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The +M effect, also known as the positive mesomeric effect, occurs when the substituent is an electron donating group. The group must have one of two things: a lone pair of electrons, or a negative charge. In the +M effect, the pi electrons are transferred from the group towards the conjugate system, increasing the density of the system.
The reaction process begins with deprotonation at the halogenated position. [3] Because of the ester substituents, this carbanion is a resonance-stabilized enolate.This nucleophile next attacks the carbonyl reagent, forming a carbon–carbon bond.
the inductive effect. Electronegative atoms adjacent to the charge will stabilize the charge; the extent of conjugation of the anion. Resonance effects can stabilize the anion. This is especially true when the anion is stabilized as a result of aromaticity. Geometry also affects the orbital hybridization of the charge-bearing carbanion. The ...
The trend of carbocation stability. Note the stabilization effects from adjacent carbons that donate electrons to the positive charge. The opposite trend is seen in carbanion stability. In isotopes, a tertiary bound hydrogen is more likely to be lost because the resulting carbocation is the most stable species. Radical reactions that cleave C ...
Hyperconjugation can be used to rationalize a variety of 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 and substituted carbon centred radicals, and the thermodynamic Zaitsev's rule for alkene stability.
These strong nonlinear effects could not be fully rationalized based on the known concepts of the isotopic effects. These and other observations make it possible that isotopes have a much more profound importance than could ever have been imagined by the pioneers. In 2011 Roman Zubarev formulated the isotope resonance hypothesis.
An example of the E1cB reaction mechanism in the degradation of a hemiketal under basic conditions. The E1cB elimination reaction is a type of elimination reaction which occurs under basic conditions, where the hydrogen to be removed is relatively acidic, while the leaving group (such as -OH or -OR) is a relatively poor one.
The aldol reaction has one underlying mechanism: a carbanion-like nucleophile attacks a carbonyl center. [ 12 ] If the base is of only moderate strength such as hydroxide ion or an alkoxide , the aldol reaction occurs via nucleophilic attack by the resonance-stabilized enolate on the carbonyl group of another molecule.