Finally, we examine cyclic allenes where the allenic moiety is constrained, thus perturbing the helical ⇡-system. Cycloallenes are synthetically interesting compounds that, given their reduced symmetry due to the ring structure, exhibit helical MOs. with increasing ring size, and will thus eventually be close to 1,3-dimethylallene. The HOMO for each of the four cycloallenes is shown in Figure . While it is visually clear that these four MOs are helical, it is not clear how their helicality rank relative to each other. Looking at the cumulated sum of twist along the carbon chain, we can see that the helicality of all four MOs is similar and follows the same trend. All four have an almost linear increase of the cumulated sum with a slight flattening close to the allenic carbon.