In the base-catalyzed ring opening of an epoxide (oxirane), the nucleophile attacks the less sterica — Alcohols Phenols and Ethers Chemistry Question
Question
In the base-catalyzed ring opening of an epoxide (oxirane), the nucleophile attacks the less sterically hindered carbon. If propylene oxide (2-methyloxirane) is attacked by methoxide ($CH_3O^-$) in methanol solvent, what is the specific locant number of the methoxy substituent in the IUPAC name of the major product?
💡 Solution & Explanation
Propylene oxide is $CH_3-CH(O)CH_2$. Under basic conditions, the methoxide nucleophile ($CH_3O^-$) attacks the less hindered terminal $CH_2$ carbon. Following protonation, the product is $CH_3-CH(OH)-CH_2-OCH_3$. The longest chain containing the principal functional group ($-OH$) is numbered to give the $-OH$ the lowest locant (carbon 2). The methoxy group is on carbon 1. The IUPAC name is 1-methoxypropan-2-ol. The locant is 1.