Functional groups determine the identity of organic molecules
Functional groups are very important in organic chemistry since they determine the identity of these molecules and therefore, depict the of them.
For example, hydroxy groups ##OH## is specific for alcohols. the general structure for alcohols is ##R-OH##.
In a similar way, ##COOH## is the functional group for carboxylic acids of a general structure ##R-COOH##.
For esters, the functional group is ##COOR’##, where esters have the general structure ##R-COOR’##.
And so on.
with different functional groups, alcohols, carboxylic acids, and esters have different chemical and physical properties and therefore, different identity.
Let us take a specific example; Propane ##CH_3CH_2CH_3##. Propane is a gaseous molecule at room temperature. Adding a hydroxy group to its structure we get ##CH_3CH_2CH_2-OH## which is the propanol. Propanol is liquid at room temperature ( change on physical property ). Propanol can react thanks to the presence of the oxygen atom in its backbone, however, propane has very limited reactivity ( change on chemical property ).
There are many other functional groups such as: Sulfides: ##R-S-R’## Thiols: ##R-SH## Ethers: ##R-O-R’## Anhydrides: ##R-CO-O-CO-R’## Ketones: ##R-CO-R’## Aldehydes: ##R-CO-H## Amides: ##R-CO-N(R’)_2## or ##R-CO-NH_2## or ##R-CO-NHR’## Amines: ##R-NH_2## or ##R-NHR’## or ##R-N(R’)_2## Nitriles: ##R-CN## Alkyl halides: ##R-X## where ##X## is an element from group 17. Alkenes: ##R-CH=CH-R’## Alkynes: ##R-C-=C-R’## etc.
