Aromatic Compounds - Definition, Examples, Features, Characteristics, FAQs

IUPAC Name of Aromatic Compounds

Previously, most chemicals with the same structure were known by different names depending on the regions in which they were synthesized. This naming system was relatively simple because it caused a great deal of confusion. Finally, a standard naming system that registered general rules was developed by IUPAC (International Union for Pure and Applied Chemistry) for compounds.

This method of naming is callecd IUPAC .

Some Rules of IUPAC for Aromatic Compound

1. Identify the Parent Compound

• The basic structure is benzene $\left(\mathrm{C}_6 \mathrm{H}_6\right)$..

• If the benzene ring is the main structure → name as a derivative of benzene.

• If the benzene ring is a side group → it is called a phenyl group $\left(-\mathrm{C}_6 \mathrm{H}_5\right)$.

2. Monosubstituted Benzene

• When only one substituent is attached, name it as a prefix before “benzene.”
  Example: $\mathrm{CH}_3-\mathrm{C}_6 \mathrm{H}_5 \rightarrow$ Methylbenzene (Toluene)

3. Disubstituted Benzene

Use numbering or position prefixes to indicate where the substituents are attached.

• 1,2– or ortho (o–)

• 1,3– or meta (m–)

• 1,4– or para (p–)
  Example: 1,3–Dinitrobenzene → m–Dinitrobenzene

4. Polysubstituted Benzene

• Number the ring to give the lowest possible locants.

• Start numbering from the substituent that gives the characteristic name (like –OH in phenol).

• List substituents in alphabetical order.
  Example: 1–Chloro–2,4–dinitrobenzene

5. Phenyl as Substituent

• When benzene is attached to a longer carbon chain (more than 6 carbons), it acts as a phenyl group.
  Example: $\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{CH}_3 \rightarrow 1$-Phenylethane

Examples of Aromatic Compounds

Fragrant hydrocarbons, with hydrocarbons containing sigma bonds and pi electrons separated between carbon atoms in the ring.

For example, benzene. They are known as aromatic because of their pleasant aroma.

Any hydrocarbon can be classified as an aromatic compound as long as it follows the Huckel rule. According to Huckel's law, for a ring to smell, it must have the following properties: The planet Complete the electron renewal in the ring

Presence of (4n + 2) π electrons in the ring when n is the sum (n = 0, 1, 2, ..)

Huckel's Law of Aromaticity

• Huckel's law states that only planets, fully monocyclic planets, have 4n + 2 electrons, where n is a whole number, i.e., n = 0, 1, 2, 3, 4, etc., which must have fragrant stability.
• The fragrant compound must be planetary and contain a circular cloud of electrons below and above the plane of the molecule.
• It has sp² atoms separated and must comply with Huckel's law.
• According to this rule, the ring system must have electrons $(4 n+2) \pi$ electrones, where n is a whole number (0, 1, 2, 3, etc.). At this time the ring systems have 2 (n = 0), 6 (n = 1), 10 (n = 2), 14 (n = 3) etc pi electrons.
• Typical examples of aromatic chemicals are benzene, naphthalene, and anthracene.

Related Topics

• Lewis Acids and Bases
• Haloalkanes Haloarenes
• Saturated Hydrocarbons
• Isomerism
• Difference between Organic and Inorganic Compounds

