Thursday, 2 October 2008

Are all enantiomers equal?

The typical statement is that the physical properties of two enantiomers are exactly the same. Differences are only in interactions with other chiral substances and polarized radiation. This is based on the intuitive assumption that a mirror image of our world would behave exactly the same as our world. In physics this is called parity symmetry [1]. But interestingly parity symmetry is not always conserved.

Out of the four forces of nature, it's the weak one that steps out of the line and breaks P- (and even CP-) symmetry. As the name suggests it is weak. And it is also short range, on the order of attometers. That's why we don't notice it. Nonetheless theory predicts energy level splittings between enantiomers. This could be on the order of 10-15 cm-1. This is apparently extremely small and even the newest experiments haven't gotten below 10-13 cm-1.

Don't bet too much money on the emergence of weak force intermediated enantiospecific synthesis yet. But even though P-violation is out of every day life it seems that with improved experiments or in different systems the effect could be observed. And then chemistry could be an interesting alternative to clashing things together with higher and higher energy, at least a complimentary tool.

Another question has been experimentally adressed. What is the minimum number of atoms you need for a chiral system? It is one. Isolated Bi atoms have been shown to rotate the plane of polarised light.

I am sorry I am not quoting literature. The information comes from a lecture by Robert Berger, Stephen Hawking's "Brief History of Time", and Wikipedia.

[1] Two other fundamental symmetries are charge and time. Conversely to separate parts, it is generally assumed that CPT symmetry is conserved in the world, i.e. that things would be the same if you simultaneously changed charge, parity and the direction of time.

[2] Yes, I am still only treating physics at the popular science level. To be honest, it was even the Illustrated Brief History of Time ...


Ψ*Ψ said...

Do you have much of a physics background? I'm beginning to wish I did. I like a few of their journals...but only the ones that cover devicey physics, because that's pretty much all I understand.

Felix said...

it's always been chemistry and math. i don't know if i would have liked physics if i had tried it. but i guess it would be too much anyway

Ψ*Ψ said...

i think i gave up on it before i got to anything cool--solid state is actually kinda awesome. at least you have the math, though...for me there was always only chemistry ;)

Felix said...

yeah, i think there are tons of cool stuff. and you just do some of it. but i think the problem is that everything is a lot of work before it may eventually get interesting