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Titolo:
Molecular structure and conformation of p-bis(trimethylsilyl)benzene: A study by gas-phase electron diffraction and theoretical calculations
Autore:
Campanelli, AR; Ramondo, F; Domenicano, A; Hargittai, I;
Indirizzi:
Univ Aquila, Dept Chem Chem Engn & Mat, I-67100 Laquila, Italy Univ Aquila Laquila Italy I-67100 hem Engn & Mat, I-67100 Laquila, Italy Univ Rome La Sapienza, Dept Chem, I-00185 Rome, Italy Univ Rome La Sapienza Rome Italy I-00185 Dept Chem, I-00185 Rome, Italy Hungarian Acad Sci, Struct Chem Res Grp, Budapest, Hungary Hungarian Acad Sci Budapest Hungary uct Chem Res Grp, Budapest, Hungary Tech Univ Budapest, Inst Gen & Analyt Chem, Budapest, Hungary Tech Univ Budapest Budapest Hungary en & Analyt Chem, Budapest, Hungary
Titolo Testata:
STRUCTURAL CHEMISTRY
fascicolo: 1, volume: 10, anno: 1999,
pagine: 29 - 40
SICI:
1040-0400(199902)10:1<29:MSACOP>2.0.ZU;2-C
Fonte:
ISI
Lingua:
ENG
Soggetto:
ORBITAL CALCULATIONS; GASEOUS-PHASE; 4,6-DINITRORESORCINOL; 2-NITRORESORCINOL; GEOMETRY;
Keywords:
p-bis(trimethylsilyl)benzene; gas-phase electron diffraction; ab initio MO calculations; molecular structure; benzene ring deformation;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
27
Recensione:
Indirizzi per estratti:
Indirizzo: Hargittai, I Univ Aquila, Dept Chem Chem Engn & Mat, I-67100 Laquila, Italy Univ Aquila Laquila Italy I-67100 t, I-67100 Laquila, Italy
Citazione:
A.R. Campanelli et al., "Molecular structure and conformation of p-bis(trimethylsilyl)benzene: A study by gas-phase electron diffraction and theoretical calculations", STRUCT CHEM, 10(1), 1999, pp. 29-40

Abstract

The molecular structure and conformation of p-bis(trimethylsilyl)benzene have been investigated by gas-phase electron diffraction, ab initio MO calculations at the HF/6-31G*, MP2(f.c.)/6-31G*, and B3LYP/6-31G* levels, and MM3 molecular mechanics calculations. The calculations indicate the syn- and anti-coplanar conformations, with two Si-Me bonds in the plane of the benzene ring, to be energy minima. The perpendicular conformations, with two Si-Me bonds in a plane orthogonal to the ring plane, are transition states. The two coplanar conformers have nearly the same energy with a low interconversion barrier, 0.3-0.5 kJ mol(-1). The calculated lengths of the Si-Me and Si-Ph bonds differ by only a few thousandths of an angstrom, in agreement with electron diffraction results from molecules containing either Si-Me or Si-Ph bonds. The geometrical distortion of the benzene ring in p-bis (trimethylsilyl) -benzene may be described by superimposing independent distortions from each of the two SiMe3 groups. The electron diffraction intensities from a previous study (Rozsondai, B.; Zelei, B.; Hargittai, I. J. Mel. Struct. 1982, 95, 187) have been reanalyzed, imposing constraints from the theoretical calculations, and using a model based on a 1 : 1 mixture of the twocoplanar conformers. The effective torsion angles of the SiMe3 groups may indicate nearly free rotation. Important geometrical parameters from the present electron diffraction analysis are [r(g)(C-C)] = 1.407 +/- 0.003 Angstrom, [r(g)(Si-C)] = 1.881 +/- 0.004 Angstrom, [r(g)(C-H)] = 1.108 +/- 0.003Angstrom, and LC,angle cortho -Cipso,, -Cortho = 117.2 +/- 0.3 degrees. While the mean bond lengths are virtually the same from the previous and present analyses, the new ipso angle is in better agreement with the MO calculations [HF, 6.9 degrees; MP2(f.c.), 117.1 degrees; B3LYP, 116.9 degrees].

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Documento generato il 30/09/20 alle ore 11:23:42