Testing for Alkene functional Group

 The chemistry for carbon is vast; there are in excess of ten million known carbon compounds. It is estimated that 300000 new carbon compounds are discovered each year. Organic molecules contain functional groups that are responsible for their chemical properties. Functional groups will react with certain regents in predictable ways, making it possible to develop diagnostic reactions to test for their presence in an organic molecule. Common functional groups found in organic molecules are listed below:

* Alkene

* Primary alcohol* Tertiary alcohol* Aldehyde* Ketone* Carboxylic acid* Ester* Halogen alkane* Phenol

AlkeneIn organic chemistry, an alkene is an unsaturated chemical compound. This means it contains a carbon – carbon bond. All alkenes are hydrocarbons, (a molecule made of carbon and hydrogen atoms), and can only form one double bond which must be involved within its structure. The arrangement of atoms around the carbon – carbon bond is known as a planner. Alkenes contain three sp2 orbitals which repel each other into a planar arrangement, the 2p orbital then lies at right angles to them.

Covalent bonds are formed by the overlap of the orbitals. An sp2 orbital from each carbon, overlaps to form a single carbon-carbon bond. The resulting bond is called a sigma (σ) bond.

The two 2p orbitals also overlap to form a second bond. This bond is known as a PI (π) bond. s orbitals in hydrogen then overlap with the sp2 orbitals in carbon to form C-H bonds. .

The general formula for an alkene is CnH2n. It is possible to test for the presence of an alkene with the use of bromine water. When an alkene is mixed with bromine water, the alkene will de-colourise the bromine water.

Primary Alcohol

Alcohols are compounds in which one or more hydrogen atoms in an alkane have been replaced by an –OH group. For example: Ethanol – CH3 – CH2 – OHThe class of the alcohol depends on how the –OH group is positioned in the chain of carbon atoms. In a primary alcohol, the carbon which carries the –OH group is only attached to one alkyl group. Methanol, however, has not got an alkyl group attached to the carbon with –OH group on it, yet it is still classed as a primary alcohol.

Tertiary Alcohol

AldehydeAldehydes feature an sp2 hybridized, planar carbon centre that is connected by a double bond to oxygen and a single bond to hydrogen.


Carboxylic AcidCarboxcylic acids contain the functional group COOH. The bonds are in a planar arrangement and include a carbonyl (C=O) group, and a hydroxyl (O-H) group. Carboxyl acids form a homologous series. This series is shown below:




It is possible to test for the presence of Carboxylic acids by mixing the Carboxylic acid with water and adding a small amount of sodium hydrogencarbonate solid or solution. As the reaction takes place, it will begin to fizz, and the colourless gas will give a white precipitate with limewater. RCOOH + NaHCO3 RCOONa + H2O + CO2