IUPAC Nomenclature of Organic Molecules: Regio- and Stereoisomers

IUPAC Nomenclature of Organic Molecules including Regio- and Stereoisomers

IUPAC name is the standardized name given to a compound according to the rule of the International Union of Pure and Applied Chemistry (IUPAC). These rules are as follows:

1. Basics of IUPAC Naming:

Structure
Prefix:
(e.g., methyl, chloro, bromo, iodo)
Parent Chain:
Count the longest chain.
Suffix:
Suffix indicates the main functional group.
(e.g., -ane, -ene, -ine, -ol)
Numbering:
The chain is numbered from the end closest to the functional group or substituent.
✳️ For stereoisomers, prefixes like cis, trans, E, Z, R, and S are used.

Regioisomers are indicated by numbers within the name.

Example of IUPAC Name of Organic Molecule:

(1)
H₃C–CH₂–CH–CH₂–CH₃
|
CH₂OH

Longest chain = 5 carbon atoms → ❌ It’s wrong

(2)

H₃C–CH₂–CH₂–CH–CH₃

|
CH₂OH

Longest chain = 4 carbon atoms → ✅ It’s correct

IUPAC Name Chart

Functional Group Name	Suffix	Functional Group Structure
Alkane	-ane	C–H atoms
Alcohol	-ol	–OH
Alkene	-ene	C=C
Alkyne	-yne	HC≡CH
Aldehyde	-al	–C(=O)H
Amine	-amide	–NH₂
Ether	-ether	–O–
Carboxylic Acid	-oate	–C(=O)O–
Ketone	-one	–C=O

Regioisomers

Regioisomers are compounds that have the same molecular formula but differ in the location of a functional group.

Rules of Regioisomerism (e.g.):

Number the carbon chain such that the functional group gets the lowest possible number.
If multiple positions are possible for a functional group, indicate the locant (the carbon number).
Use prefixes like 1-chloro, 2-butanol, etc.

Example:

1-chloropropane and 2-chloropropane

They both have the molecular formula C₃H₇Cl
But the chlorine atom is attached to the first carbon in 1-chloropropane and to the second carbon in 2-chloropropane.
This means the position directly reflects the structural difference.

Stereoisomers

Stereoisomers have the same structural formula but differ in arrangement.

Types:
1. Geometrical Isomers (cis/trans or E/Z) – for alkanes and cyclic structures.
2. Optical Isomers (R/S) – involve chiral centers.
1. Geometrical Isomers (E/Z System):
1. E/Z is based on the Cahn-Ingold-Prelog priority rules.
2. E (Entgegen): Higher priority groups are on opposite sides of the double bond.
3. Z (Zusammen): Higher priority groups are on the same side of the double bond.
2. Optical Isomers (R/S System):
1. Assign priority to the group attached to the chiral center.
2. Orient the molecule so the group with the lowest priority is pointing away.
  - Clockwise = R
  - Anticlockwise = S
Example:

2-butene:
- 2-butene-cis-2-butene or trans-2-butene
- or (Z)-2-butene or (E)-2-butene

ORGANIC CHEMISTRY ; IUPAC Nomenclature of Organic Molecules including Regio- and Stereoisomers

IUPAC Name Chart

Regioisomers

Rules of Regioisomerism (e.g.):

Example:

Stereoisomers

Types:

1. Geometrical Isomers (E/Z System):

2. Optical Isomers (R/S System):

Example:

Leave a Comment Cancel Reply