1. Conformations

2. Conformations Stereochemistry: three-dimensional aspects of molecules
Conformation: different spatial arrangements of atoms that result from rotations about single (σ) bonds
Conformer: a specific conformation of a molecule

3. Conformations
Conformational isomers - those that rapidly interconvert at room temperature; they cannot be separated. They result from rotation about C-C single bonds (and from inversion of the electron pair on nitrogen).

4. Conformations of Ethane
Of the infinite number of possible conformations of ethane, two conformations represent the extremes. These are called the eclipsed conformation and the staggered conformation.
Staggered
Eclipsed

5. Representation of conformations
There are two methods are as follows:
Sawhorse formulae-
H H H
C C
H H H
H H
C C
H H
H H
Staggered
Eclipsed

6. Representation of conformations
2) Newman projection formulae-
Newman projection

7. Difference b/w Conformation & configuration
Conformations
Configurations
1) These are three dimensional arrangements in space of the atoms in a molecule which are interconvertible by rotation around a single bond.
1)These are three dimensional arrangements in space of the atoms in a molecule which are not interconvertible by rotation around a single bond.
2)Their interconversion does not require any breaking and making of bonds.
2)Their interconversion is possible only through breaking and making of bonds.
3) Their existence leads to the phenomenon of conformational isomerism.
3) Their existence is involved in the phenomena of geometrical and optical isomerism which are also collectively known as configuration isomerism.

8. Conformational Analysis of Ethane

9. Conformations of Propane
The barrier to C-C rotation for
propane is 13 KJ/mol = 1 (CH3-H)
+ 2 (H-H) eclipsing Interactions.
A CH3-H eclipsing interaction
is 5 KJ/mol
staggered
eclipsed

10. Conformational Analysis of Butane

11. Conformational Analysis of n-Butane
Four of the important conformations are:
Anti
Eclipsed
Gauche
Fully eclipsed

12. Conformational Analysis of n-Butane

13. Conformational Analysis of Cyclohexane
The two most important conformations are:
Chair conformation
Boat conformation

14. Chair conformation

15. Boat conformation

17. Conformation of disubstituted cyclohexane derivatives

18. Thank you