# Alkene & Alkyne Additions, Epoxide Opening & Oxidation–Reduction > 32 intermediate organic-chemistry review cards on regioselective and stereospecific alkene and alkyne additions—hydrohalogenation, radical HBr addition, hydration, oxymercuration, hydroboration–oxidation, halogenation, epoxidation and ring opening, dihydroxylation, ozonolysis, hydrogenation, dissolving-metal reduction—and alcohol oxidations. - **Canonical URL:** https://flashcards.world/flashcards/sets/53c9040d-93f4-4607-a498-be02557aedfb/ - **Markdown URL:** https://flashcards.world/flashcards/sets/53c9040d-93f4-4607-a498-be02557aedfb.md - **Level:** intermediate - **Languages:** en → en - **Total Cards:** 32 ## Flashcards (32 Cards) | # | Front (Term / Prompt) | Back (Definition / Answer) | Example | Multiple-Choice Options | | :--- | :--- | :--- | :--- | :--- | | 1 | What is the regiochemical outcome when an unsymmetrical alkene is treated with Br2 in water (halohydrin formation)? | The electrophilic bromine adds to the less substituted carbon, and water attacks the more substituted carbon (bearing more partial positive charge in the bromonium ion) with anti-stereochemistry. | | | | 2 | What stereochemical addition occurs during catalytic hydrogenation of alkenes over transition metal catalysts? | Syn-addition; both hydrogen atoms are simultaneously transferred from the metal catalyst surface (Pd/C, Pt, or Ni) to the same face of the alkene double bond. | | | | 3 | What limitation affects the acid-catalyzed hydration (H2SO4 / H2O) of alkenes? | The reaction proceeds through a free carbocation intermediate, which is prone to 1,2-hydride and 1,2-alkyl rearrangements, leading to rearranged alcohol mixtures. | | | | 4 | Why is N-bromosuccinimide (NBS) used for allylic bromination instead of elemental Br2? | NBS maintains a constant, trace concentration of Br2 in solution, preventing competing electrophilic addition across the double bond and favoring free-radical allylic substitution. | | | | 5 | What carbonyl compound is produced by mercury(II)-catalyzed hydration of a terminal alkyne? | HgSO4 and aqueous H2SO4 yield a Markovnikov enol with OH on the internal carbon, which rapidly tautomerizes into a methyl ketone. | | | | 6 | What is keto-enol tautomerism and which isomer is typically thermodynamically favored? | Tautomerism is a rapid constitutional isomerization involving relocation of a proton and a double bond; the keto form is overwhelmingly favored thermodynamically due to the high C=O bond strength (~745 kJ/mol). | | | | 7 | What reagents are employed in the Swern oxidation and what is its synthetic utility? | Oxalyl chloride (COCl)2, dimethyl sulfoxide (DMSO), and triethylamine (Et3N) at -78°C; it cleanly oxidizes primary alcohols to aldehydes and secondary alcohols to ketones under non-toxic, non-heavy-metal conditions. | | | | 8 | What dictates regioselectivity during base-catalyzed nucleophilic ring opening of unsymmetrical epoxides? | The strong nucleophile attacks via an SN2 pathway, displacing the epoxide oxygen at the less sterically hindered carbon with complete stereochemical inversion. | | | | 9 | Why is oxymercuration-demercuration preferred over acid-catalyzed hydration for synthesizing Markovnikov alcohols? | Electrophilic attack by Hg(OAc)+ forms a cyclic mercurinium ion that prevents carbocation rearrangements; water attacks the more substituted carbon, and NaBH4 reduces C-Hg to C-H. | | | | 10 | Why does Pyridinium Chlorochromate (PCC) oxidize primary alcohols to aldehydes without over-oxidation? | PCC is used in anhydrous dichloromethane (CH2Cl2); lacking water, the aldehyde cannot form a gem-diol intermediate required for secondary oxidation to a carboxylic acid. | | | | 11 | What products form when an alkyne is treated with 1 versus 2 equivalents of bromine (Br2)? | One equivalent yields predominantly the trans-1,2-dibromoalkene via anti-addition; two equivalents yield a 1,1,2,2-tetrabromoalkane. | | | | 12 | What fragments are produced by oxidative cleavage of alkynes using ozone or hot KMnO4? | Internal alkynes cleave into two carboxylic acids; terminal alkynes cleave into one carboxylic acid and carbon dioxide (CO2). | | | | 13 | What product results when an alkyne is treated with 2 equivalents of hydrogen bromide (HBr)? | A geminal dihalide (both bromines bonded to the same carbon) is produced with Markovnikov regiochemistry via resonance stabilization from the first halogen. | | | | 14 | What reagent is Dess-Martin Periodinane (DMP) and what does it oxidize? | DMP is a hypervalent iodine(V) reagent that rapidly oxidizes primary alcohols to aldehydes and secondary alcohols to ketones under mild, neutral room-temperature conditions. | | | | 15 | What carbonyl compound is produced by hydroboration-oxidation of a terminal alkyne? | Hydroboration of a terminal alkyne with a sterically hindered dialkylborane (such as disiamylborane [Sia2BH] or 9-BBN, which prevents a second hydroboration addition) followed by basic H2O2 oxidation forms an anti-Markovnikov terminal enol that rapidly tautomerizes to an aldehyde. | | | | 16 | Why does treating an alkene with HBr in the presence of peroxides (ROOR) yield anti-Markovnikov regiochemistry? | Peroxides (ROOR) under heat or light initiate a free-radical chain addition (specific to HBr) in which an electrophilic bromine radical (Br•) adds first to the less substituted alkene carbon to form the more stable, more substituted carbon radical intermediate, which then abstracts H• from HBr to give the anti-Markovnikov alkyl bromide. | | | | 17 | What reagents