Infrared (IR) spectroscopy can be used to differentiate between primary, secondary, and tertiary amines based on their characteristic absorption bands. In primary amines, there are two N-H bonds, leading to two distinct absorption bands in the IR spectrum: one for N-H stretching (around 3300-3500 cm⁻¹) and another for N-H bending (around 1600 cm⁻¹). Secondary amines have only one N-H bond, resulting in a single N-H stretching band in a similar range but generally weaker and less sharp than in primary amines. Tertiary amines, which have no N-H bonds, do not show these N-H stretching or bending bands. Instead, tertiary amines may show weaker bands due to C-N stretching vibrations (around 1020-1350 cm⁻¹). Additionally, the shape and intensity of these bands can provide further information about the amine's structure and environment. Therefore, IR spectroscopy is a useful tool for identifying and distinguishing different types of amines based on their specific IR absorption patterns.

The 2,4-Dinitrophenylhydrazine (2,4-DNP) test is a common method for identifying carbonyl compounds, such as aldehydes and ketones. This test involves the reaction of 2,4-DNP with the carbonyl group to form a yellow, orange, or red precipitate, known as a 2,4-dinitrophenylhydrazone derivative. The reaction occurs as the nucleophilic nitrogen of the 2,4-DNP reacts with the electrophilic carbon of the carbonyl group, resulting in the formation of a hydrazone linkage. A positive test, indicated by the formation of a brightly colored precipitate, confirms the presence of a carbonyl group. This test is specific and sensitive, allowing the detection of even trace amounts of carbonyl compounds. Moreover, the precipitates formed have distinct melting points, which can be used to further identify the specific aldehyde or ketone present. Thus, the 2,4-DNP test is a valuable tool in organic chemistry for the qualitative analysis of carbonyl-containing compounds.

The silver mirror test, also known as the Tollens' test, is significant in organic chemistry for identifying aldehydes. In this test, the aldehyde is oxidized to a carboxylic acid, while the diamminesilver(I) ion in the Tollens' reagent is reduced to metallic silver, which deposits on the test tube's surface, forming a shiny silver mirror. This reaction occurs because aldehydes are easily oxidized due to the presence of a hydrogen atom attached to the carbonyl carbon, making the carbon atom electron-deficient and susceptible to nucleophilic attack.

Ketones, on the other hand, do not undergo this reaction. This is because ketones lack the hydrogen atom on the carbonyl carbon, making them more resistant to oxidation under mild conditions like those in the Tollens' test. The absence of this hydrogen atom means there is no easy pathway for the oxidation of the ketone to occur, preventing the formation of the silver mirror. Thus, the Tollens' test is a specific and sensitive method for distinguishing aldehydes from ketones, based on their differing oxidation behaviors.

Chromatography, particularly Thin Layer Chromatography (TLC) and Gas Chromatography (GC), plays a significant role in the identification of functional groups in organic compounds. In TLC, a mixture is separated on a stationary phase, and the presence of certain functional groups can be inferred based on the Rf values and the behaviour of compounds under UV light or specific staining reagents. For instance, compounds with hydroxyl or amino groups often show different Rf values compared to non-polar compounds. In GC, the retention time of a compound in the column can give clues about its molecular structure and functional groups. Compounds with different functional groups generally have different volatilities and interact differently with the stationary phase in the GC column, leading to distinct retention times. When coupled with mass spectrometry (GC-MS), the fragmentation patterns can be analysed to provide further insights into the functional groups present. Thus, chromatography is a vital tool in the identification and analysis of functional groups, complementing other techniques like spectroscopy and chemical testing.

The Lucas test is a qualitative method used to distinguish between primary, secondary, and tertiary alcohols based on their reactivity with Lucas reagent (a mixture of concentrated hydrochloric acid and zinc chloride). When an alcohol is added to the Lucas reagent, a secondary or tertiary alcohol will react relatively quickly, forming a cloudy solution or a separate layer due to the formation of the corresponding alkyl chloride. Tertiary alcohols react the fastest, often becoming cloudy immediately, while secondary alcohols may take a few minutes to a few hours. Primary alcohols, however, react very slowly or not at all under these conditions, showing little to no change. This difference in reactivity is due to the stability of the carbocation intermediate formed during the reaction. Tertiary carbocations are more stable than secondary ones, which are more stable than primary carbocations. This stability affects the rate at which the alcohols undergo substitution reactions with the Lucas reagent, thus providing a basis for their differentiation.