Question

2H-pyran $\xrightarrow{\text{HBr} \atop \text{(1 eq.)}}$

Answer 1

6-bromo-2H-pyran

Answer 2

The reactant is 2H-pyran, a cyclic enol ether. The reaction with HBr (1 equivalent) is an electrophilic addition. The double bonds in 2H-pyran are activated by the electron-donating oxygen atom. Protonation of the double bond at C5 leads to the formation of a resonance-stabilized allylic carbocation at C6, which is further stabilized by the adjacent oxygen atom. The bromide ion (Br-) then attacks the carbocation at C6 to yield the major product, 6-bromo-2H-pyran.