Ans: Resonance Structures: Checking Answers Correctness

[chemJan2021]

Summary:: I would like to know if my answers of each resonance structure of the eight questions is correct or not.
I think the Inductive effect (induction) attracts electrons and affects up to three bonds as electron attracting group.
And the Mesomeric effect affects Pi- bonds as long as there are Pi-bonds.
And the Electron donating group (-NR2, -OR, -R) pull the electrons and the Electron attracting group (-NO2, -CO-, -COO-, -CN, -SO3R, halogen) attract the electrons.

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[mjc123]

2 is right, the others are wrong (or 1 is incomplete). -OR is mesomerically electron donating, not attracting. Try drawing in all the lone pairs and counting electrons, and see why your suggested structures are wrong.

 

[chemJan2021]

Thank you for useful comments!
I really appreciate it! I’ll check and try drawing to get to know correct answers.

 

[chemJan2021]

I rethink the answers of these seven questions of resonance structure (1, 3-8). I hope these are correct.
I think as there are only one Pi-bond in 1-7 questions, there is no mesomeric effect in these questions.
I couldn’t understand the answer of the eighth question is wrong. The answer of the eighth question is correct?

 

[mjc123]

They are all mesomeric; it's just that the pi bond is conjugated with a lone pair rather than another pi bond. 1-4 and 8 are correct. (In 8, the unconjugated pi bond is not involved in the resonance.) In 7 you have omitted the positive charge on the N. 5 and 6 are wrong - you are trying to move the pi bond to a saturated carbon. They are analogous to 3 and 4.

 

[chemJan2021]

Thank you for your insightful comments!
I understand mesomeric effect in these resonance structure.
I understand the electrons of pi bond cannot be transferred to a saturated carbon and but to the next carbon of the pi bond. I think the electrons of pi bond can be transferred to a next cation of carbon but not to a saturated carbon.
I appreciate your quite useful teaching!

 

[mjc123]

These are now correct, except that there is a positive charge on the N in the RHS of 6. Remember to keep the total charge constant!

 

[chemJan2021]

Thank you for your useful comment!
I’ll try to check to keep the total charge constant.
I put positive charge on the M in the RHS of no.6.
Your clear explanation helped me understand these resonance structures, thank you!