cyclohexane1.pptx

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 1

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 2

3. Axial and equatorial bond 3 Axial Position Equatorial Position Axial & Equatorial Position of Cyclohexane

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

5. Four Types of Conformation in cyclohexane 5     Chair Conformation Boat Conformation Twist-boat Conformation Half Chair Conformation

6. Chair Conformation 6     The  C-C-C  bonds are very close to 109.5 o ,   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 7     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.   T he boat conformation about 30 kJ/ mol less stable than the chair conformation.

8. Twist Boat Conformation 8   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 9      In the planar portion of half chair cyclohexane the C-C bond angles are forced to 120 o  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 109.5 o  and for some of C-H bonds to not be fully eclipsed. T he half chair conformation is roughly 45 kJ/ mol less stable than the chair conformation. Half chair

10. Conformation Analysis Of cyclohexane 10

11. Conformation Analysis Of cyclohexane 11 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.