Question

Which of the following hydrocarbons undergo addition reactions:
C_2, H₆, C₃H₈, C₃H₆, C₂H₂ and CH₄.

Answer 1

An unsaturated hydrocarbon is necessary for it to go through another reaction. Either an alkene (C = C) with the general formula C_nH_2n or an alkyne (C ≡ C) with the general formula C_nH_{2n − 2} must be present in it. Among the hydrocarbons listed in the list:

• The alkene propene (C₃H₆) has a C = C bond. For n = 3, it is equivalent to the general formula C_nH_2n.
• With a C ≡ C bond, ethylene (C₂H₂) is an alkyne. When n equals n = 2, it matches the generic formula C_nH_{2n − 2}.

In other processes, these two hydrocarbons take part. They react with hydrogen to generate matching alkanes, for instance, when heated to 473 K in the presence of a nickel catalyst.

\[\begin{array}{cc}
\ce{\phantom{...}H\phantom{...}H\phantom{...}H\phantom{........................}H\phantom{...}H\phantom{...}H\phantom{...}}\phantom{}\\
\phantom{....}|\phantom{....}|\phantom{....}|\phantom{.........................}|\phantom{....}|\phantom{....}|\phantom{....}\\
\ce{H - C - \underset{Propene}{C = C} - H + H2 ->[Ni/473K] H - C - C - C - H}\\
\phantom{.}|\phantom{..................................}|\phantom{....}|\phantom{....}|\phantom{.}\\
\ce{\phantom{.}H\phantom{.................................}\underset{Propane}{H\phantom{...}H\phantom{...}H\phantom{}}}
\end{array}\]

\[\begin{array}{cc}
\ce{\phantom{...............................}H\phantom{...}H}\phantom{.}\\
\phantom{...............................}|\phantom{....}|\phantom{.}\\
\ce{H - \underset{Ethyne}{C ≡ C} - H + 2H2 ->[Ni/473K] H - C - C - H}\\
\phantom{...............................}|\phantom{....}|\phantom{.}\\
\ce{\phantom{...............................}\underset{Ethane}{H\phantom{...}H}\phantom{.}}
\end{array}\]