2 Cycloalkanes

What are cycloalkanes?

Cyclic hydrocarbons arranged in the form of a ring. They are also saturated, meaning they have no double or triple bonds.

What prefix is used to name cycloalkanes?

Cyclo-, followed by the normal alkane name.

How are the carbons of a cycloalkane numbered when there is an alkyl chain linked to the ring?

The carbons of the cycloalkane must be numbered so that the carbons with functional groups or alkyls have the lowest possible numbers.

What happens if there is an alkyl straight chain which has more carbons than the cycle?

The chain is used as the parent chain, and the cycloalkane acts as a substituent to which the "yl" suffix is added.

In what order must substituents and functional groups be placed when naming a cycloalkane?

Alphabetical order.

How are the carbons of the cycloalkane numbered when there are more than 2 substituents?

They must be numbered so that the carbons with functional or alkyl groups have the lowest possible numbers.

How are cycloalkanes represented using Haworth projections?

The ring is shown in the planar conformation (perpendicular to the plane of the paper) while other bonds are on the plane of the paper.

What is this representation often used to depict?

Sugars in their cyclic form.

Why are some cycloalkanes highly unstable?

Due to their high ring strain.

What are some factors that determine ring strain?

• angle strain (due to non-ideal bond angles)

• torsional strain: generated through simple rotation, it is caused by the eclipsing interaction between electrons

• Van der Waals strain: generated by atoms in close proximity, whose electron clouds come close enough to repel each other

Why is flatness disfavored in the case of cyclohexane?

It leads to eclipsed C-H bonds which can present considerable torsional strain.

What is notable about the chair conformation of cyclohexane?

It makes for a perfectly unstrained molecule, which no eclipsing interactions (the conformation along each C-C bond is staggered). The orientation of the atoms about each carbon are perfectly tetrahedral.

What makes the chair conformation the dominant one in solutions?

Its lack of ring strain, as well as the low energy of the molecule.

What is another possible cyclohexane conformation?

The boat conformation.

Describe the boat conformation of cyclohexane.

It presents minimal angle strain but has some torsional and Van der Waals strain.