Organic Chemistry Overview

Organic Chemistry: Definition

• The study of carbon and carbon-based compounds
• Carbon is the backbone of life

Atoms, Electrons, and Orbitals

• Atomic Structure: Four types of orbitals are based on hydrogen atoms: s, p, d, and f
  • s orbitals are spherical.
  • p orbitals are dumbbell-shaped.
  • d orbitals are cloverleaf-shaped.
  • s and p orbitals are most important for organic and biological chemistry.
• Filling Rules:
  • Electrons fill the lowest energy orbitals first.
  • Each orbital can hold a maximum of two electrons with opposite spins.
  • Electrons fill individual orbitals before pairing.
• Valence Electrons: Found in the outermost shell and used in chemical bonding
  • The number of valence electrons equals the group number of the element.
  • Example: Carbon (group IVA) has four valence electrons and oxygen (group VIA) has six.

Chemical Bonds

• Ionic Bonds: Formed between oppositely charged ions.
  • Present in salts.
  • Formed when an element on the left side of the periodic table transfers electrons to an element on the right side.
  • Metal cations (+ve charge) form when atoms lose electrons.
  • Non-metal anions (-ve charge) form when atoms gain electrons.
• Covalent Bonds: Formed by sharing electrons between atoms.
  • Occurs between nonmetals
  • The tendency for an atom to achieve a full outer shell (eight electrons) is called the octet rule.
• Types of Covalent Bonds:
  • Single Bond: Two atoms share one pair of electrons.
  • Double Bond: Two atoms share two pairs of electrons.
  • Triple Bond: Two atoms share three pairs of electrons.

Electronegativity and Polarity

• Electronegativity: The attraction an atom has for shared electrons.
  • Increases going across a period on the periodic table (from left to right).
  • Increases going up a group (from bottom to top).
• Polarity of Bonds: Determined by the difference in electronegativity between the bonded atoms.
  • Nonpolar Covalent Bond: Electronegativity difference is between 0 and 0.4.
  • Polar Covalent Bond: Electronegativity difference is between 0.5 and 1.8.
  • Ionic Bond: Electronegativity difference is greater than 1.8.

Dipole Moment

• Defined as the size of the charge multiplied by the distance between the charges.
• Measured in Debye (D).
• The direction of the dipole moment is represented by an arrow pointing towards the more electronegative atom.

Classification of Carbon and Hydrogen Atoms

• Carbon Atoms: Classified based on the number of other carbon atoms bonded to it:
  • Primary (1o): Bonded to one carbon.
  • Secondary (2o): Bonded to two carbons.
  • Tertiary (3o): Bonded to three carbons.
  • Quaternary (4o): Bonded to four carbons.
• Hydrogen Atoms: Classified similarly to carbon atoms.

Hybridization

• sp3, sp2, and sp Hybridization: Carbon atoms can hybridize their orbitals to form different types of bonds.
  • sp3: 25% s character, longest bonds, weakest bonds, and lowest C-H acidity.
  • sp2: 33% s character, with shorter bonds, stronger bonds, and higher C-H acidity.
  • sp: 50% s character, shortest bonds, strongest, and highest C-H acidity.

Factors Influencing Acidity

• Electronegativity: Increased electronegativity of the atom bonded to the hydrogen (H-A) increases acidity.
• Inductive Effects: Nearby electronegative atoms pull electron density away from the hydrogen, increasing its partial positive charge and making it more acidic.
• pKa: Acid strength and pKa are inversely related.

Physical Properties

• Boiling Point and Melting Point:
  • Increase with increasing molecular weight due to stronger van der Waals forces.
• Solubility:
  • Determined by the ability of a compound to form hydrogen bonds with the solvent.

Intermolecular Forces

• Van der Waals Forces: Temporary dipoles arising from fluctuations in electron distribution.
• Dipole-Dipole Forces: Attractions between polar molecules.
• Ion-Dipole Forces: Attractions between an ion and a polar molecule.
• Hydrogen Bonding: Strongest type of intermolecular force, formed between molecules containing hydrogen bonded to a highly electronegative atom (O, N, or F).

Representing Molecular Structure

• Lewis Structure: Uses chemical symbols and dots or lines to represent valence electrons.
• Condensed Structure: Omits lone pairs of electrons and simplifies bonds.
• Skeletal Structure: Represents carbon chains as zig-zag lines, omits carbon symbols, and only shows heteroatoms and hydrogen atoms bonded to heteroatoms or aldehydes.

This quiz explores the fundamentals of organic chemistry, focusing on the definition of organic compounds, atomic structure, and chemical bonding. Understand the significance of carbon and its role in life, as well as the types of atomic orbitals and how they influence bonding.