Dancing Resonance (exceptional stable cation) | IIT JEE …
What is the meaning of dancing resonance?
Dancing resonance is a hypothetical phenomenon which is shown in structures of carbocation attached directly to a three membered ring. The exceptional stability of cyclopropane methyl cation can be explained by the concept of dancing resonance concept.
Why is Tricyclopropyl carbocation more stable?
methylcyclopropyl carbocation is more stable than benzylic carbocation just because those inner bonds of cyclopropane are more nucleophilic than the phenyl pi system.
Why cyclopropyl methyl carbocation is more stable than benzyl carbocation?
Cyclopropyl methyl carbocation is more stable because of the bent bonds. These bonds stabilize more than the delocalisation or resonance in benzylic carbocation.
How carbocation is formed?
Cleavage of Bond of Carbon
Whenever there is cleavage of the bond of carbon and atoms attached to it, the leaving group takes away the shared electrons. Thus leaving the carbon atom as electron deficient. As a result, a positive charge is developed forming a carbocation.
What is carbocation and carbanion?
Carbocation and carbanion are terms used to describe organic chemical entities that have an electrical charge on a carbon atom. The primary distinction between carbocation and carbanion is that carbocation has a positively charged carbon atom, whereas carbanion contains a negatively charged carbon atom.
What is hyperconjugation explain?
In organic chemistry, hyperconjugation (σ-conjugation or no-bond resonance) refers to the delocalization of electrons with the participation of bonds of primarily σ-character.
Why are carbocations important?
Carbocations adjacent to another carbon-carbon double or triple bond have special stability because overlap between the empty p orbital of the carbocation with the p orbitals of the π bond allows for charge to be shared between multiple atoms.
What is hybridization of carbocation?
A carbocation is an sp2 hybridized carbon bearing three substituents, with an empty p orbital perpendicular to the plane of the other atoms (see 1).
What is geometry of carbocation?
Thus, the geometry of carbocation is trigonal planar as it has 3 sigma bonds.
How many p orbitals are in a carbocation?
Molecular Orbitals of an Allylic Carbocation
You can clearly see the interactions between all three of the p orbitals from the three carbons resulting in a really stable cation.
Why does carbocation have 6 electrons?
Methyl carbocation contains 3 bond. So it has 6 electron in last orbit and it has already 2 electron in 1s2 which is not involved in bonding. Hence total 8 electron or 4 pairs of electrons.
What are Carbanions give example?
Carbanions: Carbanions may be defined as negatively charged ions, in which carbon is having a negative charge and it has eight electrons in the valence shell. For example, Carbanions are very short-lived and highly reactive species.
Is a carbocation a radical?
Free radicals have only 7 electrons in their valence shell. They are higher in energy than atoms with 8 valence electrons. Carbocations are also electron-deficient species. Since carbocations have only 6 valence electrons, they are higher in energy than free radicals.
What is allylic and benzylic?
An allylic group is defined as a group on carbon, which is found adjacent to the double bond, whereas a benzylic group is defined as a group on carbon, which is found adjacent to the benzene ring or the substituted benzene ring. In many situations, allylic groups and benzylic groups are unusually reactive.
What is tertiary allylic?
If in one or both resonance forms of an allylic carbocation the formal charge of +1 is on a tertiary carbon, the allylic carbocation is called a tertiary (3°) allylic carbocation.
What is a vinyl carbocation?
Vinylic carbocation: A carbocation in which the carbon atom having the open octet and positive formal charge is part of a carbon-carbon double bond. The carbocation carbon has sp hybridization.
Why benzyl cation is unstable?
The phenyl carbocation is unstable because of the high bond energy of the aromatic C-H bond. The C-H bonds of benzene are sp2 hybridized. The high s character means that the electrons are closer to the nucleus, so we must add more energy to remove these electrons and break the bond.
What is isopropyl carbocation?
Isopropyl carbocation depicts the property of hyperconjugation. There is a presence of an overall +1 charge that is further shared by the seven different atoms. This carbonation is stable in nature.
Is Benzylic more stable than allylic?
Generally, the benzylic carbocations are more stable than allylic carbocations as they form more number of resonating structures and have less electron affinity.
What is benzylic radical?
A benzylic radical is a resonance-stabilized radical in each of the two equally stable major resonance forms of which the unpaired electron is on a benzylic carbon. The lightest benzylic radical 1 is called the benzyl radical.
Why benzyl carbocation is more stable than tertiary carbon cation?
Most of us believe benzyl carbocation is more stable than tertiary because benzyl carbocation involves in resonance. Some of the authors believe that Tertiary carbocation is more stable as it involves maximum +I effect and maximum hyperconjuation +H (9 alpha hydrogens).
How is a benzylic cation stabilized?
The p system of a benzene ring can stabilise an adjacent carbocation by donating electron density through resonance.
What is the difference between hyperconjugation and resonance?
Hyperconjugation is an extension of resonance since both approaches allow a molecule to stabilise by delocalizing electrons; moreover, hyperconjugation requires delocalization of sigma bond electrons along with pi bond electrons, whereas resonance induces delocalization of sigma bond electrons.
What do you mean by Baker Nathan effect?
In organic chemistry, the Baker–Nathan effect is observed with reaction rates for certain chemical reactions with certain substrates where the order in reactivity cannot be explained solely by an inductive effect of substituents. This effect was described in 1935 by John W. Baker and W. S. Nathan.
