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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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Why does a hydroxyl group decrease the acidity of an Aromatic ring?

We are currently learning about resonance and induction, but I am confused why the addition of the hydroxyl group increases the pKa. As oxygen is more electronegative, should it not increase the ...
4 votes
1 answer
139 views

Where is the negative charge localized in tetrazolate ion?

I am seeing images of tetrazolate ion where the negative charge is placed at different locations: On the nitrogen atom Inside the tetrazole ring or On the carbon atom Is there any electronic ...
3 votes
0 answers
55 views

Is cyanomethanide more stable than 2‐oxoethanide?

Which carbanion is more stable? $$\underset{(\textbf{a})}{\ce{H2\overset{-}{C}-CN}} \qquad \underset{(\textbf{b})}{\ce{H_2\overset{-}{C}-CHO}}$$ If we talk about the −M effect, $\ce{CN}$ is higher ...
0 votes
1 answer
87 views

Why does triiodide have only single bonds?

The triiodide ion ($I_3^-$) has structure [I-I-I]$^-$, but the resonance structure [I=I-I]$^-\leftrightarrow$ [I-I=I]$^-$ seems more favourable to me. After all, it disperses formal charge and has a ...
3 votes
1 answer
123 views

Why is Piperidine more basic than Pyridine? [duplicate]

Piperidine, which has sp3 carbons attached to it, experiences an increase in electron density on the nitrogen atom, making it more basic. However, when we look at the resonating structures of pyridine,...
0 votes
1 answer
158 views

Why is an Octet Complete Cation more stable than a Resonance Stabilized Cation?

Our instructor taught us about different types of cations: classical, non-classical, resonance stabilized (R.S.C.) and octet complete cation (O.C.C.), and how O.C.C is more stable than a R.S.C. I did ...
2 votes
1 answer
104 views

Is the 4H-Pyran Cation aromatic?

I guess I'm just trying to understand what "cyclic resonance" really means, from all the examples I've come across its always a cyclic system where the pi-electrons go all around the ...
1 vote
1 answer
34 views

Mesomeric effect comparison

How do I compare the -M effect due aldehyde and a carboxylic acid? Which will have stronger mesomeric effect?
4 votes
1 answer
256 views

Identify the more acidic hydrogen in 1-(methylsulfanyl)propane-2-thione

This was a question that was asked in one of my exams, in which we had to confirm if the given order was correct or incorrect. The key says the given order is correct and the professor at my high ...
6 votes
1 answer
9k views

How to explain (non-/anti-) aromaticity in fulvene with the help of resonance structures?

Can someone please explain why the resonance structures of fulvene 1 is non-aromatic and 2 is anti-aromatic? Why is fulvene non-aromatic, even though it has four $\pi$-electrons and no $\mathrm{sp^3}$...
-2 votes
1 answer
3k views

Why does Lewis dot structure of CO not have formal charges close to 0?

If we draw the Lewis dot structure of CO like this: The formal charge on each atom must be 0 But in the actual structure, formal charge on carbon is $-1$ and formal charge on oxygen is $1$. But I ...
1 vote
0 answers
32 views

Resonance stabilization : lowering of kinetic energy or electron repulsion?

Resonance stabilization, or delocalization stabilization, occurs when the overall energy of the molecule is lowered compared the localized "resonance structures". In solid state physics, or ...
-1 votes
1 answer
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Resonance Structures for mCPBA

Is this a valid resonance structure? I.e. can oxygen donate to positive carbon (i.e. are all oxygens sp2 hybridized)? If not, then why?
0 votes
2 answers
78 views

Why does boron have higher affinity for fluorine than oxygen?

$\ce{F-}$ can displace $\ce{OH}$ in $\ce{B(OH)3}$ and form $\ce{BF3}$. $\ce{BF3}$ is stable due to resonance, but donation of oxygen should be stronger, as -I power of fluorine dominates its lone pair ...
3 votes
1 answer
118 views

If a compound has a strong and weak minus I group, will the stronger group always have a δ- charge?

In a compound like acrolein (prop-2-enal or $\ce{CH2=CH-CHO}$, will the oxygen in the $\ce{-CHO}$ group always have a $\delta$- charge? Acrolein does have three resonance structures as shown below, ...
-1 votes
2 answers
454 views

What are the resonating structures of toluene?

