Overview
This lecture introduces foundational concepts in organic chemistry, including bonding, Lewis structures, functional groups, and nomenclature of organic compounds.
Bonding in Organic Chemistry
- Organic chemistry studies compounds containing carbon atoms.
- Carbon typically forms 4 bonds; hydrogen forms 1, oxygen 2, nitrogen 3, halogens (F, Cl, Br, I) usually 1.
- Covalent bonds involve electron sharing; ionic bonds involve electron transfer.
- Polar covalent bonds have unequal electron sharing due to electronegativity differences ≥ 0.5.
- Hydrogen bonds occur when hydrogen is bonded directly to N, O, or F.
Drawing Lewis Structures
- Lewis structures help represent bonding and nonbonding electrons.
- Elements in the second period (C, N, O, F) prefer to have 8 electrons (octet rule).
- Lone pairs are added to satisfy the octet rule for atoms like O and F.
Types of Covalent Bonds & Bond Properties
- Covalent bonds: nonpolar (equal sharing, e.g., C–H) and polar (unequal sharing, e.g., C–F).
- Ionic bonds form between metals and nonmetals by complete electron transfer (e.g., NaCl).
- Bond length: single > double > triple; bond strength: triple > double > single.
- Single bonds = 1 sigma bond; double bonds = 1 sigma + 1 pi; triple bonds = 1 sigma + 2 pi.
- Sigma (σ) bonds are stronger than pi (π) bonds.
Hybridization
- Hybridization is determined by the number of groups (atoms/lone pairs) attached to carbon:
- 4 groups: sp³
- 3 groups: sp²
- 2 groups: sp
- Bond hybridization is expressed by the types of orbitals involved (e.g., sp³–s).
Formal Charge & Electrons
- Formal charge = valence electrons – (bonds + lone pair dots) on an atom.
- Positive charge = cation/carbocation; negative charge = anion/carbanion; odd electrons = radical.
- Bonding electrons: 2 per bond; nonbonding electrons: 2 per lone pair.
Alkanes and Alkane Nomenclature
- Alkanes are saturated hydrocarbons (CnH2n+2): methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane.
- Alkenes (contain double bonds) and alkynes (contain triple bonds) are unsaturated hydrocarbons.
Functional Groups & Structural Formulas
- Alcohols: contain –OH, named with "-ol" (ethanol).
- Aldehydes: contain –CHO (carbonyl at end; e.g., ethanal).
- Ketones: contain a carbonyl in the chain (not at end; e.g., propanone).
- Ethers: oxygen between two carbons (dimethyl ether).
- Esters: two oxygens, one in a carbonyl, one connected to another carbon (methyl ethanoate).
- Carboxylic acids: carbonyl and hydroxyl on same carbon (pentanoic acid).
Key Terms & Definitions
- Covalent Bond — electrons shared between atoms (can be polar or nonpolar).
- Ionic Bond — complete transfer of electrons between atoms.
- Sigma Bond (σ) — first, strongest covalent bond between atoms.
- Pi Bond (π) — additional bonds in double/triple bonds.
- Hybridization — mixing of atomic orbitals (sp, sp², sp³).
- Formal Charge — calculated charge on an atom in a molecule.
- Functional Group — specific group of atoms influencing chemical behavior (alcohol, ketone, etc.).
- Alkane/Alkene/Alkyne — saturated/unsaturated hydrocarbons with single/double/triple C–C bonds.
Action Items / Next Steps
- Memorize alkane names up to decane (10 carbons).
- Practice drawing Lewis structures and assigning formal charges.
- Review functional groups and their nomenclature.
- Complete any assigned readings or homework on hybridization and bonding.