Video Transcript
The figure shows a ketone that was
made by the oxidation of an alcohol. What is the structure of the
original alcohol?
An alcohol is an organic molecule
that contains at least one hydroxy or OH group. To answer this question, we need to
understand what happens when an alcohol undergoes oxidation. During the oxidation of an alcohol,
the hydrogen atom of the hydroxy group and a hydrogen atom bonded to the same carbon
atom as the hydroxy group are removed. To make up for this loss of bonds,
a new carbon-oxygen double bond is formed. The type of product formed during
the oxidation of an alcohol depends on the identity of the R and R prime groups. When at least one of these R groups
is a hydrogen atom, the molecule is considered a primary alcohol.
When a primary alcohol reacts with
an oxidizing agent, one of two types of product may form, depending on the reaction
conditions. When excess alcohol is used and the
product is distilled as it is produced, an aldehyde is formed. When excess oxidizing agent is used
and the reaction is carried out under reflux, a carboxylic acid is produced.
We are told in the question that
the product is a ketone, not an aldehyde or a carboxylic acid. So the original alcohol cannot be a
primary alcohol. When both the R and R prime groups
are alkyl chains, the molecule is considered a secondary alcohol. Secondary alcohols react with
oxidizing agents to form ketones. So we know that the original
alcohol will be a secondary alcohol. We can use the structure of the
ketone to work backwards to the structure of the original alcohol.
During oxidation, a carbon-oxygen
double bond was formed. This means that in the original
alcohol, these two atoms were single bonded together. We also know that during oxidation,
the hydroxy group loses a hydrogen atom. So, in constructing the structure
of the original alcohol, we need to add a hydrogen atom to the oxygen atom. The carbon atom bonded to the
hydroxy group also loses a hydrogen atom during oxidation. So we’ll need to add a hydrogen
atom to the carbon atom that is bonded to the hydroxy group.
We have now worked backwards to the
structure of the original alcohol. We can see that the structure that
we drew matches the one shown in answer choice (C). Therefore, the structure of the
original alcohol that oxidizes to produce the given ketone is the structure shown in
answer choice (C).
