Topologically/Geometrically Interesting
moleculeoftheday | January 29, 2008After this weekend's discussion of chirality in advertising, I figured I'd post an interesting, more rigorous example of chirality. Most chiral (left- or right-handed)molecules have "asymmetric" carbons, or ones with all different things attached.
Helicene, by contrast, has none. However, it's got a twist that imparts chirality to it. Think of a left- and right-handed staircase. This, in itself, constitutes chirality - for example, DNA (almost always) twists right. If you put left-handed DNA in ads for your biotechnology company, scientists will make fun of you.
moleculeoftheday | August 2, 2007Aromatic rings have 4n+2 pi electrons, where n is any integer. You don't see odd numbers of carbons in aromatic rings too often because the pattern of alternating double bonds is disrupted - if you have a cation or anion, though, odd-numbered aromatics are possible.
Tropylium cation is one such aromatic ring - same pi electron count as benzene, but one extra carbon. The ion is so stable you can actually isolate tropylium fluoborate (not sure about other counterions). It is also an ubiquitous peak in EI mass spec from alkylbenzenes.
Analogously, complexes of cyclopentadienyl anion are known (…
moleculeoftheday | June 12, 2007Friday's entry on safrole inspired a number of comments on what sort of animal it looked like. One person mentioned a chestnut from a few years back: NanoPutians!
NanoPutians are molecules that look kind of like people. James M. Tour at Rice has a grant to use the little nanopeople in chemical education programs, which I think is actually a really neat idea. The jokes, however, are too easy to pass up.
The above is "NanoKid," which, perversely, is the lone progenitor of a whole army of NanoPutians. The others are generated by microwaving NanoKid with decapitated NanoPutian heads.
I have…
moleculeoftheday | March 20, 2007Ethylene oxide is the simplest possible epoxide, or three-membered cyclic ether:
It is a superior disinfectant, but it's a gas, and quite toxic, so you'll probably never use it. Even in biology labs, an autoclave is used to disinfect (essentially a pressure cooker - water is heated 12C/21.6F degrees above its normal boiling point). EtO is ubiquitous in disinfecting medical supplies - especially things like bandages and gauses, where a wet autoclave is problematic. Some beasties can happily survive (and reproduce) at autoclave temperatures.
It also has a role in the production of ethylene…
moleculeoftheday | November 29, 2006Cyclopropane is another markedly strained ring (the smallest simple ring geometrically possible, really):
It used to find some use as an anaesthetic. Strained rings being strained rings, however, it had a nasty habit of exploding. One movie made good use of this phenomenon (without commenting on it at all, there were just labels on the tanks!), where the villain used it as a weapon. No idea if the conditions were realistic, but at least the authors get some creativity points. Some have invoked the colorfully named banana bond theory to explain bonding in cyclopropanes.
moleculeoftheday | November 28, 2006Squaric acid is an unusually strong acid for an organic acid:
It's also unique because of its strained ring. In general, five- and six-membered rings dominate in chemistry - hence the endless parade of hexagons. Higher rings are tolerated but not-so-favored. Lower rings are possible, but, again, unfavored, because one tends to find atoms' electrons in clouds that don't overlap so well in this configuration. Along with some other moderately strong organic acids (such as the ubiquitous "alpha-hydroxy acids"), it's attracted some attention for (prescription) dermatological use.
moleculeoftheday | October 19, 2006For a better idea of how the bond angles look, here is an energy-minimized structure of windowpane (4.4.4.4). Notice how it's (nearly) planar. That central carbon atom (middle gray dot, blues are hydrogens) is the one to watch.
Here is 5.5.5.6 windowpane:
And here is an unstrained compound, tetramethylmethane (2,2-dimethylpropane):
The changes are subtle but result in enormous energy changes. The molecules go in increasing order of stability (Decreasing energy). This is one of the things it's a little weird to start thinking about in chemistry. Molecules are rarely completely rigid;…
moleculeoftheday | October 18, 2006Like cubane, windowpane (also named "[4.4.4.4]fenestrane" for the Latin for window) is another of those compounds people like because it looks like something anthropomorphic, with clean right angles (in contrast to the bulk of molecules, which assume their bond angles with little regard for what looks nice on paper). This introduces a great deal of strain, since quantum mechanics would rather we avoid bond angles very far from ~110 degrees in these sorts of compounds. See this entry on cubane from the old site for more information on why right and 180 degree angles are so tricky here.
In fact…