Cyclohexane

1. Presentation topics : Cyclohaxane
and their stability.
Present to:
Dr.Md Waliullah
Associate Proffesor
Department of chemistry
Comilla University
Present By:
Fareha Sultana Prema
Session:2018-19
Department of chemistry
Comilla University
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2. Cyclohexane
 The Cyclohexane ring is free of angle strain and torsional strain .
 Cycloalkane is the most stable than other.
 Non Planner.
 Zero ring strain implies the bond angle must be 109.5°(no angle strain) and
also no eclipsing interaction between the C-H bond. c
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3. Axial and equatorial bond
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Axial Position Equatorial Position
Axial & Equatorial Position of Cyclohexane

4. Ring Flipping
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"Ring flip" describes the rapid equilibrium of cyclohexane rings
between the two chair conformations

5. Four Types of Conformation in cyclohexane
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1. Chair Conformation
2. Boat Conformation
3. Twist-boat Conformation
4. Half Chair Conformation

6. Chair Conformation
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◎ The C-C-C bonds are very close to 109.5o,
◎ It is also a fully staggered conformation and so is free of torsional
strain.
The most stable conformation of cyclohexane is chair conformation.

7. Boat Conformation
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◎ Flagpole Hydrogen
◎ Close proximity of the flagpole hydrogens results in steric strain.
◎ Eclipsing of carbon-hydrogen bonds on adjacent carbon atoms (3) results in
torsional strain.
The boat conformation about 30 kJ/mol less stable than the chair conformation.

8. Twist Boat Conformation
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◎ The boat form is quite flexible and by twisting it at the bottom created
the twist-boat conformer
◎ The flagpole hydrogens move farther apart and the eight hydrogens along the
sides become largely but not completely staggered.
Though more stable than the boat conformation, the twist-boat conformation is
roughly 23 kJ/mol less stable than the chair conformation.
bs

9. Half Chair Conformation
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◎ In the planar portion of half chair cyclohexane the C-C bond angles are forced
to 120o which creates significant amounts of angle strain
◎ Also, the corresponding C-H bonds are fully eclipsed which create torsional
strain.
◎ The out-of-plane carbon allows for some of the ring's bond angles to reach
109.5o and for some of C-H bonds to not be fully eclipsed.
The half chair conformation is roughly 45 kJ/mol less stable than the chair
conformation.
Half chair

10. Conformation Analysis Of cyclohexane
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11. Conformation Analysis Of cyclohexane
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◎ The graph shows the energy of cyclohexane molecule as it
interconverts from one chair conform to the other, the
energy barrier for interconverts is 12.1 kcal/mol.
◎ The chair is the lowest energy conformations, although
since the barrier to ring the flip is fairly small, there will
always be some other conformations present.
◎ Half chair is the point of the highest energy, and is not
stable.