American Scientist

To the Editors:

Roald Hoffmann's Marginalia column ("Legally Sweet," July-August) was, as usual, insightful and entertaining. However, the sucrose and sucralose structural drawings were not correctly done, the aspartame drawing was ambiguous, and the labeling of the guanidinoacetic acid derivative drawing was misleading.

Many of the lines indicating carbon-carbon and carbon-oxygen bonds in the sucrose and sucralose drawings are mistargeted to hydrogen atoms, to subscript 2s or to somewhere vaguely between atomic symbols. The aspartame structural drawing does not indicate critical stereochemistry at the two critical chiral centers. The guanidinoacetic acid structure should have been labeled as a granidinoacetic acid derivative.

Thomas W. Flechtner
Cleveland State University

Dr. Hoffmann responds:

There is a lot of flexibility in the way chemical structures are written, and much shared sense for what people are trying to communicate. For instance very few people would imagine that -CH₂OH stands for -C-H-H-O-H. Similarly, I think the vast majority of chemists looking at the cases that Dr. Flechtner cites would know that the line heading up to the CH₂OH substituent indicates a bond to C and not H and not O. The positions of the lines could be improved, admittedly.

There is a time to show stereochemistry, as in aspartame, and there is a time to omit it; such a choice was made for aspartame stereochemistry in American Scientist. A different choice would have been made for the Merck Index.

"Granidine" and "granidinoacetic acid" are extremely rare terms, which would be unrecognized by the vast majority of organic chemists. Guanidinoacetic acid is pretty descriptive, and is the term used by chemists in the sweet taste community.