Organic Chemistry Reaction Mechanisms of Aliphatic Compounds Syllabus

Reaction Mechanisms of Aliphatic Compounds syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Reaction Mechanisms of Aliphatic Compounds in Organic Chemistry, not a summary of it.

1. 1

   Introduction to Organic Reactions

   4 topics

   • Reaction Types and Classification
   • Bond Homolysis and Heterolysis
   • Thermodynamics and Kinetics
   • Carbocation, Carbanion, and Radical Intermediates
2. 2

   Nucleophilic Substitution

   4 topics

   • SN2 Mechanism
   • SN1 Mechanism
   • Leaving Group Ability
   • SN1 vs SN2 Predictions
3. 3

   Elimination Reactions

   3 topics

   • E2 Mechanism
   • E1 Mechanism
   • Substitution vs Elimination Competition
4. 4

   Free Radical Reactions

   3 topics

   • Radical Halogenation of Alkanes
   • Allylic and Benzylic Halogenation
   • Radical Polymerization

Reaction Mechanisms of Aliphatic Compounds flashcards for Organic Chemistry

18 of 50 cards from the Reaction Mechanisms of Aliphatic Compounds deck — real questions with worked answers.

1. What are the four broad reaction types used to classify organic reactions?

   Substitution (one group replaces another), Addition (two groups add across a $\pi$ bond), Elimination (two groups are lost to form a $\pi$ bond), and Rearrangement (atoms within a molecule reorganize).

2. Distinguish a nucleophile from an electrophile in terms of electron density.

   A nucleophile is electron-rich and donates an electron pair (a Lewis base, e.g. $\ce{OH^-}$, $\ce{NH3}$); an electrophile is electron-poor and accepts an electron pair (a Lewis acid, e.g. $\ce{H^+}$, carbocations).

3. What is bond homolysis, and what species does it produce?

   Homolysis is symmetric bond cleavage in which each atom keeps one electron of the shared pair, producing two neutral free radicals: $\ce{A-B -> A^{.} + B^{.}}$.

4. What is bond heterolysis, and what species does it produce?

   Heterolysis is asymmetric bond cleavage in which one atom takes both electrons, producing oppositely charged ions: $\ce{A-B -> A^+ + B^-}$.

5. How is curved-arrow notation used differently for homolytic versus heterolytic processes?

   A full (double-barbed) arrow shows movement of an electron pair (heterolytic/polar); a single-barbed (fishhook) arrow shows movement of a single electron (homolytic/radical).

6. Write the Gibbs free energy relation that determines whether a reaction is thermodynamically favorable.

   $$\Delta G = \Delta H - T\Delta S$$ A reaction is spontaneous (favorable) when $\Delta G < 0$.

7. How does $\Delta G^{\circ}$ relate to the equilibrium constant $K_{eq}$?

   $$\Delta G^{\circ} = -RT\ln K_{eq}$$ A negative $\Delta G^{\circ}$ gives $K_{eq} > 1$, favoring products.

8. What is the difference between thermodynamic and kinetic control of a reaction?

   Thermodynamic control favors the most stable (lowest-$G$) product, typically at higher temperature/longer times; kinetic control favors the product formed fastest (lowest activation energy $E_a$), typically at lower temperature.

9. Define the activation energy $E_a$ and state its relationship to reaction rate.

   $E_a$ is the minimum energy needed to reach the transition state. A higher $E_a$ means a slower rate; the Arrhenius equation gives $k = A e^{-E_a/RT}$.

10. What is the Hammond postulate?

    The structure of a transition state resembles the species (reactant or product) nearest to it in energy. For endothermic steps the TS is 'late' (product-like); for exothermic steps it is 'early' (reactant-like).

11. What is a transition state versus a reaction intermediate?

    A transition state is an energy maximum on the reaction coordinate (cannot be isolated); an intermediate sits in an energy well (local minimum) between two transition states and has a finite lifetime.

12. Rank the stability of carbocations by substitution and give the geometry.

    Stability: $\text{methyl} < \text{1}^{\circ} < \text{2}^{\circ} < \text{3}^{\circ}$ (stabilized by hyperconjugation and induction). Carbocations are $sp^{2}$-hybridized and trigonal planar with an empty $p$ orbital.

13. Rank the stability of carbanions by substitution and give the geometry.

    Stability: $\text{3}^{\circ} < \text{2}^{\circ} < \text{1}^{\circ} < \text{methyl}$ (opposite to carbocations; alkyl groups destabilize the negative charge). Carbanions are roughly $sp^{3}$ and pyramidal with a lone pair.

14. Rank the stability of carbon radicals by substitution and give the geometry.

    Stability: $\text{methyl} < \text{1}^{\circ} < \text{2}^{\circ} < \text{3}^{\circ}$ (same order as carbocations, stabilized by hyperconjugation). Radicals are roughly planar/$sp^{2}$ with one unpaired electron.

15. How do resonance-stabilized allylic and benzylic intermediates compare in stability to simple alkyl analogues?

    Allylic and benzylic carbocations, radicals, and carbanions are more stable than comparable simple alkyl species because the charge or unpaired electron is delocalized over a $\pi$ system by resonance.

16. Describe the mechanism and molecularity of the $S_N2$ reaction.

    A concerted, one-step bimolecular reaction: the nucleophile attacks the carbon backside relative to the leaving group, passing through a single trigonal-bipyramidal transition state as the leaving group departs.

17. Write the rate law for an $S_N2$ reaction.

    $$\text{rate} = k[\text{substrate}][\text{nucleophile}]$$ It is second order overall (first order in each).

18. What stereochemical outcome characterizes the $S_N2$ reaction?

    Inversion of configuration at the stereocenter (Walden inversion) — the nucleophile enters opposite the leaving group, turning the carbon 'inside-out'.

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