I initially made the resonating structures by first converting toluene into a toluene carbocation. But the resonating structures of a neutral molecule should be neutral. So what are the correct ...
8 votes
3 answers
17k views

Why is +M effect of OH greater than OR?

In some books it is written that +M (mesomeric effect) effect of OH is less than that of OR. The reason they give is inductive effect of R (group) which sounds plausible. But in some places it is ...
-2 votes
1 answer
436 views

Why dosen't NO₂ form according to the octet rule?

Supposedly every atom that is in the second period of the periodic table has to obey the octet rule; this means that they have to be surrounded by 8 electrons (or so I was taught). Studying resonance ...
8 votes
3 answers
7k views

Order of positive mesomeric effect of halides

I learned that the order of $+M$ effect (mesomeric effect) for halogens is as follows: $\ce{F} > \ce{Cl} > \ce{Br} > \ce I$. I wonder why this is so?
0 votes
2 answers
154 views

Aromaticity of chlorobenzene [duplicate]

Hückel's rule predicts that; a planar ring molecule will have aromatic properties if it has 4n+2 π electrons in conjugation. If 4n π electrons are in cyclic conjugation, then it is anti-aromatic. So, ...
7 votes
0 answers
1k 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 ...
2 votes
1 answer
2k views

Conjugation between rings of biphenyls [closed]

I thought since both phenyl rings are not coplanar, the resonance between them is not possible. But my book says the following: Resonance effect is partially nullified Partially nullified means ...
0 votes
0 answers
30 views

Which is more stable, a secondary allylic carbanion or a primary allylic carbanion?

I came across this picture in a polymer chemistry course, specifically on anionic polymerization of conjugated dienes (butadiene). I dont understand why the secondary carbanion is more stable. Based ...
0 votes
0 answers
61 views

VBT and MOT at the same time!

In the SNAr reaction, it is said that the electron withdrawing groups should be at the ortho or para position for the effective electron delocalization to take place, and we draw Kekule's structure to ...
1 vote
1 answer
200 views

Why doesn't the reaction between molecule "B" and diethyl oxalate yield a diester?

Problem Answer Question Why isn't this structure the answer for the second reaction? From my understanding, the resonant structure (B) with the full negative charge on the oxygen is the most stable ...
8 votes
3 answers
408 views

Is 2-oxobicyclo[2.2.1]heptan-1-ide resonance stabilized?

Is the following compound resonance stabilized? I think its not resonance stabilized because the p-orbital of carbanion and pure p-orbital of carbonyl carbon are not in same plane. So they can't ...
-4 votes
1 answer
232 views

Planarity of rings [closed]

Can a 7 or less than 7 membered homocyclic ring with unsaturated C atoms and fully conjugated system, lose planarity? The smallest homocyclic non-planar ring that I know is cyclooctatetraene which is ...
3 votes
1 answer
577 views

Is size or electronegativity more important in acidity?

For the molecule below, is the hydrogen with the oxygen more acidic or is it the one with sulfur? Since both parts have the same number of resonance structures, I'm guessing it just boils down to ...
3 votes
1 answer
426 views

If charge is quantised, how can It delocalize?

As I was trying to understand resonance, I got to know that it was imaginary phenomenon and it is just a tool to explain mechanisms and structures that are unexplained by Lewis dot structures or ...
2 votes
0 answers
43 views

How are Fermi resonances between normal modes possible?

As I understand, Fermi resonances occur when two (nearly) resonant vibrational states—most commonly a fundamental and overtone or combination mode—that are of the same symmetry interact, which, in the ...
-2 votes
1 answer
145 views

Why is it okay for the central carbon to lose a bond when forming a resonance structure for acetone?

As the title reads, I'm confused as to why it's okay for the central carbon in acetone to have a +1 formal charge when we push the electrons from one of the bonds with oxygen to form a lone pair and ...
2 votes
0 answers
75 views

Which methoxy- and nitro-substituted azulene has the lower ground state energy?

My contention is that the first azulene structure, with the nitro group on the aromatic cyclopentene ring has a lower ground state energy, as the negative charge can not only resonate into the nitro ...
0 votes
0 answers
63 views

Can two resonance structures of a molecule have different cas numbers?

