Saul Winstein was a Canadian-American chemist who discovered the Winstein reaction. He argued a non-classical cation was needed to explain the stability of the norbornyl cation. This fueled a debate with Herbert C. Brown over the existence of σ-delocalized carbocations. Winstein also first proposed the concept of an intimate ion pair. He was co-author of the Grunwald–Winstein equation, concerning solvolysis rates.