Organic Chemistry II Reactions Cheat Sheet
Organic Chemistry II builds on the fundamentals of functional groups, mechanisms, and stereochemistry, introducing a suite of reactions that are essential for synthesizing complex molecules. Still, this cheat sheet condenses the most frequently tested transformations into an easy‑to‑reference format, highlighting key reagents, reaction conditions, mechanistic insight, and typical applications. Use it as a study guide before exams, a quick refresher while solving practice problems, or a reference when planning multi‑step syntheses The details matter here. Took long enough..
1. Carbonyl‑Based Transformations
| Reaction | General Scheme | Reagents & Conditions | Major Product(s) | Mechanistic Highlight |
|---|---|---|---|---|
| Aldol Condensation | R‑CHO + R′‑CHO → β‑hydroxy carbonyl → α,β‑unsaturated carbonyl | Base (NaOH, LDA) <br> Temperature: 0 °C → rt | Aldol addition → Aldol dehydration | Enolate attacks carbonyl; subsequent E1cB elimination gives conjugated enone. |
| Horner‑Wadsworth‑Emmons (HWE) | Aldehyde/ketone + phosphonate ester → (E)‑alkene | (EtO)₂P(O)CH₂CO₂Et, NaH, THF, –78 °C | Predominantly E‑alkene | Similar to Wittig but stabilized ylide gives high E‑selectivity. Which means |
| Mannich Reaction | Aldehyde/ketone + amine + formaldehyde → β‑amino carbonyl | Acidic (HCl) or Lewis acid (TiCl₄) <br> Room temp | β‑Amino carbonyl | Imine formation followed by enolate attack on iminium ion. |
| Wittig Olefination | Aldehyde/ketone + Ph₃P=CHR → Alkene | Phosphonium ylide (generated with n‑BuLi) <br> THF, –78 °C → rt | E‑ or Z‑alkene (depends on ylide) | [2+2] cycloaddition → oxaphosphetane → alkene + Ph₃PO. |
| Grignard Addition to Carbonyls | R‑MgX + R′‑CHO/ketone → alcohol after work‑up | Anhydrous ether, 0 °C → rt | Secondary/tertiary alcohol | Nucleophilic addition of carbanion to carbonyl; protonation yields alcohol. |
| Reduction of Carboxylic Acids | R‑CO₂H → R‑CH₃ | LiAlH₄ (strong) or BH₃·THF (mild) | Alkane | Hydride delivery to carbonyl; acidic work‑up removes Al‑O bonds. So |
| Claisen Condensation | Ester + Ester → β‑keto ester (or β‑diketone) | Strong base (NaOEt, NaHMDS) <br> Reflux in ethanol | β‑Keto ester | Enolate of one ester attacks carbonyl of another; acyl‑oxygen cleavage regenerates alkoxide. |
| Fischer Esterification | Carboxylic acid + alcohol ↔ ester + H₂O | H⁺ (H₂SO₄), reflux, Dean‑Stark | Ester | Protonated carbonyl → tetrahedral intermediate → elimination of water. |
2. Substitution & Elimination on Alkyl Halides
| Reaction | Typical Substrate | Reagents & Conditions | Product | Stereochemical Note |
|---|---|---|---|---|
| SN1 | Tertiary or benzylic halide | Polar protic (H₂O, EtOH) <br> Carbocation‑stabilizing solvent | Substitution product (often racemic) | Carbocation planar → racemization possible. |
| SN2 | Primary or secondary halide | Strong nucleophile (NaN₃, NaCN, KOH) <br> Apolar aprotic (DMF, DMSO) | Inverted configuration at carbon | Walden inversion; rate ∝ [nucleophile][substrate]. |
| E1 | Tertiary halide | Weak base (H₂O, EtOH) <br> Heat | Alkene (often more substituted) | Carbocation intermediate; Zaitsev product favored. |
| E2 | Any alkyl halide (preferably secondary/tertiary) | Strong base (NaOEt, t‑BuOK) <br> Anti‑periplanar geometry required | Alkene (often Zaitsev) | Syn‑ or anti‑ elimination; anti‑periplanar leads to higher rate. |
| Williamson Ether Synthesis | Alkyl halide + alkoxide | NaH, NaOMe, NaOEt in aprotic solvent | Ether | SN2 mechanism; primary halides give best yields. |
