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    JEE Main Physics Formulas 2027 - Topic wise Important Formulas

    Hyperconjugation - Practice Questions & MCQ

    Edited By admin | Updated on Sep 18, 2023 18:35 AM | #JEE Main

    Quick Facts

    • 38 Questions around this concept.

    Solve by difficulty

    IUPAC name of the following compound is

    The compound which has one isopropyl group is:

    The IUPAC name for

     

    Arrange the following nucleophile in decreasing order of their nucleophilicity 

    1) $\mathrm{CH}_3-\mathrm{CO}-\mathrm{O}^{-}$
    2) $\mathrm{CH}_3-\mathrm{O}^{-}$
    3) $C N^{-}$

    4)  

    Which of the following alkane is most stable

    Hyperconjugation involves delocalisation of ______.

    (i) electrons of carbon-hydrogen \sigma bond of an alkyl group directly attached to an atom of unsaturated system.

    (ii) electrons of carbon-hydrogen \sigma bond of alkyl group directly attached to the positively charged carbon atom.

    (iii) \pi-electrons of carbon-carbon bond

    (iv) lone pair of electrons

    Given below are two statements :
    Statement I : Hyperconjugation is not a permanent effect.
    Statement II : In general, greater the number of alkyl groups attached to a positively charged C -atom, greater is the hyperconjugation interaction and stabilization of the cation.
    In the light of the above statements, choose the correct answer from the options given below

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    Which one of the following groupings represents a collection of isoelectronic species?

    (At. nos.: Cs-­55, Br­-35)

    The correct order of statbility for the following alkoxides is:

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    The electrophile, $E^{\oplus}$ attacks the benzene ring to generate the intermediate $\sigma$ - complex. Of the following, which $\sigma$-complex is of lowest energy?

     

    Concepts Covered - 3

    Hyperconjugation

    Hyperconjugation is a general stabilising interaction. It involves delocalisation of σ electrons of C—H bond of an alkyl group directly attached to an atom of unsaturated system or to an atom with an unshared p orbital. The σ electrons of C—H bond of the alkyl group enter into partial conjugation with the attached unsaturated system or with the unshared p orbital. Hyperconjugation is a permanent effect.
    To understand hyperconjugation effect, let us take an example of CH3CH2+(ethyl cation) in which the positively charged carbon atom has an empty p orbital. One of the C-H bonds of the methyl group can align in the plane of this empty p orbital and the electrons constituting the C-H bond in plane with this p orbital can then be delocalised into the empty p orbital as shown in the figure given below:

    This type of overlap stabilises the carbocation because electron density from the adjacent σ bond helps in dispersing the positive charge.

    In general, greater the number of alkyl groups attached to a positively charged carbon atom, the greater is the hyperconjugation interaction and stabilisation of the cation. Thus, we have the following relative stability of carbocations:

    Hyperconjugation is also possible in free radicals, alkenes and alkylarenes.

    In general, greater the number of hyperconjugative structures, greater is the stability.

    Nomenclature of Compounds(Arenes) - 1

    The IUPAC names and common names of some of the compounds are given below:

                            
    IUPAC name - Methylbenzene                            
    Common name - Toluene


    IUPAC name - Ethenylbenzene
    Common name - Styrene

     


    IUPAC name - 2-Methylphenol
    Commoon name - o-Cresol

    Application of Electrophile and Nucleophile

    Electrophiles: These are those species that accept electrons. Usually, they are positively charged species.

    \text { Neutral electrophiles : } \mathrm{BF}_{3}, \mathrm{R}, \mathrm{CR}_{2}, \mathrm{AlCl}_{3}, \mathrm{FeCl}_{3}

    \textrm{Positive electrophiles : } \mathrm{H}^{+}, \mathrm{H}_{3} \mathrm{O}^{+}, \mathrm{Cl}^{+}, \mathrm{Br}^{+}, \mathrm{I}^{+}, \mathrm{N}^{+} \mathrm{O}_{2}, \mathrm{~N}^{+} \mathrm{O}, \mathrm{R}^{+}

    Nucleophiles: These are those species which has a tendency to donate electrons pairs or react at electron-poor sites.

    Study it with Videos

    Hyperconjugation
    Nomenclature of Compounds(Arenes) - 1
    Application of Electrophile and Nucleophile

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    Books

    Reference Books

    Hyperconjugation

    Chemistry Part II Textbook for Class XI

    Page No. : 355

    Line : 42

    Nomenclature of Compounds(Arenes) - 1

    Chemistry Part II Textbook for Class XI

    Page No. : 343

    Line : 1

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