Question

Which from following statements is true for tetrahydrofuran?

• A. It is homocyclic aromatic.
• B. It is heterocyclic aromatic.
• C. It is aromatic non-benzenoid.
• D. It is heterocyclic nonaromatic.

Hint:

Furan (with two double bonds) is heterocyclic aromatic, but tetrahydrofuran (fully saturated, no double bonds) is heterocyclic nonaromatic!

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
We need to classify the structural and electronic properties of the organic compound tetrahydrofuran (THF).

Step 2: Key Formula or Approach:
A homocyclic ring contains only carbon atoms, while a heterocyclic ring contains at least one non-carbon atom (like oxygen, nitrogen, or sulfur) within the ring.
For a compound to be aromatic, it must be cyclic, planar, fully conjugated, and satisfy H"uckel's rule containing $(4n + 2)$ delocalized $\pi$-electrons.

Step 3: Detailed Explanation:
Tetrahydrofuran is a five-membered cyclic ether. Its ring consists of four carbon atoms and one oxygen atom.
Because there is an oxygen atom integrated into the ring structure, it is strictly classified as a heterocyclic compound.
Furthermore, the term "tetrahydro" indicates that the furan ring has been fully saturated with hydrogen. All four carbon atoms in the ring are $sp^3$ hybridized.
Because $sp^3$ carbons lack unhybridized p-orbitals, there is no continuous $\pi$-electron conjugation around the ring, completely disqualifying it from being aromatic.
Therefore, THF is both heterocyclic and nonaromatic.

Step 4: Final Answer:
Tetrahydrofuran is a heterocyclic nonaromatic compound, which corresponds to option (D).