Further Organic Chemistry Handout 1
Isomers: Isomers are the compounds with same molecular formula but different structural formulae.
Isomerism is the existence of different compounds with the same molecular formula but structural
formulae. There are various types of isomers. They are shown below:
Isomers
Structural Isomers Stereoisomers
Position Functional Chain isomers
Group isomers
Isomers
Geometric isomers Optical isomers
Stereoisomerism: They have the same molecular formula and also the same structural formula. The
difference between them is the arrangement of the bonds in space. Stereoisomerism can i)Geometric
isomerism ii)Optical isomerism.
i) Geometric isomerism: Cis and trans isomers are molecules with the same molecular
formula, the same structural formula, but different displayed formula.
Cis isomer: It is one in which two similar atoms or groups are on the same side of the same
side of the double bond. Latin “cis” means ‘on the same side’.
Trans isomer: It is one in which two similar atoms or groups are on the opposite side of the
double bond. Latin “trans” means ‘opposite or across’.
Cis-but-2-ene Trans-but-2-ene
, *But these two compounds have different melting, boiling temperatures and densities*
Conditions to be cis-trans isomerism:
a) Compounds must have carbon-carbon double bond(C=C). So, free rotation is not
possible around carbon-carbon double bond in alkenes and this give rises to cis-trans
isomers.
b) One carbon atom of the double bond cannot bear two same atoms or groups.
General formula of cis-trans isomers:
a a a b
C C C C
b b a
b
Where “a” and “b” are different atoms or groups
Trans-but-2-ene Cis-but-2-ene
But-1-ene does not show cis-trans isomerism because one double bonded carbon contains
two same atoms (hydrogen).
E-Z system: If there are four different atoms or groups joined by the double bond, normal
(cis-trans) cannot be used. This is where cis-trans naming system breaks down and it
becomes necessary to use E-Z naming system. If two groups or atoms of higher priority are
Isomers: Isomers are the compounds with same molecular formula but different structural formulae.
Isomerism is the existence of different compounds with the same molecular formula but structural
formulae. There are various types of isomers. They are shown below:
Isomers
Structural Isomers Stereoisomers
Position Functional Chain isomers
Group isomers
Isomers
Geometric isomers Optical isomers
Stereoisomerism: They have the same molecular formula and also the same structural formula. The
difference between them is the arrangement of the bonds in space. Stereoisomerism can i)Geometric
isomerism ii)Optical isomerism.
i) Geometric isomerism: Cis and trans isomers are molecules with the same molecular
formula, the same structural formula, but different displayed formula.
Cis isomer: It is one in which two similar atoms or groups are on the same side of the same
side of the double bond. Latin “cis” means ‘on the same side’.
Trans isomer: It is one in which two similar atoms or groups are on the opposite side of the
double bond. Latin “trans” means ‘opposite or across’.
Cis-but-2-ene Trans-but-2-ene
, *But these two compounds have different melting, boiling temperatures and densities*
Conditions to be cis-trans isomerism:
a) Compounds must have carbon-carbon double bond(C=C). So, free rotation is not
possible around carbon-carbon double bond in alkenes and this give rises to cis-trans
isomers.
b) One carbon atom of the double bond cannot bear two same atoms or groups.
General formula of cis-trans isomers:
a a a b
C C C C
b b a
b
Where “a” and “b” are different atoms or groups
Trans-but-2-ene Cis-but-2-ene
But-1-ene does not show cis-trans isomerism because one double bonded carbon contains
two same atoms (hydrogen).
E-Z system: If there are four different atoms or groups joined by the double bond, normal
(cis-trans) cannot be used. This is where cis-trans naming system breaks down and it
becomes necessary to use E-Z naming system. If two groups or atoms of higher priority are
