Functional groups are specific groups of atoms within a molecule that confer specific chemical properties and reactivity to the compound. These groups play a crucial role in determining the behavior, reactions, and functions of organic molecules. The presence of different functional groups in a molecule influences its physical and chemical properties, as well as its interactions with other molecules.

Here are some common functional groups and their properties:

1. Hydroxyl Group (-OH):
   • Properties: Polar, can form hydrogen bonds, makes compounds water-soluble.
   • Examples: Alcohols (e.g., ethanol), phenols (e.g., phenol).
2. Carbonyl Group (C=O):
   • Properties: Polar, found in various compounds, reactive site.
   • Examples: Aldehydes (e.g., formaldehyde), ketones (e.g., acetone), carboxylic acids (e.g., acetic acid).
3. Amino Group (-NH2):
   • Properties: Basic, can accept protons (act as bases), forms hydrogen bonds.
   • Examples: Amines (e.g., methylamine), amino acids (building blocks of proteins).
4. Carboxyl Group (-COOH):
   • Properties: Acidic, can donate protons (act as acids), forms hydrogen bonds.
   • Examples: Carboxylic acids (e.g., acetic acid), amino acids.
5. Ester Group (-COO-):
   • Properties: Often fragrant, found in esters and lipids, important in flavor and fragrance compounds.
   • Examples: Esters (e.g., ethyl acetate), triglycerides (fats and oils).
6. Amide Group (-CONH2):
   • Properties: Found in proteins and peptides, involved in hydrogen bonding.
   • Examples: Amides (e.g., acetamide), peptides, proteins.
7. Thiol Group (-SH):
   • Properties: Can form disulfide bonds, found in some amino acids and coenzymes.
   • Examples: Thiols (e.g., ethanethiol), cysteine (amino acid).
8. Phosphate Group (-PO4-):
   • Properties: Negatively charged, involved in energy storage (ATP), important in nucleic acids.
   • Examples: Phosphates in ATP, DNA, RNA.
9. Halide Group (e.g., -Cl, -Br, -I):
   • Properties: Can influence reactivity and polarity of molecules.
   • Examples: Chloroalkanes, bromoalkanes, iodoalkanes.
10. Nitro Group (-NO2):
    • Properties: Often explosive, found in nitro compounds.
    • Examples: Nitrobenzene, nitroglycerin.

Functional groups provide a systematic way to categorize and predict the behavior of organic compounds. Compounds with the same functional group often share similar chemical reactions and properties, regardless of the larger molecule’s structure. Understanding functional groups is essential for predicting the reactivity, solubility, and interactions of organic molecules and is fundamental to organic chemistry.