A lot of people thought originally that there were two classes of elements. Organic was associated with living things. People thought things that came with living organisms couldn’t be convernted to non living and vice versa up until the 18th century. People thought there was a vital source associated with them but now we know that’s not the case. Things considered organic are things that have Carbon in them. So if you have carbons and chains of carbon atoms, they are organic compounds.
What changed the thinking about that was in the mid 1800’s, Bolar got NH4OCN (an inorganic compound)..where you have ions of NH4 and OCN. When you heat that, you come up with an organic compound, Urea.
Remember oxygens are electronegative, so they get pulled to the oxygen. This substance is not basic due to the presence of the oxygen.
There are far more organic compounds in the world than inorganic even though it involves just a couple elements because of the vast amount of bonds that could be formed.
Carbon has a unique property of 4 bonds. Another unique property it has is that you could have long chains of carbon connected to each other and still have two more bonds that could attach to other things, including carbon again. With silicon, for example, you can’t have a chain of bonds. It’s a larger atom and you can’t form chains even though it can do 4 bonds like carbon. You can’t have a complex life form without Carbon because of all the possibilities that wouldn’t be possible.
Remember when we talked about structure of molecules, carbon could form a tetrahedral structure. When you have a chain of molecules of Carbon, what is going to be the angles between them? Approximately 109 degrees. When we write out straight chains they are actually doing this zig-zag pattern. You could count on carbon always forming 4 bonds, so the main thing that’s usually attached are Hydrogens.
Hydrocarbons are things that contain only carbon and hydrogen. What are they used for? Mostly for fuels such as propane, methane, gasoline, oils, etc.
A classic compound is called an alkane with single bonds only. These compounds are called “saturated.” Saturated means you have all the hydrogens attached that you possibly could.
Nomenclature
How to recognize different classes of compounds.
The hydrocarbon is easy to recognize. If you have an OH it’s alcohol.
To name these things, recognize how many carbons you have. So there will be prefixes that hint to it.
| # of Carbons | Compound |
|---|---|
| 1 | Methane |
| 2 | Ethane |
| 3 | Propane |
| 4 | Butane |
| 5 | Pentane |
| 6 | Hexane |
| 7 | Heptane |
| 8 | Octane |
| 9 | Nonane |
| 10 | Decane |
After 5 they are just greek prefixes.
CH3CH2CHCH2CH3 with CH3 attached to a Carbon in the middle. That one CH3 is known as a methyl group. The -yl means it’s attached to a main group. If Methyl-pentane is attached to the third carbon the name of this will be 3-methyl-pentane.
If the CH3 is attached to the 4th Carbon, it won’t be 4-methyl-pentane because you could choose a different numbering system that moves from right to left so it would be 2-methyl-pentane. You choose the numbering system that gives you the lowest number.
If the CH3 is attached to the 5th carbon, it would be hexane because it doesn’t matter which way the bond is.
If you attach a Bromine (Br) to the second Carbon of hexane, it would be 2-bromo-hexane.
CnH2n+2: Relative number of carbons and hydrogens in alkanes
The number of hydrogens will be twice the number of carbons plus two..
Octane elemental composition will be eight carbons and eighteen hydrogens.
Alkenes end in -ene.
Alkenes have a double bond by taking away 2 hydrogens.
So for example, we have CH3CH=CHCH3. This normally would be butane, but because there’s a double bond it would be butene.
Then you have to identify the location of the double bond so it would be 2-butene.
If the double bond was between the first and second, it would be 1-butene.
If the double bond was between the third and fourth bond, it would be 1-butene because it’s the same thing. These are all known as isomers.
Alkynes end in -yne.
These contain a triple bond, for example, CH Ξ CCH2CH2CH3. So this has 5 carbons, it would be pentane but because there’s a triple bond it’s pentyne and since the location of the triple bond is in the front it’s 1-pentyne.
Cyclo-
If we have 6 carbons is in a circle. It would be cyclohexane.
Aromatic Hydrocarbons. Carbons in a ring, such as Benzene.
If you have C6H6, how do you reduce the hydrogens? By adding double bonds. You can’t put two double bonds next to each other cause then that would be a linear structure and you can’t have a cyclo- structure.
A carboxylic acid
An carboxylic acid group has an oxygen atom double-bond to a carbon atom, and an hydroxyl (-OH) group bond to the same carbon atom.
Aldehydes and ketones
Aldehydes and ketones are organic compounds which incorporate a carbonyl functional group, C=O. The carbon atom of this group has two remaining bonds that may be occupied by hydrogen or alkyl or aryl substituents. If at least one of these substituents is hydrogen, the compound is an aldehyde. If neither is hydrogen, the compound is a ketone.
Amines – NR3
An amine is a derivatives of the molecule ammonia, NH3, in which one or more of the hydrogens has been replaced by an alkyl substitutent (R group).
Ethers R-O-R
An ether is a molecule consisting of two alkyl groups connected to an oxygen atom.
A methyl group is CH3 attached to Carbon (not the end of the chain).
alcohol has an OH. alkanes only have single bonds. alkenes have a double bond.
alkynes have a triple bond.
An carboxylic acid group has an oxygen atom double-bond to a carbon atom, and an hydroxyl (-OH) group bond to the same carbon atom.
