# What type of intermolecular forces will dominate Diethyl ether?

Is Diethyl ether (also known as ethyl ether) a polar molecule? What type of intermolecular forces dominate it? Dipole-Dipole Interactions, London Dispersion Forces or Hydrogen Bonding? Please Explain.

• Take a look at these pictures. en.wikipedia.org/wiki/Diethyl_ether Based on only the figures, can you make some deductions as to what it might be? Please offer some reasoning and we'll be more inclined to help you. Apr 8, 2014 at 15:59
• Most organic molecules are polar by definition - they have a dipole moment (ethers included). In the context of solvents, polar refers to solvents with higher polarity, and non-polar to solvents with lower polarity. It's relative. Diethyl ether is at the lower end of the polarity scale and so is generally considered a 'non-polar' solvent . This is what I read recently about Diethyl ether's polarity. Is it correct? Apr 8, 2014 at 16:26
• Okay, so diethyl ether has a small dipole. So, now what about LDF and H-bonding? You're getting closer. Apr 8, 2014 at 16:32
• As Diethyl ether has a very low polarity, if any, so, H-bonding is not possible, I suppose. LDF are present in all either polar or non polar molecules, so they are present here too. As it is slightly polar so it may also exhibit weak dipole-dipole interactions. Apr 8, 2014 at 16:41
• Carbon-donated hydrogen bonding is a very real thing but these are very, very weak non-covalent interactions. So yes, I think your reasoning that H-bonding isn't possible is fine. LDF is present in every chemical system but these are weak as well (there are exceptions where LDF may be significant in the binding energies of certain dispersion-dominated molecules). Quick question: Is diethyl ether soluble in water? If so, what force that you listed would most likely contribute to this? Apr 8, 2014 at 18:48

## 2 Answers

As you have already figured out, diethyl ether is a small dipole due to the electronegativity difference between carbon and oxygen, which can also be seen in this electron density plot. As both dipole moment vectors point roughly in the same direction, they do not cancel each other out like in the case of carbon dioxide, so the molecule has a net dipole moment and is therefore (weakly) polar.

London dispersion forces, which result from short-lived dipoles induced by fluctuations in the electron shell of molecules, are also present. They are responsible for the weak interactions between the alkyl chains, like in other alkanes and non-polar molecules. The permanent dipoles can also interact with each other, in the form of intermolecular attractive interactions between centers with $\delta+$ and $\delta-$ partial charge (and likewise repulsion between centers of equal partial charge).

Hydrogen bonding between C-H groups and oxygens, although possible in principle (see comments to your question) and, for example, found in protein structures, can be neglected in this case due to the low number of donors and the weakness of the interaction (< 17 kJ/mol). Nevertheless, the ether oxygen can act as a hydrogen bond acceptor in combination with better hydrogen bond donors like OH groups, which explains why diethyl ether is sparingly soluble in water despite its low polarity (69 g/l at 20 °C (source)). On the other hand, the absence of hydrogen bonding between ether molecules becomes apparent in the much lower boiling point of diethyl ether (34.6 °C, source) compared to water.

Clarifying a portion of the answer in the "Best Answer" you cannot have hydrogen bonding with a C-H bond. You only have hydrogen bonding with F-H, O-H, and N-H bonds. The hydrogen bonding in proteins usually results from amide hydrogen bonding shown in the image below