Question

How would you prepare cis and trans alkene from alkyne? Give its mechanism.

25 Jan 2018
Answer :
Word Count : 505

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:

Picture 1.bmp

 

Like alkenes, alkynes readily undergo catalytic hydrogenation, either to cis

_______ ______ _____ _____ __________ ____ _____ ______.
___ _____ _____ __________ ________ _________ ______ _____ ____ ____.
____ ______ _____ ______ ________ _________ _______ _______ _______ _________ ___.
______ ______ _____ _______ _____ __________ _______.
____ __________ _________ __________ _________ _____ ____ _________.
_____ _________ _______ _______ ____ ____ ____.
_________ _____ _________ ___ _______ ______ ______ _____ _____ ____.
_______ ___ _________ _______ ___ _________ ____.
______ ________ _________ __________ ________ _______ _____.
________ _________ ________ _____ ______.
______ ___ ___ _______ ________ ___.
_______ __________ _________ _________ ________ __________ ___.
______ ________ _______ _______ ______ _______ _____ _____ ___ __________ ______ __________.
_____ __________ _______ ________ ______ _________.
_________ __________ ______ ________ _________ _______ __________ _______ _____ ___.
_________ __________ ___ _________ ________.
_____ __________ ______ ________ __________.
_____ ____ ________ __________ ______ ______ __________ ___ ________ __________ __________ _________.
______ ___ ___ __________ ________ ________ __________ ______ ______ __________ _____.
____ __________ ___ ______ ______ _______ ________.
__________ ____ ________ _______ ________ ___ ________ _______ __________ _______ _________.
_______ ___ ________ ________ ____ ________ __________ __________.
_________ __________ __________ _______ _______ ___ _____ _______.
__________ ______ __________ _________ __________ ____ __________ ________ _______ _________.
________ ____ _________ ___ ___ __________ ____ _____ _______.
___ ________ _________ __________ __________ ___ _________ _____ __________ ____ ________.
______ _______ _______ _________ ________ _________.
__________ ___ __________ ___ __________ __________ ________ _______ _________ ________.
______ _________ _____ ___ ______ _______ ______.
____ __________ _____ ____ _________ __________ __________ _________ ______ __________ ____ ______.
__________ _______ __________ ______ _____ __________ __________ _______ _____ _____ __________ _____.
__________ ______ ________ _________ ______ ___ ________ _______ ________ _________ ________ ______.
_________ ______ ______ ____ __________ _________ _________ __________ __________ ___.
_________ _____ ______ ____ ____ _______ ___ ________ __________ __________ ____.
__________ ________ _________ _____ __________ ________ ____ _______ ______ ___.
_________ ____ _________ __________ ________ _____.
__________ ___ _____ __________ _______ __________ ______ ________ ________.
______ _________ _______ ______ __________ __________ _________ ______ ____ _______.
____ ________ ___ _______ _____ _____ _______ __________ _________ ___ __________ ____.
_________ ___ _____ __________ ________ ____ ______ ____.
____ ______ __________ _________ ___ ______ _______ ___ ___ ___ ________.
__________ ____ ________ _______ ____ _____ ________ _______ __________ _________ _________.
___ _____ _____ ____ ___.
_____ _______ _____ ____ ________ __________ ________ ________ _______ ____ ______ ________.
________ ________ ______ _______ _____ ________ ________ __________ __________.
___ ___ _____.
IGNOU ACADEMY
Your IGNOU journey, made easier.
  • Solved Assignments
  • Study Notes
  • Guess Papers
  • Question Papers
Call Us WhatsApp
STUDY • PREPARE • SUCCEED
Skip in 10
Related Questions

In Wittig reaction, the methyl, primary and secondary alkyl halide can be used to
prepare Wittig reagent (ylide) but not tertiary alkyl halide.

Taking suitable examples explain 1,3-dipolar cyclo-addition reactions.

Classify organic dyes according to their chemical composition.

How are following conversions carried out?
i) 6-hydroxy-6-Methyl- 2-heptanone from 5-bromo-2-propanone using Grignard
reagent
ii) Cyclopentyl methyl ketone from acetoacetic ester
iii) Barbituric acid from molonic ester
iv) Propanol from ethylene oxide
v) Butane from chloromethane

Reaction of primary amine, in presence of an acid, with carbonyl compound
gives an imine. The rate of reaction increases by an increase in acidity but
beyond a certain limit, the rate decreases with further increase of acidity.

How are following compounds prepared using ethereal solution of diazomethane?
Write the mechanism of the reactions.
i) CH3CH2COOCH3
ii) CH3CH2OCH3

Explain the following:
i) E2 elimination does not give rearranged product.
ii) E1 elimination does not involve isotope effect;
iii) Hofmann elimination gives less substituted alkene
iv) An anti elimination is faster than syn-elimination.
v) The elimination of HCl from chlorofumaric acid is 50 times faster than
chloromalic acid.

IGNOU Solved Assignments Assignments Ignou Projects Project Previous Year Solved Exam Papers Notes Notes Sample Question Papers Sample Question Papers
Login
Top
📞
Call Support Instant phone assistance IGNOU CHE 6 2018 - How would you prepare cis and trans alkene from alkyne? Give its mecha | IGNOU Academy
→
🟢
WhatsApp Chat Fast live messaging
→
Email Us Business enquiries & support
→