I was watching Khan academy's video about molecular dipole moments, which explained what they are and how they can be calculated. I also read this article.

Both sources explain the concept similar to common organic chemistry textbooks, but they did not provide any information regarding the uses or applications of a molecular dipole's direction, nor did the google search I conducted later.

So far, two things are clear to me:

  1. A dipole moment is a vector, and therefore has a quantity and a direction.
  2. Larger dipole moment is associated with a more polar molecule. This a good enough reason to find out how large is the dipole moment.

My question is: What possible applications can knowing the direction of a molecular dipole moment have?

  • $\begingroup$ The knowledge of the direction of a molecular dipole moment can help us figure out how molecules would react, since regions of positive charge in one molecule can react with regions of negative charge in another molecule. This can also help us identify electrophiles and nucleophiles, since electrophiles have regions of low electron density (positive charge) and nucleophiles have regions of high electron density (negative charge). $\endgroup$ – DHMO Jan 5 '17 at 14:33

Take a look at chemlibretexts. I'll just write an overview.

A dipole is a vector representing the charge distribution in a molecule. It's drawn from the positive-density charge side towards the negative.

Some examples

  1. Phase change

How do we explain $\ce{CO2}$ fusion temperature is $-78\,^\circ$C while $\ce{SO2}$ is $-10\,^\circ$C? Because of its dipole magnitude. In the first one, there's no net dipole, but there is for the second one.

The bigger molecular interactions the more they oppose to temperature-increasings.

  1. Solubility is higher for alcohols than lipids* in water. Again dipole-dipole interaction is stronger (energetically more favourable) than dipole-induced dipole interaction.
  2. CO$_2$ has no electric dipole in the symmetric vibration. According to quantum mechanics, if electric dipole does not change when it absorbes light of a specific energy, it will not be susceptible of a infrared measure. This particular vibrational mode will be (and it is) infrared inactive.

As mentioned in the comments the information can be used for understanding reactivity. It can also tell the direction of an electron transfer. This is useful in materials chemistry to understand and predict where electrons and holes will prefer to go. This is applicable in, for example, organic photovoltaics or chlorophyll.


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