Could you please describe what axial chirality is? like ive indicated in the picture in the above post I would have thought that this was axial chirality,
"Optical activity" is a physical quality like a melting point or boiling point. A pure single enantiomer of a chiral compound will display optical activity but so might a mixture.
A chiral molecule has two enantiomers which are non-superimposable mirror images. Each pure enantiomer will display optical activity, that is, they will rotate plane polarised light - by the same magnitude and in opposite directions. The only reliable test
of whether a molecule is chiral is to see if its mirror images are superimposable. A clue that it may
be chiral is the presence of a stereogenic or asymmetric centre (e.g. an sp3 carbon with four different substituents). This is not proof however, because the stereogenic centre may be duplicated elsewhere leading to a meso compound. The meso compound below has two asymmetric centres, but is not chiral.
Chirality can also arise from asymmetry in the molecule that is not associated with a stereogenic centre. Two classic examples - allenes, and biphenyls with restricted rotation - are shown below. These compounds are not superimposable on their mirror images but they have no stereogenic centres. They have axial chirality.
Helical compounds can also be chiral (planar chirality) depending on whether they have a left-hand or right hand threads.
By the way, you might be interested to read here
that new limits of detectability of chirality have been set by the measurement of the Raman optical activity of (R)-[2
]-neopentane -- that is, a carbon atom with 4 different substituents being CH3
D and CD3
. Pretty amazing subtly in enatiomeric difference.