Zellinger

Quote Wiki: In electrodynamics, circular polarization of electromagnetic radiation is a polarization such that the tip of the electric field vector, at a fixed point in space, describes a circle as time progresses. The electric vector, at one point in time, describes a helix along the direction of wave propagation. This actually means that the trajectory that is described along the direction of wave propagation by electric vector is chiral to be exact. Is light thus chiral? Light is said to be chiral (left or right polarized) to describe this phenomenon but it isn't the kind of chirality we talk about in molecules. It is a description of light's behavior. Then I could say that the molecule that moves trough the vacuum with a helical trajectory is chiral, right? Light is an electromagnetic wave (combination of electric and magnetic fields) and thus cannot be chiral in the way that molecules are. You have to have a solid matter for something to be chiral.

Let's start from the term chiral - it means that an object (or phenomenon) isn't identical to it's mirror image and it comes from greek word cheir which means hand (hands are chiral in broader sense of the word). In chemical sense chiral refers to molecules with same order of binding between atoms but with different spatial relations between them. These molecules lack symmetry. See: http://home.clara.net/rod.beavon/chiralit.htm Light was ruled out from periodic table of elements around one century ago since the discovery of it's true nature so there's your answer. To correct someone who said molecules are chiral because of the light - wrong. Molecules are chiral in the dark too because they can lack symmetry even then - chiral nature of a molecule allows it to rotate polarized light so this is simply a manifestation of asymmetry of the molecule. To be chiral molecules have to have chiral center. Some molecules can have chiral center without manifesting the rotation of light's plane of polarization - so they aren't labeled as chiral. These are called meso-compounds and have a plane of symmetry - in other words can be superimposed. See meso-tartaric acid. I think that it is wrong to say they aren't chiral because in reality they do rotate light just do not manifest it because as soon as one group rotates the light polarization plane other one reverses it so no effect is observed as light interacts with them, in other word the sum effect is zero. Or maybe these molecules don't reverse light at all... hmmmm. I'm not sure exactly on the nature of interaction between light and molecules. It's electromagnetic but do they first rotates and then reverse light or simply don't rotate light at all. because electromagnetic influences of these kind of groups close together negate themselves prior to interaction with light, I'm not sure. Can some clarify this to me? In theory will a solution that of meso-compound with long aliphatic chain between two opposite chiral groups rotate light if we can separate only identical groups to different side of the solution? See this picture. I think it will and if this is right then meso-compounds are in deed chiral. Apparently light can be chiral in physical sense but this completely different phenomenon. It's like comparing apples and pears. I am not much familiar with this phenomenon so I can't really explain it but I'm sure that except same name and it's meaning in broader sense they don't have much in common. Please correct me if I'm wrong. See here for more info: http://en.wikipedia.org/wiki/Chirality_(chemistry) http://en.wikipedia.org/wiki/Chirality_(physics) p.s. By the way I don't get this chiral interacts with chiral story and what it's point. Can someone explain?

Yes, you can if know how to determine S and R configurations. Look at definitions for diastereomers and enanthiomers again.

Well no. They are in the equatorial position most of the time to avoid these repulsions but you can't say it's why they have similar energy barriers between 2 conformations. The fact that they are almost exactly the same amount of time in equatorial position is the result of the almost the same energy barriers. To demonstrate: by your reasoning you could say that tert-butyl group has the same energy barrier as the two mentioned groups between conformations because it's all the time in equatorial position. So you must realize that the fact that they are in equatorial position is the result of energy barrier between 2 conformations not vice-versa. You must concentrate on the spatial dimension of the problem. Ok? Try drawing the most stable position (with drawn hydrogen atoms; remember free rotation around single bonds if u wonder what I mean by most stable) for both equatorial and axial position of both ethyl and methyl group, then draw the same for let us say tert-butyl group and you should figure it out. I can't help you more then this without actually telling you the answer. Hint: all of these groups have similar energy levels at equatorial position as I remember since there are no axial repulsions. p.s. I hope I helped you if even a bit.

Sorry I wasn't aware of it. Question did sound a bit too basic. You should move this thread to appropriate section then.

Recommended reading: http://wetche.cmbi.ru.nl/organic/cyclohexane/jm/exer1.html or "Organic chemistry" by Stanley H. Pine

I believe the name of the product would be 1,4-naphtoquinone. Edit: you would have to add tetrahydro- in the name to indicate that two double bonds are missing.

Is anyone familiar with methods for detecting free radicals except EPR (ESR) spectroscopy? I'm particullary interested in detection of free radical via polymerization reactions i.e polymerization of acrylonitrile and acrylamide. What are the exact experimental conditions for this kind of detection to work? Well here is my problem - we have been investigating this redox reaction and we suspect that it's mechanism involves free radicals. We have done the EPR spectroscopy but results came out negative, so my mentor said we can try to do polymerization test to be sure there aren't any radicals present at all (since this result is a bit odd). Our reaction only occurs under alkaline conditions (pH = 12 or above) at significant rate. So we added acrylonitrile to our reaction mixture under inert nitrogen atmosphere (to exclude oxygen) but no turbidity appeared as it was stated in several journals. Then with tried with species we knew is in free radical form (in our case we used ascorbate, some papers state it's initiator for this reaction) but test again came out negative. So there was a problem somewhere and I couldn't figure it out. Today I have found that acrylonitrile if technical-grade contains polymerization inhibitor ethylhydroxyquinone and should be purified (it think by destillation) prior to use. But in the same article I have found out that AN polymerizes spontaneously under strong alkaline conditions which is our case so even if purified we couldn't use this reagent for detection. Does anyone know if similar reaction could be performed with acrylamide and what are exact experimental conditions? I have searched OVID journals and it's mentioned in couple of papers but I haven't found any detailed explanation of the procedure. Thank you in advance!