re: Magnitude. Its really related to the hyperpolarisability rather than havng a stereogenic centre. Thus the “lemniscular” form of [14] annulene, that also has no stereogenic centre, has a rotation of around 3500 degrees. I have seen systems with no stereogenic centres with rotations > 100,000 degrees (sic).

Its the hyperpolarizability that does it, and π-electrons are particularly polarizable. Thus any system with (di)symmetric π electrons is going to have large rotations. It is also fair to say that such systems also have enormously variable optical dispersivity, ie frequency dependence. Thus some systems with rotations > 20,000 can go from -20,000, thru zero, to + 20,000 over 400 nm or so.

Not being very familiar with the theory that gives rise to the magnitude of optical rotation, I take it that you would have expected a smaller rotation for a species lacking a stereogenic center and not being *massively* distorted from the C2h point group?

I know a spectroscopist who does a bit of CD (well, protein MCD) who I imagine may find this quite interesting.

The [α]_D is +38° (for the absolute configuration corresponding to this rotation, see DOI: 10042/to-3719), calculated for a chloroform solution at the frequency dependent value of 589nm (B3LYP/6-311G(d,p) level using Gaussian 09).

The circular dichroism (for the same absolute configuration) using time-dependent DFT is archived at 10042/to-3720 and is feature-full (I cannot post a graphic here in the comments), with positive phased peaks at 152, 142 and 133nm, and a negative phase peak at 128nm. The Cotton effect is also large (Δε ~200). (I rather doubt that commercial CD spectrometers can go so far into the UV however).

Whilst it is very unlikely that either value could be verified experimentally, it is interesting that the optical rotation is as high as it is!

I look forward to the rotation and dichroism results.

I will in fact calculate both [α]D and the OCD spectrum of the twist boat, to see exactly how large the optical properties are.

There seems to be a dearth of discussion of symmetry breaking within the context of chemical structure. An interesting paper by Applegate, Barckholtz and Miller (DOI: 10.1039/a910269h) on Jahn-Teller distortions of cyclopenadienyl radical depicts a PES gratifyingly akin to the ‘Mexican Hat Function’ and how it gives rise to fluxional ‘pseudo-rotary’ sequences of equienergetic allylic and dienic structures. This post reminded me of that.