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 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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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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Reasoning behind the formula to determine the number of hyperconjugative structures

The following formula is from Solomons, Fryhle and Snyder Organic Chemistry for JEE (Main & Advanced) Third Edition, chapter 1 "The Basics: Bonding and Molecular Structure", page 19, topic 1.6 "...
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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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153 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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37 views

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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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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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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44 views

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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103 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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2answers
59 views

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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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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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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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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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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1answer
95 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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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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242 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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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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Help in drawing resonance structures in case of polybasic acids

While drawing resonance structure of dibasic or tribasic acid, e.g. should I take out two $\ce{H+}$ (in dibasic) or three $\ce{H+}$ (in tribasic) together or one by while drawing resonance structure? ...
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Acidic strength order of mineral acids in acetic acid

Explain this acidic strength order $\ce{H2SO4} > \ce{HCl} > \ce{HNO3}$ in acetic acid. My Attempt Stability of conjugate base is proportional to the acidic strength of acids in acetic acid. $\...
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The most acidic hydrogen of 4‐hydroxybutanenitrile

Identify the most acidic hydrogen atom in the compound below: $$\ce{NC-CH2-CH2-CH2-OH}$$ My teacher said that the $\ce{H}$ connected to $\ce{O}$ is the most acidic since $\ce{O}$ is more ...
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Favoured position in nitration of pyrrole [duplicate]

I try to figure out the preferred position of nitration (determine whether compound A or B is the major product) by looking at the resonance structures of the intermediate cation. The solution then ...
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136 views

Is cyclo[18]carbon aromatic?

How does this compound even exist? Having such a massive ring strain. Is it even conjugated? As it's resonance structure will have all double bonds. Since it was reported to be found, there must be ...
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resonance structures and formal charges

hey so I have been stuck on this question for the past few hours and I can't seem to figure it out. I am moving the pi bond one carbon/bond at a time but I can't seem to come up with the correct ...
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233 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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Why does indolizine undergo EAS on C3 and not C5 of the pyrrole ring?

In Clayden, Greeves, & Warren: Organic Chemistry Second Edition, it is said that indolizine (pyrrocoline) reacts in electrophilic aromatic substitution at the C3 of the pyrrole ring, as shown. I ...
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How does cross-conjugation destabilizes a molecule?

Wikipedia article on ortho effect suggests that o-toulic acid is more acidic than benzoic acid. This fact is rationalized by suggesting that steric effect causes COOH group to "twist" out of the plane ...
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Is the 1,4-adduct of carbonyl compounds ever a major product over the 1,2-adduct?

If, say, propenal undergoes nucleophilic addition of hydrazine, will the 1,2- adduct or the 1,4-adduct be preferred? Why? There is an obvious reasonace structure with an electrophilic beta carbon so ...
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Which compound has resonance structures? [closed]

Which compound has resonance structures? A. $\ce{C6H12}$ B. $\ce{CH3CHO}$ C. $\ce{NaBr}$ D. $\ce{Na2CO3}$ The answer key says D is correct, but I do not understand why $\ce{Na2CO3},$ which ...
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Will N,N‐diethylbenzamide show geometrical isomerism?

I know for a compound to show geometrical isomerism it should have site of restricted rotation; be connected to two different groups on either side of site of restricted rotation; the distance ...
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1answer
213 views

Why is p-methoxyphenol less acidic than phenol?

They have slightly different $\mathrm{p}K_\mathrm{a}$ values of 9.9 (phenol) vs 10.2 (p-methoxyphenol). They both have the same number of resonance structures too. My guess is that the resonance ...
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1answer
112 views

Molecular Orbitals (only pi system) of Allyl system using group theory

I have just started reading group theory and their applications in the MO theory. I tried to get the equations of the pi molecular orbitals of allyl system using group theory, but I am stuck at the ...
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63 views

Can there be geometrical isomerism in resonating structures [closed]

If a double bond which has two different substituents on each of it's two ends is showing resonance with one of the substituents would the double bond exhibit Geometrical isomerism?..if yes how so ...
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Reaction enthalpy using bond energy in resonating molecules

To find out and enthalpy of a reaction using bond energy we use the formula $$\Delta H = \sum\Delta_\mathrm{bond}H_\mathrm{reactants} - \sum\Delta_\mathrm{bond}H_\mathrm{products}$$ since we use all ...
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3answers
142 views

4-Bromophenol vs 4-aminophenol pKa in water comparison confusion

Recently the other week, I was asked the following question: Would you expect 4-aminophenol to have a higher or lower pKa than 4- bromophenol when measured in water? And I thought about this on ...
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Molecular Orbital Hybridization vs Delocalization for positive charge stabilization

While studying Molecular Orbital Theory, I ran into a comparison of basicity between pyridine and piperidine. The latter was concluded to be more basic because of the sp3 hybridization of the ...
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1answer
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How does hyperconjugation explain stability of partial positive charges?

Recently I was reading this answer to the question Why does boron add to the less substituted carbon in the hydroboration of an alkene?. See the transition state given in the above answer, and the ...
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1answer
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Does 2-chloro-1,3-dinitrobenzene show resonance?

I am preparing for my exam, and then I stuck up here. The answer to this question given by my teacher was No, this doesn't show resonance because there are two bulky groups alongside chlorine, due ...
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1answer
99 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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89 views

Resonance forms of deprotonated hydroquinone

What resonance forms stabilize deprotonated hydroquinone? Deprotonated hydroquinone looks like this: Possible resonance forms include: 1 and 2 look reasonable: they don't carry multiple charges. My ...
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191 views

What is the physical origin of conjugation?

I had a question about the origins of conjugation in conjugated molecules. Take two ethylenes as compared to butadiene. Huckel seemed to argue that conjugation was the result of pi-pi stabilization ...
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131 views

Why is only one of the lone pairs on the oxygen in furan delocalized?

Both the lone pairs on the oxygen are in allylic positions, thus both should be able to participate in resonance. If both lone pairs can participate in resonance, why is only one of the lone pairs ...
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216 views

Relation between ionic resonance energy and polarity

The ionic resonance of the bonds are given as follows: $$ \begin{array}{cr} \ce{A-B} & 24.3 \\ \ce{A-C} & 50.6 \\ \ce{A-D} & 102.3 \\ \ce{A-E} & 105.9 \end{array} $$ Which of ...