Identify the unsaturated compound that does not give red ppts when treated with____________Ammonical cuprous chloride
Correct answer: D. CH2=CH2
- A. CH3-CH2-CCH (1-Butyne)
- B. CH3-CCH(1-Propyne)
- C. CH3-CH2-CH2CCH(1-Pentyne)
- D. CH2=CH2
Explanation
Terminal alkynes such as 1-butyne, 1-propyne and 1-pentyne contain an acidic terminal hydrogen and form red copper acetylide precipitates with ammoniacal cuprous chloride. Ethene is an alkene and has no terminal alkyne hydrogen, so it does not give this red precipitate. The likely mistake is choosing a terminal alkyne because all the listed compounds are unsaturated, but this test is specific to terminal alkynes.
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About Alkynes
Alkynes are unsaturated hydrocarbons containing a carbon-carbon triple bond, with sp-hybridised carbon atoms and a linear arrangement around the bond. The content includes nomenclature, preparation, acidity of terminal alkynes, and addition reactions with hydrogen, halogens, hydrogen halides and water, as well as oxidation.
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