Introduction to Organic Chemistry

Overview

• Organic Chemistry: Study of organic compounds (contain carbon atoms).
• Carbon forms 4 bonds.

Bond Preferences for Common Elements

• Hydrogen: 1 bond
• Beryllium: 2 bonds
• Boron: 3 bonds (3 valence electrons)
• Carbon: 4 bonds (4 valence electrons)
• Nitrogen: 3 bonds
• Oxygen: 2 bonds
• Halogens (Fluorine, Chlorine, Bromine, Iodine): 1 bond (can form 7 bonds in special cases)

Drawing Lewis Structures

• Water (H₂O): Oxygen forms 2 bonds, hydrogen forms 1 bond. Oxygen needs 2 lone pairs to have 8 electrons.
• Methyl fluoride: Carbon forms 4 bonds, hydrogen forms 1 bond, and fluorine forms 1 bond with 3 lone pairs.

Bonds and Polarity

• Hydrogen Bonds: Occur when hydrogen is directly attached to nitrogen, oxygen, or fluorine.
• Polar Covalent Bonds: Electronegativity difference ≥ 0.5 (e.g., C-F).
• Nonpolar Bonds: Electronegativity difference < 0.5 (e.g., C-H).
• Ionic Bonds: Electrons are transferred, not shared (e.g., NaCl).

Types of Bonds

• Covalent Bonds: Electrons are shared.
  • Nonpolar Covalent Bonds: Electrons shared equally (e.g., H₂).
  • Polar Covalent Bonds: Electrons shared unequally (e.g., HF).
• Ionic Bonds: Result from electrostatic attraction between oppositely charged ions (e.g., Na⁺ and Cl⁻).

Alkanes

• Alkanes: Saturated hydrocarbons (e.g., methane, ethane, propane, butane, pentane, etc.).
• General formula: CₙH₂ₙ₊₂.

Drawing Organic Structures

• Ethane (C₂H₆): CH₃-CH₃
• Ethene (C₂H₄): CH₂=CH₂
• Ethyne (C₂H₂): HC≡CH

Bond Lengths and Strengths

• Bond Lengths: Triple < Double < Single
• Bond Strengths: Triple > Double > Single

Sigma and Pi Bonds

• Single Bond: 1 sigma bond
• Double Bond: 1 sigma + 1 pi bond
• Triple Bond: 1 sigma + 2 pi bonds
• Sigma Bonds: Stronger than pi bonds.

Bond Order

• Single Bond: Bond order = 1
• Double Bond: Bond order = 2
• Triple Bond: Bond order = 3

Hybridization

• sp³: 4 groups around carbon
• sp²: 3 groups around carbon
• sp: 2 groups around carbon

Hybridization of Bonds

• Bond Hybridization (e.g., CH bond): Determine the hybridization of atoms in the bond (e.g., sp³-s for CH bond).

Sigma and Pi Bond Counting

• Count single, double, and triple bonds to determine sigma and pi bonds in a molecule.

Formal Charge Calculation

• Formula: Valence electrons - (Bonds + Dots)
• Example: Sulfur in H₂SO₄ has -1 formal charge.

Bonding and Nonbonding Electrons

• Lone Pairs: 2 nonbonding electrons per pair.
• Bonds: 2 bonding electrons per bond.

Functional Groups

• Alcohols: -OH group (e.g., ethanol).
• Aldehydes: -CHO group (e.g., ethanal).
• Ethers: R-O-R' group (e.g., dimethyl ether).
• Ketones: RC(=O)R' group (e.g., propanone).
• Esters: RCO₂R' group (e.g., methyl ethanoate).
• Carboxylic Acids: -CO₂H group (e.g., pentanoic acid).

Expanding Structures

• Example: CH₃CH₂OH represents ethanol.
• Key Note: Methyl groups at the end, CH₂ groups in the middle, and CH groups branched.

Complex Structures

• Expanding condensed structures by recognizing functional groups and bond preferences.
• Consider hybridizations, formal charges, and sigma/pi bonds to fully understand molecular structures.

Additional Resources

• Check online playlists and videos for specific topics in organic chemistry.
• Refer to the periodic table for group and valence electron counts.