How does oxymercuration add water across an alkene?
Oxymercuration adds water in two steps: electrophilic addition of Hg(OAc)₂ and water, followed by reduction with NaBH₄. It results in Markovnikov addition of OH (to the more substituted carbon) and H (to the less substituted carbon).
What is the regioselectivity of oxymercuration?
OH adds to the more substituted carbon due to formation of the more stable carbocation-like intermediate.
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How does oxymercuration add water across an alkene?
Oxymercuration adds water in two steps: electrophilic addition of Hg(OAc)₂ and water, followed by reduction with NaBH₄. It results in Markovnikov addition of OH (to the more substituted carbon) and H (to the less substituted carbon).
What is the regioselectivity of oxymercuration?
OH adds to the more substituted carbon due to formation of the more stable carbocation-like intermediate.
What is the stereochemical outcome of hydroboration of alkenes?
Syn addition: both H and B add to the same face of the alkene.
What is the regioselectivity of hydroboration?
Boron adds to the less substituted carbon due to steric and electronic effects.
Describe the mechanism of hydroboration of alkenes.
It is a concerted, asynchronous addition where C–B and C–H bonds form simultaneously.
How are organoboranes converted into alcohols?
By oxidation using H₂O₂ and NaOH, which retains configuration and yields alcohols from organoboranes.
What reagents are used to hydrogenate alkenes?
H₂ gas with a Pd/C (or Pt/Ni) catalyst.
What is the stereochemical outcome of alkene hydrogenation?
Syn addition of hydrogen; both hydrogens add to the same face.
What reagents are used to dihydroxylate alkenes?
OsO₄ with H₂O (and often NMO as co-oxidant) in acetone or tert-butanol.
What is the stereochemical outcome of alkene dihydroxylation?
Syn addition of two OH groups forming a cis-1,2-diol.
What are the reagents and conditions for ozonolysis of alkenes?
What products are formed from ozonolysis of alkenes?
Cleavage of the double bond yielding aldehydes or ketones (carboxylic acids under oxidative workup).
How can alkenes be epoxidised?
Using peracids like mCPBA.
What is the stereochemical outcome of epoxidation?
Syn addition; epoxide is formed with both atoms on the same face.
How do epoxides react with nucleophiles?
Via SN2-type attack with inversion of configuration at the attacked carbon.
Why are epoxides valuable in synthesis?
They can be ring-opened to create trans-1,2-disubstituted compounds with high stereocontrol.
What is the mechanism for addition of HX to alkynes?
Electrophilic addition forming a vinyl carbocation intermediate.
Why is the addition of hydrogen halides to alkynes generally poor?
Vinyl carbocations are highly unstable and hard to stabilize.
How is water added to alkynes via mercury catalysis?
Using Hg(OAc)₂, H₂O, and H₂SO₄. The initial enol tautomerizes to a ketone.
Describe the tautomerisation of enols.
Acid-catalysed proton transfer and shift of double bond convert enol to ketone.
What is the stereochemical and regiochemical outcome of alkyne hydroboration?
Boron adds to the less substituted carbon; syn addition gives cis product. Oxidation yields an enol, which tautomerises to an aldehyde.
What do organoboranes derived from alkynes form upon oxidation?
Enols, which tautomerise to carbonyl compounds (typically aldehydes).
What is the typical pKa of a terminal alkyne?
Around 25.
Why are alkynes relatively acidic?
sp-hybridised carbon has more s-character, making it more electronegative and stabilizing the conjugate base.
How are alkynes synthesized using acetylide anions?
Terminal alkynes are deprotonated with strong bases (e.g. NaNH₂), then reacted with alkyl halides to form new C–C bonds.