We proceed by applying this understanding of allene to explore the potential for achieving high optical activity in functionalized systems. Next, in Subsections 3.2 and 3.3 we treat an even-carbon cumulene and a polyyne subjugated to torsion, which have helical MOs similar to those of allene, and we discuss whether the helicity contributes to the chiroptical response. Finally, we treat achiral (D 2d ) spiropentadiene in quasi-D 2 symmetry to assess how the optical activity differs in spiroconjugated systems, which are structurally different from the carbyne-like allenes.