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.

Filter by
Sorted by
Tagged with
1
vote
0answers
16 views

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 ...
0
votes
1answer
49 views

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 ...
0
votes
0answers
40 views

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 ...
2
votes
0answers
46 views

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&...
3
votes
0answers
73 views

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): ...
1
vote
1answer
44 views

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 ...
8
votes
1answer
275 views

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 ...
2
votes
1answer
74 views

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, ...
0
votes
0answers
81 views

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 ...
0
votes
0answers
22 views

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 ...
1
vote
1answer
80 views

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?...
0
votes
0answers
95 views

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 ...
0
votes
0answers
22 views

Why can't Ethene Carbocation do Hyperconjugaion? [duplicate]

Question I was studying Hyperconjugation and taught that Hyperconjugation is like Resonance of Sigma bonds ( C-H ) when any other Carbocation or alkene or alkyne carbon influences it (sigma bonds C-H)....
1
vote
1answer
507 views

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 ...
0
votes
0answers
91 views

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 ...
2
votes
3answers
183 views

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 ...
-1
votes
1answer
511 views

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 ...
2
votes
0answers
74 views

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 $\ce{F}$ ...
0
votes
1answer
78 views

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....
1
vote
0answers
49 views

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, ...
0
votes
1answer
241 views

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" ...
3
votes
0answers
419 views

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 ...
1
vote
2answers
1k 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 ...
0
votes
1answer
512 views

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 ...
2
votes
1answer
719 views

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)...
0
votes
0answers
80 views

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 > ...
2
votes
0answers
206 views

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 ...
2
votes
2answers
1k views

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 $\ce{CF3}$, ...
1
vote
0answers
787 views

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 ...
2
votes
1answer
158 views

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 ...
0
votes
1answer
2k views

Which of the following show hyperconjugation

None of the given compounds have any alpha hydrogen to show hyperconjugation, but the given answer is c.
4
votes
1answer
258 views

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 ...
3
votes
1answer
347 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 ...
1
vote
2answers
548 views

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 ...
4
votes
3answers
1k views

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 ...
2
votes
1answer
397 views

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 ...
0
votes
1answer
115 views

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 ...
0
votes
1answer
3k views

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 ...
-1
votes
1answer
2k views

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....
2
votes
2answers
864 views

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. ...
1
vote
1answer
335 views

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 ...
6
votes
2answers
2k views

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 ...
0
votes
1answer
771 views

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 ...
5
votes
1answer
2k views

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 ...
2
votes
1answer
243 views

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 ...
4
votes
0answers
269 views

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): ...
6
votes
2answers
6k views

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. ...
-1
votes
1answer
677 views

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 ...
4
votes
1answer
5k views

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 ...
11
votes
1answer
9k views

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 ...