OAT Organic Chemistry 5

Question 1

Which of the following correctly describes the relationship between enthalpy of combustion and molecular structure for straight-chain alkanes?

Accepted Answer

Enthalpy of combustion increases as chain length increases.

Answer

Each additional CH2 unit contributes approximately 659 kJ/mol to the enthalpy of combustion, so longer chains release more energy.

Question 2

Which type of reaction converts an alkyl halide into an alkene by treatment with a strong, bulky base such as KOtBu?

Accepted Answer

E2

Answer

Bulky bases favor E2 elimination because steric hindrance prevents the nucleophilic SN2 pathway.

Question 3

What is the term for the energy difference between reactants and the transition state in a reaction?

Accepted Answer

Activation energy (Ea)

Answer

Activation energy is the minimum energy required to reach the transition state and is the energy barrier of the reaction.

Question 4

Carboxylic acid derivatives in decreasing order of reactivity toward nucleophilic acyl substitution are:

Accepted Answer

Acid chloride > anhydride > ester > amide

Answer

Reactivity decreases as the leaving group ability decreases: Cl⁻ > RCOO⁻ > RO⁻ > NH2⁻.

Question 5

What product is formed when a primary amine reacts with excess methyl iodide followed by Ag2O/H2O and heat?

Accepted Answer

The least substituted alkene (Hofmann elimination product)

Answer

Hofmann exhaustive methylation converts a quaternary ammonium hydroxide to the least hindered alkene via elimination.

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