To analyze the assertion and reason provided in the question, we will break down the concepts of aromaticity, Huckel's rule, and the structural characteristics of annulene.
### Step-by-Step Solution:
1. **Understanding Aromaticity**:
Aromatic compounds are cyclic, planar, and fully conjugated molecules that follow Huckel's rule, which states that a compound is aromatic if it has (4n + 2) π-electrons, where n is a non-negative integer.
2. **Analyzing Annulene**:
Annulene is a cyclic hydrocarbon with alternating double bonds. Specifically, 10-annulene has 10 π-electrons. According to Huckel's rule, since 10 = 4(2) + 2, it fits the criteria for aromaticity.
3. **Planarity Requirement**:
For a compound to be aromatic, it must be planar. Planarity allows for the delocalization of π-electrons across the entire ring structure, which is crucial for aromatic stability.
4. **Steric Interactions in 10-Annulene**:
In the case of 10-annulene, the presence of internal hydrogen atoms leads to steric repulsion. These interactions can cause the molecule to adopt a non-planar conformation, which disrupts the delocalization of π-electrons.
5. **Conclusion on Aromaticity**:
Although 10-annulene contains the required number of π-electrons, the steric interactions prevent it from being planar, thus making it non-aromatic. Therefore, the assertion that "10-annulene is not aromatic though it contains Huckel number of π-electrons" is true.
6. **Evaluating the Reason**:
The reason states that "steric interaction between internal hydrogens makes it non-planar." This is also true, as the internal hydrogens do indeed lead to steric hindrance, preventing the molecule from achieving a planar structure.
7. **Final Assessment**:
Since both the assertion and reason are true, and the reason correctly explains the assertion, we conclude that the statement is correct.
### Final Answer:
Both the assertion and reason are true, and the reason is the correct explanation of the assertion.
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