Overview
This lecture introduces fundamental concepts in organic chemistry, including bonding preferences, Lewis structures, types of bonds, hybridization, functional groups, and methods for naming and drawing organic compounds.
Bonding Preferences and Lewis Structures
- Organic chemistry studies compounds containing carbon, which typically forms four bonds.
- Hydrogen forms one bond; beryllium two; boron three; nitrogen three; oxygen two; halogens (F, Cl, Br, I) usually one.
- Lewis structures show atom connectivity and lone pairs; each bond equals two electrons.
- Atoms in the second row (C, N, O, F) prefer eight electrons (octet rule).
Types of Chemical Bonds
- Covalent bonds involve electron sharing: nonpolar (equal sharing) or polar (unequal sharing).
- A bond is polar if the electronegativity difference between atoms is ≥ 0.5; example: C–F.
- Hydrogen bonds occur when H is directly bonded to N, O, or F.
- Ionic bonds form by electron transfer, resulting in attraction between cations (positive ions) and anions (negative ions).
Alkanes, Alkenes, and Alkynes
- Alkanes: saturated hydrocarbons (CnH2n+2); examples: methane (CH4), ethane (C2H6), propane (C3H8).
- Alkenes: contain at least one double bond; example: ethene (C2H4).
- Alkynes: contain at least one triple bond; example: ethyne (C2H2).
- Alkanes are saturated; alkenes and alkynes are unsaturated.
Bond Lengths, Strengths & Types
- Single bonds > double bonds > triple bonds in length (longest to shortest).
- Triple bond is the strongest, single bond the weakest; easier to break fewer bonds.
- Single bond: 1 sigma bond; double: 1 sigma + 1 pi; triple: 1 sigma + 2 pi.
- Sigma bonds are stronger than pi bonds.
Hybridization and Bond Order
- sp3: 4 groups/attachments; sp2: 3 groups; sp: 2 groups.
- Bond order: single = 1, double = 2, triple = 3.
- Bond hybridization is determined by attached groups and lone pairs.
Formal Charge and Electron Counting
- Formal charge = valence electrons − (bonds + dots/lone electrons).
- Examples: carbocation (+1), carbanion (–1), radicals (odd electrons).
- Bonding electrons: 2 per bond; nonbonding: 2 per lone pair.
Functional Groups and Structure Drawing
- Alcohol: OH group (ethanol).
- Aldehyde: terminal carbonyl (CHO, ethanal).
- Ketone: internal carbonyl (propanone/acetone).
- Ether: oxygen between carbons (dimethyl ether).
- Ester: COO group (methyl ethanoate).
- Carboxylic acid: COOH group (pentanoic acid).
- Methyl (CH3) groups usually at ends; CH2 in the middle; CH groups often branch with special attachments.
Key Terms & Definitions
- Covalent Bond — electron-sharing bond (equal or unequal).
- Ionic Bond — bond formed by electron transfer and attraction of oppositely charged ions.
- Sigma Bond — single, strong bond along the internuclear axis.
- Pi Bond — side-to-side overlap; found in double/triple bonds.
- Hybridization — mixing of atomic orbitals to form new orbitals (sp, sp2, sp3).
- Formal Charge — calculated charge on an atom within a structure.
- Functional Group — specific atom/group providing characteristic reactivity.
Action Items / Next Steps
- Memorize common functional groups and alkane names (up to 10 carbons).
- Practice drawing and expanding condensed organic structures.
- Review how to assign formal charges and hybridizations.
- Suggested: search for "organic chemistry playlist" for more examples and topics.