Introduction
In an organic molecule, the presence of an electron attacking reagent causes electron displacement which leads to polarization of bonds. The effects are magnified in the form of the electromeric effect and hyperconjugation. In this article, students will learn about the two concepts of electromeric effect and hyperconjugation during an attack of a reagent on an organic compound.
Electromeric Effect
The electromeric effect is the instantaneous formation of a dipole molecule of an organic compound. It is a temporary effect and remains as long as the attacking reagent is present. In the electromeric effect, the complete transfer of a mutual pair of π-electrons occurs from one atom to another. The electromeric effect can be broadly classified into two categories:
Positive Electromeric Effect (+E) is defined as the transfer of pi-electrons of the atoms to which the attacking reagent gets attached. It can be seen in a reaction between an acid and an alkene. The acid attaches itself to the atom which obtains an electron pair in the transfer. This effect is generally observed when the attacking reagent is an electrophile and the π-electrons get actively transferred towards the positively charged atom.
Negative Electromeric Effect (-E) is defined as the transfer of the pi-electrons to the atom to which the attacking reagent is not attached. In this type of effect, the attacking reagent itself loses the electron pair in the transfer. It is generally observed when the attacking reagent is nucleophilic and the π-electrons get transferred to the atom with which the reagent does not bond.
Concept of Hyperconjugation
The concept of hyperconjugation is mostly the same as the electromeric effect; the only factor is that hyperconjugation is a permanent effect. In this effect, localization of σ electrons of C-H bond of an alkali group directly attached either to an unsaturated system's atom, or an unshared p orbitals atom takes place.
Hyperconjugation is the reason for the stabilization of glucose so that it allows the spreading of the positive charge. The greater the alkyl group number attached to a positively charged carbon atom, the greater is the stabilization and hyperconjugation interaction of the carbonation.
Causes
Hyperconjugation is basically a stabilization reaction resulting from the interaction between electrons in a σ-bond with either an adjacent partially filled or empty p-orbital or a π-orbital to form an extended molecular orbital.
Applications
There are many applications of hyperconjugation but most importantly it is used in rationalizing numerous chemical phenomena such as the gauche effect, the anomeric effect, the beta-silicon effect, the rotational barrier of ethane, the relative stability of the substituted carbocations & substituted carbon-centered radicals, the vibrational frequency of the exocyclic carbonyl groups, and the thermodynamic Zaitsev's rule for alkene stability.
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FAQs on Hyperconjugation - Electromeric Effect
1. What is hyperconjugation?
Hyperconjugation is a chemical phenomenon in an organic compound where the C-H bond's localization of σ electrons of an alkyl group is directly attached either to an unsaturated system's atom or an unshared p orbitals atom takes place. It is a permanent effect and allows the stabilization of organic compounds such as glucose.
2. What is the resonance effect?
The resonance effect is defined as the polarity caused in a molecule due to interaction between either a π bond or the lone pair electron or the interaction of 2 π bonds in the adjacent atoms. It is mostly found in molecules with conjugated double bonds or in molecules with at least 1 lone pair and 1 double bond. To know more about the resonance effect, visit Vedantu's website and get free study material which you can download in PDF format.
3. What are the types of electromeric effects?
There are two types of electromeric effect:
Positive Electromeric Effect or the +E effect denoting the transfer of π−electrons to the atom, where the reagent gets attached, and
Negative Electromeric Effect or the -E effect in which the transfer of several bonds to the atom, where the reagent is not attached.
4. Why is the resonance effect more powerful than hyperconjugation?
In the resonance effect, π-electrons are transferred while in the hyperconjugation effect,σ-electrons are transferred. Pi bonds are weaker than sigma bonds so it is easier to displace pi bonded electrons than sigma ones, thus, resonance takes place more easily than hyperconjugation. Hence, the resonance effect is stronger than the hyperconjugation effect.
5. What is the mesomeric effect?
The mesomeric effect is defined as a property of substituents or functional groups that are present in a chemical compound. The mesomeric effect is also known as negative resonance can be denoted by -M or -R.
6. Explain How Hyperconjugation Increases Stability.
The stability of free radical or carbocation will increase with an increase in the alpha Hydrogen. Alpha Hydrogen is hydrogen, which is connected to either sp3 hybridized carbon or active carbon.
7. Give an Example of Hyperconjugation?
One of the Hyperconjugation examples can be given as follows.
The CH3-CH=CH2 is more stable and has a higher heat if the hydrogenation than CH2=CH2, due to propylene's hyperconjugation stabilization.
