1. The lecture discusses the conformations of cyclohexane and its derivatives including chairs, boats, and substituent effects.
2. Cyclohexane can adopt chair and boat conformations to minimize angle strain and allow tetrahedral geometry at each carbon.
3. Monosubstituted cyclohexanes prefer the equatorial position, while disubstituted cyclohexanes depend on the relative stereochemistry of the substituents to determine the favored conformation.
3. CH264
3
Angle strain in rings
24.5° 9.5° 0.5° -5° "angle strain" (divided between two ring bonds)
9.17 6.58 1.24 0.02
38.4 27.5 5.19 0.09
strain per CH2 group (kcal mol-1)
strain per CH2 group (kJ mol-1)
"angle strain" is (109° - ring angle)/2
4. CH264
4
Cyclohexane is ‘strain free’
A planar arrangement of the six methylene groups in cyclohexane does not
give a tetrahedral shape for every carbon atom - this is achieved by puckering
the ring. Cyclohexane does this by adopting mainly two conformations the
CHAIR and the BOAT.
chair boat chair
CGW p.371
17. CH264
17
You should be able to:
(i) Draw cyclohexane as chair conformers
(ii) Ring-flip monosubstituted cyclohexane
(iii) Show which conformer is favoured in mono- and di-
substituted cyclohexanes
Outputs