Question

I. Alkene Properties, Structure, and Reactivity

Mechanisms

Write a mechanism for the reaction of   HX, H₃O⁺, X₂, X₂/H₂O, with an alkene to produce the corresponding product.

Discuss how the Hammond postulate can be used in explaining the basis for the Markovnikov’s rule.

Explain the mechanism of catalytic hydrogenation of alkenes using appropriate diagrams and reaction arrows.

Explain why the hydroboration-oxidation reaction shows non-MKV regiochemistry

Explain why hydrohalogenation and hydration obeys the MKV (Markovnikov) rule.

Explain why the alkene halogenation and the alkene halohydrin reaction are stereoselective, i.e., the trans isomer is produced but not the cis isomer.

Miscellaneous

Given the chemical structure of a compound or given the molecular formula determine the degree of unsaturation of the compound.

II. Alkynes:

Mechanisms

Explain why terminal alkynes give an aldehyde when the reagent is BH₃ / H₂O₂/NaOH but methyl ketones when the reagent is Hg²⁺and H₃O⁺,

Write a mechanism for either the base or acid catalyzed tautomerization of an enol to its keto form.

Synthesis

Write a synthesis for an aldehyde starting with a terminal alkyne. (..two new C atoms & hydration with BH₃ via enol …e.g. convert ethyne to butanal….)

Write a synthesis for a ketone starting with a terminal alkyne (..two new C atoms & hydration with Hg²⁺ via enol ….e.g. convert ethyne to butanone…)

Stereochemistry and Reagents

Explain the stereochemistry seen with the reagents listed below.

Na/NH₃                               A reagent that gives a stereoselective product ( i.e. a trans alkene isomer)

Lindlar catalyst        A reagent that gives a stereoselective product ( i.e. a cis alkene isomer)

Miscellaneous

Explain why terminal alkynes ( pKa ~ 25 ) are much more acidic than terminal alkenes ( pKa ~ 44)

Given a ketone or aldehyde write the corresponding enol form and vice versa ( i.e given an enol, write the keto tautomer)

Name or draw structures for simple to moderately complex alkynes.

Answer 1