From: Geoffrey H. <ge...@ge...> - 2007-12-17 04:49:54
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>> The stereo-chemistry concepts I'm aware of are: >> >> 1) Chiral atoms (with at least 4 distinct substituents) >> 2) (E)/(Z) isomerism on double bonds >> 3) cis/trans isomerism on ring systems >> 4) Chiral spiro compounds >> >> There might be more... > > Out of curiosity, circular DNA twists around N times - the link > number - and DNA topoisomerase changes the number of twists. Does > this count as stereochemistry? Interestingly, this problem came up when I was considering Ph.D. projects. You need a measure of "helicity." I believe one such measure is the distance of a "unit cell." and an indication (i.e., +/- sign) of the direction of the turn. There are non-tetrahedral stereochemistries. SMILES has one such designation. Rich Apodaca is fond of compiling interesting stereochemistry questions on his blog depth-first.com. They're usually in posts titled "How Would Your Cheminformatics Tool Handle This?" Cheers, -Geoff |