Organic chemistry/Functional groups

From Wikiversity
Jump to navigation Jump to search

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

[edit | edit source]

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

[edit | edit source]


[edit | edit source]

General Alcohol Formula: CnH2n+1OH

Suffix: "ol"

Example: CH3CH2OH - Ethanol (IUPAC)

Example: CH3CH2OH - Ethyl Alcohol (Common Name)

Example: CH3CH2CH2OH - 1-Propanol (IUPAC)

Example: CH3CH2CH2OH - Propyl Alcohol (Common)

Example: CH3CHOHCH3 - Propan-2-ol (IUPAC)

Example: CH3CHOHCH3 - Isopropyl Alcohol (Common)

The numbered prefix is indicative of an isomer, not the location of a double bond.


[edit | edit source]

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: CnH(2(n-1)+2)O

Suffix: "one"

Examples of ketones include:

CH3COCH3 Name: propanone. This is the lowest member of the series.

CH3COCH2CH3 Name: butanone.

CH3CH2COCH2CH3 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.


[edit | edit source]

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,

CH3OCH3 is a simple ether whose common name is Dimethyl Ether and the IUPAC name is Methoxy Methane.

C2H5OCH3 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.


[edit | edit source]

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.


[edit | edit source]

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: CnH2n+1CHO

Functional Group: CHO

Examples of aldehydes:

CH2O Formaldehyde (common name) or Methanal (IUPAC), is the simplest aldehyde.

CH3CH2CHO Propanal

CH3CH2CH2CHO Butanal

Carboxylic Acids

[edit | edit source]

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: CnH2n-1COOH

Functional Group: COOH

Examples of carboxylic acids:

CH3COOH Ethanoic Acid (usually called Acetic acid)

CH3CH2COOH Propanoic Acid

Benzene and phenols

[edit | edit source]

Benzenes, part of the aromatic group, are all based on the benzene ring (C6H6). 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: C6H6

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: C6H5CH3 - 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.