Table of Contents
- 1 What is sigma complex and how it get stability?
- 2 Which sigma complex is more stable?
- 3 Which of the following reacts slower than benzene in electrophilic substitution?
- 4 Which meta resonance structure is the most stable?
- 5 What is a sigma complex in benzene?
- 6 What is an electrophilic aromatic substitution for benzene?
What is sigma complex and how it get stability?
When the nitro group adds at the ortho or para position, the stability of the sigma complex is increased by the presence of a fourth resonance form . The greater the stability of the sigma complex causes the ortho and para products for form faster than meta.
Which sigma complex is more stable?
So, 3-methoxy-6-nitrocyclohexa-2,4-dien-1-ylium is a more stable sigma complex.
What is sigma complex in benzene?
The sigma complex usually refers to the structure of protonated benzene C6H7+ having the proton attached to a particular carbon by a sigma bond, rather than having the proton loosely attached to the ring via the pi orbitals. See arenium ion (Wikipedia) for more details.
Why is the sigma complex for the ortho para attack of a halogenated aromatic more stable than the meta attack?
Since the sigma complexes for ortho (and para) attack have resonance forms with tertiary carbons, they are more stable than the corresponding resonance forms for benzene’s reaction with nitronium ion. Thus toluene reacts faster than benzene at the ortho and para positions.
Which of the following reacts slower than benzene in electrophilic substitution?
nitrobenzene
Due to presence of electron withdrawing group, nitrobenzene reacts slower than benzene in electrophilic reactions.
Which meta resonance structure is the most stable?
Bottom line: the meta carbocation intermediate is more stable than either the ortho– or the para- intermediates.
What is the sigma complex in electrophilic aromatic substitution and why is it important?
When the electrophile adds to the aromatic ring, it produces a carbocation intermediate. The formation of the sigma complex in electrophilic aromatic substitution has a higher activation energy than the formation of a carbocation in electrophilic addition to an alkene (Figure 13.1).
What do you mean by sigma complex?
In chemistry, a sigma complex or σ-complex usually refers to a family of coordination complexes where one or more ligand interacts with the metal using the bonding electrons in a sigma bond. A subset of sigma complexes are agostic complexes, where a C-H sigma bond functions as the donor ligand.
What is a sigma complex in benzene?
• Resonance-stabilized carbocation is called a sigma complexbecause the electrophile is joined to the benzene ring by a new sigma bond • Aromaticity is regained by loss of a proton © 2013 Pearson Education, Inc. 5 Electrophilic Aromatic Substitution: Mechanism Step 1: Attack on the electrophile forms the sigma complex.
What is an electrophilic aromatic substitution for benzene?
Electrophilic Aromatic Substitution • benzene’s pi electrons are available to attack a strong electrophile to give a carbocation • Resonance-stabilized carbocation is called a sigma complexbecause the electrophile is joined to the benzene ring by a new sigma bond
Why is benzene more stable than cyclohexane?
And so benzene is more stable than cyclohexane. At first you might think that the stability is due to the fact that benzene is conjugated, but numerous other experiments have shown that it is even more stable than we would expect. And that extra stability is called aromaticity or aromatic stabilization.
What is the hybrid structure of benzene in real life?
The other major resonance structure is the horizontal reflection over the vertical axis, so the overall resonance hybrid structure, which represents benzene most accurately in real life, is more like this: