism in the organic compound having same

molecular formula but rotates the plane polarized light in different direction is

called optical isomerism. Optical isomers are named like this because of their

effect on plane polarized light.

Optical isomers can occur when there is an asymmetric carbon atom. An

asymmetric carbon atom is one which is bonded to four different groups. The

term optical activity is derived from the interaction of chiral materials with

polarized light. This property was first observed by Jean-Baptiste Biot in

1815.


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Representation

I. Wedge-Dash formula : It is commonly used for cyclic system.

As with straight chains, cyclic Wedge-Dash Notation has two

bonds drawn in the plane of the page (sticks), one bond drawn

coming toward us, out of the page and above the ring

(wedged), and one bond drawn going away from us, behind the

page and below the ring (dashed). Example

II. Fischer Projection: It is the 2-d representation of 3-d organic

molecules by projection. All bonds are represented as

horizontal or vertical line. In a Fischer projection, all horizontal

bonds project toward the viewer, while vertical bonds project

away from the viewer.

Naming Conventions :

I. By R & S configuration: Priority is assigned on the basis of

atomic number. It labels each chiral centerR orSaccording to


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a system by which its substituent are each assigned a priority,

according to the Cahn Ingold Prelog priority rules (CIP), based

on atomic number. If move from higher priority group to

lower in clockwise direction, the configuration is R & if we are

moving in the anticlockwise direction, the configuration is S.

II. By Optical activity: when the plane of PPL is rotated in

clockwise direction it is dextro (D) form while when the

rotation is in the anti-clockwise direction it is laevo (L) form.

Examples:

Butan-2-ol:

2-hydroxypropanoic acid (lactic acid):

2-aminopropanoic acid (alanine):


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4. Isomerism in Inorganic Chemistry

It is one of the important characteristics of the transition metals to form complexes which

are called Coordination Compounds. In inorganic chemistry, coordination compounds

often show various types of the Isomerism.

5. Types of Isomerism in Inorganic Chemistry

As in the case of organic compounds, coordination compounds show two main types of

Isomerism:

I. STRUCTURAL ISOMERISM: It occurs due to the difference in the ligands.

It is further divided into:


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a) Ionization Isomerism: in this, coordination sphere must be cationic. The

anionic ligand present must be different from the anion present outside of

the coordination sphere. This isomerism arises, due to exchange of anionic

ligand with anion present outside of the coordination sphere.

Example:

[Co(NH3)5Cl]SO4 & [Co(NH3)5SO4]Cl

[Co(NH3)4Br2]Cl & [Co(NH3)4BrCl]Br

b) Coordination Isomerism: this isomerism arises due to exchange of ligand

between two coordination spheres. Both cation and anion must be

complex.

Example:

[Cr(NH3)5(CN)] & [Cr(NH3)(CN)5]

[Cr(NH3)4(CN)2] & [Cr(NH2CN)4]

c) Hydrate Isomerism: It arises due to the exchange of H2O within

coordination sphere & outside of it. H2O must be present as a ligand.

Example:

[Co(H2O)6]Cl3 & [Co(H2O)5Cl]Cl2.H2O

[Co(H2O)4Cl2]Cl.2H2O &

[Co (H2O)3 Cl3].3H2O

d) Linkage or Salt Isomerism: this type of isomerism is shown by the

compound having ambidentate ligand.


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Example:

[Co(NH3)5NO2]Cl2 &

[Co (NH3)5ONO]Cl2

e) Ligand Isomerism: this isomerism arises when more than one structures

are all possible for any ligand.

Example:

[Fe(H2O)2 C3H6(NH2)2 Cl2]


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f) Coordination Position Isomerism: It arises due to the exchange of ligand

associated with the central metal atom. In compounds, bridge ligands must

be present.

Example:

II. STEREO ISOMERISM : It arises due to the difference in the orientation of the

ligands.

It is sub-divided into:

a) Geometrical Isomerism [5]: If due to exchange of ligand within

coordination sphere changes arrangement in compound then aroused

isomerism is called as Geometrical Isomerism. Tetrahedral complex do

not show geometrical isomerism, only square planar & octahedral

complexes show geometrical isomerism.

If the identical ligands are aligned with an angle of 90o

with the central

metal, it is cis form while if the identical ligands are aligned at an angle of

180o with the central metal, it is Trans form. Example:

[PtBrClNH3(py)]


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Cis-dichloro tetra ammine cobalt(III) &Trans -dichloride tetra

ammine cobalt (III)

b) Optical Isomerism: Coordination compounds which are non super

imposable mirror images of each other are called as optical isomers or

enantiomers. They are of two typesd & l and they do not have any

plane of symmetry.

Square planar complexes do not show optical isomerism only tetrahedral

complex of type Mabcd (where M is the central metal and a, b, c, d ligands)

show optical isomerism.

Example:

[Co(en)2Cl2]+


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Mirror image

[Fe(Ox)3]3-:

Mirror image


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6. Reference Site

1> http://www.creative-chemistry.org.uk/molecules/chain.htm#

2>

http://en.wikipedia.org/wiki/Functional_isomer#Functional_group_isomerism
http://www.creative-chemistry.org.uk/molecules/chain.htmhttp://en.wikipedia.org/wiki/Functional_isomer#Functional_group_isomerismhttp://www.creative-chemistry.org.uk/molecules/chain.htmhttp://en.wikipedia.org/wiki/Functional_isomer#Functional_group_isomerism


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3> http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6THS-

4TTMN7R-

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sion=1&_urlVersion=0&_userid=10&md5=a1f0fa3ef693f916361207b13d317

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4>http://images.google.co.in/imgres?

imgurl=http://i.ehow.com/images/GlobalPhoto/Articles/5340486/337263_Full.j

pg&imgrefurl=http://www.ehow.com/about_5340486_structure-fumaric-

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ev=/images%3Fq%3Dfumaric%2Bacid%2Bstructure%26hl%3Den%26um%3D1

5> http://wwwchem.uwimona.edu.jm:1104/courses/IC10Kiso.html
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