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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Between compounds having same functional groups, why does the one with greater -I effect have higher acidic strength

Consider the two compounds $\ce{FCH2COOH}$ and $\ce{ClCH2COOH}$. Since fluorine is more electronegative than $\ce{Cl}$ it will show a greater –I effect. It will pull the the electrons closer towards ...
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How is propene more reactive as well as more stable than ethene?

I know that hyperconjugation stabilises a double bond. But in propene an electron-donating group $(\ce{-CH3})$ is increasing the electron density at the double bond, so its nucleophilicity should be ...
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How does Hyperconjugation stabilize a Carbon Free Radical? [closed]

I tried drawing the resonance structures but just cannot see how donating two electrons to a carbon that only needs one electron make it more stable? I stumbled upon this question asked years ago ...
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Why are the unsaturated fatty acids usually unconjugated?

My textbook gives the structures of the unsaturated fatty acids in food including oleic acid, linoleic acid, linolenic acid and docosatetraenoic acid. I figure that when two or more $\ce{C=C}$ double ...
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Reactivity of Alkenes with HBr [closed]

I am new in the Organic Chemistry (World of Reactions). I had got one question in my test. But, when I had seen it, I got no proper logic to tick the correct answer, and then when I saw solution, then ...
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Ortho effect and the relative acidity in aromatic acids [duplicate]

What is the order of the acidity of 2-methyl benzoic acid and 2-isopropyl benzoic acid? I know about ortho effect which states that the acidity of ortho- substituted aromatic carboxylic acids is ...
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How come the methyl group (-CH3) is electron donating?

If the inductive effect operates purely through electronegativity differences, how come the methyl group is considered to donate electrons through the inductive effect? My textbook says that there is ...
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Why is the carbanion stability order the way it is? (3*<2*<1*)

According to the lecture notes I made, a 1* carbanion is more stable than a 3* carbanion. I can't grasp exactly why. (I had a look at the similar questions, the answers didn't help) With my very ...
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Question regarding conflicting results of checking the electron-preciseness of isoelectronic species via NBO and EHM calculations

It is well known that the tert-butyl cation's empty 2p orbital on the central carbon is stabilised by hyperconjugation from neighboring C-H bonds. This would mean that the central 2p "lone pair&...
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Does vinyl chloride deactivate the benzene ring?

I came across the following option of a multiple choice question (The options are in the form of assertion and reasoning side-by-side and the incorrectly matched statements are to be marked): ...
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Carbocation formation and stability from bromo compounds

When heated,the following bromo-species all form carbocations via $\sigma$ bond cleavage. For each structure draw the corresponding carbocation and briefly describe how it is stabilised. This is my ...
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How to compare stability between 5‐methylcyclohexa‐1,3‐diene and 3‐methylenecyclohexene?

Problem Compare stability of 1 and 2: Answer My approach Both have the same number of π-bonds. Both have one resonance structure. Both are non-aromatic. In 1 there are three α-hydrogens, whereas ...
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Choosing hyperconjugation when resonance doesn't give a reason for stability

Which of the following structures would be least stable? I initially approached it like this: As both are allylic carbocations, and that both are in fact resonating structures of the same molecule, ...
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Stabillity of ethyl, iso propyl and vinyl free radicals

Well this might seem like a dumb question but I was just wondering if any other factor would apply here as well? By simply looking at the number of hyperconjugative structures, I could easily tell ...
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How would we arrange these in the increasing order of stability? [duplicate]

Here we have three isomers of butene there structure of who I have attached: cis-butene trans-butene iso-butene I was able to figure out that the trans isomer would obviously be more stable than the ...
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Does hyperconjugation only arise from C–H bonds?

I have to an extent understood hyperconjugation but I don't understand why the donation can only occur from a $\mathrm{sp^3}$-hybridised orbital bonded with hydrogen? What about other bonding partners?...
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Which enol form is more stable?

I came across an example today while I was studying tautomerism. It is an example of tautomerism exhibited by acetylactone/1,3-diketone; given under the keto-enol systems under 1-3 migration/triad ...
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Total number of “hyperconjugable” hydrogens in 1-(3-ethyl-4-methylphenyl)-2-methylprop-1-ylium

How do I find the total number of “hyperconjugable” structures for 1-(3-ethyl-4-methylphenyl)-2-methylprop-1-ylium? I read some sources stating that the total number of “hyperconjugable” structures ...
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Application of Markovnikov's rule with EWG's and Resonance

I want to ask a question concerning Markovnikov's rule. Consider the following question: We can tell that there will be two types of stabilisation upon formation of the carbocation: Resonance via ...
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Why is 1,2,3,4,5,8-hexahydronaphthalene more stable than 1,4,4a,5,8,8a-hexahydronaphthalene? [closed]

Why is 1,2,3,4,5,8-hexahydronaphthalene (1) more stable than 1,4,4a,5,8,8a-hexahydronaphthalene (2)? A follow-up question is about stability being estimated by counting the α-hydrogens. In the first ...
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Comparing reactivity of 1-chloroethane and 1-chloropropane in an SN1 reaction

Beginning with a reference to a well known question. Order by reactivity towards SN1 reaction. According to some facts about SN1 reactions, rate depends on: Stability of carbocations Better leaving ...
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2 votes
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Hyperconjugation and inductive effect on carbocations [duplicate]

(I know there are many related questions, so please tell me which posts can solve my doubts before you close this question, thank you.) $1$. $\ce{^+CH2F}$ is very unstable. This is because $\ce{F}$ ...
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Hyperconjugation - concept clarification

As I currently understand it, Hyperconjugation occurs in carbocations and alkenes via the interaction of the electrons in the MO of a C-H bond at an adjacent carbon to bring stability to the system....
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Methyl group and acidic nature [duplicate]

After reading various answers here on StackExchange (like Why is the methyl group electron-donating via the inductive effect? and Strongest negative inductive effect group between trimethylammonium, ...
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Hyperconjugation, stability of molecules, and heat of formation

I recently asked a question about why the heat of formation of organic radicals and positive ions decreases with their size and degree of branching at the radical or ionic site. The user "Buttonwood" ...
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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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3 votes
1 answer
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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 than ...
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3 votes
1 answer
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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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1 vote
2 answers
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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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1 answer
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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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1 answer
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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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2 votes
2 answers
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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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1 vote
1 answer
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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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2 votes
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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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4 votes
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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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