100 Nano-Stories: Ethers (Part 2)!
Episode #69: Appearance + Properties!
Preface! ✨
It’s your favorite material science & nanotechnology enthusiast! Today, I want to introduce a branch of organic chemistry that has huge potential in polymer aerogels: Ethers!
I recently published the first half of ethers, which I highly recommend reading if you want to understand the concepts discussed in this article!
Don’t worry, it’s only a 5-minute read! 😁
A brief overview of essential concepts of ethers:
Ether → Alkane Substituents (aka “alkyl”) are attached to an oxygen atom.
Substituents → Carbon Rings or Carbon molecules that are not part of the longest carbon chain (main carbon chain). They are chemically bonded parts of molecules attached to a larger backbone/ring; “yl”.
Alkane → An organic compound that is only made out of carbon & hydrogen atoms, only single covalent bonds “alk-/-ane”.
Once you finish reading how to me ethers, jump on the train, because we are going to explode some neurons with some knowledge bombs! 😛
Ethers Explained! 💡
Appearances! 🔑
Sometimes, you will see ethers in either one of these two photos:
They are both the same chemical (diethyl ether/1-ethoxy ethane), but all the “R” means is this:
“R” → A methyl group, (CH3).
The apostrophe in the “(R’)” stands that it could be a different carbon chain than the original “R” chain.
Properties! 🔑
Ethers have no hydrogen bonding, despite the ethers having hydrogen and oxygen in the same molecule. This property all comes down to electronegativity.
Electronegativity is the chance that a pair of elections will be attached to a certain atom. If the difference between the electronegativity is greater or equal to 0.5, the molecule is polar. If the difference in electronegativity in the molecule is less than 0.5, the molecule is non-polar. Covalent bonds occur at an electronegativity below around 1.7, and ionic bonds occur at an electronegativity equal to or greater around 1.7.
Polar molecules → The electrical charges of the molecule are not evenly distributed. This leads to electronegativity. But in aerogels, you can find OH groups attached to the surface of the aerogel. Anything that is directly attached to hydrogen (hydrogen-bonding) is a polar molecule.
Non-polar molecules → The electrical charges of the molecule are evenly distributed. No positive or negative charges are formed in the molecule. There is still electronegativity, but the electronegativity is low enough for them to repel water or have hydrophobicity.
Water molecules contain only oxygen and hydrogen. The overall difference in electronegativity in water is 1.34, which is more than the required 0.5 difference in electronegativity to become a polar/hydrophilic molecule. This can also result in hydrogen bonding.
Hydrogen Bonding is when positive charges in the hydrogen (its electrons) tend to get closer to the oxygen atom with a negative charge.
But if you notice in the molecule of diethyl ether, it also contains carbon atoms and methyl groups. Methyl groups have an overall difference in electronegativity is 0.4, which is less than the required 0.5 difference in electronegativity. The difference in electronegativity results in a non-polar/hydrophobic molecule.
There is no hydrogen bonding, only Van der Waal Forces/ London Dispersion Forces (you can learn more about this phenomena in an article linked below in bonus resources!)
The lower the overall difference in electronegativity, the lower the melting & boiling point. This is because the bonds between the molecules are not strong enough, so it takes less heat to rip the bonds and the molecule apart.
But Carlos, that doesn’t solve the problem on why there is no hydrogen bonding in ethers, even though there is an oxygen atom present! 🤔
If you look at the photo, you will notice that the oxygen atom is attached to the carbon atom, not the hydrogen atoms!
This means that it is not able to bond to hydrogen to create the higher melting & boiling point and the overall electronegativity of 1.34! This is why ethers have such low melting & boiling points! 🎆
Playing With Melting & Boiling Points! 🔑
One way you can increase the melting & boiling point of ethers is by adding more methyl groups (CH3, R) because there are more Van der Waal Forces taking place in methyl groups! The more carbons you add to the alkyl groups, the harder it is to rip them apart, therefore higher melting & boiling points!
The other way you can increase the melting & boiling point of ethers is to add an OH Group Substituent! This will result in hydrogen bonding (by itself or with other molecules). Hydrogen bonding is one of the strongest bonds in organic chemistry, which will result in having to increase the melting and boiling points to break the bonds in the ether!
Closing Thoughts! 💭
Well, there you have it! Boiling points are critical when we sometimes have to dry polymer aerogels that contain ethers, and sometimes, they may have high or low melting boiling points, all depending on hydrogen bonding and Van der Waal Forces!
See you tomorrow for Part 3 to talk about Crown Ethers! ✌🏽
Vocabulary! 📓
Ether → Alkane Substituents (aka “alkyl”) are attached to an oxygen atom.
Substituents → Carbon Rings or Carbon molecules that are not part of the longest carbon chain (main carbon chain). They are chemically bonded parts of molecules attached to a larger backbone/ring; “yl”.
Alkane → An organic compound that is only made out of carbon & hydrogen atoms, only single covalent bonds “alk-/-ane”.
“R” → A methyl group, (CH3).
“(R’)” → There is a probability that it could be a different carbon chain than the original “R” chain/group.
Electronegativity → The chance that a pair of elections will be attached to a certain atom. If the difference between the electronegativity is greater or equal to 0.5, the molecule is polar. If the difference in electronegativity in the molecule is less than 0.5, the molecule is non-polar. Covalent bonds occur at an electronegativity below around 1.7, and ionic bonds occur at an electronegativity equal to or greater around 1.7.
Van der Waal Forces/London Dispersion Forces → An attraction of intermolecular forces between two molecules, and are found in all molecular forces, but they are the strongest in non-polar molecules.
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© 2021 by Carlos Manuel Jarquin Sanchez. All Rights Reserved.
