Detection of Functional Groups

In the discipline of organic chemistry, functional groups are the substituent atoms or groups of substituent atoms that are bonded to specific molecules in a way that makes them more stable. These moieties (the part of the molecule that can be found in a variety of other compounds) are responsible for the chemical reactions that the molecule to which they are connected is involved in.

In organic chemistry, a functional group is a collection of atoms or bonds inside a substance that is responsible for the substance’s specific chemical reactions. A functional group is made up of atoms or bonds that are responsible for the substance’s unique chemical reactions. It doesn’t matter what chemical it is present in; the same functional group will behave and react in the same way no matter where it is found.

It is possible for two molecules of differing sizes but with the same functional groups to participate in chemical processes that are similar or identical. Having a functional group in a compound suggests that the behaviour and chemical reactions of the compound in question can be anticipated with high accuracy. Functional groups are found in proteins, carbohydrates, and fats.

Detection of functional groups in organic compounds

Natural organic chemistry is a sub-field of chemistry that is concerned with the structure, characteristics, and interactions of organic molecules that include carbon. Organic chemistry is concerned with the study of hydrocarbons, compounds containing carbon and hydrogen, and compositions based on carbon but comprising other elements, among other things. Organometallic compounds are the building blocks of all life on Earth, and their variety of applications is vast. They are the primary ingredients of pharmaceuticals, petrochemicals, paints, food, plastics, and explosive materials, among other things.

The existence of functional groups in a molecule has an effect on the solubility of the molecule in question as well as its potential to form complexes with other molecules. The solubility of a solution rises when the functional groups of the solute and the solvent interact well. For example, because the -OH (hydroxyl) group is present in both sugar and water, sugar can be easily dissolved in water when the two are combined.

Functional group detection test

Let’s have a look at some of the most important functional groupings and the tests that are used to identify them.

Reactions that distinguish saturated aliphatic hydrocarbons from unsaturated aliphatic hydrocarbons 

• The test of bromine addition.

As a result of the addition process, unsaturated hydrocarbons and other chemicals with unsaturated bonds discolour bromine solution, causing it to appear yellow.

The following procedure should be followed: dropwise add 1 percent acetic acid solution of bromine to approximately 0.5 millilitres of material dissolved in acetic acid or another organic solvent The contents of the test tube should be thoroughly mixed. The pink colour of bromine quickly fades away until the point at which the total number of multiple bonds is saturated.

• The test with potassium permanganate by Lehman

It has been observed that the solution of KMnO4 undergoes decolorization in the presence of unsaturated bonding chemicals. This is the result of the manganese concentration being reduced from +7 to +2. It is possible that the brown precipitate of manganese dioxide will occur in the reaction mixture during the reaction because the solution becomes alkaline (KOH is produced).

The following procedure should be followed: To approximately 1 ml of the investigated material, add a dropwise 0.1 percent acetone solution of KMnO4 in acetone. After each drop of KMnO4 has been added, thoroughly mix the solution and wait for the pink hue to vanish completely. The volume of decolorized solution produced and the speed with which it decolorizes are dependent on the number of multiple bonds present in the molecule of the investigated substance.

Characteristic reactions of alcohols

• The Lucas test 

Depending on the type of alcohol used, primary, secondary, and tertiary alcohols will react differently with Lucas’ reagent (the solution of anhydrous zinc chloride in concentrated hydrochloric acid). In the absence of reaction, primary alcohols (those having less than six carbon atoms) are obtained as clear, somewhat dark solution. When using secondary alcohols, turbidity in solution 2 occurs, resulting in the formation of a two-phase solution after 1-1.5 hours. In the presence of tertiary alcohols, the turbidity of the solution and the separation of the solution into two phases occur relatively quickly. The reaction of tertiary alcohols with concentrated HCl occurs even in the absence of ZnCl2.

The following procedure should be followed: Fill three dry test tubes with ground-in stoppers, each containing primary, secondary, and tertiary alcohols, with 5 ml of Lucas’ reagent. Repeat this procedure three more times (0.5 ml). Allow for some mixing time before putting them away in the laboratory rack and determining the time difference required in each case for turbidity and the development of two-phase solutions.

• The esterification test for detection of methanol. 

Salicylic acid is a kind of acid. The compound methyl ester (methyl salicylate) is created by heating methyl alcohol with salicylic acid in the presence of concentrated sulfuric acid, which acts as a catalyst as well as a water bonding agent in the process.

The following procedure should be followed: To 1 ml of methanol, add a pinch of salicylic acid and approximately 1 ml of concentrated H2SO4 to dilute it. After mixing, place the sample in a hot water bath for a few minutes. After a few minutes, a distinct resinous aroma associated with methyl salicylate will emerge.

• The iodoform test for detection of ethanol

Only ethanol is subjected to the iodination reaction when it comes to primary alcohols.

The following procedure should be followed:  Add approximately 1 mL of iodine in potassium iodide solution (Lugol’s solution) to 0.5 mL of ethanol solution (Lugol’s solution). Then, dropwise (2-4 drops at a time) add 5 percent NaOH water solution, stirring constantly, until the yellow tint of the iodine is gone. It will be possible to detect a distinct scent and yellow crystals of iodoform after mixing and heating the tube content to 60o C.

Characteristic reaction of aliphatic amines 

A reaction between the primary (1o) amino group, which is found on the alpha carbon atom of each amino acid, and nitrous acid results in the formation of alpha-hydroxy acid, nitrogen gas, and water.

The following procedure should be followed:  dissolve a little amount of sodium nitrite salt (NaNO2) in 1 ml of 2 M sulfuric acid solution and mix thoroughly. Observe the steady bubbling of the nitric oxide gas that has been produced. Then, in a hood compartment, add a few drops of amino acid (glycine) solution to the tube and shake well. Observe a large amount of nitrogen gas bubbling up and generating gas bubbles that land on the tube walls.

Conclusion

Organic molecules’ functional groups are made up of groups of atoms that are bonded to the carbon backbone of the molecule. The chemical reactions that distinguish organic substances are responsible for the formation of functional groupings. They are less stable than the carbon backbone and are more prone to participate in chemical processes as a result.

Functional groups in organic chemistry are specific groups of atoms within molecules that are responsible for the chemical reactions that are characteristic of those molecules. In organic chemistry, functional groups are responsible for the chemical reactions that are characteristic of those molecules.