This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.

Contribute Thoughts | Search Serendip for Other Papers | Serendip Home Page

Beauty,Spring 2005
Second Web Papers
On Serendip

The Elegance of NMR and Superconductivity

Rachel Usala

Professor Burgmayer tilted a cup that held clear, misty liquid nitrogen. The nitrogen shrouded the black metal magnet that was displayed on the white table, danced across the surface, and rolled off to the floor. She then dropped a metal filament onto the magnet that had been cooled by the liquid nitrogen, and the filament floated and spun. Having seen such demonstrations before, I felt no particular surprise or wonderment, even though I did not know what caused the exhibited phenomenon. Perhaps I have been overexposed to science and suffer like the art historian that cannot feel overwhelmed or cry in the face of a masterpiece. I listened with only mild interest as Dr. Burgmayer talked, but then she turned to me and said, "It's a superconductor, like in NMR." I came fully alert. Nuclear magnetic resonance (NMR) is a tool used in chemistry to study the structures of molecules based on the nuclear spin of atoms, and I have studied this in my organic chemistry class. NMR's power as a chemist's tool fascinates me. The demonstration, in this context, interested me exceedingly, and I listened eagerly to the end. Afterwards, I researched superconductors.

When cooled below a critical temperature in an applied magnetic field, certain metals called superconductors experience zero internal magnetic field. This is known as the Meissner effect. The magnetic field becomes zero because currents induced by the superconductor cancel out the applied magnetic field. The magnetic levitation that was demonstrated results from the repulsion between the permanent magnetic field of the magnet and the magnetic field produced by currents induced by the superconductor(1).

By itself, neither this demonstration nor the explanations for superconductivity hold any beauty for me. My interest in the demonstration resulted from my background knowledge of the utility of superconductors. I mentioned NMR. NMR utilizes two principles of electricity and magnetic fields. First, "electric currents have associated magnetic fields." Second, "magnetic fields can generate electric currents (2)." NMR magnets are superconductors that apply a strong magnetic field to a sample of molecules that a chemist wishes to identify. Under the strong magnetic field, electrons circulate, creating a current. The current likewise produces a magnetic field that points in the opposite direction of the originally applied electric field. The opposing magnetic field "cancels out" some of the larger, external magnetic field. This cancellation of magnetic field, described here in simplified terms, is measured and used to identify the structure of molecules with marvelous insight.

To me, the story of NMR as a scientist's tool is beautiful. It is of the caliber that Roald Hoffmann describes: it has "the hallmarks that literary theorists have seen in narratives, small and grand (3)." There is temporality. A scientist synthesizes something. He or she uses NMR to describe the molecule, but the picture produced is often complex, a puzzle that must be solved; it can take hours to unravel a complex NMR spectrum. The scientist concludes from the NMR spectrum that the synthesis of the desired molecule was successful or unsuccessful. There is causation. The chemist uses NMR to identify a molecule or to confirm that a particular synthesis protocol has been successful. In the more global perspective, an organic chemist synthesizes in order to make medicines, to produce molecules with conducting properties, or to construct polymers for long underwear and car paint adhesive. There is human interest. The labor of human hands and minds, the collaboration of many scientists, and the successes and failures of the project are all recorded by the succession of NMR spectrums that a scientist uses to tell his or her story.

To look at a NMR spectrum, one has to agree with Hoffmann's theory that " to be found, precarious, at some tense edge where symmetry and asymmetry, simplicity and complexity, order and chaos, contend (3)."
This is a 1H NMR spectrum of 1-bromopropane that has the structure of a bromine atom attached to a CH2 molecule which is attached to a CH2 molecule which is in turn attached to another CH2 molecule. (The shorthand for 1-bromopropane is Br-CH2-CH2-CH2.) How the above spectrum tells the scientist that the studied molecule is indeed 1-bromopropane is not important for this discussion, but I would like the reader to take notice of the exquisite symmetry of the picture. There are three peaks: one at approximately 1ppm, one starting at approximately 1.7ppm and a final peak at 3.4ppm. Within the first peak at 1ppm are three, symmetrical spikes. The middle spike is the largest and the two on the right and left sides are slightly smaller. A similar construction occurs at 3.4ppm. There is a more interesting peak that ranges from 1.7ppm to 2.2ppm, and it is more striking for its symmetry. It is has multiple spikes. The largest spike is again the center spike, and the sizes of the other spikes gently fall off at each side. The symmetry is clear, but there is a component of asymmetry as well. The right spike is larger than the left spike at the 3.4ppm peak, and the left spike is larger than the right spike at the 1ppm peak. (This is a phenomenon called "leaning.") The picture has some resemblance to canyon peaks: both images are symmetric but not perfectly so.
Yet, for scientists this is not the beauty. The beauty is the utter complexity and amount of information that can be obtained from the simple picture of a NMR spectrum. The NMR spectrum provides information about how many atoms of hydrogen are in a molecule, how many neighbors a hydrogen has, what types of molecules a hydrogen is close to, and what types of bonding occur in the molecule. Within a sample submitted for NMR, there are millions of molecules crashing together, interacting, vibrating, stretching, and rotating. Nevertheless, the NMR spectrum is able to bring order to the chaos and produce an image that compactly describes the structure of a single molecule. The NMR spectrum is as powerful a tool to a chemist as a mathematical formula is to a mathematician or physicist. NMR explains the interaction of molecules like the mathematical formula F=ma explains the interaction of force to mass and acceleration.

Nevertheless, to say that NMR is conclusively reliable because it is beautiful to an organic chemist, as Zee and McAllister suggest, is an oversimplification. I imagine many chemists don't find NMR at all beautiful: beauty and utility are not always hand in hand. Thousands of experiments and the collaboration of data from other scientific instrumentation have tested the reliability of NMR and insured its acceptance into the realm of academia. I think Dr. Peter Beckman's theory about the relation between beauty and truth comes closest to explaining why chemists find NMR elegant. NMR is useful.

NMR is the unification of many things. It harmonizes the theories of magnetism and electricity, which are seemingly unconnected phenomenon. It integrates the efforts of many types of scientists and mathematicians. Engineers construct the large and elaborate NMR magnet. Computer scientists design the software to process the enormous amount of information. NMR theory draws upon vector mathematics, calculus, and probability to explain the appearance of several spikes within a peak and their relative sizes. It uses physics to harness the usefulness of the phenomenon of nuclear spin and energy absorption. Chemists primarily utilize it for product identification. The lines of categorization between physics, mathematics, engineering, computer science, and chemistry that academia has created blur, dissolve, and disappear in order to collaborate on a project that has value as a tool and as a model for the world. I think this is what scientists find most beautiful about NMR and superconductivity. To utilize NMR and superconductivity one must be everything at once: mathematician, chemist, computer scientist, engineer, and physicist. There is only one goal: to model the laws of nature that command and direct nuclear spin and to harness their power as a conclusive description of molecular structure.

1. Tipler, Paul and Mosca, Gene. Physics for Scientists and Engineers. Volume 2B. New York: W.H. Freeman and Company, p. 922.
2. Nerz-Stormes, Maryellen. Organic Chemistry Laboratory Manual. Bryn Mawr College: Fall 2004.
3. Hoffmann, Roald. Narrative. American Scientist On-line, July-August 2000.

Online Picture Sources:

| Course Home Page | Course Forum | Science in Culture | Serendip Home |

Send us your comments at Serendip

© by Serendip 1994- - Last Modified: Wednesday, 02-May-2018 10:51:35 CDT