JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD Pharm. D I Year PHARMACEUTICAL ORGANIC CHEMISTRY Previous Question Paper (September/October - 2021 - R08)

Physical properties of organic compounds are governed by the nature of their chemical bonds and intermolecular interactions:

• Melting Point (M.P.): The temperature at which a solid transitions to a liquid. It depends on molecular symmetry and crystal lattice packing. Highly symmetrical molecules pack more efficiently, resulting in higher melting points.
• Boiling Point (B.P.): The temperature at which vapor pressure equals external pressure. It is influenced by molecular weight and intermolecular forces; stronger forces or higher molecular weights generally increase the boiling point.
• Intermolecular Forces: These are attractive forces between molecules, including hydrogen bonding, dipole-dipole interactions, and London dispersion forces. These forces determine the physical state and thermal properties of the compound.
• Polarity of Bonds and Molecules: Bond polarity arises from electronegativity differences between bonded atoms. Molecular polarity is the vector sum of individual bond dipoles; a molecule is polar if it possesses a net dipole moment, which significantly influences solubility and reactivity.

The Lewis theory defines acids and bases based on electron pair transfer, providing a broader scope than the Arrhenius or Brønsted-Lowry theories.

• Lewis Acid: Defined as an electron pair acceptor. These species are typically electron-deficient, such as cations or molecules with incomplete octets (e.g., BF3, AlCl3, H+).
• Lewis Base: Defined as an electron pair donor. These species must possess at least one lone pair of electrons available for donation to an acid (e.g., NH3, H2O, OH-).
• Neutralization: The reaction between a Lewis acid and a Lewis base results in the formation of a coordinate covalent bond, also known as a dative bond, producing a coordination complex or adduct.

This theory is fundamental in organic chemistry for explaining mechanisms such as nucleophilic substitution and electrophilic addition, where the nucleophile acts as a Lewis base and the electrophile as a Lewis acid.