Among the following compounds, which are not aromatic?

Compounds from Options A and C contain sp³ carbon atoms. Hence, they are not aromatic.

X-ray diffraction studies have shown that Octatetraene in Option D is non planar and hence, it not aromatic.

Thiophene in option B has a lone pair of electrons on sulphur atom, which participates in resonance along with 4$\mathrm{\pi }$electrons in the ring. Thus, it is aromatic and also a planar molecule.

So, among the given answer choices, A, C, and D are not aromatic.