3
$\begingroup$

Substituted aniline and benzamide structures

  1. Determine the reactivity of the above compounds (activating or deactivating; ortho-para or meta directing). Explain your answers. You may use resonance structures in your explanation. Which molecule will have the highest rate of reaction?
  2. What are the products formed when the above compounds are reacted with $\ce{Br_2}$ and $\ce{FeBr_3}$. Predict the major and minor compound, if there is any.

My answers:

For Question (1): E is an activating group because it has a nitrogen with a lone pair. F is a deactivating group because $\ce{C=O}$ is directly attached to the benzene ring. In G, $\ce{N}$ is an activating group but $\ce{C=O}$ is deactivating, so I'm not sure if G is an activating or deactivating compound. Also, How can resonance structures help to explain the reactivity of the compound? I'm not sure how to draw the resonance structures. How do we draw resonance structures that has two substituents such as G. For F, does the lone pair on $\ce{N}$ affect the resonance?

For Question (2): E: $\ce{Br}$ will attach at ortho and para, so it has two products.
F: $\ce{Br}$ will attach at meta with 93 % (major) and ortho 7 % (minor).
G: I think $\ce{Br}$ will attach para to $\ce{N}$ because $\ce{N}$ is a strong activating group and it will not go to between the two substituents because it is crowded, is this true?

$\endgroup$
2
$\begingroup$

I'm not sure if G is an activating or deactivating compound.

You may want to look at the relative order of activation/deactivation of some substituents,

(source: www.chem.ucalgary.ca)

enter image description here

As per the image, $\ce{-NR2}$ is a strongly activating group, while $\ce{-CONH2}$ is a moderately deactivating group (bcoz, it lies somewhere in between $\ce{-COOH}$ and $\ce{-COCl}$). Hence, the net effect would be activating.

How can resonance structures help to explain the reactivity of the compound?

Resonance structures can tell whether the substituent is o,p -directing or m -directing. It can't say anything about rate of reaction.

How do we draw resonance structures that has two substituents such as G?

Just like you've drawn for a single substituent. The only difference is that the other substituent has replaced one of the $\ce{H}$ from the resonance structure drawn with single one. So, the other may participate in delocalization.

For F, does the lone pair on N affect the resonance?

Obviously, but not significantly, as it will participate in resonance too.

I think Br will attach para to N because N is a strong activating group and it will not go to between the two substituents because it is crowded, is this true?

Yes, but it is partially true.

para product (wrt. $\ce{-NR2}$) will be major, however, ortho product (wrt. $\ce{-NR2}$) will be also present as the minor one.

| improve this answer | |
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.