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Titolo:
ISODESMIC AND HOMODESMOTIC STABILIZATION ENERGIES OF [N]ANNULENES ANDTHEIR RELEVANCE TO AROMATICITY AND ANTIAROMATICITY - IS ABSOLUTE ANTIAROMATICITY POSSIBLE
Autore:
GLUKHOVTSEV MN; BACH RD; LAITER S;
Indirizzi:
UNIV DELAWARE,DEPT CHEM & BIOCHEM NEWARK DE 19716 UNIV N CAROLINA,SCH PHARM,LAB MOL MODELING CHAPEL HILL NC 27599
Titolo Testata:
Journal of molecular structure. Theochem
fascicolo: 1-2, volume: 417, anno: 1997,
pagine: 123 - 129
SICI:
0166-1280(1997)417:1-2<123:IAHSEO>2.0.ZU;2-I
Fonte:
ISI
Lingua:
ENG
Soggetto:
RESONANCE ENERGIES; CONJUGATED HYDROCARBONS; BENZENE; CYCLOBUTADIENE; DELOCALIZATION; BUTADIENE; ABINITIO; 1,3-BUTADIENE; TETRAHEDRANE; SURFACES;
Keywords:
[N]ANNULENES; AROMATICITY; ANTIAROMATICITY; ISODESMIC STABILIZATION ENERGY; HOMODESMOTIC STABILIZATION ENERGY;
Tipo documento:
Article
Natura:
Periodico
Citazioni:
54
Recensione:
Indirizzi per estratti:
Citazione:
M.N. Glukhovtsev et al., "ISODESMIC AND HOMODESMOTIC STABILIZATION ENERGIES OF [N]ANNULENES ANDTHEIR RELEVANCE TO AROMATICITY AND ANTIAROMATICITY - IS ABSOLUTE ANTIAROMATICITY POSSIBLE", Journal of molecular structure. Theochem, 417(1-2), 1997, pp. 123-129

Abstract

Isodesmic stabilization energies (ISEs) for conjugated molecules, which are determined by a balance of the stabilizing pi-electron non-cyclic delocalization and either stabilizing aromatic or destabilizing antiaromatic pi-electron cyclic delocalization, do not yield a reasonableestimation of aromaticity or antiaromaticity, Homodesmotic stabilization energies (HSEs) should be used for this purpose. The ISEs for [n]annulenes are larger by the (n/2) ISE(s-trans-1,3-butadiene) value thanthe corresponding HSEs. The experimental value of the ISE(s-trans-1,3-butadiene) is 59.4 +/- 4.1 kJ mol(-1) at 298 K. While cyclooctatetraene has only the relative antiaromatic character, cyclobutadiene features both relative and absolute antiaromaticity. Since the HSE and ISE of cyclobutadiene, corrected for its strain energy, are still negative (-174.0 and -55.2 kJ mol(-1), respectively, at the MP4SDTQ/6-31G(d,p) ZPE(HF/6-31G(d)) level, pi-antiaromaticity rather than sigma-strain is at the origin of the remarkable instability of cyclobutadiene, At the MP4SDTQ/6-31G(d,p)//MP2/6-31G(d,p) + ZPE(HF/6-31G(d)) level, the antiaromatic destabilization of cyclobutadiene corrected for the ring-strain and normalized per pi-electron is -43.5 kJ mol(-1), a value that is larger (in absolute value) than the antiaromatic destabilization ofplanar D-4h cyclooctatetraene (-14.9 kJ mol(-1) per pi-electron) and the aromatic stabilization of benzene (17.7 kJ mol(-1) per pi-electron). In contrast to cyclobutadiene, planar D-4h Cyclooctatetraene has a positive ISE(118.8 kJ mol(-1)) indicating that the stabilizing pi-electron non-cyclic delocalization overbalances the destabilizing antiaromatic pi-electron cyclic delocalization. Nevertheless, planar cyclooctatetraene is assigned to the class of antiaromatic molecules since its HSE is -118.8 kJ mol(-1) at the MP4SDTQ/6-31G(d,p)//MP2/6-31G(d,p)+ ZPE(HF/6-31G(d)) level. (C) 1997 Elsevier Science B.V.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 28/11/20 alle ore 00:57:02