Organic Chemistry - Lecture Notes

Introduction to Organic Chemistry

• Focus: Organic compounds containing carbon atoms.
• Carbon properties: Typically forms 4 bonds.

Element Bond Preferences

• Hydrogen (H): 1 bond.
• Beryllium (Be): 2 bonds.
• Boron (B): 3 bonds.
• Carbon (C): 4 bonds.
• Nitrogen (N): 3 bonds (usually).
• Oxygen (O): 2 bonds.
• Fluorine (F) and other Halogens (Cl, Br, I): 1 bond, but can form up to 7 (not covered in detail).

Lewis Structures

• Water (H2O): Oxygen forms 2 bonds, hydrogen 1. Structure includes 2 lone pairs on oxygen.
• Methyl Fluoride (CH3F): Carbon in the middle, hydrogen forms 1 bond each, fluorine forms 1 bond, and has 3 lone pairs.
• Bond Types: Understanding polar vs non-polar bonds.
  • Polar Bonds: Electronegativity difference ≥ 0.5.
  • Non-Polar Bonds: Electronegativity difference < 0.5.
  • Examples:
    • C-F Bond: Polar covalent bond (C: 2.5, F: 4.0).
    • C-H Bond: Non-polar covalent bond (C: 2.5, H: 2.1).
  • Hydrogen Bonds: Special case of polar covalent bonds.

Bond Types and Properties

• Covalent Bonds: Electron sharing (equal or unequal).
  • Non-polar covalent (e.g., H2).
  • Polar covalent (e.g., HF).
• Ionic Bonds: Electron transfer.
  • Example: NaCl (Sodium transfers an electron to chlorine).
  • Electrostatic Force: Attraction between oppositely charged ions.

Alkanes, Alkenes, Alkynes

Alkanes

• Saturated Compounds: Maximum hydrogen atoms.
• Examples: Methane (CH4), Ethane (C2H6), Propane (C3H8), Butane (C4H10).
• General Formula: CnH2n+2.

Alkenes

• Unsaturated Compounds: Contains double bonds.
• Example: Ethene (C2H4).

Alkynes

• Unsaturated Compounds: Contains triple bonds.
• Example: Ethyne (C2H2).

Bond Characteristics

• Length: Single > Double > Triple.
• Strength: Triple > Double > Single.
• Sigma Bonds: Always present in single bonds, one in double and one in triple bonds.
• Pi Bonds: Present in double (1 pi) and triple bonds (2 pi).
• Bond Order: Single (1), Double (2), Triple (3).

Hybridization

• Determining Hybridization: Count atoms and lone pairs around carbon.
• Examples:
  • sp3: 4 groups (single bonds).
  • sp2: 3 groups (one double bond).
  • sp: 2 groups (triple bond).
• Bond Hybridization: Determined by atoms involved.
• Example: CH bond in sp3 C and s H = sp3-s.

Formal Charge Calculation

• Formula: Valence electrons - (bonds + dots).
• Examples:
  • Carbon with 3 bonds: +1 formal charge.
  • Sulfur with 1 bond, 6 dots: -1 formal charge.
  • Nitrogen in NH4+ ion: +1 formal charge.

Functional Groups and Drawing Structures

• Alcohol (OH): Example - Ethanol (C2H5OH).
• Aldehyde (CHO): Example - Ethanal (CH3CHO).
• Ether (R-O-R): Example - Dimethyl Ether (CH3OCH3).
• Ketone (C=O): Example - Propanone (CH3COCH3).
• Carboxylic Acid (COOH): Example - Pentanoic Acid (C5H10O2).
• Ester (R-COO-R): Example - Methyl Ethanoate (C3H6O2).

Expansion of Condensed Structures

• Understanding how to draw detailed structure from condensed formula.
  • Example: (CH3)3CCHBrCH2CH2CH3.
  • Teachings: Recognizing and placing methyl (CH3), methylene (CH2), and other groups correctly.

Summary

• Electronegativity and Bond Polarity: Crucial for understanding molecular behavior.
• Structural Types: Recognizing different organic molecules and their unique properties aids in predicting reactivity and stability.
• Hybridization and Bond Character: Key for predicting molecular geometry and bond strength.