April 19th - Alicyclics and Aromatics

Today, we learned about alicyclics and aromatics.

Carbon is capable of forming 2 kinds of closed loops. Alicyclics are loops usually made with single bonds. If the parent chain is a loop, standard naming rules apply (except ‘-cyclo’ is added before the parent chain).

In this example, we have cyclopentane. It’s simple, as there are no side chains.

Numbering can start anywhere, but side chain numbers must be the lowest possible.

Here are a few more examples:

Ex.) Draw: 1, 3, 5 trimethyl cyclohexane

This one is pretty easy. First, we draw the cyclohexane (which is a carbon chain of 6 with the ends connected). We then add side chains (methyl) at three spots. Easy.

Ex.) Name: 

The parent chain here is cyclobutane. There are 2 methyl side chains, both at position 1. Therefore, the name is 1,1 dimethyl cyclobutane. 

Loops can also be in side chains. The same rules apply for naming, except the side chain is given the ‘cyclo-‘ prefix.

Here's an example:

Ex.) Draw: 2 methyl 3 cyclopropyl pentane

This is done by first drawing the parent chain (5 carbons). Then, we add the methyl at the 2nd carbon. Finally, we add the cyclopropyl at the third carbon. Done!

Benzene (C₆H₆) is a cyclic hydrocarbon with unique bonds between the carbon atoms. Structurally, is can be drawn with alternating double bonds:

In the case of benzene, all 6 carbon-carbon bonds are identical and really represent a 1.5 bond all around. This is due to electron resonance. Another way to thing about it is that the electrons are free to move all around the ring. We can draw benzene like so:

Benzene can be a parent chain or a side chain. As a side chain, it is called ‘phenyl’.

Here's an example with benzene:

Ex.) Draw: 1, 2, 3, 4, 5, 6 hexamethyl benzene

First, draw the benzene. Then, simply add 6 methyls. 

As always, the obligatory video:

Posted by Michael.