Organic Chemistry Lecture Notes

Introduction

• Target Audience: First semester organic chemistry students
• Focus: Organic compounds (contain carbon atoms)

Bonding Preferences

Carbon and Other Elements

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

Lewis Structures

General Guidelines

• Bonds represent 2 electrons
• Octet rule: Elements in second row typically seek 8 electrons

Water (H₂O) Example

• Structure: H-O-H with two lone pairs on oxygen
• Bond Type: Hydrogen bond (special type of covalent bond)

Methyl Fluoride (CH₃F) Example

• Structure: Carbon center, three Hydrogens, one Fluorine with three lone pairs
• Bond Types: Polar covalent bond (C-F), Non-polar covalent bond (C-H)

Polar vs. Non-Polar Bonds

• Polar Bond: Electronegativity difference ≥ 0.5 (unequally shared electrons)
• Non-Polar Bond: Electronegativity difference < 0.5 (equally shared electrons)
• Example: C-F bond is polar, C-H bond is non-polar

Types of Bonds

Covalent Bonds

• Non-Polar Covalent Bonds: e.g., H₂ molecule
• Polar Covalent Bonds: Unequal sharing of electrons, e.g., HF

Ionic Bonds

• Electrons are transferred, not shared
• Example: Sodium (Na) and Chlorine (Cl) forming Na⁺ and Cl⁻ ions
• Electrostatic force of attraction creates ionic bond

Alkanes

• Saturated hydrocarbons
• General formula: CₙH₂ₙ₊₂
• Common Names:
  • Methane: CH₄
  • Ethane: C₂H₆
  • Propane: C₃H₈
  • Butane: C₄H₁₀
  • Pentane, Hexane, Heptane, Octane, Nonane, Decane up to 10 carbons

Drawing Lewis Structures for Alkanes

Ethane (C₂H₆)

• Structure: CH₃-CH₃

Ethene (C₂H₄)

• Structure: CH₂=CH₂ (double bond)

Ethyne (C₂H₂)

• Structure: CH≡CH (triple bond)

Bond Lengths

• Single bond > Double bond > Triple bond
• Single bond: 154 pm, Double bond: 133 pm, Triple bond: 120 pm

Bond Strength

• Single bond < Double bond < Triple bond
• Sigma bonds are stronger than pi bonds

Bond Order

• Single bond: 1
• Double bond: 2
• Triple bond: 3

Hybridization

• Determined by the number of groups (atoms + lone pairs) attached

Examples

• sp³: 4 groups (tetrahedral)
• sp²: 3 groups (trigonal planar)
• sp: 2 groups (linear)

Bond Hybridization Examples

• CH₄: sp³
• C₂H₄: sp²
• C₂H₂: sp
• Bond hybridization (e.g., C-H bond in sp³-s or sp-s)

Sigma and Pi Bonds in Organic Compounds

• Sigma bonds: Single bonds
• Pi bonds: Additional bonds in double and triple bonds
• Example: C₂H▵C ≡ C₂H₂ has 6 sigma bonds and 2 pi bonds

Formal Charge Calculation

• Formula: Formal Charge = Valence Electrons - (Bonds + Lone Pairs)

Examples

• Calculating formal charges on carbon atoms and other elements

Functional Groups & Naming

• Alcohol (OH group): Ethanol (two carbons)
• Aldehyde (CHO group): Ethanal
• Ether (R-O-R'): Dimethyl ether
• Ketone (RCOR'): Propanone
• Carboxylic Acid (COOH group): Pentanoic acid
• Ester (RCOOR'): Methyl ethanoate

Expanding Condensed Structures

• Example walkthrough of expanding condensed formulae
• Recognize functional groups and proper placement (e.g., methyl, methylene groups)

Radicals

• Odd number of electrons
• Example: Methyl radical (CH₃•)

Miscellaneous

• Practice problems provided and solved during the lecture
• Mention of additional resources available on YouTube