Leave it to the Genius

X-ray diffraction machine

Yesterday we had a lecture on X-ray diffraction. I learned two major things during that lecture. First, some people are geniuses. Second, I am not one of them.

I was able to follow the lecture to an extent, thanks in large part to taking both physics and multivariable calculus this past semester. Unfortunately, most of the lecture stayed right up over my head, occasionally coming down to grace me with a tiny light-bulb moment.

In the corresponding lab, all I can say is there was a lot of math involved. Some simple, some not so simple. There was a drawing element involved, where I found out that Claire can draw super straight lines, whereas mine look like something from a Dr. Seuss book. There was a statistics element, of course, as there always seems to be nowadays, but there was also a nice fun element as well, which you may find smack dab in between fluorine, uranium, and nitrogen on the periodic table (I apologize for the bad joke…it’s late). All in all, it was really cool. We matched a diffraction spectrum to the crystals that originally formed them. It was a long process, but doing everything manually made me realize how much goes into this technique.

X-rays reacting with a sample

First of all, for those of you who weren’t in the lecture or lab today, X-ray diffraction is a method that studies the arrangement of atoms in crystals and other solids. X-rays hit the crystal or powder and diffract into many different waves that destructively or constructively interfere with each other. Think Young’s double slit experiment or its multi-slit counterpart. From just the diffraction angles and intensities (and a lot of math), you can obtain a picture of how atoms and electrons are arranged in the solid you started with. That’s the basic idea.  

Crown ether. Isn't it pretty?

In chemistry, x-ray crystallography led to an in depth study of chemical bonds. In 1928, it helped differentiate between the bond lengths of a typical C-C bond and the C-C bonds in benzene (1.54 angstroms vs. ~1.4 angstroms, respectively). This in turn led to the idea of resonance, which is a big deal for anyone who has taken organic. X-ray diffraction led to developments everywhere: in inorganic chemistry with metal-metal double and quadruple bonds, in supramolecular chemistry with crown ethers (those funny molecules from 221), in revealing interactions with hydrogen bonding, and even in the pharmaceutical industry, establishing how drugs interact with their targets. This technique helped do all of that, and more.

So all in all, x-ray diffraction led to serious growth as far as chemistry is concerned. For now, it may be confusing and a little over our heads, and maybe one day I'll completely understand it. For now, however, I'll leave it to the geniuses.

References:

http://www.google.it/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&ved=0CJQBEBYwBw&url=http%3A%2F%2Fepswww.unm.edu%2Fxrd%2Fxrdbasics.pdf&ei=B7rbT4fWE9P44QSKmr3KCg&usg=AFQjCNGZNByYiZEOWyu0I5irqdJHFm3I2A

http://www.google.it/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CGMQFjAC&url=http%3A%2F%2Fwww.iucr.org%2F__data%2Fassets%2Fpdf_file%2F0015%2F735%2Fchap18.pdf&ei=hNPbT--WAa7E4gTwh4DQCg&usg=AFQjCNFKEFCTlSQGniYY-JrompqQ0dXxlA

http://en.wikipedia.org/wiki/X-ray_crystallography