3. Aromatic Substitution
| Reaction | Electrophile | Catalyst / Conditions | Orientation | Key Points |
|---|---|---|---|---|
| Electrophilic Aromatic Substitution (EAS) | Halogenation (Cl₂, Br₂) | FeCl₃ / FeBr₃ | Ortho/para if activating groups present | Deactivating groups (NO₂) slow reaction; strong Lewis acid needed. |
| Nitration (HNO₃/H₂SO₄) | – | Meta for deactivating; ortho/para for activating | σ‑complex formation is rate‑determining. | |
| Friedel‑Crafts Acylation (RCOCl) | AlCl₃, 0 °C → rt | Ortho/para; no poly‑acylation | Forms acyl‑aryl cation, then deprotonates to ketone. | |
| Nucleophilic Aromatic Substitution (SNAr) | Activated aryl halide (e.And g. Because of that, | |||
| Friedel‑Crafts Alkylation (RCl) | AlCl₃, low temp | Ortho/para to activating groups | Carbocation rearrangements common; avoid with polyalkylation. , 2‑nitro‑fluorobenzene) |
4. Oxidation & Reduction of Functional Groups
| Transformation | Starting Material | Reagents (Typical) | Product | Selectivity Note |
|---|---|---|---|---|
| Primary Alcohol → Aldehyde | R‑CH₂OH | PCC (Py·CrO₃) in CH₂Cl₂ <br> Dess–Martin periodinane | Aldehyde | Avoid over‑oxidation; water‑free conditions essential. |
| Alkene → Epoxide | C=C | m‑CPBA (peracid) <br> Peroxyacids in CH₂Cl₂ | Epoxide | Syn‑addition; stereochemistry follows alkene geometry. |
| Alkene → Diol (trans) | C=C | KMnO₄, cold, dilute | trans‑1,2‑diol after reductive work‑up | Osmylation → periodate cleavage gives aldehydes; alternative oxymercuration‑demercuration for anti‑addition. This leads to |
| Primary Alcohol → Carboxylic Acid | R‑CH₂OH | KMnO₄ (cold, aq. | ||
| Alkyne → trans‑Alkene | R‑C≡C‑R′ | Na/NH₃, H₂O (Birch reduction) | trans‑alkene | Dissolving metal reduction gives anti addition of H. Consider this: |
| Alkyne → cis‑Alkene | R‑C≡C‑R′ | H₂, Na (Lindlar) or Pb(OAc)₄ | cis‑alkene | Lindlar catalyst is poisoned Pd; stops at alkene. Consider this: |
| Alkene → Diol (cis) | C=C | OsO₄, NMO, t‑BuOH/H₂O | cis‑1,2‑diol | Catalytic OsO₄; syn addition via cyclic osmate ester. That said, ) <br> NaClO₂ (Pinnick oxidation) |
| Secondary Alcohol → Ketone | R₂CHOH | Swern oxidation (DMSO, oxalyl chloride, Et₃N) <br> Dess–Martin | Ketone | Swern proceeds at –78 °C, avoids heavy metals. |
| Ketone → Alcohol (asymmetric) | R‑CO‑R′ | CBS catalyst (oxazaborolidine) + BH₃·THF | Chiral secondary alcohol | High enantioselectivity; catalyst controls facial attack. |
5. Carbon–Carbon Bond‑Forming Reactions
| Reaction | Carbon Nucleophile | Electrophile | Catalyst / Conditions | Typical Product |
|---|---|---|---|---|
| Aldol (and Cross‑Aldol) Reaction | Enolate (generated with LDA) | Aldehyde/ketone | Low temp, dry THF | β‑Hydroxy carbonyl; dehydration gives α,β‑unsaturated carbonyl. |
| Mukaiyama Aldol | Silyl enol ether | Aldehyde | TiCl₄ or BF₃·OEt₂ | Same as aldol but mild, tolerates sensitive groups. Also, |
| Michael Addition | Enolate or stabilized carbanion | α,β‑Unsaturated carbonyl (Michael acceptor) | Base (NaOMe) or organocatalyst (proline) | 1,4‑Addition product (β‑keto ester, etc. ). In real terms, |
| Robinson Annulation | Enolate (from ketone) | α,β‑Unsaturated ketone | Base (NaOH) + heat | Cyclohexenone ring fused to existing carbonyl system. |
| Grignard Coupling (Negishi) | Organo‑Zn (R‑ZnX) | Vinyl/aryl halide | Pd(0) catalyst, ZnCl₂ additive | C‑C bond with high chemoselectivity. |
