[I] When propene (C₃H₆) undergoes electrophilic addition with HBr, it forms 2-bromopropane as the major product. Explain why 2-bromopropane is favored over 1-bromopropane, using the concept of carbocation stability.
Markovnikov’s Rule
“The rich get richer”: Hydrogen adds to the carbon with more hydrogens
More stable 2° carbocation forms vs. less stable 1° carbocation
[II] Explain how inductive effects from alkyl groups stabilize carbocations in alkenes.
[III] Write down the structural formulas for 2-methylbutane and 2,2-dimethylpropane. (Quick Check 11.1)
Structural Formulas
2-methylbutane: C-C-C-C with methyl on 2nd carbon
2,2-dimethylpropane: Central carbon with 3 methyl groups
[IV] Eicosane is a straight chain alkane whose molecules contain 20 carbon atoms. What is the molecular formula of eicosane? (Quick Check 11.1)
Alkane General Formula
General formula: CₙH₂ₙ₊₂
For n=20: C₂₀H₄₂
[V] Why the order of stability of carbocation is 3° > 2° > 1°? (Quick Check 11.6)
[VI] How alkene react with an electrophile? (Quick Check 11.7)
[VII] Write the mechanism of heterolytic cleavage of H-Br.
Heterolytic Cleavage
H-Br → H⁺ + Br⁻
Both electrons go to bromine, forming ions
[VIII] How can we distinguish between different mechanisms using arrow notations?
[IX] What is meant by paraffins?
[X] Why do alkanes not participate in electrophilic or nucleophilic reactions?
[xi] Define substitution reaction with an example.
[xii] Write the propagation steps involved in the chlorination of methane.
Free Radical Mechanism
CH₄ + Cl· → CH₃· + HCl
CH₃· + Cl₂ → CH₃Cl + Cl·
[xiii] Name the first member of the alkene family.
[xiv] What is the shape of ethene molecule?