Questions tagged [resonance]

Resonance refers to the representation of the electronic structure of a molecular entity in terms of contributing structures. The tag should be applied to any question that concern resonance structures or resonance energy. This tag should not be applied to questions about aromatic compounds (use the [aromatic-compounds] tag instead)

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how are order for effects in organic chemistry given [closed]

I would like to know how are the orders for various effects in organic chemistry ( +M , +I etc..). I asked this to my teacher and he said they are assigned experimentally. So if they are assigned ...
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1answer
558 views

Which hydrogen of 3-methylcyclohex-2-en-1-one is the least acidic?

Which hydrogen of 3-methylcyclohex-2-en-1-one is the least acidic? According to me it should be 2, as on its removal there won't be any resonance stabilization as would happen in the other ...
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1answer
50 views

Why aren't all bonds in cyclobutadiene not equal? [duplicate]

Cyclobutadiene is like benzene in that it has alternating single and double bonds in a ring. However, it's bonds are not the same length, the double bonds being shorter than single bonds. The molecule ...
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1answer
49 views

Confused about identifying delocalized electron pairs in Isoniazid

I have to identify delocalized electron pairs in Isoniazid (pairs not shown in the image below): I know the nitrogen in the ring has a localized electron pair, since it already forms a pi bond. I'm ...
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2answers
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Why does having equivalent resonance structures give more stability?

Although the phenolate ion has more resonance structures (4) compared to acetate ion (2), acetate is more stable because it has two equivalent resonance structures of same energy. Why does having ...
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5answers
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Oxygen or carbon with a positive charge? (comparison of canonical structures)

Which of the contributing structures of the resonance is more stable? I'm watching a video lecture by a professor of my college where he puts this question to the class. The class unanimously ...
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4answers
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How to determine the worst resonance structures out of a given set?

So I was "happily" doing organic chemistry homework when I came across this question: For 1-methoxy-1,3-butadiene, which of the following resonating structure is the least stable? $$\begin{...
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1answer
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How to determine the relative contribution of resonance structures when different rules give contradictory outcomes?

In order to determine the relative contributions of resonance structures, my textbook gives the following rules (in order): The more covalent bonds a structure has, the higher it scores. Structures ...
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Delocalization of positive charge

How is positive charge delocalized? I understand how negative charge can be delocalized. Electrons are mobile and they can move around. But what about positive charge? For example, consider this ...
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What is Baker Nathan effect?

The following statement is from Solomons, Fryhle and Snyder Organic Chemistry: In 1935, Baker Nathan effect explained that hyperconjugation dominates inductive effect. [...] The electron donation ...
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Can this sp2 lone pair resonate?

In methyl isocyanate, $\ce{CH3CNO}$, shown below, it seems that the nitrogen lone pair can resonate with the carbon oxygen double bond, generating a resonance structure something like acetonitrile ...
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What is the reason for the exceptional stability of tricyclopropyl-cyclopropenyl carbocation?

The stability order of the following is: A. III > II > I > IV B. II > III > I > IV C. I > III > IV > II D. I > III > II > IV Answer: I came across a question where we had to ...
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How far does the delocalisation (resonance) effects for substituents extend for a conjugated system?

Let's say we have a conjugated system like this one: Now, the delocalisation of the benzene electrons with the nitrate system means that the ortho, and para positions on the immediate benzene ring ...
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1answer
344 views

Which of the resonance structures is more stable?

I am quoting a rule on resonance from Organic Chemistry by T.W. Graham Solomons, Craig B. Fryhle, 12th edition, page 25. Structures in which all the atoms have a complete valence shell of ...
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IUPAC name of Dewar benzene [closed]

Dewar benzene according to Wikipedia has the IUPAC name bicyclo[2.2.0]hexa-2,5-diene. Is it correct to give this name because resonance takes place and if we fix a certain numbering, as resonance ...
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What is the significance of the downward arrows in energy level diagrams in organic chemistry?