achieve syn-dihydroxylation of an alkene to form a 1,2-diol (glycol)? | Cold, dilute, basic potassium permanganate (KMnO4) or catalytic osmium tetroxide (OsO4) with N-methylmorpholine N-oxide (NMO), which form cyclic diester intermediates across one face. | | | | 18 | What intermediate explains the anti-stereospecific addition observed during alkene halogenation (Br2 or Cl2)? | Formation of a cyclic, three-membered halonium ion (bromonium or chloronium) intermediate forces the second halide to attack from the opposite face via backside displacement. | | | | 19 | What is Markovnikov's rule in electrophilic additions of HX to asymmetric alkenes? | The electrophilic proton adds to the less substituted carbon of the double bond to generate the more stable, more substituted carbocation intermediate before halide capture. | | | | 20 | How do products differ when alkene ozonolysis is followed by an oxidative workup (O3, then H2O2)? | Under oxidative ozonolysis (1. O3; 2. H2O2), monosubstituted (=CHR) alkene carbons are oxidized to carboxylic acids, unsubstituted terminal (=CH2) carbons are oxidized to carbon dioxide (CO2), and disubstituted (=CR2) carbons remain ketones. | | | | 21 | How do peroxyacids (such as mCPBA) react with alkenes to form epoxides? | Via a concerted, single-step 'butterfly' mechanism where electrophilic peroxy oxygen is transferred to the double bond, preserving the alkene's cis or trans stereochemistry in the oxirane ring. | | | | 22 | What cleavage products are generated from ozonolysis of an alkene with reductive workup (O3, then DMS or Zn/H2O)? | The carbon-carbon double bond is oxidatively cleaved into two carbonyl compounds: unsubstituted (=CH2) carbons yield formaldehyde (H2C=O), monosubstituted (=CHR) carbons yield aldehydes, and disubstituted (=CR2) carbons yield ketones. | | | | 23 | What dictates regioselectivity during acid-catalyzed ring opening of unsymmetrical epoxides in alcohol? | Under acidic conditions, protonation of the epoxide oxygen creates a positively charged oxiranium ion. If the more substituted carbon is tertiary (3°), allylic, or benzylic, substantial partial carbocation character (SN1-like transition state) directs the weak nucleophile (ROH or H2O) to attack that more substituted carbon with inversion of configuration; however, if the epoxide contains only primary (1°) and secondary (2°) carbons, steric effects often favor nucleophilic attack at the less hindered 1° carbon. | | | | 24 | What product is formed when a primary alcohol is reacted with Jones reagent (CrO3 / H2SO4 / H2O)? | The primary alcohol is oxidized first to an aldehyde, which hydrates to a gem-diol in water and is further oxidized completely into a carboxylic acid. | | | | 25 | How does dissolving metal reduction (Na or Li in liquid NH3) reduce internal alkynes? | It proceeds through radical-anion intermediates where trans-radical geometries minimize electron-electron repulsion, stereoselectively yielding trans (E) alkenes. | | | | 26 | What reagents constitute the Simmons-Smith cyclopropanation and what is its stereospecificity? | Diiodomethane (CH2I2) and a zinc-copper couple (Zn-Cu) generate a zinc carbenoid (ICH2ZnI) that transfers a methylene group to the alkene via concerted syn-addition with retention of configuration. | | | | 27 | How can an alkene be converted into an anti-1,2-diol stereospecifically? | By reacting the alkene with a peroxyacid (mCPBA) to synthesize an epoxide, followed by aqueous acid-catalyzed (H3O+) ring opening via backside attack. | | | | 28 | How is a terminal alkyne converted into a carbon nucleophile (acetylide anion)? | Treatment with a sufficiently strong base such as sodium amide (NaNH2, conjugate acid NH3 pKa ≈ 38) or an organolithium/Grignard reagent deprotonates the terminal sp-hybridized C–H bond (pKa ≈ 25) to generate a nucleophilic acetylide (alkynide) anion (whereas hydroxide or alkoxide bases, pKa ≈ 16–18, are too weak). | | | | 29 | What product is obtained when an alkyne undergoes catalytic hydrogenation with excess H2 over Pd/C? | Complete four-electron reduction directly to the corresponding alkane, as the intermediate alkene is typically more reactive toward hydrogenation than the starting alkyne. | | | | 30 | How does hydrogenation over Lindlar's catalyst reduce an internal alkyne stereoselectively? | Lindlar's catalyst (Pd poisoned with CaCO3 and lead acetate) partially reduces internal alkynes exclusively to cis (Z) alkenes via syn-addition of hydrogen. | | | | 31 | What reaction occurs when a sodium acetylide is treated with a primary versus a secondary or tertiary alkyl halide? | With a methyl or unhindered primary (1°) alkyl halide, the strongly nucleophilic acetylide anion undergoes SN2 backside substitution to form a new C–C bond and yield an internal alkyne; with a secondary (2°) or tertiary (3°) alkyl halide, the strongly basic acetylide instead promotes E2 elimination to give an alkene. | | | | 32 | What are the regiochemical and stereochemical outcomes of hydroboration-oxidation of alkenes? | Hydroboration-oxidation (1. BH3·THF; 2. H2O2, aqueous NaOH) gives anti-Markovnikov alcohol regiochemistry via concerted syn-addition of B and H across the same alkene face, followed by hydroperoxide oxidation that replaces the C–B bond with a C–OH bond with complete retention of configuration (net syn-hydration). | | | --- Study this deck interactively with FSRS-6 spaced repetition, audio review, and multiple-choice mode at [Flashcards World](https://flashcards.world/flashcards/sets/53c9040d-93f4-4607-a498-be02557aedfb/).