Question

Unknown Letter Identity Unknown Letter Identity QUESTIONS How would you distinguish between cyclohexane and cyclohexene? How would you distinguish between cyclohexanol and 1-hexanol?

Answer 1

A) Ans- Cyclohexene is unsaturated whereas cyclohexane is saturated hydrocarbon. There are different tests that can be used to distinguish between cyclohexene and cyclohexane:

1 Reaction with Bromine. There is a rapid reaction between the unsaturated hydrocarbon and bromine. The reaction is the addition of the bromine to the carbons of the multiple bonds. Unsaturated hydrocarbons reaction with bromine in solution to produce the corresponding dibromoalkane. The yellow/orange color of bromine disappears on reaction with unsaturated hydrocarbons because the bromoalkane products are usually colorless. As unsaturated hydrocarbons have only single C-C bonds present then no reaction with bromine is observed.

(Yellow/Orange)

+ Br2 - No reaction (Yellow/Orange)

2 Baeyers Test. Reaction with Aqueous Potassium Permanganate. Potassium permanganate is an oxidizing agent that reacts with unsaturated aliphatic hydrocarbons but does not react with alkanes. The color of dilute KmnO₄ is deep purple and on reaction with unsaturated hydrocarbons, it produces MnO₂, a brown precipitate. There is no reaction with saturated hydrocarbons.

[ H2 O + 2MnO2 + 2KOH + 2KMnO4 (Purple Color) OH (Brown ppt) 0 + 2KMNO, H20 HO + 2KMnO4 - (Purple Color) Noreaction No reaction

The above given two tests can be used to distinguish between cyclohexane and cyclohexene.

B) Ans- Distinguish between cyclohexanol and 1-hexanol. 1-hexanol is a type of primary alcohol whereas cyclohexanol is secondary alcohol. Lucas test can be used to distinguish between the two. This test is based on the difference in reactivity of alcohols with HCl in an S_N1 reaction:

ROH + HCl $\rightarrow$ RCl + H₂O

This reaction works because secondary carbocations are more stable and hence form faster than primary carbocations.

Lucas reagent is an equimolar mixture of ZnCl₂ and HCl. For the test, a few drops of alcohol are added to the reagent in the test tube. Secondary alcohol will react within 3-5 min to form the alkyl halide, which is insoluble and forms an oily layer.

Whereas primary alcohol does not noticeably react with Lucas reagent at room temperature.

ZnCl2, HCI + H20 Cyclohexanol Chlorocyclohexane ZnCl, HCI OH - No reaction hex an-1-01

Hence, by using the above-discussed method we can distinguish between cyclohexanol and 1-hexanol.