What is the difference between conjugation and hyperconjugation?
The two terms conjugation and hyperconjugation describe unsaturated organic compounds. The main difference between conjugation and hyperconjugation is that conjugation is the overlap of p-orbitals across a σ bond whereas hyperconjugation is the interaction of σ-bonds with a pi network.
What is no bond resonance?
Hyperconjugation is called no bond resonance. Hyperconjugation takes place when the delocalization of σ-electrons or lone pair of electrons takes place into adjacent π-orbital or p-orbital.
What is meant by plus I Effect?
Acidity and basicity
Groups having +I effect (Inductive effect) attached to a molecule increases the overall electron density on the molecule and the molecule is able to donate electrons, making it basic.
What is hyperconjugation and Electromeric effect?
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.
What is hyperconjugation and inductive effect give example?
The key difference between hyperconjugation and inductive effect is that hyperconjugation explains the interaction between sigma bonds and pi bonds whereas inductive effect explains the transmission of an electrical charge through a chain of atoms.
What is sacrificial hyperconjugation?
Sacrificial hyperconjugation refers to the hyperconjugation where canonical form involves no bond resonance but in the main form involves no charge distribution. This type of hyperconjugation is also known as “no bond hyperconjugation”.
Why does hyperconjugation occur?
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”.
Is resonance effect permanent?
It is a permanent effect that operates in unsaturated molecules and especially in those unsaturated molecules which involve conjugation. Permanent and complete shifting of pi-electron pair of a multiple bonds to one of the bonded atoms or to the adjacent single bond is called resonance effect.
What is phenyl carbocation?
The phenyl cation is an unstable, high-energy species. Because of the high bond energy of the aromatic C−H bond, the phenyl carbocation is unstable. Note: Because the phenyl cation core has two ligands but no lone pairs, sp is the most stable hybridization.
Why 3 degree carbocation is most reactive?
A tertiary carbocation is more stable than a secondary carbocation which is more stable than a primary carbocation. Greater the stability of the carbocation, greater will be the ease of formation of carbocation, and hence faster will be the rate of the reaction.
Why tertiary carbanion is unstable?
Stability order of carbanions decreases as we move from primary to tertiary anion because due to +I effect of methyl groups there is an increased intensity of negative charge on central carbon of tertiary carbanion which further makes it unstable.
What is the geometry of carbanion?
 The carbanion exists in a trigonal pyramidal geometry. Formally, a carbanion is the conjugate base of a carbon acid.
Why is 2 degree carbocation more stable?
As more alkyl groups are attached to the carbocation more inductive electron donation occurs and the carbocation becomes more stable. The second reason alkyl groups stabilize carbocations is through hyperconjugation.
Which carbanion is more stable?
An electron withdrawing group (such as nitro group) stabilises carbanion. −NO2 group is electron withdrawing by both −I effect and −R effect. Hence, (c) is the most stable.
What is a hydride shift?
Hydride shift is a rearrangement of a hydrogen atom in a carbocation to make the intermediate structure more stable. It is generally observed in rearrangement reactions. After shifting a hydrogen atom from one carbon to another, structural isomers of compounds are formed.
Is tertiary more stable than primary?
Tertiary carbon free radicals are more stable than secondary and primary since the radical is stabilised by electrical effects of the other attached groups because it will effectively be hyperconjugation in this situation.
Which is more stable carbocation or carbanion?
Carbocation is more stable. For example, because of the presence of the three donor methyl groups that donate electrons, tert-butyl carbocation (CH3)3-C+, this charged ion is highly stabilised and thus largely stabilises the positive charge.
What is allylic and vinylic position?
Allylic carbon is a carbon atom bonded to a carbon atom that in turn is doubly bonded to another carbon atom. Vinylic carbon is a carbon that is involved in a double bond with another carbon.
What is Vinylic?
(ˈvaɪˈnɪlɪk ) adjective. of or relating to vinyl.
What is the difference between allylic and vinylic?
Difference between Allylic and Vinyllic carbon is that allylic carbon is the carbon atom that is adjacent to double bonded carbon atom wherease vinylic carbon atom is one of the two atoms that shares the double bond.
What is a vinylic position?
Vinylic position: On, or bonded to, the carbon of an alkene. This molecule has four vinylic positions, each marked with *. Lewis structure of vinyl chloride, a vinylic halide. Related terms: Vinyl group, vinylic hydrogen, vinylic carbocation, allylic position, benzylic position, propargylic position.
What is a vinyl hydrogen?
Vinylic hydrogen: A hydrogen atom bonded to an sp2 carbon of an alkene. The vinylic hydrogens are shown in red. None of the other hydrogens are vinylic.
Which resonance is not possible?
In the molecule, CH2=CHN⊕Me3 resonance is not possible. There is no lone pair of electrons on N atoms as all valence electrons on N atom are involved in bond formation.
What is benzylic carbon?
A benzylic carbon is a saturated carbon residing on an aryl group in an organic species.
What is alkyl carbocation?
Alkyl carbocations are sp2 hybridised, planar systems at the cationic C centre. The p-orbital that is not utilised in the hybrids is empty and is often shown bearing the positive charge since it represents the orbital available to accept electrons.
Aromaticity & Dancing Resonance Cl-51 Free Organic …
DANCING RESONANCE OR SIGMA BOND RESONANCE
Dancing Resonance (exceptional stable cation) | Vineet Khatri