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revati joshi Grade: 12
        what is the overall use of thid topic?
7 years ago

Answers : (2)

AskiitianExpert Shine
10 Points
										

Hi


Hyperconjugation in organic chemistry is the stabilizing interaction that results from the interaction of the electrons in a sigma bond (usually C-H or C-C) with an adjacent empty (or partially filled) non-bonding p-orbital or antibonding π orbital or filled π orbital to give an extended molecular orbital that increases the stability of the system.  Only electrons in bonds that are β to the positively charged carbon can stabilize a carbocation by hyperconjugation.


Hyperconjugation can be used for rationalizing a variety of other chemical phenomena, including the anomeric effect, the gauche effect, the rotational barrier of ethane, the beta-silicon effect, the vibrational frequency of exocyclic carbonyl groups, and the relative stability of substituted carbocations. Hyperconjugation is proposed by quantum mechanical modeling to be the correct explanation for the preference of the staggered conformation rather than the old textbook notion of steric hindrance.



yperconjugation has an effect on several chemical properties 



  1. Bond length: Hyperconjugation is suggested as a key factor in shortening of sigma bonds (σ bonds) in such systems. For example, the single C-C bonds in 1,3-butadiene and methylacetylene are approximately 1.46 angstrom in length, much less than the value (1.54 angstrom) found in saturated hydrocarbons. This is due mainly to hyperconjugation that gives partial double-bond character of the bond.




  2. Dipole moments: The large increase in dipole moment of 1,1,1-trichloroethane as compared with chloroform can be attributed to hyperconjugated structures.

    Effectondipolemoment.jpg



  3. The heat of formation of such molecules are greater than sum of their bond energies; and the heats of hydrogenation per double bond are less than the heat of hydrogenation of ethylene.

  4. Stability of carbocations:


(CH3)3C+ > (CH3)2CH+ > (CH3)CH2+ > CH3+
The C-C σ bond adjacent to the cation is free to rotate, and as it does so, the three C-H σ bonds of the methyl group in turn undergoes the stabilization interaction. The more adjacent C-H bonds are, the larger hyperconjugation stabilization is.

7 years ago
suchintan mondal
8 Points
										

this is one of the most important basic tool of organic chemistry. It is generally used to explain stability of certain species.


One instance is-saytzeff's rule is based on & explained by hyperconjugation

7 years ago
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