Aldehydes, Esters and Ethers
An aldehyde is most commonly known for their pungent smell. It is often used for preservative purposes and are found in laboratories all over the world. The aldehyde is one that contains a carbonyl group which is a carbon double bonded to an oxygen atom. This carbonyl group, however, is part of a greater group that is known as a formyl group where it is a carbon double bonded to an oxygen atom and single bonded to a hydrogen atom. Since it is single bonded to the hydrogen atom, the formyl group must be at the ends of the hydrocarbon chains. Thus, the aldehyde is a hydrocarbon chain that includes a formyl group.
NOTE:
- When naming Aldehydes, the chemical formula is always written as -CHO- and never as -COH- as it could be confused as an alcohol.
Properties of Aldehydes
All melting and boiling points are determined by the intermolecular forces of the molecule. Within the aldehyde model, there are London Dispersion Forces and Dipole-Dipole Forces, these forces are caused by the carbonyl group of the aldehydes. This group is very polar because of the Oxygen bond with the Carbon bond which causes a polar end. In this case there are dipole-dipole forces that connect the two molecules of aldehydes together. With this type of force, the longer the carbon chains, the higher the boiling points, because there are more electrons in the molecule for the positive end to bind to making stronger forces. This creates a very strong pull between two molecules, thus raising the boiling point. In comparison with the other functional groups such as alcohols, aldehydes have a slightly smaller boiling point than alcohols because of the lack of the Hydrogen bonding needed for strong intermolecular forces.
As with solubility, the smaller chains of aldehydes are soluble in water because of the smaller non-polar hydrocarbon chains. As the hydrocarbon chain becomes larger and larger, and the non-polar end of the molecule begins to overpower the more polar end of the molecule making it harder and harder for the molecule to become soluble in the polar water. |
FACT!
- Carbon chains of three to fourteen carbon long are liquids at room temperature while longer fifteen carbon chain aldehydes are waxy solids.
Esters
Esters are are a derivative of what happens when an acid of either organic or inorganic roots react with an alcohol. This reaction yields an ester and water as a result. This reaction can be seen in the following picture.
The above reaction shows how the -OH from the acid and the -H from the alcohol leaves the molecules and then combines to form water, meanwhile the the acid and alcohol bond to form an ester where the oxygen of the alcohol is bonded to the carbon of the acid. This forward reaction is known as condensation and the reverse of this reaction is known as hydrolysis. Which will be further explained in the following chapters.
Ester's are broken down into two parts the first is known as the parent acid. This is the part where the former acid once was (now without the OH), this includes any hydrocarbon chain that is bonded to the C=O. The next group is known as the alkyl group where it is any hydrocarbon chain that is bonded not on the other side of the oxygen where there is no C=O.
Esters are very unique in which they are responsible for the pleasant fruity odor of fruit and vegetables.
Ester's are broken down into two parts the first is known as the parent acid. This is the part where the former acid once was (now without the OH), this includes any hydrocarbon chain that is bonded to the C=O. The next group is known as the alkyl group where it is any hydrocarbon chain that is bonded not on the other side of the oxygen where there is no C=O.
Esters are very unique in which they are responsible for the pleasant fruity odor of fruit and vegetables.
Naming Esters
|
Properties of Esters
Esters are very similar to aldehydes and ketones in which they have similar physical properties of alcohols and although they may have the C=O bond, the electronegativity is not enough to make it completely polar, meaning it's polarity is not as strong as the H-O bond that is often seen in alcohol.
Smaller esters similar boiling points with those of keytones and aldehydes. Their relatively small polar parts do contain London Dispersion Forces and Dipole-Dipole forces, but they are weak forces when compared to hydrogen bonding and thus do not have as high as a boiling point as alcohols or carboxylic acids of the same number carbon chain.
In addition to this, the solubility of the ester also suffers when the chain length lengthens. The one polar bonds becomes overwhelmed by the relatively non-polar hydrocarbon chain and thus becomes less polar overall. This can cause solubility in water to drop when the carbon chain grows longer. This effect can be explained, because the longer the chain is the more the non-polar ends will get in the way of the ester bonds having intermolecular forces with the water molecules. This will decrease solubility.
Smaller esters similar boiling points with those of keytones and aldehydes. Their relatively small polar parts do contain London Dispersion Forces and Dipole-Dipole forces, but they are weak forces when compared to hydrogen bonding and thus do not have as high as a boiling point as alcohols or carboxylic acids of the same number carbon chain.
In addition to this, the solubility of the ester also suffers when the chain length lengthens. The one polar bonds becomes overwhelmed by the relatively non-polar hydrocarbon chain and thus becomes less polar overall. This can cause solubility in water to drop when the carbon chain grows longer. This effect can be explained, because the longer the chain is the more the non-polar ends will get in the way of the ester bonds having intermolecular forces with the water molecules. This will decrease solubility.
Ethers
The only difference between an ether an an ester is the C=O bond. While the Ester has the C=O bond which is bonded to another oxygen, the ether bond is only an oxygen atom in the middle of a hydrocarbon chain. Its that simple. This molecule is found in nucleic acids such as DNA and RNA and is commonly used as anesthetics. It is usually denoted by the "R-O-R'" notation where the "R" represents any hydrocarbon chain that is bonded to the oxygen.
Notice on the right that at the top of the sugar molecule there is an oxygen bonded to two carbons. This is the Ether bond. In addition to being used in DNA and RNA molecules, they are also useful as anesthetic uses back in the day. |
Naming Ethers
|
Properties of Ethers
As a result of the nature of their bent bond angles, ethers will have a small and slight polarity to it. It will have higher boiling points but not too high. Relative to other compounds such as alcohols and carboxylic acids, ethers have a lower boiling point, smaller density and smaller solubility amount. Because the lack of the strong intermolecular forces, they have a lower boiling point and the smaller chains are gasses at room temperature, while the longer carbon chains are liquids at room temperature.
The picture on the right of the hydrogen bonding is a great illustration of how an ether does not have hydrogen bonding with other ethers. However, between an ether and a hydrogen bonding molecule, hydrogen bonding can occur, meaning that there are intermolecular forces that can make it soluble in water. |
|