McMurry (Kap.4,2)

Question 1

What is one main difference in the chemistry of open chain alkane and the cycloalkane?

Answer 1

Cycloalkanes are less flexible, in contrast with the open rotational freedom in an open chain alkane.

No bond rotation can take place around the carbons in a (cyclopropane for example), without breaking open the ring.

Question 2

Does all cycloalkanes have no rotation around the C-atoms, or only some?

Answer 2

They all have some hindrance, but some have more then others.

For example larger cycloalkanes have increased rotational freedom, and very large rings are so floppy that they are hard to distinguish from open end alkanes.

Smaller cycloalkanes have more restricted rotation.

Question 3

Define the word stereoisomers, specifically the cis and trans ones, and how do they affect the cycloalkanes.

Answer 3

Because the cycloalkane have a 2 face look (top and bottom), isomerism is possible.

Isomerism = same molecular formula but different structures or arrangements of atoms.

The two isomerism forms that can occur is when the substituents on the ring face the same side of the face, or opposite sides of the face.

Both isomers are stable, and cant be converted into each other, without breaking and reforming covalent bonds.

Sterioisomers = Atoms connected in the same order, but differ in the 3d orientation.

Cis-trans steriochemistry.
Cis = same side of the face substituents.
Trans = opposite sides.