Organic Chemistry Reactions and Mechanisms Flashcards

Comprehensive vocabulary flashcards covering alkene reactions, alkyne reactions, substitution and elimination pathways, leaving group conversions, oxidation/reduction reagents, and ether/epoxide chemistry.

$\text{HCl}$ (cold) Addition to Alkenes

Reaction: Alkene + $\text{HCl} \rightarrow$ alkyl chloride. Regiochemistry: Markovnikov. Stereochemistry: Not stereospecific. Notes: Involves carbocation intermediate; rearrangements possible.

$\text{HBr}$ (normal conditions) Addition to Alkenes

Regiochemistry: Markovnikov. Stereochemistry: Not stereospecific. Notes: Involves carbocation intermediate; rearrangements possible.

$\text{HBr}$ (ROOR / peroxides) Addition to Alkenes

Regiochemistry: Anti-Markovnikov. Stereochemistry: Radical mechanism. Notes: ONLY $\text{HBr}$ does the peroxide effect.

$\text{Br}_2$ (dark, no water) Addition to Alkenes

Product: Vicinal dibromide. Stereochemistry: Anti addition. Regiochemistry: N/A. Notes: Bromonium ion intermediate.

$\text{Br}_2 / \text{H}_2\text{O}$ (Halohydrin Formation)

Product: $\text{Br}$ and $\text{OH}$. Regiochemistry: $\text{OH}$ to MORE substituted carbon. Stereochemistry: Anti. Notes: Bromonium intermediate followed by water attack.

mCPBA / peroxyacid Epoxidation

Product: Epoxide. Stereochemistry: Syn. Notes: Stereospecific (cis $\rightarrow$ cis epoxide; trans $\rightarrow$ trans).

$\text{OsO}_4$ Dihydroxylation

Product: Cis diol. Stereochemistry: Syn. Notes: Often with NMO co-oxidant.

$\text{KMnO}_4$ (cold, dilute) Dihydroxylation

Product: Cis diol. Stereochemistry: Syn. Notes: Weaker $\text{OsO}_4$ mimic.

$\text{HIO}_4$ Cleavage

Product: Carbonyl cleavage of 1,2-diols. Notes: Cleaves the $\text{C}-\text{C}$ bond.

$\text{O}_3$ then $\text{Zn}/\text{H}_2\text{O}$ (reductive ozonolysis)

Product: Aldehydes + ketones. Notes: "Normal ozonolysis."

$\text{O}_3$ then $\text{H}_2\text{O}$ (oxidative ozonolysis)

Product: Carboxylic acids. Notes: Stronger workup.

$\text{H}_2$ + metal catalyst (Pd/C) Hydrogenation

Product: Alkane. Stereochemistry: Syn. Notes: Fully reduces double bond.

$\text{CH}_3\text{OH}$ / acid Addition to Alkenes

Product: Markovnikov ether. Stereochemistry: Not stereospecific.

Acid-Catalyzed Hydration ($\text{H}_3\text{O}^+$)

Regiochemistry: Markovnikov. Stereochemistry: Nonspecific. Notes: Rearrangements possible.

Hydroboration-Oxidation ($\text{BH}_3/\text{THF} \rightarrow \text{H}_2\text{O}_2/\text{NaOH}$)

Product: Alcohol. Regiochemistry: Anti-Markovnikov. Stereochemistry: Syn. Notes: No rearrangements.

$\text{NaNH}_2$ (1 equivalent)

Function: Deprotonates terminal alkyne $\rightarrow$ acetylide ion.

$\text{NaNH}_2$ (3 eq) + heat

Function: Double elimination $\rightarrow$ forms terminal alkyne from dihalide.

Lindlar's Catalyst ($\text{H}_2$, Lindlar)

Product: CIS alkene. Notes: Stops at alkene.

$\text{Na} / \text{NH}_3$ (liquid ammonia)

Product: TRANS alkene. Notes: Radical anion mechanism.

$\text{HBr}$ (1 equivalent) Addition to Alkynes

Product: Vinyl bromide. Regiochemistry: Markovnikov. Notes: Adds across triple bond.

$\text{HBr}$ (excess) Addition to Alkynes

Product: Dibromide (geminal or vicinal). Notes: Markovnikov still applies.

$\text{HBr} / \text{peroxides}$ Addition to Alkynes

Regiochemistry: Anti-Markovnikov. Notes: Radical; polymerization danger.

$\text{H}_2\text{SO}_4, \text{H}_2\text{O}, \text{HgSO}_4$ (alkyne hydration)

Product: Ketone. Regiochemistry: Markovnikov. Notes: Via enol $\rightarrow$ tautomer.

$\text{BH}_3/\text{THF} \rightarrow \text{H}_2\text{O}_2, \text{NaOH}$ (alkyne hydroboration-oxidation)

Product: Aldehyde (terminal) or ketone (internal). Regiochemistry: Anti-Markovnikov. Notes: Always tautomerization.

Ozonolysis of Alkynes ($\text{O}_3 \rightarrow \text{H}_2\text{O}$)

Product: Carboxylic acids. Notes: Always oxidative with alkynes.

$\text{S}_\text{N}2$ Requirements

Substrate: Primary > secondary. Nucleophile: Strong, small. Solvent: Polar aprotic. Stereochemistry: Inversion. Notes: NEVER tertiary.

