Classes Of Functional Groups
Organic Chemistry deals mostly with carbon and hydrogens, also called hydrocarbons, but those groups which replace hydrogen and bonds with carbon to give a characteristic nature, unique of their own, to the hydrocarbon they are attached to, are called functional groups. All the compounds belonging to a functional group undergo reactions in a similar pattern and are known to have similar physical and chemical properties.
Characteristics Of Functional Groups
In organic chemistry, we encounter a number of special substituent groups which are attached to the hydrocarbon backbone. These groups impart certain characteristics to the molecule of which it is a part of and thus, become the highlight of that particular molecule.
IUPAC Nomenclature
In Chemistry, IUPAC stands for International Union of Pure and Applied Chemistry which suggested a systematic naming approach for the organic and inorganic compounds, as in the beginning stage of nomenclature one single chemical compound was named in many ways by which lead to confusion. The need for this approach aroused as the number of chemical compounds newly discovered were increasing (approximately 32 million compounds) and the basic concept of nomenclature i.e. the trivial nomenclature and the derived system of nomenclature failed to overcome the challenge. It is an important task to name a chemical compound systematically and unambiguously which reduces lots of confusion about the newly reported compounds.
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**Explanation of Structures:**
1. **First structure (Option 1):** This is a primary radical.
\[
\text{{CH}}_{3}-\text{{CH}}_{2}-\text{{CH}}_{2} \cdot
\]
2. **Second structure (Option 2):** This is a primary radical adjoining a double bond (conjugated system).
\[
\text{{CH}}_{3}-\text{{CH}}_{2}-\overline{}\text{{C}}=\text{{CH}}_{2}\cdot
\]
3. **Third structure (Option 3):** This is a secondary radical.
\[
\text{{CH}}_{3}-\text{{C}}H \cdot-\text{{CH}}_{2}-\text{{CH}}_{3}
\]
4. **Fourth structure (Option 4):** This is an allylic radical, adjacent to a double bond.
\[
\text{{CH}}_{2}\cdot-\text{{CH}}=\text{{CH}}-\text{{CH}}_{2}-\text{{CH}}_{3}
\]
**Detailed Analysis and Answer:**
The stability of radicals is influenced by several factors, including hyperconjugation, resonance, and the inductive effect. Among these factors, resonance plays a crucial role in stabilizing radicals.
### Allylic Radical (Option 4)
The allylic radical, present in Option 4, is stabilized by resonance. The radical electron is delocalized through the π-system of the conjugated double bond, significantly increasing its stability. This delocalization is not present in the other structures to the same extent.
### Conclusion
Considering the stabilization effects, the most stable radical is found in the fourth structure (Option 4). The allylic radical benefits from resonance stabilization, making it the most stable radical in the set.
**Correct Answer: Option 4**:
```plaintext
○ Option 1
○ Option 2
☑ Option 3
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