Questions tagged [hyperconjugation]

Hyperconjugation involves the donation of electrons from a filled orbital (commonly the bonding C-H sigma molecular orbital) into an adjacent/partially occupied p-orbital (for instance an adjacent carbocation) leading to stabilisation. The tag should be applied to questions where hyperconjugation is involved, even if the question does not explicitly refer to it.

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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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Counting the number of conjugated pi bonds in a complex aromatic molecule

So for multiple bonds to be conjugated, they must be in an alternating double bond – single bond – double bond, etc arrangement. However, do they need to be continuous? In my textbook, they count the ...
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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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Role of tautomerism and its difference from hyperconjugation [closed]

I would like to know the role of tautomerism, if any, in increasing stability of an organic compound. Moreover, how is it different from that of hyperconjugation? I know that hyperconjugation ...
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Hyperconjugation in bridged carbon systems

While studying about hyperconjugation, I came across the following compound which posseses one α-hydrogen (with respect to the $\mathrm{sp^2}$ hybridised carbon atom with an empty $\mathrm{p}$-orbital)...
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Stability of alkenes

The following question was asked on myPAT website: I started with the solution by counting the hyper-conjugative structures available to each alkene. Based on this concept only, order is: I > ...
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If alkyl-substituted alkenes are more stable, how does one explain their increased addition reactivity?

My understanding is that in alkyl-substituted alkenes there is hyperconjugation between $𝜎(\ce{C−X})$ and $𝜋^∗(\ce{C=C})$. I also have read that more alkyl-substituted alkenes are many folds more ...
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Negative hyperconjugation

Compare the acidity of the following compounds: $\ce{CF3OH}$ and $\ce{CCl3OH}$. My attempt: according to me $\ce{CCl3}$ group will show a stronger Negative hyperconjugation effect than $\ce{CF3}$, ...
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Number of hyperconjugative structures in aromatic systems

I know that to find the number of hyperconjugative structures in aliphatic systems we use the formula $a + 1$ (where $a$ is the number of α-hydrogens in that compound) However, my teacher answered ...
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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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Which of the following show hyperconjugation

None of the given compounds have any alpha hydrogen to show hyperconjugation, but the given answer is c.
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Which of the two structures is more stable?

Which of the two structures is more stable? As far as I know, alkenes with a greater number of hyperconjugating structures are more stable. Hyperconjugation has a greater stabilizing effect ...
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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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Why does delocalization lead to stability? [duplicate]

If the electrons are relatively more stable when they are delocalized than when they are localized between two atoms, then why do we have bonds formed in the first place? Forming of bonds between two ...
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How does hyperconjugation lead to stability?

I know that hyperconjugation leads to delocalization of electrons between filled and unfilled orbitals and thus greater stability (that's what most textbooks said). However, I think that it reduces ...
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Hyperconjugation and the stability of alkenes

Clearly, this issue has been touched on here and here. However, I would like to raise a new point on the issue. I have always thought that stabilisation of the $\ce {C=C}$ $\pi$ bond via ...
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Stability of alkene

Sorry for this silly doubt but why is CR2=CH2 alkene more stable than CHR=CHR alkene? Both have same number of alpha hydrogens. I thought that the latter is more stable as in its trans isomer, the R ...
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How does hyperconjugation explain the stability of alkenes?

The more the number of alpha hydrogens, the higher is the stability of alkenes, because the more the number of hyperconjugative structures. Why is this so? Has it got something to do with the ...
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Stability order of methy benzyl cations?

I know that meta position shown no resonance effect and hyperconjugation effect . So According to the order given I guess Hyperconjugating effect is taken into account as -CH3 has no Resonance effects....
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The delocalised nature of hyperconjugation

I have always thought I understood hyperconjugation well until recently, in my post on Regioselectivity of bromination of alkenes, I began to question my understanding of this concept. ...
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Is there a simple way to predict the molecular pi orbitals in conjugated pi systems?

Particularly for longer alkyl chains. Or is predicting these molecular orbitals from quantum mechanics too complex to be able to be translated easily as a geometric pattern? If Frost Circles exist, I ...
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Hyperconjugation in ethane conformers

I refer you to this set of presentation slides. On slide 8, the author explains the preference for the staggered conformation of ethane by saying that there is a favourable hyperconjugative ...
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Can hyperconjugation take place between lone pairs of an atom attached to an sp2 carbon?

When $\ce{HBr}$ is added to 2-chloro-2-butene, the proton preferentially bonds to the $sp^2$ carbon that's not bonded to chlorine. Does this mean that hyperconjugation takes place between the lone ...
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Does hyperconjugation stabilize a carbocation more than a free radical?

Which of the following statements is correct about methyl group? It stabilizes both carbocation and free radical equally. It stabilizes a free radical more than a carbocation. It ...
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Hyperconjugation involving other bonds

Hyperconjugation is often illustrated with C-C and C-H bonds donating electron density to the p orbital in the adjacent carbon atom. Since the concept revolves around sigma bonding orbitals donating ...
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On the directing nature of these groups in electrophilic aromatic substitution

These three groups are listed in our workbook. I don't know the answer and our teacher isn't sure either: (each has a free valency through which it is attached to a benzene ring): ...
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Hyperconjugation in cresol

In cresol both $+I$ effect as well as hyperconjugation work together to determine its acidity. When the methyl group is present in the ortho- and para-position both of them can act upon phenol. ...
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positive charge on oxygen of carbonyl group in acetic acid [closed]

I refer to a previous post by Ron on hyper conjugation in acetic acid(Link:https://chemistry stack exchange.com/.../hyper conjugation in-in-acetic-acid)wherein it is stated that "In acetic acid there ...
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Stabilisation of carbocations through hyperconjugation

Our teachers told us that greater the number of alpha H, greater is the stability of carbocation. But consider this: $\ce{CH3CH2+}$ and. $\ce{CH3CH2CH2+}$ The first one has 3 alpha H ...
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What is the directive influence of the tert-butyl group in electrophilic aromatic substitution?

