Organic Chemistry Lecture Notes

Introduction

• Focus on organic compounds containing carbon atoms.
• Carbon tends to form four bonds.
• Understanding bonding preferences helps in drawing Lewis structures.

Bond Formation Preferences

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

Drawing Lewis Structures

• Water (H2O): Oxygen forms 2 bonds, Hydrogen forms 1 bond. Add lone pairs to fulfill octet.
• Methyl Fluoride (CH3F): Carbon forms 4 bonds. Fluorine forms 1 bond, with lone pairs.

Types of Bonds

• Polar Covalent Bonds: Electronegativity difference ≥ 0.5
  • Ex: C-F bond in methyl fluoride is polar
• Non-Polar Covalent Bonds: Electronegativity difference < 0.5
  • Ex: C-H bond
• Hydrogen Bonds: Occur when H is directly attached to N, O, or F
• Ionic Bonds: Involve transfer of electrons (e.g., NaCl)

Alkane Naming and Structure

• Alkanes: Saturated hydrocarbons (only single bonds)
  • Methane (CH4), Ethane (C2H6), Propane (C3H8), etc.
• Formula: CnH2n+2

Lewis Structures of Organic Compounds

• Ethane (C2H6): Single bonds
• Ethene (C2H4): Double bond
• Ethyne (C2H2): Triple bond

Bond Length and Strength

• Bond Length: Triple < Double < Single (shortest to longest)
• Bond Strength: Triple > Double > Single (strongest to weakest)

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 are stronger than pi bonds.

Hybridization

• SP3 Hybridization: 4 groups/atoms attached
• SP2 Hybridization: 3 groups/atoms attached
• SP Hybridization: 2 groups/atoms attached

Formal Charge

• Calculation: Number of valence electrons - (number of bonds + number of dots)
• Positive Charge: More bonds, fewer dots
• Negative Charge: Fewer bonds, more dots

Functional Groups

• Alcohol: -OH group
• Aldehyde: Carbonyl group (C=O) at the end
• Ether: Oxygen between two carbon atoms
• Ketone: Carbonyl group in the middle
• Carboxylic Acid: Carbonyl group + hydroxyl group
• Ester: Carbonyl group + oxygen linked to another carbon

Challenges in Expanding Structures

• Branching: CH groups often indicate branching.
• Methyl (CH3): End of structure
• Methylene (CH2): Middle of structure

Conclusion

• Understanding the basic principles of bonding, structure drawing, and functional groups is essential for mastering organic chemistry.