Which of the following hydrocarbons undergo addition reaction: #C_2H_6#, #C_3H_8#, #C_3H_6#, #C_2H_2# and #CH_4#?

1 Answer
P dilip_k · Ernest Z.
Apr 9, 2016

#"C"_3"H"_6# and #"C"_2"H"_2# undergo addition reactions.

Explanation:

Unsaturated compounds having one or more carbon-carbon double bonds or triple bonds or both type of bonds undergo addition reactions .

For open chain hydrocarbons, the general molecular formula of a saturated compound (alkane category) is #C_nH_(2n+2)#.

The general molecular formula of an aliphatic hydrocarbon with one double bond is #C_nH_(2n)#, and the general molecular formula of a hydrocarbon having one triple bond or two double bonds is #C_nH_(2n-2)#.

Matching with these formulas, we can decide whether the the compound is unsaturated or not.

Here, #C_3H_8=C_3H_(2xx3+2)#, #C_2H_6= C_2H_(2xx2+2)#, and #CH_4=CH_(2xx1+2)#.

All three follow the general formula of a saturated compound, i.e.#CnH_(2n+2)#, so they will not undergo addition reaction

#C_3H_6=C_3H_(2xx3)# follows the general formula #C_nH_(2n)#,
and #C_2H_2=C_2H_(2xx2-2)# follows the general formula #C_nH_(2n-2)#, so they are unsaturated and undergo addition reactions.

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