state hukel's rule??
Answers
In 1931, German chemist and physicist Erich Hückel proposed a rule to determine if a planar ring molecule would have aromatic properties. This rule states that if a cyclic, planar molecule has 4n+2π electrons, it is aromatic. This rule would come to be known as Hückel's Rule.
Answer:
Huckel’s Rule is used in order to estimate the aromatic qualities of any planar ring-shaped molecule in the field of organic chemistry. The supporting quantum mechanics required for the formulation of this rule was solved first by the German physical chemist and physicist Erich Armand Arthur Joseph Huckel in the year 1931.
The Huckel 4n + 2 Pi Electron Rule
A ring-shaped cyclic molecule is said to follow the Huckel rule when the total number of pi electrons belonging to the molecule can be equated to the formula ‘4n + 2’ where n can be any integer with a positive value (including zero).
Examples of molecules following Huckel’s rule have only been established for values of ‘n’ ranging from zero to six. The total number of pi electrons in the benzene molecule depicted below can be found to be 6, obeying the 4n+2 electron rule where n=1.
Huckel's Rule Confirms Benzene Aromaticity.
Thus, the aromaticity of the benzene molecule is established since it obeys the Huckel rule.
This rule is also justified with the help of the Pariser-Parr-Pople method and the linear combination of atomic orbitals (LCAO) method.
Generally, aromatic compounds are quite stable due to the resonance energy or the delocalized electron cloud. For a molecule to exhibit aromatic qualities, the following conditions must be met by it:
There must be 4n + 2 electrons present in a system of connected p orbitals (where the electrons are delocalized) belonging to the molecule.
In order to meet the first condition, the molecule must have an approximately planar structure wherein the p orbitals are more or less parallel and have the ability to interact with each other.
The molecule must have a cyclic structure and must have a ring of p orbitals which doesn’t have any sp3 hybridized atoms.
Other examples of aromatic compounds that comply with Huckel’s Rule include pyrrole, pyridine, and furan. All three of these examples have 6 pi electrons each, so the value of n for them would be one.