The Cahn–Ingold–Prelog (CIP) priority rules are a set of conventions that rank the groups attached to a stereogenic carbon. Working outward from the carbon, the group whose first point of difference has the higher atomic number is given the higher priority. They matter because this ranking provides the unambiguous basis for assigning R/S configurations at a stereocentre (and Z/E configurations across a double bond), giving every stereoisomer a definite name.

卡恩–英戈尔德–普雷洛格(CIP)优先次序规则是一套对连在手性碳上的各基团进行排序的约定。从该碳向外比较,在第一个出现差异之处原子序数较高的基团被赋予较高优先级。它们之所以重要,是因为这种排序为指定立体中心的 R/S 构型(以及双键的 Z/E 构型)提供了明确依据,从而使每一种立体异构体都有确定的名称。