User talk:98.21.240.33

READER BEWARE!

the author of this article is slightly less than rigorous with the useage of nomenclature and terminology which may lead the reader to confuse the abstract concept of absolute configuration about a chiral center, with the purely physical property commonly referred to as "optical activity."

within the context of this article, capitalized letters "D" and "L" refer to the absolute configuration of the chiral center of an amino acid. they have NO correlation to the purely physical properties of levorotatory and dextrorotatory. some "L" compounds are actually dextrorotatory and some "D" compounds are actually levorotatory.

small letters "d" and "l" stand for dextrorotatory and levorotatory respectively and describe the experimentally observed direction of rotation (CW or CCW respectively) of the plane of polarization of beam of plane-polarized light passing through a sample. they have no correlation to the absolute configuration(s) of the chiral center(s) in the molecule.

the "L" in the name L-DOPA means that it is the enantiomer of 3-(3',4'-dihydroxyphenyl)-2-aminopropanoic acid that has the same absolute configuration about the chiral carbon bearing the amino and carboxyl groups as levorotatory-alanine. (l)-alanine, in the CAHN-INGOLD-PRELOG formalism, is equivalent to (S)-alanine or (S)-2-aminopropanoic acid. therefore, the "L" in the name L-DOPA means that the absolute configuration of the chiral alpha-carbon is likewise (S). that is the ONLY thing it means.

the "L" in the name L-DOPA does NOT imply that the observed optical rotation of L-DOPA will be levorotatory. it may be EITHER levorotatory (l) or dextrorotatory (d), and there is no way to predict which. that can only be known by experimental observation. only in the single case of alanine do we know (by definition) that L-alanine is levorotatory.

the word "levodopa" may well have been used as a commercial trade name for L-DOPA, that i cannot say one way or the other, but L-DOPA is NOT to be confused with (l)-DOPA or levorotatory-DOPA.

in science, accuracy and precision are EVERYTHING, including accuracy and precision in nomenclature as well as conceptual understanding. something as simple as misusing capitalization in a chemical name can lead to confusing an experimentally observed physical property with an arbitrary theoretical structural isomorphism.

cite my sources? I'M my source. i was a chemistry professor long before there was a wikipedia or an internet.

Billyrayjoejimbob (talk) 03:16, 28 November 2017 (UTC)