Question

Furan undergoes electrophilic substitution with bromine, to yield 2-bromofuran, under milder conditions that benzene (no FeBrs catalyst required).

 a)  Is furan aromatic? Give a justification that considers its reactivity and whether it meets all criteria for aromaticity.

 b)  Propose electrophilic aromatic substitution mechanisms for the bromination of furan at the 2-position and at the 3-position. Include sufficient electron-pushing arrows to account for all electrons involved. Include any important resonance structures.

 c)  Draw schematic reaction coordinate diagrams (energy on the y-axis and reaction coordinate on the x-axis) for both mechanisms, with the goal of pointing out any expected differences between the two pathways. A complete reaction coordinate diagram will show structures for high and low points along the energy profile.

 d)  Provide reasoning that explains why substitution occurs at the 2-position and not the 3- position. Provide statement as to whether the reason is thermodynamic, kinetic, or both.

Answer 1