How would you prepare cis and trans alkene from alkyne? Give its mechanism.
Hydrogenation of an Alkyne to a Cis-Alkene
Because hydrogenation is an interruptible process involving a series of steps, hydrogenation can be stopped, using modified catalysts (e.g., Lindlar’s Catalyst) at the transitional alkene stage. Lindar’s catalyst has three components: Palladium-Calcium Carbonate, lead acetate and quinoline. The quinoline serves to prevent complete hydrogenation of the alkyne to an alkane. Lindlar’s Catalyst transforms an alkyne to a cis-alkene.
R-C≡C-R + H2 & Lindlar catalyst ——> cis R-CH=CH-R
Lindlar's Catalyst:
Like alkenes, alkynes readily undergo catalytic hydrogenation, either to cis or trans alkenes, or to alkanes, depending on the reaction
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Draw and explain potential energy diagram for the reaction of addition of HCl to 1, 3- butadiene at a low and high temperatures.
How are following compounds prepared using ethereal solution of diazomethane?
Write the mechanism of the reactions.
i) CH3CH2COOCH3
ii) CH3CH2OCH3
Using FMO method explain why [1,3] sigmatropic rearrangement of protons in
alkenyl chain does not occur.
Classify organic dyes according to their chemical composition.
Write the mechanism of Paterno-Buechi reaction.
In the following pairs which of the carbocation is more stable and why?
i) NC – CH – CH2 +CH2 CH3 or NC - CH2 - +CH2 H2
sec. carbocation p – carbocation
ii) CH3 CH2 +CH - CH2 CH2 CH3 or CH3 (CH2)4 +CH2
sec. carbocation p – carbocation
Write the product and indicate the type of reaction that is taking place in the following:
