Isopropyl and Butyl Groups - Relative Priorities This does not compute for me:



Why would the four-carbon butyl group have a lower relative priority than the 3 carbon isopropyl group?

If we compare the carbons one by one between the isopropyl and the butyl group, we'd run out of carbons in the isopropyl group first! How then can isopropyl possibly have a higher priority than the butyl group?
Comparing IsoPropyl and n-Butyl


On first position both have C.
On second position IsoPropyl has two C's whereas n-Butyl has only one C.
Thus IsoPropyl has higher priority and we do not see the further chain.