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Functional Groups


Functional groups are considered to be the reactive chemical group existing within a molecule. Each of these functional group have their own characteristics and reactivity series. These characteristics also get modified or become specific according to the position they occupy in the molecule. These modifications can also take place due to the presence of another one or two functional groups.

Define Functional Group

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If we look at organic compounds having a carbon chain bearing functional groups, they might be having these groups distributed on either side of the main long straight chain. These straight chains can be considered as the backbone and functional groups as their splayed arms showing specific characters. Apart from the characteristics the functional groups also arranged in a specific manner. These arrangement are either conformed in boat shape or chair shape. 

This might sound surprising but the shapes of chair and boat actually bear that structure where the functional groups if present on same side can be considered as boat shaped and in case they are present on either side or opposite side then categorised as chair conformation.

Based on the presence the bonding can be either considered as axial or equatorial. These C – H bonds are then replaced by substituents, they come across different interactions and these steric relationships helps in influencing the carbon skeleton structure of a particular compound as well as their functional groups.

Functional groups can also be considered as systematic and formal sense co related by a series of redox and substitutive transformations. Whenever a hydrogen atom is replaced from carbon chain, the functional group gives a specific character to the molecule. 

For example, the functional group which contains two alkoxy attached to same carbon atom can become Acetal group but when carbon gets attached to three alkoxy groups, it is termed as ortho ester. The halogen, oxygen and nitrogen are electronegative in character and are in fact more than carbon and hence the alkyl halides, carbonyl or even the imine group shows the shift of electron pair when get attached to the carbon chain.

In case the difference of electronegative value is small between the functional and main chain carbon then the more electropositive partner forms further away from the nucleus as the bonding orbitals are spread apart. These actually affects both (σ) and pi (π) bonds. 

The reactivityof the positoons adjacent to a specific functional group is then modified by functional group. Some specific names are provided such positions as they derive their nomenclature from the position they occupy in the main chain.

The position next to alkene is known as allylic while the position next to benzene ring is termed as benzylic. Whenever two functional groups like hydroxyl are placed side by side they are termed as vicinal groups, while two groups when bonded to same carbon atom are termed as germinal groups.

Organic Functional Groups

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Organic functional groups are mainly considered from the view that these are sourced from non-metals combination and bonded with each other covalently. The functional groups are alkyl halides, alcohols, ethers, aldehydes, ketones amines, carbonyl groups amides and alkaloids. Two major functional groups still remain to be considered. The carboxylic and amines although are important to biochemistry, especially from soluble medicinal combinations show little or no solubility as soon they are bonded with big organic molecules.

The common nomenclature for amines as well as carboxylic give rise to some other forms of bigger molecule chains. These usually result in primary form, secondary and tertiary forms of amines. If an organic molecule dissolves completely or even partially in non-aqueous or lipid formulations, then it results in either water loving or water hating molecule series. 

So these are categorised as hydrophilic, lipophilic, lipo-phobic and hydrophobic. The functional groups can either bond to a water loving or lipid loving molecules. On other hand a molecule that cannot bond to water begins showing degree of solubility as soon it bonds with water loving functional groups.

Common Functional Groups

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The common functional groups that we get to see are mainly the halogens, hydroxyl, carbonyl, carboxyl, amides, ketones and aldehydes.

The nomenclature also begins to take specific norms as soon these functional groups are attached to main chain. For halogens, the prefix is more important, while for hydroxyl it ends with –ol or in case there are more than one –OH groups then it is termed with numbers or by di, tri etc norms.

Functional Groups of Amino Acids

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Amino acids are mostly found in proteins and each of the amino acids which works out as base groups and are abbreviated by three letter combinations or symbol. Of all the amino acids that are found in proteins, its only glycine that has got one or more chiral carbon and exist as optical isomers. 

All of these amino acids have at least two functional groups and they are alpha carboxyl (α- carboxyl) and alpha amino (α – amino) group. Many of these have the third functional group as well attached to their side chain. The chemical nature of side chain varies with some of these amino acids having aliphatic side chain whereas some have aromatic side chain. 

Based on their side chains structure some amino acids in proteins have five aliphatic amino acids and they are alanine, glycine, isoleucine, leucine and valine. 
  • Three aromatic amino acids are phenylamine, tryptophan and tyrosine.
  • Two sulphur amino acids are cysteine and methionine.
  • Two hydroxyl amino acids are serine and threonine.
  • Two acidic amino acids are aspartic and glutamic acids.
  • Three basic amino acids are arginine, histidine and lysine.

Identifying Functional Groups

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Identifying functional groups of organic compounds are carried out in order to understand the changes that are occurring in our immediate surroundings and to what extent these changes have brought in at the macro level and what kind of impact we have in our daily life.

These are also helpful in assigning species to each functional groups as they help in identifying the dietary composition of many of the organisms we get to see around us. Interpretation of these data gives a direct pattern to understand the distribution patterns in both biogeographic as well as geographic areas and natural pH these organisms thrive in or survive better.

In order to identify unsaturated compounds we use carry out Bayer’s test and bromine water tests.In order to identify and isolate alcohols we usually carry out idoform tests, ester tests and sodium metal tests. Along with this we might also get good results with acetyl chloride tests.

In order to identify phenolic groups we might carry out the phthalein dye test and ferric chloride tests. In order to get the identification of carboxylic groups we have to use the sodium bi sulphite tests. The Schiff test, Fehling test and Tollen’s test are carried out to check aldehyde confirmation. To identify ketones from aldehydes there are two tests which are carried out in labs. They are di-nitro benzene test and sodium nitro prusside tests. In order to identify amines, Azo dye test and carbylamines tests are carried out.