Zipora Apeloig - Academia.edu (original) (raw)

Papers by Zipora Apeloig

Journal of The Chemical Society-perkin Transactions 2, 1995

ChemInform, 1996

organic chemistry, review organic chemistry, review Z 0200 51 -294 Silylenes and Multiple Bonds t... more organic chemistry, review organic chemistry, review Z 0200 51 -294 Silylenes and Multiple Bonds to Silicon: Synergism Between Theory and Experiment -(¿ 27 refs.). -(APELOIG, Y.; KARNI, M.; MULLER, T.; Organosilicon Chem. II, (Muench. Silicontage), 2nd 2 (1994) 263-288; Edited by Auner, N.; Weis, J.; VCH Verlagsges. mbh, D-69451 Weinheim, Germany; EN)

Journal of The American Chemical Society, 2006

Tetrahedron Letters, 1994

Abstm& Ab initio (6_3lG* and ~3~~3lG*//~3lG~ ~~l~io~ sbow that vinyl cations substituted with u-C... more Abstm& Ab initio (6_3lG* and ~3~~3lG*//~3lG~ ~~l~io~ sbow that vinyl cations substituted with u-CN, ECHO and P-CF, gmups are by 15-M kcallmol less stable than their samated anatogues and am among the least stable carbenium ions g%nexated to date via EOlvOlySiS.

Organosilicon Chemistry Set, 2005

ABSTRACT According to structural, thermodynamic, electronic, and magnetic criteria silole and ger... more ABSTRACT According to structural, thermodynamic, electronic, and magnetic criteria silole and germole dianions show indications of cyclic derealization. The degree of aromaticity in the silole- 1(Si) and germole dianions 1(Ge) is of the same magnitude as that in the cyclopentadienyl anion.

Journal of the Chemical Society, Perkin Transactions 2, 1994

... Joseph Frey, Etti Schottland, Zvi Rappoport, Dmitry Bravo-Zhivotovskii, Moshe Nakash, Mark Bo... more ... Joseph Frey, Etti Schottland, Zvi Rappoport, Dmitry Bravo-Zhivotovskii, Moshe Nakash, Mark Botoshansky, Menahem Kaftory and Yitzhak Apeloig. ... Chem., Int. Ed. Engl., 1993, 32, 414 ; (b) SP Mallela, I. Bernal and RA Geanangel, Inorg. Chem., 1992, 31, 1616 Search PubMed . ...

Chemical Science, 2010

Stable N-heterocyclic carbenes and germylenes were allowed to react with a phosphonyl radical, (i... more Stable N-heterocyclic carbenes and germylenes were allowed to react with a phosphonyl radical, (i-PrO) 2 (O)Ṗ (7), generated by photolysis of [(i-PrO) 2 (O)P] 2 Hg. The products were identified by EPR spectroscopy. An unsaturated carbene (1) and germylene (3) react with 7 at the divalent atom to give unstable radical products (s ½ ¼ 0.2 s). A benzo-annulated carbene (4) and a saturated germylene (6) react with 7 to give more active radicals. An unsaturated (2) and a saturated silylene (5) undergo rapid reaction (in the dark) with [(i-PrO) 2 (O)P] 2 Hg to yield unusual silyl phosphites. In these cases only secondary radicals were observed. DFT (PBE0/TZVP//B3LYP/6-31+G(d)) calculations of the radical adducts of the different (C, Si, Ge) unsaturated N-heterocyclic divalent species with the phosphonyl radical show that the unpaired electron is delocalized over the five-membered ring; the spin density on the central atoms decreases in the order C, 39% > Si, 14% > Ge, 2%. These trends can be understood in terms of a zwitterionic structure of the radical adducts. The calculations of the radical adducts of 4, 5 and 6 with 7 indicate larger spin density on the central atom, 47%, 58% and 42% on C, Si, Ge, respectively. † Dedicated to Professor Wataru Ando, a pioneer of silicon chemistry, on the occasion of his 75th birthday.

