Isomerism Definition Types

1. Isomerism
BIO-104
By Alia Rafique

2. Isomerism
• It is a phenomenon where two or more compounds have the same chemical
formula but possesses different structural formulas and different properties.
• This is mainly because of different structural or spatial arrangements.

3. Types of isomerism

4. Structural isomerism (Constitutional)
• Isomers are structural isomers when they have the same molecular formula
but different structures.
• Example:There are two different butanes, C4H10, and these two molecules,
called butane and isobutane, are constitutional isomers.

5. Types of structural isomerism
1) Chain Isomerism
• Isomers are chain isomers when two or more compounds have the same
molecular formula but differ in the arrangement of the carbon chains, that
may be branched or straight.
• For example, we can represent C5H12 as three compounds:
CH3CH2CH2CH2CH3– pentane

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2) Position Isomerism
• Isomers are position isomers when the two or more compounds differ in the
position of the functional group or substituent atoms.
• For example, we can represent C3H7OH in two arrangements:

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3) Functional group isomerism:
• Functional group isomerism, also called functional isomerism, occurs when
the atoms form different functional groups.
• An example the compound with molecular formula C2H6O, of which there
are two isomers: dimethyl ether and ethanol or ethyl alcohol, that have
different functional groups, an ether group, –O–, and a hydroxyl group, –
OH, respectively.

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4) Metamerism
• This is exhibited by compounds due to the presence of different alkyl chains
on either side of the functional group.
• For example, we can represent C4H10O as ethoxyethane (C2H5OC2H5) and
methoxypropane (CH3OC3H7)

9. Sterioisomerism
• Stereoisomerism is a phenomenon in which compounds have the same
molecular formula but differ in the relative positioning or orientation of atoms
in space.
• Stereoisomers are the compounds exhibiting stereoisomerism.
• Sterioisomerism are further classified into:
1. Geometrical isomerism
2. Optical isomerism

10. Types of sterioisomerism
1) Geometric Isomerism:
• It is shown by molecules in which their spatial positions are locked to each
other due to the presence of a ring structure or a double bond.
• Also known as cis-trans isomerism or E-Z isomerism.

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2) Optical Isomerism:
• Two or more compounds that have the same molecular arrangement but
differ in the optical activity are optical isomers.
• Such isomers are the mirror images of each other.
• Optical isomers were given their name because they were first able to be
distinguished by how they rotated plane-polarized light.