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Putting a spin into chemistry.

Putting a spin into chemistry

Chemists have found a way to build amolecular propeller. The recently synthesized molecule, consisting of three six-membered rings made up of carbon atoms radiating from a central axis (diagram 1), looks like a three-bladed propeller. Its name, appropriately, is propellahexaene.


"It's a very attractive molecule,' sayschemist Leo A. Paquette of Ohio State University in Columbus. "It's nicely symmetric and has all the features one would expect if one were to describe a molecular propeller.' Paquette and Liladhar Waykole report their successful synthesis in the May 13 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY.

Achieving the synthesis was no simplematter. It took about 20 steps and many years of work to end up with the correct ring structure. Locking three rings together was relatively easy. The trick was to strip away any unnecessary molecular appendages hanging from the rings without causing a major rearrangement of the molecular structure.

The new compound turns out to beremarkably stable in air. It appears in the form of fine, colorless, needle-like crystals, which melt at 48|C.

Paquette and his colleagues are hopingto produce larger quantities of the hexaene to study its crystal structure and its chemical reactivity. In terms of its chemistry, he says, "we don't know what to expect--except complications.'

Propellahexaene is also of interest tochemists because it comes in two forms: a right-handed and a left-handed conformation. The rings are strongly curved, and the whole system rapidly flips back and forth between one form and the other (diagrams 2 and 3). Chemists are interested in the factors that determine how easily this switching occurs and how much energy is involved.

It may be possible to lock such amolecular propeller in one position, says Paquette, perhaps by making the rings heavier. That could be done by using double instead of single rings for each blade. Paquette says he can also imagine stacking hexaene molecules to create a molecular screw, "but I wouldn't want to come to grips yet with the task of making them.'
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Title Annotation:propellahexaene - propeller-shaped synthesized molecule
Author:Peterson, Ivars
Publication:Science News
Date:Jun 6, 1987
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