Pharmaceutical Chemistry Ch2.2-2.5

Unique Properties of Carbon

  • Diversity of Compounds:

    • Forms a vast array of compounds, including:

      • Alkanes and alkenes

      • Alcohols and amines

      • Carboxylic acids

  • Versatility in Bonding:

    • Bonds with various elements from different blocks of the periodic table:

      • S block (e.g., lithium, magnesium)

      • P block (e.g., nitrogen, oxygen, halogens)

      • D block (e.g., iron, copper, zinc)

      • F block (e.g., cerium, uranium)

  • Catenation:

    • Ability to form long chains of carbon atoms, rare among elements.

  • Bonding Types:

    • Can form single, double, or triple bonds with neighboring carbon atoms, leading to diverse molecular shapes.

  • Covalent Bonding Preference:

    • Carbon typically participates in covalent bonding rather than ionic bonding.

Allotropes of Carbon

  • Traditional Allotropes:

    • Ancient knowledge of diamond and graphite.

  • Recent Discoveries:

    • Buckminsterfullerenes (Bucky-balls): Discovered in 1985, arranged in a spherical shape (60 carbon atoms).

    • Graphene: Single layers of carbon atoms, discovered by separating graphite using adhesive tape.

  • Nobel Prizes:

    • Harry Kroto for Bucky-balls in 1996, Andre Geim and Kostya Novoselov for graphene in 2010.

Molecular Shape Importance

  • Pharmaceutical Relevance:

    • Shape affects substrate binding to enzymes and drug actions.

    • Correct fit between drug and receptor is critical for therapeutic effectiveness.

  • Example:

    • Ibuprofen's mirror image (inactive form) contrasts with its active form.

  • Hormonal Impact:

    • Adrenaline vs Salbutamol: Similar shapes but different physiological effects,

    • Introduction of Salbutamol as an asthma treatment with fewer side effects.

Electronic Configuration of Carbon

  • Atomic Structure:

    • Carbon has six electrons with ground state configuration: 1s² 2s² 2p².

  • Hybridization Explanation:

    • Ground state prediction that carbon is divalent contrasts with tetravalent behavior observed in compounds.

    • Electrons in 2p orbitals do not explain bonding angles and bond strengths (ideal bond angles: 109°, 120°, or 180°).

Hybridization Concepts

  1. Excited State:

    • Allows formation of four unpaired electrons leading to tetravalency.

  2. Hybrid Orbitals:

    • sp³ Hybridization:

      • Four equivalent sp³ hybrid orbitals formed from 2s and three 2p orbitals for saturated compounds (e.g. CH₄).

    • Bond Shape & Angles:

      • Tetrahedral arrangement with bond angles near 109.5°.

    • sp² Hybridization:

      • Three sp² hybrid orbitals formed from 2s and two 2p orbitals for unsaturated compounds (e.g. C₂H₄).

      • Bond angles around 120°.

    • sp Hybridization:

      • Two sp hybrid orbitals from 2s and one 2p orbital, yielding linear shape (e.g. C₂H₂).

      • Bond angles of 180°.

Intermolecular Forces

  • Significance in Physical Properties:

    • Intermolecular forces are weaker than covalent bonds but critical for states of matter.

    • Water's boiling point exemplifies strong intermolecular forces.

  • Types of Intermolecular Forces:

    1. London (van der Waals) Forces: Weak attractive forces due to temporary dipoles.

    2. Dipole-Dipole Interactions: Occur between permanently polar molecules.

    3. Hydrogen Bonding: Strong electrostatic attraction involving H-F, H-O, or H-N interactions.

Reaction Types in Organic Chemistry

  • Classification of Reactions:

    1. Substitution: One group is replaced by another (e.g., formation of propanenitrile).

    2. Elimination: Two groups are lost, forming double or triple bonds.

    3. Addition: Adding groups across a double or triple bond.

    4. Rearrangement: Atoms re-bond in a different configuration.

  • Mechanisms of Reactions:

    • Describe the 'how' of reactions, further explored in mechanisms.