Q15-34E - Organic Chemistry (Mcmurry)

Question

How might you convert 1, 3, 5, 7-cyclononatetraene to an aromatic substance?

Step-by-Step Solution

Answer

   1, 3, 5, 7-cyclononatetraene                                cyclononatetraenyl anion

        (8 electrons)                                                             (10 electrons)

       Conversion of 1, 3, 5, 7-cyclononatetraene to aromatic substance

Step-by-Step Solution Step 1: Aromaticity

The aromaticity of a molecule is decided by Huckel’s $\mathbf{4}\mathbf{n}\mathbf{+}\mathbf{2}\mathbf{\pi }$rule. According to this rule, an aromatic compound is a planar, conjugated system that contains a total of $\mathbf{4}\mathbf{n}\mathbf{+}\mathbf{2}\mathbf{\pi }$delocalized electrons ( where n is an integer). Thus, aromatic compounds contain 2,6,10,14, and 18…., pi electrons. Molecules with electrons are not aromatic systems. These systems are called antiaromatic and are often very unstable.

Step 2: Structure of 1, 3, 5, 7-cyclononatetraene

To make a 1, 3, 5, 7-cyclononatetraene aromatic compound, abstract a proton from the labeled ${\text{CH}}_{\text{2}}$carbon as shown. This will generate cyclononatetraenyl anion, which is a planar aromatic molecule with 10 electrons. 

1,3,5,7-cyclononatetraene                                cyclononatetraenyl anion

(8 electrons)                                                             (10 electrons)

Conversion of 1,3,5,7-cyclononatetraene to aromatic substance