The following text is from Solomons, Fryhle and Snyder Organic Chemistry Third Edition, chapter 1 "The Basics: Bonding and Molecular Structure", page 13, topic 1.5 "Resonance Theory", sub topic 1.5B "...
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1answer
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Can someone help with this resonance form question [closed]

Struggling to understand the concept of resonance and how it provides stability to compounds, my basic understanding is that the delocalized pi electrons can move and place a negative charge on the ...
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2answers
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Why hyperconjugation can't stabilize carbanion?

If Resonance can stabilize both carbo cation and anion then why can't hyperconjugation stabilize carbanion ? Since both Resonance and Hyperconjugation are pretty much the same, i.e both involve ...
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240 views

Which one is the strongest base among the following compounds?

I am confused between option (2) and (4). Both lone pairs of nitrogen are localized, so next, I looked at the hybridization of $\ce{N}$ in each compound. As in (2), the $\ce{N}$ is $\mathrm{sp^2}$ ...
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Is nitrogen of aniline sp² or sp³ hybridized? [duplicate]

I found a thread which discussed this which totally confused me. (refer to the part of the link which talks about $\ce{sp^2/sp^3}$) The question "How to rationalise the resonance structures and ...
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What is “dancing resonance”?

While searching the Internet for information about the tricyclopropylmethyl carbocation, I found a site (askiitians.com) where it said that its stability was due to "dancing (superfast) resonance". ...
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How many valid resonance forms can be constructed for aniline?

Based on the above picture, it seems that there are four. However, I have two questions: Aren't the top right and bottom left forms simply mirror images of each other, and thus considered the same? ...
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Stabilization by resonance

My textbook (NCERT Chemistry. Part I. Textbook for Class XI [1, p. 106]) states that Resonance stabilizes the molecule as the energy of the resonance hybrid is less than the energy of any single ...
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2answers
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Rules to identify the most stable resonance structures

While studying resonance from this Chemistry LibreTexts article, I found the rules to follow in order to decide which structure is the most stable. Among them: The structure with the least number of ...
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Difference in transition lifetimes for near-resonant v/s non-resonant Raman effect

I have read that a virtual state is created when Raman scattering occurs. Since this state is forbidden, the molecule upon absorbing a photon (not enough to take it to the next electronically excited ...
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1answer
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Which one is the most stable canonical structure?And why? [closed]

According to my book the answer is given that structure III is the most stable because all the atoms have complete octets. But I think it should be II because of, (a) Structure III has positive ...
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Structure of dihydrogen peroxy-phosphate ion

In structure of Dihydrogen peroxy-phosphate ion $\ce{H2PO5-}$, shouldn't negative charge be on oxygen linked directly to phosphorus, rather than on oxygen linked through peroxy linkage with another ...
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Why are only two bond structures considered for ozone and not three? [duplicate]

We were taught in chemistry that: Formal charges can be determined by drawing the Lewis dot structure, then subtracting the nonbonding electrons and half of the bonding electrons from the number of ...
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1answer
174 views

How many resonance structures can be drawn for the following molecule?

For Question 2; I think that the molecule can be drawn in three ways but the book says that the correct answer is option D i.e.,2 can anyone explain how ?
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How can we calculate the “degree” of conjugation?

So a conjugated system is a system of connected p orbitals or alternating single and multiple bonds. I know that conventionally, we count the number of adjacent parallel p orbitals or alternating ...
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How does the relative acidity of 2,3-dinitrophenol compare to that of 2,4-dinitrophenol?

I am assuming that the -I inductive effect in 2,3-dinitrophenol is stronger than in 2,4-dinitrophenol since it operates through less bonds, therefore on inductive grounds it should have a lower $\...
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1answer
742 views

Acidic strength of organic acids. Substituted PhCOOH acids

Could someone please explain the order of acidity of ortho, para and meta substituted benzoic acids with the substituent as methyl group? Methyl group operates +I and +R effect, I believe.
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Why is benzoic acid more acidic than p-chlorobenzoic acid?

We know that in case of halogens, inductive effect is more dominant than resonance effect. So, the -$\ce{Cl}$ on the para position will withdraw electrons by a -I effect and should make p-...
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Difference between Resonance Effect and Mesomeric Effect

While studying electron displacement effects in organic chemistry, I read that the Resonance Effect and Mesomeric Effect are the same. Every source I checked used the heading or opening "The Resonance ...
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Why is an alkyne substituent on benzene is electron withdrawing, but alkane and alkene are electron donating?

