The question asks which structure is not obtainable by intramolecular aldol condensation.

However, the image/structures corresponding to options A, B, C, D are missing in the provided text. Since intramolecular aldol condensation depends entirely on the given carbonyl substrate and the ring size / enone product shown in each option, the answer cannot be derived from the text alone.

Key chemistry idea

In intramolecular aldol condensation:

1. A molecule containing two carbonyl groups forms an enolate at one carbonyl.
2. That enolate attacks the other carbonyl within the same molecule.
3. The reaction usually favors formation of 5-membered or 6-membered rings.
4. After dehydration, it gives an $\alpha,\beta$-unsaturated carbonyl compound.

So, the option that is not a product would typically be the one requiring:

• an unfavorable 3- or 4-membered ring, or
• an unfavorable 7-membered or larger ring in the usual aldol setup, or
• an impossible connectivity for enolate attack.

But here

Because the actual structures for options A–D are not visible, I cannot independently verify which one is impossible.

The stored correct answer is B, but without the structures I cannot confirm it rigorously.