Essential Principles of General and Organic Chemistry
1. Molecular Orbital Method Basics
Atoms lose their individual identity, and the molecule is viewed as a collection of nuclei and electrons. The Schrödinger equation is solved for the molecule to obtain a series of energy values, known as molecular orbitals. These are formed by combining atomic orbitals that have similar energy and significant overlap along the valence axis.
2. Valence Electron Interactions
- Antiparallel spins: Covalent bond formation.
- Parallel spins: Atoms repel; no bond is formed.
3. Hydrogen Bond Formation
A hydrogen bond occurs when a polar molecule containing a hydrogen atom interacts with a strongly electronegative atom (F, Cl, O, N).
4. Intermolecular Interactions
- Orientational (dipole-dipole): Occurs between polar molecules with constant dipole moments.
- Inductive: Arises when a polar molecule induces a dipole in a nonpolar molecule.
- Dispersion (London) forces: Occurs between nonpolar molecules due to momentary microdipoles.
5. Diffusion and Osmotic Properties
- Osmosis: Movement of solvent through a semi-permeable membrane to equalize concentration.
- Osmotic Pressure: The force required to equalize solution concentrations.
- Vapor Pressure: Pressure exerted by saturated vapor over a liquid.
- Van’t Hoff Equation: Π = Cm × R × T
6. Acids and Bases
- Protolith Theory: Acids accept electron pairs; bases provide electron pairs.
- Lewis Theory: Acids accept electron pairs; bases donate electron pairs.
7. Buffer Solutions
Buffer solutions maintain a constant pH when strong acids or bases are added. They typically consist of a weak acid and its salt or a weak base and its salt.
8. Alcohols and Phenols
Alcohols and phenols are hydroxyl derivatives of hydrocarbons. In alcohols, the carbon atom attached to the OH group is sp³ hybridized. In phenols, both the carbon and oxygen atoms are sp² hybridized, with the OH group acting as an ortho- and para-orientant.
9. Carbohydrates and Lipids
- Monosaccharides: Simplest carbohydrates (3–8 carbon atoms) that do not hydrolyze.
- Disaccharides: Sugars containing two monosaccharide residues linked by glycosidic bonds.
- Lipids: Organic substances insoluble in water but soluble in organic solvents like alcohol or benzene.
10. Quantum Rules
- Pauli Principle: No two electrons in an atomic system can have the same four quantum numbers.
- Hund’s Rule: Degenerate orbitals are occupied by one electron each before pairing begins.
- Klechkowski’s Rule: Atomic orbital energy increases with the sum of (n + l).
11. Coordination Compounds
Complexes consist of a central atom coordinated by ligands. The inner coordination sphere contains ligands directly bonded to the central atom, while the outer sphere contains ions not directly bonded.
12. Aromatic Compounds
Aromatic compounds, such as pyrrole and imidazole, follow Hückel’s rule (4n + 2 π-electrons in a cyclic, planar system). They typically undergo substitution reactions rather than addition reactions.