Video Transcript
The reaction scheme below shows
various reactions a molecule of propan-2-ol can undergo. Which product would be a
ketone?
Propan-2-ol is a secondary
alcohol. When a secondary alcohol is reacted
with a hydrohalic acid, such as hydrochloric acid, a substitution reaction occurs
and a haloalkane is produced. When a secondary alcohol reacts
with concentrated sulfuric acid at temperatures greater than 180 degrees Celsius, a
dehydration reaction occurs and an alkene is produced. When a secondary alcohol reacts
with acidified potassium dichromate under reflux, an oxidation reaction occurs and a
ketone, in this case propanone, is produced. Therefore, the product that would
be a ketone is B.
Part (b) what name would product C
have? (A) 2-Chloropropan-2-ol, (B)
2-chloropropane, (C) 1-chloropropane.
Product C was formed via a
substitution reaction. A substitution reaction is a
chemical reaction where a part of the molecule is removed and replaced with
something else. In this substitution reaction, the
hydroxy group is removed and is replaced by the halogen, in this case chlorine. This means that the product will
have a chlorine atom bonded to the second carbon atom, the same position as the
hydroxy group in the original molecule. To name this haloalkane, we
indicate the position of the chlorine atom by writing two dash chloro, where the
number two indicates that the chlorine atom is bonded to the second carbon atom. Then, we name the carbon base chain
propane, prop- for three carbon atoms and -ane for alkane, indicating that the
carbon atoms are single bonded. The correct name of product C is
answer choice (B) 2-chloropropane.
For the next part of the question,
I will isolate the important information.
Part (c) how many different
positional isomers would result from the reaction to form product A? (A) One isomer, (B) two isomers,
(C) four isomers, (D) three isomers.
We have already established that
this reaction is a dehydration reaction, a chemical reaction in which a water
molecule is eliminated from the reactant. Over the course of this reaction,
the hydroxy group and one hydrogen atom bonded to a carbon atom two positions away
from the hydroxy group will be removed. And a new carbon-carbon double bond
will form between the two carbon atoms that each lost a substituent. There are six possible hydrogen
atoms that can be removed in addition to the hydroxy group. If any of the leftmost hydrogen
atoms are lost during dehydration, a double bond will be formed between the leftmost
and middle carbon atoms, giving us the product propene. If any of the rightmost hydrogen
atoms are lost during dehydration, a double bond will be formed between the middle
and rightmost carbon atoms. This would also produce the product
propene. As the products are the same, the
correct answer choice is answer choice (A). Only one positional isomer would
result from this reaction.
