- **Alkanes**: Hydrocarbons only having C-C and C-H bonds - **Acyclic Alkanes**: $C_{n}H_{2n+2}$ Linear or branched chains of carbon atoms - **Cyclic Alkanes**: $C_{n}H_{2n}$ Carbon atoms form a ring/cycle - **Alkenes**: Hydrocarbons with one or more double bonds, can be linear or cyclic - **Alkynes**: Hydrocarbons with one or more triple bonds ### Alkenes - Strong, non-polar C-C and C-H σ bonds - Negligible electrophilic character (unless special substituents) - Relatively low acidity (pKa 40-45) - Relatively weak π bond (ca. 65 kcal/mol vs. 89 kcal/mol for σ bond) - Polarizable π electrons - moderate nucleophilic character - Eagerly reacts with strong electrophiles - Alkenes are stabilized by delocalization with adjacent π-bonds - Alkenes are stabilized by hyperconjugation (e.g., alkyl substitution) - Alkenes are destabilized by non-bonded interactions of cis-substituents - E alkenes are generally lower in energy than the corresponding Z isomers - Alkenes are destabilized by angle strain ### Alkynes - Strong C-C and C-H σ bonds - Negligible electrophilic character (unless special substituents) - Relatively weak π bond with polarizable π electrons - Moderate nucleophilic character - Eagerly reacts with strong electrophiles - Depending on mechanism, rate of addition may be faster (e.g., hydrogenation) or slower (e.g., HBr ionic addition, Br$_{2}$ addition) compared to alkenes - Relatively acidic proton (pKa = ca. 25) due to sp "orbital electronegativity" ### Alkanes