Hyperconjugation in Organic Chemistry | Explained by IITian | IIT-Jee Mains, Advance, BITSAT & AIIMS
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- เผยแพร่เมื่อ 13 ต.ค. 2024
- Hello Guys, Hyperconjugation is one of the most important topic for IIT-Jee Mains, Advance, AIIMS, NEET & BITSAT.
The delocalization of σ-electrons or lone pair of electrons into adjacent π-orbital or p-orbital is called hyperconjugation.
It occurs due to overlapping of σ-bonding orbital or the orbital containing a lone pair with adjacent π-orbital or p-orbital.
It is also known as "no bond resonance" or "Baker-Nathan effect".
Conditions for hyperconjugation
There must be an α-CH group or a lone pair on atom adjacent to sp2 hybrid carbon or other atoms like nitrogen, oxygen etc.
E.g., Alkenes, alkyl carbocations, alkyl free radicals, nitro compounds with α- hydrogen
The displacement of σ-electrons towards the multiple bond occurs when there are hydrogens on the α-carbon (which is adjacent to the multiple bond). This results in the polarization of the multiple bond.
E.g. In propene, the σ-electrons of C-H bond of methyl group can be delocalized into the π-orbital of doubly bonded carbon as represented in the lecture.
In the same way, the other hydrogens on the methyl group also participate in the hyperconjugation. This is possible due to free rotation of C-C bond so that the other C-H bonds can also participate in the hyperconjugation. Thus the propene molecule can show following resonance structures, which confer stability to it.
CONSEQUENCES & APPLICATIONS OF HYPERCONJUGATION:-
The increasing order of stability of alkenes with increases in the number of methyl groups on the double bond is explained inside the lecture.
This order is supported by the heat of hydrogenation data of these alkenes. The values of heats of hydrogenation decrease with increase in the stability of alkenes.
Also the heats of formation of more substituted alkenes are higher than expected.
However it is important to note that the alkyl groups attached to the double bond must contain at least one hydrogen atom for hyperconjugation. For example, in case of the 3,3-Dimethyl Butene-1 containing a tert-butyl group on doubly bonded carbon, the hyperconjugation is not possible.
It is also important to note that the effect of hyperconjugation is stronger than the inductive effect.
For example, the positive inductive effect of ethyl group is stronger than that of methyl group. Hence based on inductive effect, 1-butene is expected to be more stable than propene.
However propene is more stable than 1-butene. This is because there are three hydrogens on α-methyl group involved in hyperconjugation. Whereas, in 1-butene there are only two hydrogen atoms on -CH2 group that can take part in hyperconjugation.
2) Stability of carbocations (carbonium ions):
The ethyl carbocation, CH3-CH2+ is more stable than the methyl carbocation, CH3+. This is because, the σ-electrons of the α-C-H bond in ethyl group are delocalized into the empty p-orbital of the positive carbon center and thus by giving rise to 'no bond resonance structures' as shown below. Whereas hyperconjugation is not possible in methyl carbocation and hence is less stable.
In general, the stability of carbonium ions increases with increase in the number of alkyl groups (containing hydrogen) attached to the positively charged carbon due to increase in the number of contributing structures to hyperconjugation.
Note: This type of hyperconjugation can also referred to as isovalent hyperconjugation since there is no decrease in the number bonds in the no bond resonance forms.
Thus the increasing order of stability of carbocations can be given as: methyl , primary, secondary , tertiary as depicted below:
3) Stability of free radicals:
The stability of free radicals is influenced by hyperconjugation as in case of carbonium ions. The the σ-electrons of the α-C-H bond can be delocalized into the p-orbital of carbon containing an odd electron.
Due to hyperconjugation, the stability of free radicals also follow the same order as that of carbonium ions i.e., methyl , primary , secondary ,tertiary.
4) Dipole moment & bond length:
The dipole moment of the molecules is greatly affected due to hyperconjugation since the contributing structures show considerable polarity.
The bond lengths are also altered due to change in the bond order during hyperconjugation. The single bond may get partial double bond character and vice versa.
E.g. The observed dipole moment of nitro methane is greater than the calculated value due to hyperconjugation. The observed C -N bond length is also less than the expected value due to same reason.
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Hyperconjugation using MOT. #yourbiggestfan
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Hyperconjugation in 5th dimension 😲🤯mind blowing enlightment guruji
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1) at the moment when hypercongucation take place, is it right to say that sp3 carbon is converted into sp2 hybridised.
yes
Sir aapne deuterium exchange keto enol tautomerism ka video banaya hai kya mujhe nahi mil Raha hai ???
wow sir best organic chemistry teacher ever.. whenever i used to ask my teachers why this happens in organic..most of the time they say it's experimental and ask me to simply cram it!.. thanks sir
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priya sehgal can u plz tell me hyperconjugation kiya pura explain kara gya hai is topic mai
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sir plz explain how u know that PI (star) MO is empty and PI MO is filled due to C=C bond ??
