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The following structural formula (source: Wikimedia) is labelled ᴅ-amphetamine:

Strukturformel

A Fischer projection of this molecule would contain, I think, the following line:

$$\ce{H2N-C-H},$$

and I would have labelled the molecule therefore as ʟ-amphetamine.

Why am I wrong? Why is it called ᴅ-amphetamine?

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The L and D nomenclature is directly transform from its origin, D- and L-phenylalanine. The following scheme summarize the transformation:

D-amphetamine & L-amphetamine

The blue box in right-hand corner explains how L- and D-$\alpha$-amino acids get their names using Fischer projection (this is similar to D- and L-monosaccharides, replacing $\ce{OH}$ group by $\ce{NH2}$ group). If you reduced the carboxylate group of amino acid to a methyl group, the optical rotation of $\alpha$-carbon change from $(S)$ to $(R)$ because second highest priority of $\ce{COOH}$ group to third highest ($\ce{CH3}$ group) based on the size of the $\ce{R}$ group (see general formula of amino acid in top right corner). For example, when $\ce{R=CH2Ph}$ group, the amino acid is phenylalanine, which has $(S)$-rotation, but reduction of caboxylate group to methyl make the rotation $(R)$. However, the product $(R)$-amphetamine still carries the original L-nomenclature (see examples in bottom red box).

Note: The conversion of phenylalanine to amphetamine in several steps were achieved in beginning of 21st century (Ref.1).This is the ultimate enanthimerically pure version.

Reference:

  1. Dominick A. Quagliato, Patrick M. Andrae, Edward M. Matelan, “Efficient Procedure for the Reduction of α-Amino Acids to Enantiomerically Pure α-Methylamines,” J. Org. Chem. 2000, 65(16), 5037–5042 (https://doi.org/10.1021/jo000242h).
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  • $\begingroup$ That's great input. I'm grateful for the idea to derive the prefix from phenylalanine. But is this truly the source of the prefix or just a happy coincidence? From the comments to the question itself I came to believe that the D- was unfortunately capitalized and might have originally been a lowercase d- and chosen because of the optical effects of the substance. Now you explain the D- based on a Fischer projection, but you write the substance with the C1 atom at the bottom and the C3 atom at the top. How does somebody who wants to name the substance know that? $\endgroup$ – Wolfram Jul 19 at 15:12
  • $\begingroup$ D and L in sugars and amino acids are nothing to do with common d and l, which are based on optical rotation. However, they starts with stereoisomers (e.g., L- and D-glyceraldehyde). You can find a good description here. $\endgroup$ – Mathew Mahindaratne Jul 19 at 15:55

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