Question

The dipole moments of furan and tetrahydrofurZan are in the same direction. One compound has a dipole moment of 0.70 D, and the other has a dipole moment of 1.73 D. Which is which?

Short answer

The dipole moment of furan is 0.10 D and that of tetrahydrofuran is 1.73 D.

Step-by-step solution

Dipole moment  

A dipole moment is observed in compounds with separation of charge. It happens due to the variation in electronegativity between two chemically connected atoms.

The two electric charges in a molecule are denoted as${\mathrm{\delta }}^{+}$ and${\mathrm{\delta }}^{-}$ , which comprise equal magnitude and opposite signs.

Identifying the dipole moments of furan and tetrahydrofuran 

The oxygen is on the negative end of the dipole in both the compounds. Tetrahydrofuran comprises a greater dipole moment as compared to furan, because the effect of the electron-withdrawing oxygen is reduced by the capability of the oxygen to contribute electrons to the ring by resonance.

In furan, there is resonance delocalization of the lone pair of electrons present on the oxygen into the ring. Hence, the electrons are pushed away from the oxygen. This makes the furan’s dipole moment lower than tetrahydrofuran.

So, the dipole moment of furan is 0.10 D and that of tetrahydrofuran is 1.73 D.

Dipole moment of furan and tetrahydrofuran