Question 26.SE.8: Write the structural formula for the product of the hydrogen...
Write the structural formula for the product of the hydrogenation of 3-methyl-1-pentene.
Analyse We are asked to predict the compound formed when a particular alkene undergoes hydrogenation (reaction with H_2).
Plan To determine the structural formula of the reaction product, we must first write the structural formula or Lewis structure of the reactant. In the hydrogenation of the alkene, H_2 adds to the double bond, producing an alkane. (That is, each carbon atom of the double bond forms a bond to an H atom, and the double bond is converted to a single bond.)
Solve The name of the starting compound tells us that we have a chain of five C atoms with a double bond at one end (position 1) and a methyl group on the third C from that end (position 3):
\begin{matrix} & & CH_3 \,\,\,\\ CH_2= & CH— & \overset{|}{C}H—&CH_2— &CH_3\end{matrix}
Hydrogenation—the addition of two H atoms to the carbons of the double bond—leads to the following alkane:
\begin{matrix} & & CH_3 \,\,\,\\ CH_3— & CH_2— & \overset{|}{C}H—&CH_2— &CH_3\end{matrix}
Comment The longest chain in the product alkane has five carbon atoms; its name is therefore 3-methylpentane.