Baird's rule

In organic chemistry, Baird's rule estimates whether a lowest triplet state of planar cyclic structure will have aromatic properties. The quantum mechanical basis for its formulation was first worked out by physical chemist N. Colin Baird at the University of Western Ontario in 1972.[1][2]

The lowest triplet state of a ring structure follows Baird's rule when it has 4n π-electrons, where n is any positive integer. A 4n π electron count makes a ring system antiaromatic in the ground state by Hückel's rule, but that rule is for the ground state, which is usually at the singlet state. Baird's rule instead looks at the excited state, where the electron-count patterns for aromaticity and antiaromaticity are reversed.

See also

References

  1. ↑ Baird, N. Colin (1972), "Quantum organic photochemistry. II. Resonance and aromaticity in the lowest 3ππ* state of cyclic hydrocarbons", Journal of the American Chemical Society, 94 (7/12): 4941, doi:10.1021/ja00769a025
  2. ↑ Ottosson, Henrik (2012), "Organic photochemistry: Exciting excited-state aromaticity", Nature Chemistry, 4 (12): 969–971, Bibcode:2012NatCh...4..969O, doi:10.1038/nchem.1518
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