What makes an electrophile strong

What is the electrophile in the nitration of benzene? Why does benzene undergo electrophilic substitution reaction easily? Excess Reagent.

Metathesis Reaction. E2 Reaction. March 24, at am. Leave a Reply Cancel reply Your email address will not be published.

Trending Topics Hydrohalogenation. Catalytic Reaction Catalysis. Aufbau Principle. Lewis Structure. Elementary Reaction. Formal Charge. Buffer Solution. One of the most important factors to consider when looking at the electrophile in a nucleophilic substitution reaction is steric hindrance. However, backside attack on the tertiary carbon electrophile is blocked by the bulky methyl groups, preventing access to the site of electrophilicity.

The degree of steric hindrance determines relative rates of reaction: unhindered methyl electrophiles react fastest, and more hindered secondary carbon electrophiles react slowest, assuming all other reactions conditions are identical. Think back to Chapter 7, when we were learning how to evaluate the strength of an acid.

In many cases, this conjugate base was an anion — a center of excess electron density. Anything that can draw some of this electron density away— in other words, any electron withdrawing group — will stabilize the anion. Conversely, a carbocation is stabilized by an electron donating group, and de stabilized by an electron withdrawing group.

A positively charged species such as a carbocation is electron-poor, and thus anything which donates electron density to the center of electron poverty will help to stabilize it.

Alkyl groups, because of the electrons in their carbon-carbon and carbon-hydrogen bonds, are weak electron-donating groups, and will stabilize nearby carbocations. What this means is that, in general, more substituted carbocations are more stable: a tert-butyl carbocation, for example, is more stable than an isopropyl carbocation. Primary carbocations are highly unstable and not often observed as reaction intermediates; methyl cations are even less stable.

This overlap effectively spreads the positive charge over a larger area. As the degree of substitution on a carbocation increases, so does the capacity for stabilizing hyperconjugation interactions.

The presence of an electron-withdrawing group - such as a fluorine atom - will significantly destabilize a carbocation through the inductive effect.

It is possible to demonstrate in the laboratory we'll see how in problem The positive charge in cation B is closer to the electron withdrawing carbonyl substitution, and as we learned in section 7. Stabilization of a carbocation can also occur through resonance effects. Recall from section 7. A positive charge is also stabilized when it can be delocalized over more than one atom.

Consider a benzylic carbocation, where the positively-charged carbon is bonded directly to an aromatic ring. In example A, a carbonyl is shown. We know that the carbon of the carbonyl is electrophilic because we can place a positive charge on it via resonance.

This means that a nucleophile will attack the carbonyl at this carbon atom. In example B, we show diatomic chlorine. Diatomic halogen molecules are electrophilic because the bond between the halogen atoms as polarizable, meaning that the electrons can reside on either atom at any time, making one of the atoms more electrophilic than the other. In example C, we see that alkyl halides are also electrophilic because of a polarizable bond between the carbon and the chlorine atoms. Unlike example B, example C is a permanent dipole.

Example D is an example of a strong acid completely disassociating, which gives off a proton as the electrophilic species. Finally in example E, we see it you can create an electrophile from a non-electrophilic molecule. Here we have reacted nitric acid with sulfuric acid to form the nitronium ion, which is highly electrophilic. Electrophiles are also Lewis Acids. Lewis acids accept electron density, because they are electron deficient.

The reagent acting as the Lewis Acid can suck electron density from the electrophile, making even more electron deficient and therefore even more reactive.