Number the longest continuous chain or ring. Begin numbering at the end of the chain nearest the first branch. In a ring, start numbering at a substituent. If there is more than one possible set of numbers, choose the lowest possible set. If the set of numbers is identical, base numbering on alphabetization of substituents.
Numbers appear before substituent names.
Use hyphens to separate numbers and letters Use commas to separate numbers form each other. If a substituent group appears more than once, provide a number for each substituent location.