Organic Chemistry : Identifying Aromatic Compounds

Study concepts, example questions & explanations for Organic Chemistry

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Example Question #11 : Organic Functional Groups And Molecules

Octagon

Assuming that this molecule is planar, determine whether this molecule is aromatic, and name the number of  electrons ( molecular orbitals).

Possible Answers:

Aromatic, 8  electrons

Aromatic, 6  electrons

Non aromatic, 6  electrons

Not aromatic, 8  electrons

Correct answer:

Not aromatic, 8  electrons

Explanation:

There is no p orbital surrounding the Boron atom, so the ring does not have a fully conjugated pi system. In addition, there are 8  electrons, which does not follow Huckel's rule (an aromatic system contains 4n+2 electrons). The pi electrons include the lone pair (not shown, but implicit) on the nitrogen atom, which is why the answers with "6 electrons" are not correct.

Example Question #11 : Organic Functional Groups

1

Assuming that this molecule is planar, determine whether this molecule is aromatic, and name the number of  electrons (not  molecular orbitals). 

Possible Answers:

Aromatic, 6  electrons. 

Not aromatic, 8  electrons.

Aromatic, 8  electrons.

Not aromatic, 6  electrons. 

Correct answer:

Aromatic, 6  electrons. 

Explanation:

The lone pairs on the two nitrogen atoms reside in sp2 orbitals, meaning they do not participate in resonance. Within the ring, there are three  bonds, meaning there are six  electrons. Thus, the molecule is aromatic because it is planar and follows Huckel's rule. 

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