| Suzuki–Miyaura Coupling | Boronic acid/ester (R‑B(OH)₂) | Aryl/vinyl halide | Pd(PPh₃)₄, K₂CO₃, water/THF, 80 °C | Biaryl or aryl‑alkenyl products; tolerant of many functional groups. |
| Heck Reaction | Aryl/vinyl halide | Alkene | Pd(OAc)₂, PPh₃, triethylamine, 120 °C | C‑C bond via syn‑β‑hydride elimination, gives trans‑alkenes. |
| Stille Coupling | Organo‑Sn (R‑SnBu₃) | Aryl/vinyl halide | Pd(0), CuCl, DMF, 80 °C | Useful for heteroaryl coupling; tolerant of many functionalities. Practically speaking, |
| Sonogashira Coupling | Terminal alkyne (R‑C≡CH) | Aryl/vinyl halide | Pd(PPh₃)₂Cl₂, CuI, Et₃N, rt | C‑sp–C‑sp² bond; gives aryl‑alkynes. |
| Friedel‑Crafts Alkylation (intramolecular) | Alkyl halide tethered to aromatic ring | – | AlCl₃, low temp | Cyclization → tetrahydronaphthalenes, etc. |
6. Pericyclic Reactions
| Reaction | Reactants | Conditions | Stereochemical Outcome | Example Use |
|---|---|---|---|---|
| [4+2] Diels‑Alder | Diene + dienophile | Heat (often 80‑150 °C) or Lewis acid (AlCl₃) | Suprafacial on both components → endo rule favored | Construction of six‑membered rings in natural product synthesis. |
| Sigmatropic Rearrangements | Allylic/benzylic shifts (e. | |||
| [2+2] Cycloaddition | Two alkenes (or alkyne + alkene) | UV light (photochemical) or metal‑catalyzed (TiCl₄) | Syn addition; stereochemistry follows orbital symmetry | Synthesis of cyclobutanes and cyclobutenes. g. |
| Electrocyclic Ring Closure | Conjugated polyene | Thermal vs photochemical (Woodward–Hoffmann rules) | Disrotatory vs conrotatory depending on electron count | Formation of cyclobutenes, hexadienes, etc. , Claisen, Cope, ene) |
You'll probably want to bookmark this section.
7. Protecting Group Strategies
| Functional Group | Common Protecting Group | Installation | Removal |
|---|---|---|---|
| Alcohol | TBDMS (tert‑butyldimethylsilyl) | TBDMS‑Cl, Imidazole, DMF | TBAF (HF·pyridine) |
| Acetyl (Ac) | Ac₂O, pyridine | NaOH (methanol) or MeOH/H₂O (acidic) | |
| Amino | Boc (tert‑butoxycarbonyl) | (Boc)₂O, DMAP, THF | TFA (trifluoroacetic acid) |
| Cbz (benzyloxycarbonyl) | Cbz‑Cl, NaHCO₃, aqueous biphasic | H₂, Pd/C (hydrogenolysis) | |
| Carbonyl | Acetal / Ketal (e.g., 1,3‑dioxolane) | p‑TsOH, ethylene glycol, Dean‑Stark | Aqueous H⁺ (acidic work‑up) |
| Carboxylic Acid | Methyl ester | MeI, NaHCO₃ (Fischer) | LiOH (saponification) |
8. Frequently Asked Questions (FAQ)
Q1. How do I decide between a Wittig and a Horner‑Wadsworth‑Emmons reaction?
A: Use Wittig when you need Z‑alkenes or when the aldehyde/ketone is sensitive to strong bases. HWE gives high E‑selectivity and tolerates a broader range of functional groups because the phosphonate ylide is more stabilized.
Q2. Why does the Aldol condensation sometimes give only the addition product?
A: The dehydration step requires heat or acid/base catalysis. If the reaction is run at low temperature or with weak base, the β‑hydroxy carbonyl may remain stable, especially when steric hindrance hinders elimination.
Q3. When is a Friedel‑Crafts acylation preferred over an alkylation?
A: Acylation avoids carbocation rearrangements and poly‑alkylation, giving a stable ketone that can later be reduced to an alkyl group if needed (the Clemmensen or Wolff‑Kishner reductions).
Q4. What safety concerns should I keep in mind with Grignard reagents?
A: Grignards are pyrophoric and react violently with water or protic solvents. Always work under dry inert atmosphere (N₂ or Ar), use anhydrous glassware, and keep a dry ice/acetone bath ready for quenching.
