FUNDAMENTAL PRINCIPLES OF ORGANIC CHEMISTRY

(a) Definition of Organic Chemistry

• Organic Chemistry is the branch of chemistry that deals with carbon compounds (except simple oxides of carbon like CO and CO₂, carbonates, and carbides).
• In simple words, Organic chemistry is the study of compounds having carbon elements.

(b) Definition of Organic Compounds

• Organic compounds are either hydrocarbons or their derivatives.
• They may also contain other elements like oxygen (O), nitrogen (N), sulfur (S), halogens (F, Cl, Br, I), and phosphorus (P).
• Examples:
  • Methane (CH₄)
  • Ethanol (C₂H₅OH)
  • Glucose (C₆H₁₂O₆)

(c) Importance of Organic Chemistry in Medicine

• Organic compounds form the basis of life and medicine.
• Examples:
  • Carbohydrates → energy source
  • Proteins → building material of body
  • Vitamins & Hormones → regulation of body functions
  • Medicines (like aspirin, antibiotics, anesthetics) → all are organic in nature

13.2 Classification of Organic Compounds on Structural Basis

Organic compounds can be classified into three main categories:

(a) Acyclic (Open-Chain) Compounds

• Carbon atoms are joined in straight chains or branched chains.
• They are also called aliphatic compounds.
• Examples:
  • Propane (CH₃–CH₂–CH₃)
  • Butane (CH₃–CH₂–CH₂–CH₃)

(b) Cyclic Compounds

• Carbon atoms form rings.
• They are further divided into:
  1. Homocyclic (Carbocyclic) Compounds
     • Ring contains only carbon atoms.
     • Two types:
       • Alicyclic: Non-aromatic rings (e.g., cyclohexane).
       • Aromatic: Rings with alternating double bonds (e.g., benzene).
  2. Heterocyclic Compounds
     • Ring contains carbon atoms and at least one other atom (like O, N, or S).
     • Examples: Pyridine (C₅H₅N), Furan (C₄H₄O).

(c) Aromatic vs. Non-Aromatic

• Aromatic compounds: Special stable ring systems with delocalized π-electrons (e.g., Benzene).
• Non-aromatic compounds: Do not have this special stability (e.g., Cyclohexane).

13.3 Functional Group

(a) Definition

• A functional group is an atom or group of atoms in an organic molecule that determines its chemical properties and reactions.
• Example:
  • In alcohols, the –OH group is the functional group.
  • In aldehydes, the –CHO group is the functional group.

(b) Common Functional Groups

• C=C/C≡C (double/triple bond) → Alkenes/Alkynes, e.g, ethene (CH₂=CH₂ /ethyne (CH≡CH)
• -X (Halog group) → Alkyl Halides (e.g, Chloroethane, C₂H₅Cl)

• –OH (Hydroxyl group) → Alcohols (e.g, Ethanol, C₂H₅OH)
• –CHO (Aldehyde group) → Aldehydes (e.g, Ethanal, CH₃CHO)
• –COOH (Carboxyl group) → Carboxylic acids (e.g, Acetic acid, CH₃COOH)
• -COOR (Ester group) → Esters (e.g, methylethanoate, CH₃COOCH₃)
• R–CO–R (ketone group) → Ketones (e.g., Propanone, CH₃COCH₃)
• –NH₂ (Amino group) → Amines (e.g., Ethylamine, C₂H₅NH₂)
• -(RCO)₂O (anhydride group) →  Anhydrides (e.g, Acetic anhydride, CH₃CO₂OCH₃)

(c) Importance of Functional Groups in Medicine

• The biological activity of a compound depends on its functional group.
• Example:
  • Alcohol group in ethanol → depressant effect
  • Carboxyl group in aspirin → pain-relieving effect