Difference Between Conformational and Configurational Isomerism
Both conformational and configurational isomerism are types of stereoisomerism, but they differ in how the isomers interconvert.
| Feature | Conformational Isomerism | Configurational Isomerism |
|---|---|---|
| Definition | Isomers differ due to rotation around single (σ) bonds. | Isomers differ in the fixed spatial arrangement of atoms. |
| Interconversion | Easily interconvert without breaking any bonds. | Cannot interconvert without breaking and reforming bonds. |
| Energy Barrier | Usually low. | Usually high. |
| Bond Breaking Required? | No. | Yes. |
| Isolation of Isomers | Usually difficult because they rapidly interconvert. | Usually possible because isomers are stable. |
| Examples | Staggered and eclipsed ethane, anti and gauche butane. | Enantiomers, diastereomers, cis-trans isomers, E/Z isomers. |
| Cause | Rotation about single bonds. | Restricted rotation or presence of chiral centers. |
1. Conformational Isomerism
Conformational isomers (conformers) arise from rotation around a single carbon-carbon σ bond.
Example: Ethane
When viewed along the C–C bond:
- Staggered conformation → most stable
- Eclipsed conformation → least stable
These forms continuously convert into one another at room temperature without bond breaking.
Example: Butane
- Anti conformation (most stable)
- Gauche conformation
- Eclipsed conformations
2. Configurational Isomerism
Configurational isomers possess different arrangements of atoms that cannot be changed by simple bond rotation.
A. Geometrical Isomerism
Example: But-2-ene
- Cis-2-butene: CH₃ groups on the same side
- Trans-2-butene: CH₃ groups on opposite sides
Conversion between cis and trans forms requires breaking the π bond.
B. Optical Isomerism
Example: Lactic Acid
- (R)-Lactic acid
- (S)-Lactic acid
These are mirror-image molecules (enantiomers) and cannot be interconverted without breaking bonds at the chiral center.

