Video Transcript
Consider the following
reaction. Which of the following products is
produced from the reaction?
Let’s begin by examining the given
reaction. The first reactant is a carboxylic
acid. We can tell from the structural
formula that this molecule is a carboxylic acid because it contains the carboxyl
group. The name of this carboxylic acid is
ethanoic acid. Let’s look closely at the name. The eth- portion of the name
indicates there are two carbon atoms in the carbon chain. The -an- part of the name indicates
that there are single bonds between the carbon atoms in the chain. And the suffix -oic and the word
“acid” are added to the name of the carbon chain when naming any carboxylic
acid.
The second reactant in the reaction
is an alcohol. We can identify this molecule as an
alcohol because of the presence of the hydroxy group. Like all alcohols, the oxygen atom
of the hydroxy group is connected to the carbon base chain of the alcohol by a
single bond. The name of this alcohol is
ethanol. The eth- part of the name indicates
that there are two carbon atoms in the carbon chain, while the -an- part tells us
that there are single bonds between the two carbon atoms in the chain. Finally, the suffix -ol is added to
an alcohol with one hydroxy group.
In the reaction, an acid catalyst,
H2SO4, is used. When a carboxylic acid reacts with
an alcohol in the presence of an acid catalyst, the products are an ester and
water. The reaction is known as
acid-catalyzed esterification of a carboxylic acid. The reaction is reversible, but we
will ignore that for the purpose of this video.
To solve this problem, we need to
determine which of the structural formulas given in the answer choices is the ester
formed by the reaction. Let’s start by writing condensed
formulas for the two reactants. The condensed formula for the
carboxylic acid is CH3COOH. The condensed formula for the
alcohol is CH3CH2OH. During the reaction, the CH3CO
portion of the carboxylic acid will combine with the OCH2CH3 portion of the
alcohol. The ester formed has a condensed
formula of CH3COOCH2CH3. The COO portion of the molecule is
the ester functional group.
Let’s pause here and take a look at
the answer choices below. Choice (B) is not a correct answer
choice. The molecule does not contain the
ester functional group, so it is not an ester. Let’s take a look at choice
(E). Choice (E) is also an incorrect
choice. The molecule does not contain the
ester functional group. Therefore, it is not an ester. Choices (A), (C), and (D) all have
something in common. All of these molecules contain the
ester functional group. Let’s draw a more complete
structural formula for the ester formed in the reaction. So the ester that we’re looking for
contains a total of four carbon atoms. By quickly scanning the answer
choices, we see that choice (C) is an ester which contains four total carbon
atoms. The correct answer is choice
(C).
