  Chiral structures, breaking spatial inversion symmetry, exhibit non-zero
chiroptical activity (COA) due to the interaction between their electric and
magnetic responses under external electromagnetic fields, an effect that is
otherwise absent in achiral systems. Non-magnetic chiral structures also
exhibit Chiral Induced Spin Selectivity (CISS), where spin-polarization (SP)
emerges without external magnetic influence. We have obtained a COA-SP
connection for a model system of an electron constrained to a helix including
spin-orbit coupling (SOC), and in the presence of an external electromagnetic
field. Despite its simplicity, this model captures the relevant physics
required to address the problem. In particular, our results reveal that the
norm of the SP vector can be used as a predictor of COA. In addition to SOC and
the breaking of space inversion, a non-vanishing SP requires the breaking of
time-reversal symmetry (TRS), as demanded by Onsager's reciprocity. Beyond the
relationship between SP and COA, we obtain the novel result that TRS breaking
is also necessary to yield a non-vanishing contribution of the SOC to the COA.