From this Wikipedia article : Specifically, when a molecular structure is said to be represented by a resonance hybrid, it does not mean that electrons of the molecule are "resonating" or ...
3 votes
1 answer
379 views

Non Aromaticty due to Cross Conjugated Systems

I was going through this site looking for some answer on aromatic character, definition and other ways of judging an aromatic compound, when is tumbled upon this question: Are p‐xylylene and fulvene ...
-4 votes
2 answers
100 views

Resonance energy of organic compounds [closed]

I was solving a problem in organic chemistry, where I had to find the resonance energy of a compound with some information which was given in the question itself. Basically, what I had to do was, to ...
-1 votes
2 answers
325 views

Why does the conjugate base of peracetic acid not have any resonance structures?

Peroxyacetic acid, $\ce{CH3C(O)OOH}$ has its anion form when a proton is detached, like $\ce{CH3C(O)OO-}$. I think it can have two resonance forms like I drew (even though they have several charge ...
-3 votes
1 answer
114 views

+M or -I for chlorine? Major product in free radical chlorination and bromination of 2-chloropropane?

Is the +M or -I effect more dominant in when an alkyl (mono)halide is subject to free radical chlorination/bromination? For example what will be the major product in case of free radical (mono)...
-2 votes
3 answers
855 views

Why is chloroethene said to be a conjugated system?

Why is chloroethene said to be a conjugated system?Is it because of p orbitals present in chlorine or something?
2 votes
2 answers
860 views

Why do certain groups withdraw/ donate electron to double bond or conjugated system in resonance effect?

Why for the Resonance effect certain group of substituents/functional group donate electron from the double bond or to a conjugated system while some withdraw electron from the double bond or to a ...
5 votes
2 answers
4k views

What is the most stable structure amongst the keto-enol tautomers of pentane-2,4-dione?

I was assigned the following question and I cannot decide which is the correct answer. Which is the most stable structure? (a) pentane-2,4-dione (b) 4-hydroxypent-4-en-2-one (c) (Z)-4-...
1 vote
2 answers
803 views

What is the difference between resonance and π conjugation

I have seen electron delocalization mentioned frequently in 2 separate contexts: resonance (ozone, carbonate / nitrate...) and π-conjugation systems (aromatic compounds). While the 2 initially sound ...
-4 votes
2 answers
227 views

Why is the dipole moment of Anisole less than that of Phenol? [closed]

According to Wikidata, anisole has a dipole moment of 1.38D and according to this page on Researchgate, phenol has a dipole moment of 1.70D. Resonance in anisole: Resonance in phenol: According to my ...
4 votes
2 answers
916 views

Acidic strength of nitrophenols

I've seen the pKa values of Nitrophenol as follows:- pKa of o-nitrophenol= 7.23 pKa of p-nitrohenol= 7.14 so p-nitrophenol is more acidic than p-nitrophenol But both phenoxide ions are stabilized ...
-2 votes
1 answer
86 views

Acidic strength order among hydroxytetralones [closed]

I can understand in 1 the conjugate base has more stability for better resonance but in 2 and 3 the effect of resonance cannot be considered. How can we compare the inductive effect in such case?
9 votes
2 answers
8k 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 ...
0 votes
0 answers
49 views

How does borane target a specific double bond on an indene?

According to the text I am using (Organic Chem, Seyan Ege, 3rd ed, problem 12.57) the halide in the electrophile borane (BH3) binds at site G. But I need to make sure I understand why. First, I ...
-2 votes
3 answers
2k views

When does replacing a double bond with a lone pair result in a valid resonance structure?

Take molecules A and B below. In A, we can move the electrons from the green pi bond into a lone pair on oxygen, then move the blue lone pair of electrons from the other oxygen to form a new π bond, ...
0 votes
0 answers
793 views

Lewis structure and resonance for arginine ion

I'm working through a problem set in MIT's open courseware 'Principles of Chemical Science' course here. In question 5, it asks: The skeletal structures of two amino acids, leucine and arginine, are ...
7 votes
1 answer
10k views

Does the carboxylate group show a positive or a negative inductive effect?

In the benzoate ion, does the carboxylate group show a $-I$ or a $+I$ effect? I learnt that the carboxylate group is a $-I$ group, but according to a website the carboxylate group in benzoate shows a ...
1 vote
1 answer
1k views

Does propene have resonance structures? [closed]

Propene is an alkene with a double bond between 2 carbon atoms. $\ce{C3H6}$ may have 2 resonance structures due to 2 possible placings of the double bond. E.g. it can be C=C-C or C-C=C (ignoring ...

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