We know that hydrocarbon side-chains on a benzene ring influence electrophilic substitutions by directing the incoming electrophile to attack at ortho and para positions. The following ...
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Why is a C–D bond stronger than a C–H bond?

I have heard that the carbon–deuterium bond is stronger than the carbon–hydrogen bond. What are the possible reasons for it? Is this also the reason that C–H bonds participate more in hyperconjugation ...
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On baker nathan hyperconjugation

Recently I have been reading about the history of the Baker Nathan reaction. In addition to the large rate increase for Me vs H, all the other alkyl groups showed decreases with respect to Me ...
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Electron density in benzene ring

What would be the order of electron density in the benzene ring in the following compounds? Methyl Benzene Ethyl Benzene t-butyl benzene I would say that t-butyl benzene would have the highest ...
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Gauche effect and bond length

Which of the following compounds has the longest bond length? (A) $\ce{H3C-CF3}$ (B) $\ce{FCH2-CH2F}$ (C) $\ce{F2CH-CHF2}$ (D) $\ce{F3C-CF3}$ My logic was based on the relative ...
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Why it is only carbons that have hydrogens attached (and not just hydrogens directly attached) to the charged carbon which result in hyperconjugation?

For the following compound: Looking at figure 2, my understanding of hyperconjugation is that carbon 2 is more electronegative than the hydrogens attached to it, and so pulls charge towards carbon 2, ...
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Confusion about gauche effect

This recent question about the gauche effect led me to read this rather older answer. The problem is that I notice I am still confused. To take the case of 1,2 difluoroethane, I drew these orbitals: ...
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Negative hyperconjugation stabilizes tricyclopentane derivate

As far as I know, negative hyperconjugation means, that we have electrons that are transferred from a p- or $\pi$- to a $\sigma^*$-orbital. In the lecture, we analyzed a TMS-substituted ...
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Why are tertiary carbocations so stable?

Today our lecturer provided this data to illustrate the relative stability of carbocations. \begin{array}{|c|c|c|c|c|} \hline \text{Substrate} & \ce{t-BuBr} & \ce{i-PrBr} & \ce{EtBr} &...
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Why is the eclipsed conformer more stable than the bisected conformer in 1-butene?

I have just started learning conformational analysis, and a major doubt came into my mind. In simple alkanes such as ethane, the staggered conformer is much more stable than the eclipsed conformer. ...
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Hyperconjugation vs. steric hindrance: which is stronger?

If we talk about a series of molecules: ethene, prop-1-ene, but-2-ene, etc., we see both hyperconjugation (which increases stability) and steric hindrance (which decreases stability). So which one is ...
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Alpha hydrogen and hyperconjugation

Why do we say that an alpha hydrogen is necessary for hyperconjugation? What exactly is an alpha hydrogen? From what I read online, it is the hydrogen attached to a functional group. Why is that ...
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How does hyperconjugation affect bond lengths in alkenes?

How does the number of hyperconjugates affect the $\ce{C=C}$ bond length in the compounds propene and 3,3-dimethylbut-1-ene? In general, is bond length directly or inversely proportional to the ...
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Why don't we have hyperconjugation with C-C bonds?

C-C bonds are weaker than C-H bonds.So why is hyperconjugation with C-C bonds not possible?
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How is hyperconjugation into antibonding orbitals stabilizing?

So I learned that hyperconjugation is electron delocalization from a $\ce{C-H}$ $\unicode[Times]{x3C3}$ bond into an empty p orbital (on a carbocation for example) or an antibonding orbital. I get how ...
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Stability of carbocation intermediates: secondary alkane versus primary allyl?

Say I have the following carbocations: The first is secondary; the second is resonance stabilized, but primary. Which is more stable and why? I've been looking around in my textbooks and haven't ...
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Why the H+ ion remains with the molecule even though there is no bond between it and hyperconjugative structure?

In hyperconjugation, it is known that form an $\alpha$ hydrogen, one $\sigma$ electron goes to the corresponding carbon carbon bond, and there is apparently or practically, no bond between the ...
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Why does hyperconjugation help for ring cleavage?

The question was to rationalize it the ring cleavage happens concerted or non-concerted. The papers "The Mechanism of the Thermal Decomposition of 1-Pyrazolines and Its Relationship to ...
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Through bond interaction in biradical dioxo compound and its correlation diagram

I'd like to investigate into the ring opening, the migratory reverse reaction of the electrocyclic ring-closure of Dimethyldioxirane: As a first question I'd like to ask if I have drawn the through ...
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Need of hyperconjugation?

Recently I read about Hyperconjugation. But i have a doubt. What is the need of hyperconjugation in this structure when there is charge separation resulting in lesser stable structure.
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Does hyperconjugation and induction always have the same effect?

My professor does not believe in the hyperconjugative effect. Instead, we only consider inductive effects. So do both effects have the same general effect? I know for methyl groups both have the ...