Organic Chemistry I

Professor Carl C. Wamser

Chapter 3 Notes

Conformations of Alkanes and Cycloalkanes

Conformations

Ethane Conformations

C-H bonds on the two carbons may or may not align

eclipsed: C-H bonds are aligned

staggered: C-H bonds fit in between

Newman Projections

Potential Energy Diagrams

Butane conformations

Types of strain:

Small cycloalkanes

Cyclohexane

Monosubstituted cyclohexanes

PRACTICE DRAWING ACCURATE CHAIR FORMS WITH SUBSTITUENTS

equatorial generally preferred over axial
see the table in the text with delta G for axial vs equatorial

Disubstituted cyclohexanes - cis & trans isomerism

Depending on the substitution pattern, disubstituted cyclohexanes have different combinations of axial and equatorial substituents.

substitution

cis

trans

1,2-

e,a <==> a,e

e,e <==> a,a

1,3-

e,e <==> a,a

e,a <==> a,e

1,4-

e,a <==> a,e

e,e <==> a,a

Example - the two chair conformations for cis-1-chloro-3-methylcyclohexane involve either two axial substituents or two equatorial substituents. The latter is more stable.