$\text{S}_\text{N}1$ Requirements

Substrate: Tertiary > secondary. Nucleophile: Weak. Solvent: Polar protic. Stereochemistry: Racemic mixture. Notes: Carbocation rearrangements.

E2 Requirements

Base: Strong. Geometry: Anti-periplanar. Substrate: Any, but fastest with tertiary. Notes: One-step mechanism.

E1 Requirements

Requirements: Same as $\text{S}_\text{N}1$ but with heat. Product: Zaitsev alkene. Stereochemistry: Nonspecific.

Common $\text{S}_\text{N}2$ Nucleophiles

$\text{NaCN}$, $\text{NaN}_3$, $\text{LiSCH}_3$, $\text{CH}_3\text{O}^-$, $\text{EtO}^-$, and $\text{NaI (acetone)}$.

Common E2 Bases

$\text{t-BuOK}$, $\text{NaOEt} + \text{heat}$, $\text{NaH}$, and $\text{KOC}(\text{CH}_3)_3$.

Substitution & Elimination Competition: Primary Substrates

$\text{S}_\text{N}2 > \text{E}2$.

Substitution & Elimination Competition: Secondary Substrates

$\text{S}_\text{N}2$ vs $\text{E}2$ vs $\text{S}_\text{N}1$ (depends on reaction conditions).

Substitution & Elimination Competition: Tertiary Substrates

Yields E2 with a strong base, or $\text{S}_\text{N}1/\text{E}1$ with weak species.

$\text{SOCl}_2$ + pyridine

Product: Alkyl chloride. Stereochemistry: Inversion. Mechanism: $\text{S}_\text{N}2$ at sulfur $\rightarrow$ backside attack on carbon.

$$\text{PBr}_3$$

Product: Alkyl bromide. Stereochemistry: Inversion. Good for: Primary/secondary alcohols only.

Mesyl Chloride (MsCl; $\text{CH}_3\text{SO}_2\text{Cl}$, pyridine)

Product: OMs (great leaving group). Stereochemistry: Retention. Notes: Second $\text{S}_\text{N}2 =$ inversion overall.

TsCl / pyridine

Product: OTs. Stereochemistry: Retention. Notes: Then $\text{S}_\text{N}2$ inverts.

$\text{HBr} / \text{HX}$ on Alcohols

Product: Alkyl halide. Primary alcohols react via $\text{S}_\text{N}2$; tertiary alcohols react via $\text{S}_\text{N}1$ (rearrangements).

$$\text{PCC} + \text{CH}_2\text{Cl}_2$$

Converts primary alcohol $\rightarrow$ aldehyde; secondary alcohol $\rightarrow$ ketone. No overoxidation.

Jones Reagent ($\text{CrO}_3 / \text{H}_2\text{SO}_4; \text{Na}_2\text{Cr}_2\text{O}_7$)

Converts primary alcohol $\rightarrow$ carboxylic acid; secondary alcohol $\rightarrow$ ketone.

$$\text{LiAlH}_4$$

Reduces EVERYTHING: Esters $\rightarrow$ 2 alcohols; Carboxylic acids $\rightarrow$ alcohols; Epoxides $\rightarrow$ opens least substituted.

$$\text{NaBH}_4$$

Reduces G only.

Keto-Enol Tautomerization

Equilibrium that always ends as ketone (more stable).

$$\text{H}_2 / \text{Pt}$$

Complete reduction: Alkene/alkyne $\rightarrow$ alkane.

Williamson Ether Synthesis

Reactants: Alkoxide + primary alkyl halide. Mechanism: $\text{S}_\text{N}2$. Stereochemistry: Inversion at carbon.

tert-Butyl Ether Formation

Formed by using isobutene + methanol (acid) OR tert-butoxide + alkyl halide (primary only).

Halohydrin Formation

Regiochemistry: $\text{OH}$ to more substituted carbon. Stereochemistry: Anti. Mechanism: Bromonium ion.

Halohydrin $\rightarrow$ Epoxide Conversion

Base deprotonates $\text{OH} \rightarrow$ intramolecular $\text{S}_\text{N}2$. Stereochemistry: Inversion at attacked carbon (cis halohydrin $\rightarrow$ trans epoxide; trans $\rightarrow$ cis epoxide).

Epoxide Opening (Basic Conditions)

Attacks least substituted carbon with inversion of stereochemistry.

Epoxide Opening (Acidic Conditions)

Protonate epoxide $\rightarrow$ attack more substituted carbon with inversion of stereochemistry.

$\text{CH}_3\text{O}^-, \text{EtO}^-$ on Epoxides

Always attack least substituted carbon with inversion. Product: Alcohol.

Grignard on Epoxides

Attacks least substituted carbon with inversion. Product: Extended alcohol.

$\text{LiAlH}_4$ on Epoxides

$\text{H}^-$ attacks least substituted carbon with inversion. Product: Alcohol.

Ether Cleavage by $\text{HI}$ or $\text{HBr}$

Mechanism: $\text{S}_\text{N}1/\text{S}_\text{N}2$ depending on structure (Primary: $\text{S}_\text{N}2$ where halide attacks carbon; Tertiary: $\text{S}_\text{N}1$). Product: Alkyl halides + alcohols.