Hammett constants for alkyls/vinyls/etc. are all negative (i.e. toluene), and my understanding is that they donate electrons through inductive/resonance effects. However, ethynylbenzene has a ...
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Relative Energies of Resonance Contributors & Stability of Borazine

We know that Borazine (Inorganic Benzene) is aromatic in nature. The following image shows the resonance contributors of borazine: What are the relative energies of these three resonance contributors?...
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Natural Bond Orbital analysis: Significance of stabilization energy determined by 2nd order perturbation

PREFACE: I am no expert on this topic. My questions at the bottom may be off base. I have some experience with symmetry-adapted perturbation theory (SAPT) when it comes to analyzing intermolecular ...
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Resonance structures and mechanism

I wrote the following resonance structures and our teacher wants us to write the curved arrows showing the mechanism as well... I was wondering if it's okay to show in which direction the mechanism ...
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2answers
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How are the hybrid orbitals of sulfur hexafluoride shaped?

On the fluorine end the fluoride atoms are simply completing a $3p$ orbital. On the sulfur end one could posit a hybrid of one $3s$ orbital, two $3p$ orbitals and a three inner $2p$ orbitals. However,...
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101 views

What is the stability order of the carbocation and carboanion?

So I came up with examples as below: 1 2 Now I am confused about the +I and -I effect in these structures since to my knowledge it can only be applied when there is a substituent (I might be wrong)...
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1answer
104 views

Consequences of ortho effect on resonance

Consider any carboxylic acid with any group at ortho position. According to ortho effect, the resonance of the $\ce{C=O}$ with the ring is inhibited. Is this resonance entirely lost? Or some little ...
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Which of the following carbocations is more stable?

Which of the following carbocations is more stable? I know two major factors in determining carbocation stability: resonance and the number of carbon atoms neighboring the positive carbon. Does ...
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How can a conjugated system of open hydrocarbon chains have delocalization?

If conjugated systems have delocalized electrons, and delocalization takes place when there are two possible structures how come I can only find one for conjugated systems of chained hydrocarbons like ...
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1answer
304 views

Cross-conjugation

Could somebody please explain the concept of “cross-conjugation” (Organic Chemistry) to me? In what kind of conjugated systems is it observed, what are its effects on resonance of the system as a ...
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1answer
14k views

What is a sigma complex?

According to Wikipedia, "sigma complex" refers to an arenium ion. The suffix "-ium" denotes a positively charged ion. So, it is correct to call the resonance structures in the below picture ...
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Electrophilic aromatic substitution of napthalene

It is known that the $\alpha$-position (or 1-position) for napthalene is the preferable position for substitution to occur at. However, I am getting two different explanations as to why this is the ...
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1answer
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Reactivity of thioesters with respect to nucleophilic attack

Why are thioesters relatively reactive with regard to nucleophilic attack? Prof says to wait until pchem 3 when we learn about orbital symmetry. He also said that sulfur’s d-orbitals (?!) don't have ...
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1answer
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How does resonance fail in approximating chemical structures?

In the book "Concise Inorganic Chemistry" by Prof. JD Lee, it says here: These contributing structures do not actually exist. The $\ce{CO3^2-}$ does not consist of a mixture of these structures, ...
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Which compound reacts faster in the Cannizzaro Reaction?

Which reacts faster in the Cannizzaro Reaction? a) $\ce{OHC-C6H4-NO2}$ b) $\ce{OHC-C6H4-OCH3}$ Obviously, a better hydride releasing group will react faster. Therefore my answer was b, as $\ce{-...
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Why should 2,6-Dimethyl-4-nitrophenol be more acidic than 3,5-Dimethyl-4-nitrophenol

I was trying to compare acidity of some organic compounds but can't understand some: Why should 2,6-dimethyl-4-nitrophenol be more acidic than 3,5-dimethyl-4-nitrophenol? I have been trying to ...

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