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sir it is hyper explaination for hyperconjugation .very very helpful.thanks sir
thnku so much sir mujhe phele hyperconjugation kuch bhi nhi samja tha......aap ki video dekhne ke baad samaj mai aya..........sir or video banate raho............n i am a neet student......n thanks for the video sir
sir i have been taught that no. of hyperconjugative structures = no of alpha hydrogens...in the example of ch3ch2+ there are only 3 hyperconjugative structures but u have counted the 4th one also which was the one whose hyperconjugative structures are to be found
Sir I have a question sir why carbonyl compounds like acetone etc don't show hyperconjugation although they have alpha carbon with alpha hydrogen???
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University lectures
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During sigma to pi conversion of bond ...the sigma bond of hydrogen is formed by hybride orbital...and for formation of pi bond a unhybridize orbital is required how the hybride orbita of carbon become unhybride to form pi bond with another carbon
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Sir at 11:55 , if the carbon containing positive charge is sp2 hybridized, then why do you represent it's hydrogen as wedge and dash?isn't all hydrogen should be in same plane?
thank you sir, i want to know ki agar hydrogen k jagah uska isotopes (deuterium, tritium ) rhe to hyperconjugation ka effect kaise vary karega (explain)...
How much time will it take to reply ?
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Sir e back bonding k jasa hai kya? Oor rotation k time ohapar busting of electron hoga?
Guruji Please reply
I was your unacademy student had had completed GOC from there. In that you had taught ‘Carbon-carbon hyper conjugation’ but my chemistry teacher does not agree to it. Is there any experimental evidence for it Guruji?
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Sir 6 alpha hydrogen h to 6 bar hydrogen ion banega to seventh wala hyperconjugating structure kon sa le rhe h.. jiske hyperconjugating structures ban rhe h..Usko to lenge nhi ??? Kyunki uske to ban hi rhe h to saatva konsa.
How no.of hyperconjugating structures= no.of alpha hydrogen + 1
Do all the hydrogens in carbon atom show hyperconjugation simultaneously
Chemistry itni bhi ashan ho sakti hai kabhi socha ni tha
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sir aap aromaticity &huckel rule dal do
**Read description also**
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Thank you guruji for this free brain stoming video on hyperconjugation
If delocalisation happens both the carbon will become sp2 hybridised and free rotation about Sigma bond will get hindered, don't you think so?
Clearly concept ho giya sir. thank you very much sir
does ketone adjacent alpha hydrogen show hyperconjugation like ch3-co-ch2 ,,does it show hyperconjugation
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There is my two question ...why adjusment carbon should not sp2 which is connected with that doubly bonded carbon or carbo cation
Sir will alkynes show hyperconjugation?
Sir alfa hydrogen k place pr agr carbon ho to vo q nhi apna electron shift kr skta h vacant p orbital me.
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Sir at 49:27 can we use the logic that in gem alkenes the same carbocation is stablised by two ch3 groups. Is it correct to use this
logic ? Sir plzz reply!!
Sr last me dehydration ke products me ek compund ke pas 2 alpha hydrogen ha so 3 hyperconjugating structure bnegi
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Pls sir say the difference between tautomerism and hyperconjugation. In both delocalisation of electrons happen. So tautomerism is kind of hyperconjugation. But its not true. Why sir pls clarify. ......
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number of hyper conjugating structure (or no bond resonating structure)= number of alpha hydrogen
please upload video on reverse hyperconjugation
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Sir I have read number of H. S is equal to number of alpha hydrogen but you say in your lecture number of H. S is equal to number of alpha hydrogen +1.I do not understand and as well as please say what is negative hypercojugation.,what is it application
Yes you are no of hyperconjugation structure is equal to alpha Hydrogen
Sir I have a simple question that you said that (Me)3 C-Ph have more inductive effect.. but why since there is no alpha hydrogen on alpha carbon atom so there will be no hyperconjugation so why other methyl group show electron donating effect if there will be no hyperconjugation...As we know hyperconjugation is real reason behind electron donating nature of methyl group.
Ya it's true that benzene carbon is sp2 hybridized so it will have more electronegativity..So Carbon adjacent to benzene will have some partial positive charge but why presence of three methyl group increase the inductive effect if there is no hyperconjugation. Pls reply.
I am talking about 33:31 part of video pls have a look
Sir 26:00 me jo alkene banaya he usme to 5 alpha hydrogen he to waha to 6 hyperconjugation structures honge na ? Aapne 4 kyu bola sir?
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Cyclohexane carbocation m hyperconjugation kaise hoti h
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Hat's off to you sir for the way you explained the hyperconjugation in propene there is no proper explaination of these in any channel thanks sir
23:23 sir why should we take +1? No of hyper conjugative structures= no of alpha hydrogen's isn't it why should we take +1 please explain
Including original me +1
Without original me only equal to alpha hydrogen
Pls agar aapko samajh aaya ho to mujhe bhi samjha de
Sir π bond formation k baad rotation restrict nehi ho jayega kya???
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