Importance of Identifying Functional Groups:

• Identification and classification of compounds
• Prediction of chemical reactions
• Determination of physical properties such as boiling point, polarity, and solubility
• Design of synthetic pathways in pharmaceuticals, food industries, polymers, and petrochemicals

 

Major Categories of Functional Groups and Their Properties

1. A) Oxygen-Containing Groups

• Alcohols (–OH): Polar, water-soluble, capable of hydrogen bonding

 

 

• Carbonyls (C=O): Includes aldehydes, ketones, carboxylic acids, and esters

• Carboxylic acids (–COOH): Acidic, reactive in soil pH environments

• Esters (–COO–): Pleasant-smelling, used in bio-pesticides

1. B) Nitrogen-Containing Groups

• Amines (–NH₂): Basic, participate in acid-base reactions
• Amides (–CONH₂): Found in proteins and organic fertilizers
• Nitro groups (–NO₂): Electron-withdrawing, increase reactivity in aromatic compounds

1. C) Sulfur-Containing Groups

• Thiols (–SH): Strong odor, involved in antimicrobial compounds
• Sulfonic acids (–SO₃H): Strongest organic acids, used in detergents and some fertilizers

1. D) Halogenated Groups

• Organic halides (–Cl, –Br, –F): Stable, used in degradation-resistant pesticides

 

1. E) Unsaturated Groups

• Alkenes (C=C) and Alkynes (C≡C): Contain double/triple bonds, more reactive than alkanes

 

Methods of Identifying Functional Groups

Infrared Spectroscopy (FTIR)

One of the most commonly used methods for identifying functional groups. Chemical bonds absorb IR light at specific wavelengths, producing distinct absorption bands.

Wavenumber (cm⁻¹)	Functional Group	Absorption Characteristic
1700–1720	C=O (Carbonyl)	Strong absorption
3200–3500	O–H or N–H	Broad and diffuse absorption
2100–2260	C≡C or C≡N	Sharp, distinct absorption

 

 

Nuclear Magnetic Resonance (NMR) Spectroscopy

A precise method for determining molecular structure. Signal analysis reveals the type and position of functional groups within a molecule.

 

Gas Chromatography–Mass Spectrometry (GC–MS)

Combines separation and identification. Fragmentation patterns in the mass spectrum indicate the presence of specific functional groups.

High-Performance Liquid Chromatography (HPLC)

Used for non-volatile compounds. Excellent for analyzing organic fertilizers, antibiotics, and bio-pesticides.

 

 

 

 

Application of Functional Groups in Agricultural Chemistry

1. A) In Fertilizer Formulation

Organic and synthetic fertilizers are designed with specific functional groups to enhance plant absorption and effectiveness.

Functional Group	Application in Fertilizer	Role
–COOH	Humic and fulvic acids	Enhances micronutrient uptake, improves solubility
–OH	Biopolysaccharides, sugar alcohols	Improves soil interaction, retains moisture
–NH₂	Amino fertilizers	Promotes growth, involved in protein synthesis
–PO₄³⁻	Phosphate fertilizers	Enhances phosphorus uptake by roots

 

1. B) In Pesticides and Agrochemicals

Functional groups are essential in designing effective, degradable, and stable pesticide molecules.

Functional Group	Example Pesticide	Function and Importance
–NO₂	Nitrofen, nitro-aromatic compounds	Increases toxicity, aids in pest penetration
–C≡N	Carbamates, neonicotinoids	Disrupts insect nervous systems
Halogens	Dichloropropene, chlorpyrifos	Enhances environmental stability, increases uptake
Esters (–COO–)	Pyrethrins	Controlled photodegradation, rapid but degradable

• Identifying functional groups helps predict pesticide degradation rates, allowing for estimation of pesticide pre-harvest intervals (PHI).
• Residue analysis of functional groups aids in environmental risk assessment.
• Enables the design of selective pesticides tailored to insect enzymatic profiles.

 

1. C) In Soil and Water Pollution Control

Identifying functional groups in residue helps researchers:

• Predict which organic compounds remain in soil or get leached into water.
• Modify pH levels to regulate the presence or activity of functional groups and control plant absorption.