Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watnot!watmath!clyde!cbatt!ihnp4!ptsfa!lll-lcc!seismo!nbires!isis!udenva!agranok From: agranok@udenva.UUCP Newsgroups: sci.bio Subject: Re: Human asymmetry Message-ID: <3432@udenva.UUCP> Date: Thu, 9-Apr-87 15:14:28 EST Article-I.D.: udenva.3432 Posted: Thu Apr 9 15:14:28 1987 Date-Received: Sat, 11-Apr-87 23:43:22 EST References: <1003@aecom.UUCP> <586@batcomputer.tn.cornell.edu> <2190@PUCC.PRINCETON.EDU> <1013@aecom.UUCP> Reply-To: agranok@udenva.UUCP (Alexander Granok) Distribution: sci Organization: U of Denver Lines: 33 Keywords: chirality Summary: Assignment of R and S In article <1013@aecom.UUCP> werner@aecom.UUCP (Craig Werner) writes: > > H > A prochiral center such as XCH has 2 Hydrogens that are identical. > Y > With a three dimensional model, it is easy to point to one in >the pro-R and another in the pro-S... Can you make assignments such as R and S in this case? It all depends upon what your reference point is. Consider the following: H (1) | 0 0 / 0 0\ / \/ \ X Y H (2) Where X and H (2) are out of the screen and Y is into the screen. Also, have X be a higher precedence group than Y. Now, when viewed opposite hydrogen (2), the molecule has an R configuration, but when viewed opposite hydrogen (1), it has an S configuration. Maybe I'm not getting all of your terminology, but I thought that R and S configurations could only be assigned when there was a chiral center. A molecule can't be both R and S with respect to the same cen- ter within the *same* molecule. Of course, the same center can be R or S in different molecules. Could you please elaborate? -- Alex Granok hao!udenva!agranok "A slow sort of country!" said the Queen. "Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!"