Utente:Grasso Luigi/sanbox1/Diradicale
Un diradicale in chimica organica è una specie molecolare con due elettroni che occupano orbitali molecolari (MO) degeneri.[1][2] The term "diradical" is mainly used to describe organic compounds, where most diradical are extremely reactive and in fact rarely isolated. Diradicals are even-electron molecules but have one fewer bond than the number permitted by the octet rule.
Stati di spin[modifica | modifica wikitesto]
Diradicals are usually triplets. The phrases singlet and triplet are derived from the multiplicity of states of diradicals in electron spin resonance: a singlet diradical has one state (S=0, Ms=2*0+1=1, ms=0) and exhibits no signal in EPR and a triplet diradical has 3 states (S=1, Ms=2*1+1=3, ms=-1;0;1) and shows in EPR 2 peaks (if no hyperfine splitting).
The triplet state has total spin quantum number S = 1 and is paramagnetic.[3] The singlet state has S = 0 and is diamagnetic. The degeneracy of each state can be found with Hund's rule of maximum multiplicity: 2S + 1.
Esempi[modifica | modifica wikitesto]
Stable, isolable, diradicals include singlet oxygen and triplet oxygen. Other important diradicals are certain carbenes and nitrenes. Lesser known diradicals are nitrenium ions, carbon chains[4] and organic so-called non-Kekulé molecules in which the electrons reside on different carbon atoms.
In inorganic chemistry, the concept of diradical is not applied although many metal complexes have triplet ground states.
Bibliografia[modifica | modifica wikitesto]
- (EN) Diradicals, su meta-synthesis.com. URL consultato il 20-02-2020.
- (EN) Pedersen, S.; Herek J. L.; Zewail, A. H., The Validity of the "Diradical" Hypothesis: Direct Femtoscond Studies of the Transition-State Structures, in Science , vol. 266, n. 5189, 1994, pp. 1359–1364, Bibcode:1994Sci...266.1359P, DOI:10.1126/science.266.5189.1359, PMID 17772843.
- (EN) Zewail, A. H., <2586::aid-anie2586>3.0.co;2-o Femtochemistry, in Angew. Chem. Int. Ed., vol. 39, n. 15, 2000, pp. 2586–2631, DOI:10.1002/1521-3773(20000804)39:15<2586::aid-anie2586>3.0.co;2-o, PMID 10934390.
Note[modifica | modifica wikitesto]
- ^ (EN) Compendium of Chemical Terminology, 2ed, IUPAC, ("Gold Book") (1997). Versione online: (1995) "Diradicals".DOI: 10.1351/goldbook.D01765
- ^ (EN) Manabu Abe, Diradicals, in Chem. Rev., vol. 113, 2013, pp. 7011-7088, DOI:10.1021/cr400056a.
- ^ Triplet State, in Gold Book, IUPAC.
- ^ Sonai Seenithurai, Effect of Li Termination on the Electronic and Hydrogen Storage Properties of Linear Carbon Chains: A TAO-DFT Study, in Scientific Reports, vol. 7, n. 1, 9 febbraio 2017, p. 4966, DOI:10.1038/s41598-017-05202-6.
