We investigate the presence of helical character and chirality using a
vector-based charge density perspective instead of energetic or
structural measures. The vector-based perspective of the chemical
bonding, constructed using the most preferred direction of charge
density accumulation, finds the presence of induced symmetry-breaking
for α,ω-disubstituted [4]cumulenes as the end groups are torsioned.
The stress tensor trajectories Tσ(s) are used to provide the additional
symmetry-breaking required to quantify the degree and nature of the
chirality and helical character. We find an absence of chirality for
[4]cumulene but a very significant degree of axiality as
demonstrated by the purely axial form of the Tσ(s) indicating a lack of
helical character. The S-1,5-dimethyl-[4]cumulene contains a very
low degree of chiral character but significant axiality(helicity)
resulting in a weakly helical morphology of the corresponding Tσ(s). The
(-)S(-), (+)S(-) and (+)S(+) conformations of
S-1,5-diamino-[4]cumulene contain very significant degrees of both
chirality and helical character resulting in helical morphology of the
corresponding Tσ(s). The chirality assignments are in agreement with the
Cahn–Ingold–Prelog (CIP) classifications for the (-)S(-), (+)S(-) and
(+)S(+) conformations of S-1,5-diamino-[4]cumulene. We discuss the
consequences for the Tσ(s) in locating chiral character in these
molecules in future experiment investigations.
Enhanced reliability of phase-change memory via modulation of local structure and chemical bonding by incorporating carbon in Ge2Sb2Te5
