Video Transcript
A singly substituted benzene
derivative is shown. Which molecular group for X will
result in further substitution occurring mostly at the meta position? (A) Cl, (B) OH, (C) CH3, (D) NH2,
or (E) NO2.
The question presents a singly
substituted benzene ring. And we must determine which group
for X promotes further substitution at the meta position.
Let’s start by explaining
conventions for naming a disubstituted benzene derivative. It’s important to know that naming
positions on a benzene ring must be relative to an existing functional group. For example, if X is attached to
carbon one, then the two carbons adjacent to carbon one are called the ortho
positions. The carbons that are one position
beyond that, labeled three, are the meta positions. And finally, the farthest carbon
from carbon one is the para position. And so, the question is asking us
which functional group option will result in products with functionality at the meta
position.
Meta-directing groups increase the
formation of meta-disubstituted benzene derivatives. This is controlled by the electron
density distribution of the benzene ring. The table shows some meta-directing
groups that you might already have come across in a chemistry textbook. You’ll notice that one of the
meta-directing groups in the table is the nitro group substituent with the formula
NO2. Each of the other answer choices
are ortho/para directors, which facilitate substitution at the ortho and para
positions.
And now we should be able to answer
the question. A singly substituted benzene
derivative is shown. Which molecular group for X will
result in further substitution occurring mostly at the meta position? And because the nitro group is the
only strong meta director in our answer choices, we can correctly choose answer
choice (E), NO2.
