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Re: whats the diff. between adderall and dexedrine SLS

Posted by chemist on July 23, 2004, at 19:20:29

In reply to Re: whats the diff. between adderall and dexedrine, posted by SLS on July 23, 2004, at 18:42:40

> > hello there, chemist here...actually, a d- or l- designation tells us that there are two compounds that are chiral and interact with polarized light in different ways (rotation relative to laboratory axis): this does indicate that the compounds in question are not achiral and are, in fact, enantiomers, as you note.but we need not go directly to optics in order to answer the question: an enantiomer is a stereoisomer with the specific condition that the mirror images of the compounds are non-superposable. the d- and l- forms of amphetamine are, of course, chiral at the alpha carbon and cannot be superposed. hence, we can work with the simpler definition of enantiomer without getting into optics or the nomenclature of fischer or cahn et al., the former being troublesome and the latter, in my opinion, being of more utility. all the best, chemist
hello there, chemist here.....if you are talking about a pair of stereoisomers with one - and only one - chiral center, you are, by definition, talking about a pair of enantiomers which will indeed be differentiated by +/- rotation of plane-polarized light. R and S do NOT correlate with optical activity or +/- rotation of plane-polarized light. R and S designations are not subject to misinterpretations as fischer projections can be: as you note, R and S simply differentiate absolute configurations (spatial) of molecules. this is useful in accord with IUPAC naming conventions, which do not (alone) indicate whether or not one or more chiral centers are present. i work with nicotine extensively, and (S)-nicotine binds with a higher affinity to the neuronal nicotine receptor alpha_{7} homopentameric and alpha_{4}beta_{2} heteropentameric subtypes than does (R)-nicotine. because i am a theorist, and there the allosteric nature of the binding in this case, i am interested in derivatives of (S)-nicotine and not (R)-nicotine. i can tell by looking at a ball-and-stick model whether or not it is R or S: i cannot tell if it is d- or l-. the R and S is more useful in this regard, because a putative (or known) structure can be classified instantly without going into the laboratory. further, if i can designate R and S configurations, then i know that the molecule is chiral and optically active, and i still have not gone into the lab. the only remaining issue is whether R = d or l or, alternatively, S = d or l, and this is determined in the lab. all the best, chemist
> Will enantiomers differing at only one chiral center always rotate polarized light in opposite directions?
> When do scientists decide to use the d,l optical nomenclature as opposed to the r,s configuration designation, and why? Is it a matter of not knowing the molecular structure?
> - Scott




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