Words Do Matter

“The Ways To Words” impugns the term “π-stacking” and claims that it has an unclear definition (C&EN, Feb. 10, page 28). I suggest reading “The Nature of π-π Interactions” by Christopher A. Hunter and Jeremy K. M. Sanders (J. Am. Chem. Soc. 1990, DOI: 10.1021/ja00170a016). They argue that “π-π interactions ... occur when the attractive interactions between π-electrons and the σ-framework outweigh unfavorable contributions such as π-electron repulsion.”

Ernest L. Lippert
Toledo, Ohio

“The Ways To Words” makes a cogent point. For many years I have been telling my fellow atmospheric scientists to stop using the expression “carbonyls” in place of carbonyl compounds (aldehydes and ketones), because chemists have reserved the term carbonyl for metal-carbon-monoxide addition compounds, such as nickel tetracarbonyl, Ni(CO)₄ (melting point -25 °C, boiling point 43 °C). The practice of using “carbonyl” for carbonyl compound may have its origin in laboratory jargon; it definitely should be discontinued to avoid misunderstanding.

Peter Warneck
Mainz, Germany