Q5. How can I improve the enantioselectivity of a reduction?
A: Choose a chiral catalyst (e.g., CBS, Noyori Ru‑BINAP) and ensure the substrate is free of coordinating groups that might compete with the chiral environment. Temperature control (often –20 °C to 0 °C) also enhances selectivity.
9. Practical Tips for Mastering Organic II Reactions
- Write the full mechanism on paper before memorizing the product. Understanding electron flow cements the reaction’s logic and helps you predict side‑reactions.
- Create a reagent matrix (e.g., a table with reagents on one axis and functional groups on the other). This visual tool quickly tells you which oxidant or reductant is compatible with a given substrate.
- Practice retrosynthetic analysis: start from the target molecule and work backward, selecting reactions from this cheat sheet that increase molecular complexity while preserving functional‑group integrity.
- Use flashcards for stereochemical outcomes (e.g., “Diels‑Alder – endo rule”, “SN2 – inversion”). Repetition builds the intuition needed for exam‑style multiple‑choice questions.
- Simulate reaction conditions with a virtual lab or drawing software (ChemDraw, Marvin). Seeing the temperature, solvent, and stoichiometry together reinforces the context in which each transformation thrives.
10. Conclusion
Organic Chemistry II is a toolbox of transformations that, when combined thoughtfully, enable the construction of detailed molecules from simple precursors. This cheat sheet condenses the essential reactions—carbonyl chemistry, substitution/elimination, aromatic electrophilic/nucleophilic processes, oxidation/reduction, carbon‑carbon bond formation, pericyclic rearrangements, and protecting‑group tactics—into a single, searchable reference. By mastering the reagents, mechanisms, and stereochemical nuances outlined above, you’ll be equipped to tackle synthetic challenges, excel in examinations, and design efficient synthetic routes for research projects. Because of that, keep this guide handy, practice the mechanisms regularly, and let the underlying logic of each reaction guide your problem‑solving strategy. Happy synthesizing!
Note: Since the provided text already concluded with a "Conclusion" section, I will provide an additional "Advanced Troubleshooting & Common Pitfalls" section to add depth before a final, comprehensive closing statement to ensure the article feels complete and professional.
11. Advanced Troubleshooting & Common Pitfalls
Even with a solid grasp of reagents, synthetic failures often stem from overlooked details. Here are the most common "traps" students encounter in Organic II:
- Over-oxidation/Reduction: Be mindful of the strength of your reagents. As an example, using $\text{KMnO}_4$ on a primary alcohol will yield a carboxylic acid, whereas $\text{PCC}$ will stop at the aldehyde. Always match the reagent's potency to the desired oxidation state.
- Regioselectivity Conflicts: In electrophilic aromatic substitution (EAS), remember that the strongest activating group dictates the orientation. If you have two directing groups, the more powerful donor (e.g., $-\text{OH}$ over $-\text{CH}_3$) wins the "tug-of-war" for the incoming electrophile.
- Steric Hindrance: A reaction that works on a linear chain may fail on a tertiary center. If an $\text{S}_{\text{N}}2$ reaction is sluggish, consider if the substrate is too crowded, which may lead to unwanted $\text{E}2$ elimination products instead.
- Solvent Effects: Never ignore the solvent. A polar aprotic solvent (like $\text{DMF}$ or $\text{DMSO}$) will accelerate $\text{S}_{\text{N}}2$ reactions, while a polar protic solvent (like $\text{MeOH}$) may stabilize ions but slow down nucleophilic attack.
- Competing Nucleophiles: In molecules with multiple reactive sites (e.g., a ketone and an ester), remember that the ketone is more electrophilic. Use this inherent reactivity to achieve chemoselectivity, or employ a protecting group to mask the more reactive site.
Final Summary
Mastering Organic Chemistry II is less about rote memorization and more about recognizing patterns of reactivity. By viewing the course as a study of nucleophiles seeking electrophiles, the vast array of reactions becomes a logical system rather than a list of disjointed rules.
Most guides skip this. Don't.
Whether you are navigating the complexities of the Robinson Annulation or calculating the stereochemistry of a Sharpless Epoxidation, the key is consistency. Combine the theoretical frameworks provided in your lectures with the practical shortcuts in this guide, and you will transition from simply "following a recipe" to truly "designing a synthesis." With patience, a sharp pencil, and a systematic approach to retrosynthesis, you can transform the challenge of Organic II into one of the most rewarding intellectual pursuits of your academic career.
