Functional Groups in Organic Molecules
- 2:13 Alcohol
- 2:59 Alkyl Halides
- 3:45 Ketones & Aldehydes
- 4:41 Ethers
- 5:09 Carboxylic Acids
- 5:48 Esters
Learn what an organic compound is and how their functional groups affect them. Identify the different types of functional groups including alcohols, alkyl halides, ketones, aldehydes, ethers, carboxylic acids and esters.
Functional Groups in Organic Compounds
Functional groups are important in chemistry because they are the portion of a molecule that is capable of characteristic reactions. They, therefore, determine the properties and chemistry of many organic compounds. An organic compound is any compound that contains carbon and another element. A functional group is an atom or group of atoms that is responsible for a particular chemical property of an organic compound. Organic compounds can be classified according to their functional groups.
A functional group gives an organic compound a property that is different than it would otherwise have. For instance, take a look at the following four-carbon compounds. They all have four carbons, but they are all different because of the functional groups they have.
|Name||Formula||Melting point||Boiling point|
So when you look at these compounds, you can see that just by adding an -OH group to butane, you greatly increase its boiling point. Adding a COOH group to form butanoic acid raises it even more.
There are seven functional groups for organic molecules that we are going to talk about. They are alcohols, alkyl halides, ketones, aldehydes, ethers, carboxylic acids and esters. When scientists talk about functional groups, they use a short hand way of writing them called 'the general formula.' They write an R, which stands for the rest of the compound, and then a dash and the functional group. So, it looks like this: R-OH, or R-O-R.
An alcohol is an organic compound that contains one or more hydroxyl groups. A hydroxyl group is composed of -OH, so one oxygen and one hydrogen. Alcohols have higher boiling points and tend to be flammable. Alcohols are used all the time. Glycerol is an alcohol and is used in lipstick, body lotion and other cosmetics that need to be moist. Ethanol is an alcohol that is used for fuel in some cars. This isn't precisely the alcohol that you drink in an alcoholic beverage. An alcohol group is just the -OH. What you drink is usually ethyl alcohol, CH3CH2OH. It does have the -OH group, but is a bit more complicated.
A hydrocarbon is a compound made up of only carbon and hydrogen. An alkyl halide is an organic compound where a halogen atom - F, Cl, Br or I (fluorine, chlorine, bromine or iodine) - takes the place of one or more hydrogens in a hydrocarbon. Since scientists often use the letter -X to represent a halogen, a general formula for alkyl halide is R-X. A very common group of alkyl halides are chlorofluorocarbons. You may know them as CFCs. CFCs were commonly used in air conditioners, refrigerators and aerosol cans, for example, but they have been found to harm the ozone layer of the earth's atmosphere, so they are now regulated and rarely used.
Ketones and Aldehydes
A ketone is a compound in which the carbon of a carbonyl group shares bonds with to two other carbons. A carbonyl group is an oxygen double-bonded to a carbon O=C. The general formula is RCOR.
An aldehyde is a compound in which the carbon of the carbonyl group shares a bond with at least one hydrogen. The general formula is RCHO.
Due to their carbonyl groups, both aldehydes and ketones share similar properties. They are both soluble in nonpolar solvents and have variable solubility in water depending on their size. Many have very penetrating odors. Formaldehyde is an example. Also the flavor of almonds is caused by an aldehyde known as benzaldehyde, and cinnamaldehyde gives cinnamon its distinctive odor.
An ether is an organic compound where oxygen is bonded to two carbon atoms. The general formula is R-O-R. Ethers usually have lower boiling points than similarly sized alcohols. They are fairly soluble in water. Diethyl ether, commonly referred to as 'ether,' was frequently used as an anesthetic, but it is highly flammable and tends to cause nausea, so it has been replaced by other pharmaceuticals.
A carboxylic acid is a compound with a carboxyl group. A carboxyl group is -COOH, arranged like this. The general formula for a carboxylic acid is RCOOH. Carboxylic acids have higher boiling and melting points than other compounds of similar size. They have strong odors and are polar. Their solubility in water depends on their length, with shorter ones being more soluble than longer ones. Carboxylic acids are found everywhere in nature, and the one you are probably most familiar with is acetic acid, or more commonly, vinegar.
Esters are derivatives of carboxylic acids. The -OH of the carboxyl group gets replaced by an -OR from an ether. Esters contain a carbonyl group and an ether link to the carbonyl carbon. Their general formula is RCOOR, and they look like this. In general, esters have lower boiling points than carboxylic acids. When they are smaller they are soluble in water, but the bigger ones aren't. Possibly the best thing about esters is their pleasant, fruity odors. They are what give fruit their characteristic aromas. They are frequently used in fragrances and perfumes.
Organic compounds are compounds that contain carbon. Organic compounds can be classified according to their functional groups. Functional groups are atoms or groups of atoms that are responsible for particular chemical properties and reactions of organic compounds. We talked about seven types of functional groups, and they are listed in the table below, along with their general formulas.
|Functional Group||General Formula|
Chapters in Chemistry 101: General Chemistry
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