Hydrocarbons: Compounds made up of C and H atoms only.
Homologous series: Family of organic compounds that have
the same general formula
similar chemical properties
same functional group.
They are :
Alkane
Alkene
Alcohol
Carboxylic Acid
Ester
Amine
Nitrile
Halogenalkane
Aldehyde
Ketone
Skeletal Formula
A skeletal formula is drawn by linking carbon atoms with a line.
The symbols for carbon or hydrogen are not shown.
The symbols for a functional group must be shown.
Displayed formula Skeletal formula Name
Isomerism
Structural Isomerism
Chain isomerism
Chain isomers have the same molecular formula but different carbon chains.
They have a different number of carbon atoms in their long chain.
Example - 1
C4H10
Butane has four carbon in the long chain.
In the second figure (2-methylpropane), three carbons are in the long chain.
Both compounds have the same number of carbon and Hydrogen.
As they have different lengths of the carbon chain, they are chain isomers.
Example - 2
C5H10O2
1
2
3
All of the compounds above are isomers of each other.
They have varying lengths of the carbon chain.
They have the same molecular formula.
They belong to the same homologous series of carboxylic acid.
Positional Isomerism
They have the same molecular formula.
They have different positions of functional groups/groups of atoms/ specific atoms.
To count the position of an atom or functional group always consider the shortest one.
Example- 1
C3H6Cl2
- Cl is bonded to the first carbon.
- Cl is bonded to the second carbon.
- One Cl is bonded to the first and the other one is with the third.
- One Cl is bonded to the first and the other one is with the second.
The compounds above have different positions of Cl atoms.
They have the same molecular formula of C3H6Cl2.
They are positional isomers of each other.
Example- 2
C5H12O
The compounds above have different positions of the hydroxyl group(OH).
They have the same molecular formula of C5H12O.
They are positional isomers of each other.
Functional group Isomerism
They have the same molecular formula.
They have different functional groups.
Example:1
** If an organic compound follows a general formula of CnH2nO2, this organic
compound may be an ester & a carboxylic acid.
C3H6O2
(a) Methyl Ethanoate
(b) Propanoic Acid
Example- 2
C5H10O ** If an organic compound follows a
general formula of CnH2nO, this organic
compound may be an aldehyde & a ketone.
Pentanal
Pentanone
Stereo-isomerism
Geometrical isomerism
Conditions for geometrical isomerism
A double bond between carbons must be present.
Restricted rotation between the double bond in Carbon. (C=C)
The double bond containing carbon has two different atoms or groups of atoms bonded to it.
Example
C4H8
But-1-ene
The possible isomers are as follows
Cis-but-2-ene
Trans-but-2-ene
A compound can have both types of isomers.
Example
Cis-Cis-isomers
Cis-trans-isomers
Trans-trans-isomers
Optical isomerism
Chiral Carbon
A carbon atom that has four different atoms or groups of atoms bonded to it.
Examples
The carbon with an asterisk is chiral as it has four different groups bonded to it.
*The carbon at the centre is not a chiral carbon as the groups bonded to it on the right and left(circled in red) are the same.
The compound has two chiral carbons.
Optical isomers
Organic compounds that have chiral carbon will form optical isomers.
Optical isomers are mirror images of each other.
The line between the two isomers is the mirror line.
The carbon at the centre must be chiral.
The different shapes of the bond are used to show the 3D structure of the isomers.
The shapes can be used at any position.
Example:
CH3CH(OH)COOH
Reactions of organic compounds:
Organic compound undergoes the following reaction,
Alkane - Free radical substitution
Alkene- Electrophilic addition
Halogenalkane-Nucleophilic substitution
Aldehyde- Nucleophilic addition
Ketone-Nucleophilic addition
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