Among the bicycle [3.3.0] octane diones given below, which one will exhibit five signals in the broad band decoupled 13C NMR spectrum? A. B. C. D.

The correct answer is A.

The other options, B, C, and D, all have six signals in their broad band decoupled 13C NMR spectra. This is because each of these compounds has six carbon atoms that are not equivalent to each other.

In compound A, however, all of the carbon atoms are equivalent to each other. This is because the compound is a symmetrical bicycle [3.3.0] octane dione. In a symmetrical molecule, all of the carbon atoms are equivalent to each other, and therefore they will all give rise to the same signal in the 13C NMR spectrum.

Therefore, the correct answer is A.