A rule that chemistry students have learned for generations may need a new explanation. Researchers say the inductive effect, one of the basic ideas in organic chemistry, does not behave the way textbooks describe.
What the textbooks say
The inductive effect describes how atoms pull on electrons inside a molecule. Standard teaching holds that the influence of a given atom travels through three or four chemical bonds and gets weaker with distance. That description has appeared in courses for almost 100 years.
The new work says the evidence points elsewhere. "In our latest paper, we find that the inductive effect does not behave in this way," said Dr Mark Elliott, lead author from Cardiff University's School of Chemistry. "Instead, we show that the inductive effect in a neutral molecule does not extend beyond one bond."
One bond, not three or four
The team, which includes researchers at the University of Newcastle in Australia and the University of New England, did not base the conclusion on one experiment. They gathered data already scattered across the scientific literature and combined it with their own consistent dataset. An earlier 2024 paper by the same group concluded textbooks had described the effect incorrectly for nearly a century.
"While some data supporting our conclusions is already available within the research literature, it is not widely known," Elliott said. "What we have done is pull all the existing data together, supported by our own coherent data set, to show the generality and teaching implications of this approach."
The researchers credit better tools rather than better insight. Earlier chemists had to draw indirect conclusions from limited experimental data. Modern computational methods let scientists examine molecular structures and electron distributions directly.
"We didn't initially feel comfortable challenging the established wisdom," Elliott said. "We certainly aren't smarter than those pioneers, of course. But we have better tools nowadays."
Exam boards are already reviewing
Two A-level exam boards have announced reviews of how they teach the inductive effect and cited the research as part of the reason. The new paper, "Rethinking the Nature and Extent of Inductive Effects in Organic Compounds," appears in the Journal of Chemical Education.
The stakes reach beyond the classroom. Organic chemists work with chains of atoms that form the basis of medicines, advanced materials, agrochemicals and polymers. If the reach of the inductive effect has been misunderstood, explanations built on the old model may need revisiting.
"If a foundational concept is taught inaccurately, misunderstandings can carry into more advanced science and research," said co-author Dr Edwin Johnson of the University of Newcastle.