# Organic chemistry/Functional groups

Functional groups: they are what makes a compound a compound: they give a compound its character. There are two types of functional groups: carbon side-chains and non carbon groups.

## Carbon Chains

Carbon chains are composed of carbon molecules, and these are named as according to their length:
Carbon chart :
| Carbon chain length | Name prefix |
| 1 | Meth- |
| 2 | Eth- |
| 3 | Prop- |
| 4 | But- |
| 5 | Pent- |
| 6 | Hex- |
The carbon main chain nomenclature is covered in Organic Chemistry/Naming, and the same rules apply to side chains.

## Functional Groups with Oxygen
### Alcohols

General Alcohol Formula: C$_n$H$_{2n+1}$OH
Suffix: "ol"
Example: CH$_3$CH$_2$OH - Ethanol (IUPAC)
Example: CH$_3$CH$_2$OH - Ethyl Alcohol (Common Name)
Example: CH$_3$CH$_2$CH$_2$OH - 1-Propanol (IUPAC)
Example: CH$_3$CH$_2$CH$_2$OH - Propyl Alcohol (Common)
Example: CH$_3$CHOHCH$_3$ - Propan-2-ol (IUPAC)
Example: CH$_3$CHOHCH$_3$ - Isopropyl Alcohol (Common)
The numbered prefix is indicative of an isomer, not the location of a double bond.

### Ketones

Ketones are carbonyl compounds. Thus they contain the C=O group. This group is responsible for the typical peak present in the mass spectrometer profiles for carbonyl compounds. The suffix "-one" is added to the alkane name to indicate a ketone. Ketones, if formed from alcohols, must be formed from secondary alcohols as you need to have two groups either side of the "carbonyl" carbon.
General Ketone Formula: C$_n$H$_{(2(n-1)+2)}$O
Suffix: "one"
Examples of ketones include:
CH$_3$COCH$_3$ Name: propanone. This is the lowest member of the series.
CH$_3$COCH$_2$CH$_3$ Name: butanone.
CH$_3$CH$_2$COCH$_2$CH$_3$ Name: pentan-3-one. The "-3-" indicates the position of the C=O (carbonyl) group. It shows that the carbonyl group is present on the third carbon atom in the chain. Such naming is essential in ketones (except propanone and butanone). For example, an isomer of pentan-3-one is pentan-2-one, which has a different structural formula.

### Ethers

In Ethers the functional group is -O-. The General Formula of ethers is R-O-R or R-O-R'. R-O-R are simple ethers. Whereas R-O-R' represents mixed ethers. R and R' are different alkyl groups. According to IUPAC they are called Alkoxy Alkanes (O-R is alkoxy group).
For Example,
CH$_3$OCH$_3$ is a simple ether whose common name is Dimethyl Ether and the IUPAC name is Methoxy Methane.
C$_2$H$_5$OCH$_3$ is a mixed ether whose common name is Ethyl Methyl ether and the IUPAC name is Methoxy Ethane. You should name with the lowest group first: methyl, then ethyl, etc... which explains the IUPAC difference in naming, as the methyl come before the ethyl.

### Esters

Carbon Compounds consisting of a carbonyl carbon adjacent to an ether (-COO-). Esters are often characterized by a unique smell or taste. Esters are used by manufacturers due to their unique smells and tastes. Suffix is -oate.

### Aldehydes

Aldehydes are carbonyl compounds with a C=O and a H bonded to the same carbon. The suffix attached to an aldehyde is "al". The quickest way to form an aldehyde is to oxidise a primary alcohol using potassium dichromate.
Suffix: "al"
General formula: C$_n$H2$_{n+1}$CHO
Functional Group: CHO
Examples of aldehydes:
CH$_2$O Formaldehyde (common name) or Methanal (IUPAC), is the simplest aldehyde.
CH$_3$CH$_2$CHO Propanal
CH$_3$CH$_2$CH$_2$CHO Butanal

### Carboxylic Acids

Carboxylic acids are carbonyl compounds containing a C=O and an -OH group bonded to the same carbon. They can be obtained by oxidising a aldehyde or a primary alcohol using potassium dichromate (K2Cr2O7) with concentrated sulphuric acid.
Suffix: "oic acid"
General formula: C$_n$H$_{2n-1}$COOH
Functional Group: COOH
Examples of carboxylic acids:
CH$_3$COOH Ethanoic Acid (usually called Acetic acid)
CH$_3$CH$_2$COOH Propanoic Acid

## Benzene and phenols

Benzenes, part of the aromatic group, are all based on the benzene ring (C$_6$H$_6$). In it, there are three double bonds that create a resonance structure. Resonance theory states that we can draw two different structures for benzene where the double bonds are in different places, but neither structure adequately represent the molecule, so instead we think of the molecule as a resonance hybrid, a combination of the two. Benzene is incredibly stable, and is also planar. Although the term aromatic should refer to a smell, is really referring to a Huckel number of pi electrons.
General formula: C$_6$H$_6$
Derivatives of benzene are named by numbering the C atoms in a clockwise manner, starting at one for the first group. Alkyl monosubstituted benzenes are names as alkyl benzenes.
Example: C$_6$H$_5$CH$_3$ - Methylbenzene, or Toluene.
If the alkyl branch is attached to the benzene ring by a carbon other than an end carbon, the benzene is then considered a branch of the carbon chain, and is called phenyl.