Characteristics of Aromatic Compounds

1. It has to be Cyclic.

2. You must have (4n + 2) pi Electrons (n = 1,2,3,4, ...)

3. Oppose Add but Select Substitutions.

4. You Must Find the Power of Resonance

Non-benzenoid Aromatic Compounds

• Azulene, which consists of a structure of seven-limbed and five-limbed rings, is a typical non-benzenoid fragrant compound.
• Three effective methods of production have been identified so far as follows: The first method, developed by Ziegler and Hafner, is a ring-salt or pyrylium salt reaction with cyclopentadienides.
• The second, developed by Nzoe and Seto et al. regenerative reactions of tropone containing halogen, methoxy, or tosyloxy groups in area 2 and active methylene compounds, such as cyanoacetates and malonates, where the base is located.
• The latter method, developed by Yasunami and Takase et al., Reactions of oxaazulanones with enzymes.
• The elements of tropolone are also classified as unhealthy benzenoid chemicals. Hinokitiol, the generic site of tropolone, is known to show an anti-bacterial effect.
• Colchicine, an alkaloid compound with a tropone ring, shows strong antitumor effects.
• Tropolone compounds have potential in the field of medicine, especially in anti-cancer drugs.

Also Read -

Some Solved Examples

Question 1: Among the following, the aromatic compounds are :

Choose the correct answer from the following options:

1) (A), (B), and (C) only

2) (B), (C), and (D) only

3) (A) and (B) only

4) (correct) (B) and (C) only

Solution:

(A) Non-Aromatic
(B) Aromatic - $6 \pi$ electron
(C) Aromatic - $6 \pi$ electron
(D) Anti-Aromatic - $4 \pi$ electron

The aromatic compounds are (B) and (C) only.
Hence, the answer is option (4).

Question 2: Among the given organic compounds, the total number of aromatic compounds is _______ .

Solution:

Aromaticity -
Aromaticity is defined as "An aromatic compound having a cyclic planar structure with $(4 n+2) \pi$ electrons and has high resonance energy and stability due to delocalization of $\pi$ electrons." Any compound is aromatic if the following conditions are fulfilled:
- It has complete delocalization of $\pi$ electrons.
- Has a high resonance energy.
- Has a conjugate system.
- Has several $\pi$ electrons according to $4 n+2$ or Huckel's rule is $2,6,10,14,18$. Here, $n=0,1,2 \ldots$
- If the number of $\pi$ electrons is 4 " $n$ ' i.e., $4,8,12,16$, it will be anti-aromatic.
- If any of these conditions is not obeyed, it will be non-aromatic.

2, 3, and 4 are aromatic.

Hence, the answer is (3).

Question 3: What is the general formula of aromatic compounds?
1) (correct) $\mathrm{C}_{\mathrm{n}} \mathrm{H}_{\mathrm{n}}$

2) $\mathrm{C}_{\mathrm{n}} \mathrm{H}_{2 \mathrm{n}}$

3) $\mathrm{C}_{2 \mathrm{n}} \mathrm{H}_{\mathrm{n}}$

4) $\mathrm{C}_n \mathrm{H}_{2 n+2}$

Solution :

Aromatic compounds: These compounds consist of at least one benzene ring, i.e, a six-membered carbocyclic ring having alternate single and double bonds. Generally, these compounds have some fragrant odour and are hence named aromatic.

The general formula of aromatic is $C_n H_n$.
Benzene formula is $\mathrm{C}_6 \mathrm{H}_6$ which is $\mathrm{C}_n \mathrm{H}_n$ for $\mathrm{n}=6$.
Hence, the answer is option (1).

Question 4: Which compound (s) out of the following is/are not aromatic?

1) (A) and (C)

2) (C) and (D)

3) (correct) (B), (C), and (D)

4) (B)

Solution:

As we have learned,
Aromatic compounds are cyclic, planar, and have $(4 n+2) \pi$ electrons in complete conjugation. If any of these conditions are not satisfied then the compound is not aromatic.

Compound (A) is Aromatic.
Compound $(\mathrm{B})$ is anti-aromatic as it has $4 \pi$ electrons
Compound $(\mathrm{C})$ is non-planar as the negative charge occupies an $s p^3$ hybridized orbital and hence it is non-aromatic
Compound (D) is non-aromatic as it does not have complete conjugation.
Therefore, compounds $\mathrm{B}, \mathrm{C}$, and D are not aromatic.
Hence, the answer is option (3).

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