Preferred Label : Hückel (4n 2) rule;
IUPAC definition : Monocyclic planar (or almost planar) systems of trigonally (or sometimes digonally)
hybridized atoms that contain (4 i n /i 2) π-electrons (where i n /i is a non-negative
integer) will exhibit aromatic character. The rule is generally limited to i n /i
0–5. This rule is derived from the Hückel MO calculation on planar monocyclic conjugated
hydrocarbons (CH) sub i m /i /sub where i m /i is an integer equal to or greater
than 3 according to which (4 i n /i 2) π-electrons are contained in a closed-shell
system. Examples of systems that obey the Hückel rule include: Systems containing
4 i n /i π-electrons (such as cyclobutadiene and the cyclopentadienyl cation) are
'antiaromatic'.;
Origin ID : H02867;
See also
Monocyclic planar (or almost planar) systems of trigonally (or sometimes digonally)
hybridized atoms that contain (4 i n /i 2) π-electrons (where i n /i is a non-negative
integer) will exhibit aromatic character. The rule is generally limited to i n /i
0–5. This rule is derived from the Hückel MO calculation on planar monocyclic conjugated
hydrocarbons (CH) sub i m /i /sub where i m /i is an integer equal to or greater
than 3 according to which (4 i n /i 2) π-electrons are contained in a closed-shell
system. Examples of systems that obey the Hückel rule include: Systems containing
4 i n /i π-electrons (such as cyclobutadiene and the cyclopentadienyl cation) are
'antiaromatic'.
