Video Transcript
Ethene can react with hydrogen to
form ethane in a hydrogenation reaction. Which of the following compounds
will also undergo a hydrogenation reaction? (A) Acrolein, (B)
2,3-dimethylpentane, (C) 2-propanol, (D) ethanol, or (E) methylcyclobutane.
Hydrogenation is a type of addition
reaction in which molecular hydrogen reacts with a compound typically in the
presence of a catalyst. We are told in the question that
ethene can react with hydrogen to form ethane in a hydrogenation reaction. Let’s examine the structures of
ethene and ethane to see what happens during this reaction.
Ethene is a two-carbon alkene. When it reacts with molecular
hydrogen in the presence of a catalyst such as Raney nickel, the two-carbon alkane
ethane is formed. We should be able to see from this
reaction scheme that during the reaction, the 𝜋 bond between the two carbon atoms
in ethene is broken, as is the bond between the two hydrogen atoms. This allows for the formation of
two new carbon–hydrogen bonds.
Because this reaction involves the
breaking of a 𝜋 bond, we can further specify that a hydrogenation reaction is a
type of addition reaction in which molecular hydrogen reacts with an unsaturated
compound. In other words, compounds which
contain double or triple bonds can undergo a hydrogenation reaction. Alkenes, alkynes, and aldehydes are
just a few examples of compounds that undergo hydrogenation.
To answer the question, we need to
determine which of the answer choices will undergo a hydrogenation reaction. We can see that answer choices (B),
(C), (D), and (E) are all saturated molecules, while answer choice (A) is
unsaturated. As hydrogenation reactions occur
with unsaturated molecules and answer choice (A) is both an alkene and an aldehyde,
the compound that will undergo a hydrogenation reaction is answer choice (A),
acrolein.
