Conformations of Cyclic Hydrocarbons

Lecture Notes on Conformations of Cycloalkanes
SHAPES OF CYCLOALKANES Are the rings planar or nonplanar?

Cyclohexane has a heat of combustion that is about the same as for an unbranched alkane
CONFORMATIONS OF CYCLOHEXANE Heat of Combustion Data suggests that cyclohexane is free of angle strain. To get tetrahedral geometries for the carbons, the ring must be nonplanar.




AXIAL & EQUITORIAL BONDS IN CYCLOHEXANE









CONFORMATIONAL INVERSION OR "RING-FLIPPING" IN CYCLOHEXANE


In the ring-flipping process, the chair goes through the following conformations: half-chair boat half-chair to get to the other chair conformation
CONFORMATIONAL ANALYSIS OF MONOSUBSTITUTED CYCLOHEXANES The most stable conformation is a chair with the substituent occupying an equitorial position



Constitutional isomers differ in the order of their atomic connections. Stereoisomers have their atoms bonded in the same order, but they differ in the arrangement of atoms in space.
The compound in the box exists as a pair of stereoisomers.

The cis isomer is less stable due to steric crowding.
DISUBSTITUTED CYCLOHEXANES

Lecture Notes on Conformations of Cycloalkanes