The importance of parentheses

Ironically, C&EN’s Oct. 17 issue (which features the cover title “Too Much Plastic?”) contains nomenclature errors on polymeric materials.

The first occurs in a letter to the editor titled “Vanilla Headache” (page 3). The writer refers to “polyvinylidene chloride.” The vinylidene moiety is C=CH₂; it is a carbene. Note that the prefix “poly” only applies to the “vinylidene” moiety and not the “chloride.” Yet, the proper name for the intended polymer is “poly(vinylidene chloride).”

Then on page 13, reference is made to “polyethylene terephthalate.” Again because the “poly” applies only to “ethylene,” taken literally this would be (CH₂CH₂)_nOOC-p-C₆H₄-COO(CH₂CH₂)_n. The author meant to refer to [CH₂CH₂OOC-p-C₆H₄-COO]_n. The correct designation of this important commercial polymer is poly(ethylene terephthalate); in this name, the prefix “poly” now refers to the ethylene terephthalate repeat unit.

Note how the presence or absence of the parentheses denotes two different materials in these and many (that is, most) other cases! In nomenclature, the parentheses are more than mere punctuation marks; they are critical for precisely specifying the structure.

Harry W. Gibson
Blacksburg, Va.

Jeff Huber, C&EN’s copy editor, responds: The use of parentheses in both of these instances would have been correct. However, C&EN decided to not use parentheses in the two cases cited by Gibson because both concerned business-related news, and the chemical industry typically omits parentheses in its discussion of polymers. Put another way, C&EN was attempting to reflect industry style by not including parentheses in these polymer names.

Corrections

Sept. 26, page 13: In the news story about Sarepta Therapeutics receiving approval for a new Duchenne muscular dystrophy drug, the phosphorodiamidate morpholino oligomer structure was drawn incorrectly. The phosphoroamidate bond should go to the ring carbon next to the morpholine oxygen, not to the oxygen.

Oct. 3, page 46: Bristol-Myers Squibb didn’t acquire Galecto Biotech and Promedior but rather signed agreements giving it the right to buy the two firms.

Oct. 10, page 18: The feature story about the Institute of Chemistry of the Chinese Academy of Sciences incorrectly stated that the organization’s 2015 budget was 686 CNY. It was 686 million CNY, or ~$103 million.