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Functional Groups in Carbon Compounds

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Topics

  • Functional Groups
  • Types of Functional Groups
  • Role of Functional Groups in Organic Chemistry

Functional Groups

Carbon compounds are formed by bonding carbon with other elements like hydrogen, halogens, oxygen, nitrogen, and sulphur. When one or more hydrogen atoms in a hydrocarbon are replaced by these elements or groups containing them, the resulting compound exhibits specific chemical properties. These specific atoms or groups responsible for the characteristic behaviour of a compound are called Functional Groups.

'A functional group is an atom or group of atoms that determines the chemical properties of a molecule, regardless of its carbon chain length.'

Key Characteristics of Functional Groups:

  1. Defines Chemical Reactions: Determines how the molecule reacts.
  2. Independent Behaviour: Reacts in a similar way across different molecules.
  3. Predictable Properties: Helps in systematic synthesis and identification of compounds.
  4. Affects Solubility: A functional group influences polarity and solubility (e.g., alcohols dissolve in water due to the -OH group).
  5. Can Carry Charges: Some functional groups exist in ionic forms (e.g., -COO⁻ in carboxylates).
  6. Affect Molecular Structure & Reactivity: Influence how molecules interact with other substances.

Types of Functional Groups

1. Hydrocarbon Functional Groups

  • Contain only carbon (C) and hydrogen (H).
  • Classified based on bond types between carbon atoms.
Functional Group Structural Formula Prefix Suffix Example
Alkane R-H None -ane Methane (CH₄)
Alkene R=R None -ene Ethene (C₂H₄)
Alkyne R≡R None -yne Ethyne (C₂H₂)
Aromatic (Benzene) C₆H₆ None -benzene Toluene (C₆H₅CH₃)

2. Halogen-Containing Functional Groups

A halogen (Cl, Br, I, F) replaces hydrogen in hydrocarbons.

Functional Group Structural Formula Prefix Suffix Example
Haloalkane (Alkyl Halide) R-X (X = Cl, Br, I, F) Halo- -halide Chloroethane (C₂H₅Cl)

3. Oxygen-Containing Functional Groups

These contain oxygen in different bonding patterns.

Functional Group Structural Formula Prefix Suffix Example
Alcohol R-OH Hydroxy- -ol Ethanol (C₂H₅OH)
Aldehyde R-CHO Formyl- -al Ethanal (CH₃CHO)
Ketone R-CO-R' Oxo- -one Propanone (Acetone) (CH₃COCH₃)
Carboxylic Acid R-COOH Carboxy- -oic acid Ethanoic Acid (CH₃COOH)
Ester R-COO-R' Alkoxycarbonyl- -oate Methyl Ethanoate (CH₃COOCH₃)
Ether R-O-R' Alkoxy- -ether Dimethyl Ether (CH₃OCH₃)

4. Nitrogen-Containing Functional Groups

These groups contain nitrogen in different bonding structures.

Functional Group Structural Formula Prefix Suffix Example
Amine (Primary) R-NH₂ Amino- -amine Methylamine (CH₃NH₂)
Amine (Secondary) R₂NH - -amine Dimethylamine (CH₃NHCH₃)
Amine (Tertiary) R₃N - -amine Trimethylamine (N(CH₃)₃)
Amide R-CO-NH₂ Carbamoyl- -amide Ethanamide (CH₃CONH₂)
Nitrile R-CN Cyano- -nitrile Ethanenitrile (CH₃CN)

5. Sulfur-Containing Functional Groups

These contain sulphur, affecting properties like smell and reactivity.

Functional Group Structural Formula Prefix Suffix Example
Thiol (Mercaptan) R-SH Mercapto- -thiol Methanethiol (CH₃SH)
Sulfide (Thioether) R-S-R' - -sulphide Dimethyl Sulfide (CH₃SCH₃)

Some functional groups in carbon compounds:

Hetero Atom Functional Group Structural Formula Condensed Structural Formula
Halogen (chlorine, bromine, iodine) Halo (chloro/bromo/iodo) -X (-Cl, -Br, -I) -X (-Cl, -Br, -I)
Oxygen 1. Alcohol -O-H -OH
  2. Aldehyde \[\begin{array}{cc}
\ce{O}\phantom{..}\\
||\phantom{..}\\
\phantom{}\ce{- C - H}
\end{array}\]		 -CHO
  3. Ketone \[\begin{array}{cc}
\ce{O}\phantom{}\\
||\phantom{}\\
\phantom{}\ce{- C -}
\end{array}\]		 -CO-
  4. Carboxylic Acid \[\begin{array}{cc}
\ce{O}\phantom{......}\\
||\phantom{......}\\
\phantom{}\ce{- C - O - H}
\end{array}\]		 -COOH
  5. Ether -O- -O-
  6. Ester \[\begin{array}{cc}
\ce{O}\phantom{.....}\\
||\phantom{.....}\\
\phantom{}\ce{- C - O -}
\end{array}\]		 -COO-
Nitrogen Amines \[\begin{array}{cc}
\phantom{}\ce{- N - H}\\
|\phantom{..}\\
\ce{H}\phantom{..}\\
\end{array}\]		 NH₂

 

Role of Functional Groups in Organic Chemistry

1. Chemical Reactivity

Functional groups determine the reactivity of molecules. They can modify each other’s behaviour and undergo interconversion (e.g., alcohol to aldehyde or carboxylic acid).

2. Bonding and Structural Influence

Covalent bonds link functional groups to molecules. In polymers, they attach to the carbon backbone, altering chemical properties. Some functional groups exist in ionic forms (e.g., -COO⁻ in carboxylates).

3. Coordination Complexes

Functional groups act as ligands, binding to metal centres, affecting stability, colour, and reactivity.

4. Solubility & Polarity

Functional groups influence solubility based on polarity. Similar functional groups in solute and solvent increase solubility (e.g., sugar dissolves in water due to -OH). Electronegative groups can induce polarity in nonpolar molecules, enhancing water solubility.

5. Molecular Interactions

Functional groups contribute to hydrogen bonding, dipole interactions, and ionic forces, affecting boiling/melting points and biological activity.

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