Treatment of tetrahydrofuran with excess HBr results in the formation of what major organic product?

A) 1-bromobutane
B) 1,2-dibromobutane
C) 1,4-dibromobutane
D) 1-bromopentane
E) 1,5-dibromopentane

Tetrahydrofuran has a ring structure with an oxygen atom, and excess HBr will result in the ring opening reaction via acid-catalyzed nucleophilic addition to the oxygen atom. The first addition generates a primary carbocation that then undergoes further nucleophilic attack by another HBr molecule. The major product obtained from this reaction is 1,4-dibromobutane, which is formed by the addition of two HBr molecules to the opposite carbons of the butane chain. This reaction is an example of anti-Markovnikov addition.