Hückel (4n + 2) rule

{
  "id": "MLC-T-CHM-005410",
  "term": "Hückel (4n + 2) rule",
  "field": "Chemistry",
  "definition": "A criterion for aromatic character in a planar, fully conjugated monocyclic system: the ring is aromatic when the number of pi electrons in its cyclic conjugation equals 4n + 2 for some whole number n of 0 or more. Benzene, with six pi electrons (n = 1), fits the rule, as do the cyclopentadienyl anion with six and the cyclopropenyl cation with two. Cyclobutadiene, with four, is antiaromatic.",
  "subject": "Organic and Biomolecular Chemistry",
  "see_also": [
    "Möbius aromaticity",
    "aromatic",
    "cation",
    "conjugated system",
    "hydrocarbons"
  ],
  "references": [
    "PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1122 (https://doi.org/10.1351/pac199466051077)"
  ],
  "url": "https://mlchart.com/terminology/chemistry/huckel-4n-plus-2-rule/"
}