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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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8
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3answers
23k views

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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0answers
20 views

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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0answers
11 views

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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1answer
3k views

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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0answers
26 views

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 ...
8
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2answers
2k views

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,...
1
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1answer
58 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)...
2
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1answer
85 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 ...
3
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2answers
108 views

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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0answers
27 views

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
69 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 ...
15
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1answer
13k 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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0answers
38 views

Meaning of arrow from nitrogen to oxygen in resonance effect [duplicate]

What is the meaning of the arrow that is pointing from nitrogen to oxygen in this picture?
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2answers
153 views

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
7k views

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 ...
3
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1answer
69 views

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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3answers
5k views

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{-...
6
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2answers
4k views

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 ...
2
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2answers
220 views

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? ...
2
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0answers
72 views

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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1answer
11k views

What is the meaning of “charge separation” in resonance?

I've read that the resonance structures in which there is lesser 'charge separation' contribute more to the resonance hybrid than the ones with greater charge separation. But I am unable to ...
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1answer
101 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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0answers
34 views

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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0answers
25 views

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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0answers
83 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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2answers
24 views

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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1answer
194 views

Which has greater N-O bond length: NO or NOCl?

I came across this question. According to me NO should have a shorter bond length as it has a triple bond, while NOCl has a double bond. But the answer is given that NO has greater bond length than ...
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2answers
1k views

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 ...
3
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2answers
4k views

The most stable resonance structure [duplicate]

I came across this question: Which is the most stable resonating structure of p-nitrosobenzene among the following? I have been taught about the priorities for resonance structure ...
2
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0answers
21 views

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 ...
21
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1answer
685 views

How does the cyclopropyl group influence conjugation and aromaticity?

While answering the question Why isn't cyclobutane planar?, I recollected that cyclopropane and its derivatives behave like double-bond compounds, e.g. a cyclopropyl group can potentially be ...
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0answers
131 views

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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0answers
24 views

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 ...
3
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1answer
94 views

Does hyperconjugation into sigma-star explain methylamine's increased basicity relative to ammonia?

The inductive effect with the polarisation of the C-N bond obviously plays a role in stabilising the positive charge of the conjugate acid. But given the similar electronegativities for C and H, CH3 ...
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1answer
54 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 ...
0
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1answer
60 views

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 ...
8
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1answer
611 views

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 ...
7
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2answers
4k views

What is the “resonance hybrid” of benzene?

In my book, to explain the structure of benzene, it referred to the idea of resonance: The idea of resonance is that the actual molecule is a definite structure that is a hybrid of two or more ...
6
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2answers
3k views

Can we break the covalent bonds of water molecules using resonance frequencies?

Can we break the covalent bonds of water molecules $\ce{H2O}$ using resonance frequencies? What is the wavelegth of the water's molecule? Can we create a vibration like this and use it to separate ...
3
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0answers
102 views

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 ...
6
votes
1answer
831 views

Steric inhibition of resonance vs. hydrogen bonding

I have to compare the acidic strength of these compounds: Now, in A and B hydrogen bonding will be present which will help stabilize the negative charge of the conjugate base. However, the hydroxyl ...
0
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1answer
93 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 ...
0
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1answer
665 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.
20
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2answers
8k views

How to rationalise the resonance structures and hybridisation of the nitrogen in a conjugated amine?

I was given the first structure, and then drew the other 5 resonance structures: First of all, are they correct? ChemBioDraw had some complaints, but as far as I can see there's the same number of ...
1
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1answer
77 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 ...
21
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1answer
11k views

Stability Comparison between the Tropylium and Tricyclopropylcarbinyl Carbocation

Why is the Tropylium carbocation less stable than the tricyclopropylcarbinyl carbocation? The tricyclopropylcarbinyl carbocation undergoes a sigma-tropic rearrangement whereas tropylium is highly ...
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0answers
18 views

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 ...
32
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3answers
2k views

Pauli exclusion principle and resonance

I've always been a bit uncomfortable with the concept of more than two electrons in a single orbital-like region(probability-wise) which occurs in resonance. This seems to disobey Pauli's exclusion ...
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0answers
81 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 ...
0
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3answers
116 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 ...