Neo- vs. Tert- and Sec- vs. Iso-

[Austin Hyun 1F]

So just to clarify, a substituent would be referred to as tertbutyl over neobutyl, and isopropyl over secpropyl? Why are these priorities inconsistent (i.e. iso- over sec-, but neo not over tert-)?

[Amy Pai]

Are you asking about priority in how to name the substitutent? If so, then it's because iso has that V at the end, while sec specifies a chain with the second C attaching to the parent. You might think there's an overlap with isopropyl and sec propyl, but sec starts only with butyl.

Tert and Neo are fundamentally different, so there is no overlap like with isopropyl and a potential "sec-propyl". Tert has a tertiary carbon while Neo has a secondary carbon. And regardless, Neo starts with Neo-pentyl, because that is the simplest Neo possible.