Organic Chemistry Lecture Notes

Introduction

• Focus: Organic compounds containing carbon atoms.
• Key concept: Carbon forms four bonds.

Bonding Preferences of Elements

• Hydrogen: Forms one bond.
• Beryllium: Forms two bonds.
• Boron: Forms three bonds.
• Carbon: Forms four bonds.
• Nitrogen: Typically forms three bonds.
• Oxygen: Forms two bonds.
• Halogens (F, Cl, Br, I): Typically form one bond, but can form more in specific scenarios.

Lewis Structures

• Water (H₂O): Oxygen forms two bonds and has two lone pairs.
• Methyl Fluoride (CH₃F): Carbon forms four bonds, with fluorine using three lone pairs.

Bond Types

• Polar Bonds: Electronegativity difference ≥ 0.5.
  • Example: C-F bond, polar due to fluorine's higher electronegativity.
• Non-Polar Bonds: Electronegativity difference < 0.5.
  • Example: C-H bond.
• Hydrogen Bonds: Special type of polar covalent bond.
• Ionic Bonds: Involve electron transfer; example: NaCl.

Saturated and Unsaturated Hydrocarbons

• Alkanes: Saturated, single bonds, follow CₙH₂ₙ₊₂ formula.
  • Names: methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane.
• Alkenes: Unsaturated, contain double bonds.
  • Example: Ethene (C₂H₄).
• Alkynes: Unsaturated, contain triple bonds.
  • Example: Ethyne (C₂H₂).

Bond Length and Strength

• Length: Single > Double > Triple bonds.
  • Example: C-C bond lengths: single (1.54 Å) > double (1.33 Å) > triple (1.20 Å).
• Strength: Triple > Double > Single bonds.

Sigma and Pi Bonds

• Single Bond: 1 Sigma bond.
• Double Bond: 1 Sigma + 1 Pi bond.
• Triple Bond: 1 Sigma + 2 Pi bonds.
• Strength: Sigma bonds are stronger than Pi bonds.

Hybridization

• sp³: Carbon with four single bonds.
• sp²: Carbon with one double bond.
• sp: Carbon with one triple bond.
• Hybridization of bonds: Based on atoms connected (e.g., sp³-s for a C-H bond).

Formal Charge Calculation

• Formula: Valence electrons - (number of bonds + lone pair electrons).
• Examples:
  • Positive and neutral charges in carbon atoms.
  • Sulfur and nitrogen formal charges in molecular ions (e.g., sulfide and ammonium).

Functional Groups and Naming

• Alcohols: R-OH; Ethanol as an example.
• Aldehydes: R-CHO; Ethanal (acetaldehyde).
• Ketones: R-CO-R'; Propanone (acetone).
• Esters: R-COO-R'; Methyl ethanoate.
• Carboxylic Acids: R-COOH; Pentanoic acid.

Practical Exercises

• Expanding Molecular Structures: Understanding condensed formulae to expanded structures.
• Identifying functional groups and hybridization in complex structures.

Additional Resources

• Online Searches: Organic chemistry playlists and topics.
• Examples and Practice: Naming esters, expanded structural questions.