I have been struggling over this weekend to find an answer for the overall polarity of this molecule: 2,3,7,8-tetrachlorobenzofuran

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In order to find intramolecular forces, I determined the difference in electronegativity:

C-C = 0 and C-H = 0.4 --> non-polar covalent bond

C-O = 0.8 --> polar covalent bond C-Cl = 0.6 --> polar covalent bond

As the molecular shape is not symmetrical, and there are polar bonds present (unbalanced), I thought it is a polar molecule. However, the research suggests that it is "non-polar molecule, therefore insoluble in water".

Can I ask the reason why it is considered a non-polar molecule?

  • 2
    $\begingroup$ The molecule is symmetric, along the axis that "splits" the oxygen in the furan and the 2 carbons at the base of the pentagon the defines the furan. There's a permanent dipole moment, that's for sure. Whether or not it has been determined to be "soluble" is something that, experimentally, usually is defined by detection limits. $\endgroup$ – Todd Minehardt May 15 '17 at 2:26
  • $\begingroup$ If you want to calculate the dipole accurately you need to have the atom's coordinates and add the dipole vectors along each bond (except CC as this dipole is zero). You can see that these vectors will not add up to zero. By the reflection symmetry the x components do add to zero however. Alternatively you can use tracing paper and draw vectors along bonds in proportion to dipole length then you must keep orientation & cut out & superimpose base of each vector. Add up to find dipole; messy but possible :) $\endgroup$ – porphyrin May 15 '17 at 8:00
  • $\begingroup$ It has more nonpolar moieties than polar ones, and it has been empirically observed not to be soluble in water. That's a nonpolar molecule for you, relatively speaking. $\endgroup$ – electronpusher May 17 '17 at 7:55

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