Isomerism Test - 3

Structural Isomers are compounds with the same molecular formula but the different spatial arrangement of atoms in the molecule i.e. they have the same numbers of atoms of the same element but their atoms are arranged differently.

Types of Structural Isomerism:

(i) Chain Isomerism: Chain isomerism occurs when there is a difference in the atomic arrangement of the carbon to the carbon chain of a molecule. If two or more compounds having the same type of molecular formula with different main chains, then they are said to exhibit the property of Chain isomerism. This phenomenon is also called skeletal isomerism.
(ii) Position Isomerism: Positional isomerism arises when there is a difference in the positions occupied by the substituent atoms or a group of atoms or due to the unsaturation occurring in the chain. When the position of the functional groups with respect to the main chain atom changes, the phenomenon is called position isomerism.
(iii) Functional Group Isomerism: Functional group isomerism occurs when there is a  presence of the odd form of functional groups with the same chemical formula. When some compound has two different structures but the same chemical formula, then it is said to exhibit functional isomerism.

In chain isomerism, or skeletal isomerism, components of the usually carbon skeleton are distinctly re-ordered to create different structures. 
Pentane exists as three isomers: 
n-pentane (often called simply pentane), isopentane (2-methylbutane), and neopentane (dimethylpropane).
Skeletal isomerism of pentane​

Two molecules are described as stereoisomers if they are made of the same atoms connected in the same sequence, but the atoms are positioned differently in space.
Stereoisomers can be subdivided into: 
(i) Optical isomers 
(ii) Geometric isomers

Meso forms of isomers are single compound and their molecules are achiral and hence they cannot be separated into pairs.

Since the molecular formula is the same for both aldehyde and ketone. Hence they are functional isomers.

Aldehyde = propanal

Ketone = propanone

It is a phenomenon where two or more compounds have the same chemical formula but possesses different structural formulas, that is, different properties. This is mainly because of different structural or spatial arrangements. Isomers are the compounds exhibiting isomerism.

Stereoisomers are molecules that have the same molecular formula and differ only in how their atoms are arranged in three-dimensional space.

Be careful not to confuse them with constitutional isomers which also have the same molecular formula but differ in the way their atoms are connected.

The isomer of ethanol(CH₃-CH₂-OH) is dimethyl ether(CH₃-O-CH₃). This is a functional isomer of ethanol.