Video Transcript
Part of the reaction scheme for
Baeyer’s test with ethene is shown in the following diagram. What product is formed from this
reaction? (A) Ethanol; (B) ethene-1,2-diol;
(C) ethane-1,2-diol; (D) ethenol ,vinyl alcohol; or (E) ethane-1,1-diol.
The Baeyer test is a qualitative
test used to test for the presence of unsaturation. To perform the Baeyer test, cold
alkaline potassium permanganate solution, which is purple in color, is added to an
unidentified chemical substance. The potassium permanganate acts as
an oxidizing agent during this test. If the potassium permanganate is
decolorized and a brown precipitate forms, the unidentified substance is likely an
unsaturated compound such as an alkene, alkyne, or aldehyde.
The composition of the product
molecules formed during the Baeyer test depends on the location and type of
unsaturation, the length of the reactant molecules, and the concentration and
temperature of the potassium permanganate solution. Let’s take a look at the reaction
scheme provided in the question.
The substance being tested using
the Baeyer test is ethene. The O in brackets represents the
oxygen provided by the oxidizing agent, in this case potassium permanganate. Over the course of this reaction,
the 𝜋 bond between the two carbon atoms in ethene is broken, and each carbon atom
forms a new bond with a hydroxy group. This is a simplification of a more
complex reaction scheme, but we can see from this diagram that the product contains
two carbon atoms and two hydroxy groups.
Now, we need to determine which of
the answer choices is the correct name of this molecule. We see that each of the answer
choices begins with the term eth-. This term indicates that the
longest continuous chain of carbon atoms is two carbon atoms long, which is the case
for our product. The next portion of the name
indicates the type of bond between the carbon atoms. A-N indicates a single bond and E-N
indicates a double bond. The bond between the two carbon
atoms in the product is a single bond. So, we can eliminate answer choices
(B) and (D).
We see that the remaining answer
choices all end in O-L, indicating that the molecule is an alcohol and contains a
hydroxy group. Answer choices (C) and (E) contain
the term di- in front of O-L. This term indicates that the
molecule contains two hydroxy groups. As the product does contain two
hydroxy groups, we can eliminate answer choice (A) as the di- term is not included
in the name.
The only difference between answer
choices (C) and (E) are the numbers in the middle of the name. These numbers are position numbers
that indicate which carbon atoms in the chain the hydroxy groups are bonded to. We can see that the two hydroxy
groups are bonded to separate carbon atoms or carbon atoms number one and two. This means that answer choice (C),
which identifies the carbon positions as one and two, is the correct answer.
Therefore, the product of the
Baeyer test with ethene is answer choice (C), ethane-1,2-diol.
