Cahn-Ingold-Prelog rules: A series of rules used to establish priority of attachments (lone pairs, single atoms, or groups) for purposes such as assigning R/S configuration to an sp³ stereocenter or E/Z configuration to an alkene.

Priorities: HO > CH₃CH₂ > CH₃ > H
Name: (R)-2-Butanol


Priorities: I > CH₃ and CH₃CH₂ > H
Name: (Z)-2-Iodo-2-pentene