Organosilicon Chemistry II, 1995

ABSTRACT Silylenes, R2Si: have singlet ground states, unlike simple carbenes which are ground-sta... more ABSTRACT Silylenes, R2Si: have singlet ground states, unlike simple carbenes which are ground-state triplet species. The reason for this difference between silylenes and carbenes is considered in the light of SCF MO calculations. A stable silylene 5 has been synthesized and its properties investigated. Theoretical and experimental data suggest that the unprecedented stability of 5 results in part from aromatic stabilization in the 6π-electron ring. Novel reactions of 5 are described. Silylene 13, the saturated analog of 5, has also been isolated but is less stable than 5.

Tetrahedron Letters, 1973

Tetrahedron Letters, 1981

PHz despite its strong inherent v-donor ability, stabilizes silicenium ions less than NH, because... more PHz despite its strong inherent v-donor ability, stabilizes silicenium ions less than NH, because of the high+barrier to yyramidalization at phosphorus which de;tabllizes the planar H2PSiHZ . HSSiHz and HOSIHZ have similar stabilities while CISiHL 1s less stable than FSiH2 . In contrast to carbenium ions, the analogous trivalent positively charged silicon cations (silicenium ions) have proven to be elusive chemical species. Numerous experimental attempts to observe R, Si .+ ions in solution have uniformly fai1ed.l Although silicenium ions Y.A. thanks Professor J.A. Pople and S.A.G. thanks Professor W. Hehre for making the 3-2lG basis set available prior to publication, and Professor K. Morokuma for the use of his modified Gaussian 70 program. Discussions with Professors J.A. Pople, P.v.R. Schleyel and Dr. T. Clark were most valuable. S.A.G. would also like to acknowledge the assistance given by C. S. Parkhurst.

Tetrahedron Letters, 1986

ABSTRACT

Organometallics, 2003

The singlet-triplet energy difference in CH 2 and SiH 2 was calculated at the CASSCF level of the... more The singlet-triplet energy difference in CH 2 and SiH 2 was calculated at the CASSCF level of theory using large Gaussian basis sets that included f-type functions. The total energy was separated into nuclear repulsion and electronic energy, and the latter was further decomposed into the contributions coming from the two electrons highest in energy (the "frontier" electrons, denoted by "f") and from all the other electrons (denoted by "c" for "core"). The contribution of the frontier electrons was further decomposed into the following terms: E (f) , which is the sum of the kinetic energy and the attraction energy to the nucleus of the two frontier electrons and their repulsion energy from all other electrons, and E ee (f) , the repulsion energy between the two frontier electrons. The results are used to explain why CH 2 is a ground state triplet (lying ca. 10 kcal/mol lower in energy than the singlet) while SiH 2 is a ground state singlet (with the triplet lying ca. 20 kcal/mol higher in energy). The major conclusions are as follows: (1) In addition to the frontier electrons, the "core" electrons and the nuclear repulsion energy also affect the singlet-triplet gap.

Organometallics, 1997

Substituent effects on the potential energy surface (PES) of RHSiC (R ) H, CH 3 , SiH 3 , F, OH) ... more Substituent effects on the potential energy surface (PES) of RHSiC (R ) H, CH 3 , SiH 3 , F, OH) were studied by ab initio molecular orbital methods. The unimolecular and kinetic stability of silaacetylenes is strongly dependent on the substituent, pointing to FSitCH and R′OSitCH as viable candidates for experimental observation.

Organometallics, 2006

Three novel nonsolvated gem-dilithiosilanes,(R2SiLi2), were prepared by reacting in hexane lithiu... more Three novel nonsolvated gem-dilithiosilanes,(R2SiLi2), were prepared by reacting in hexane lithium metal with silyl mercury precursors. X-ray structure analysis showed for two of them an unprecedented coaggregation of two R2SiLi2 molecules with two R&amp;#x27;Li ...

Organometallics, 2005

The syntheses of the first two disilynes were reported recently: the first by Wiberg and co-worke... more The syntheses of the first two disilynes were reported recently: the first by Wiberg and co-workers, who synthesized RSitSiR (1; R ) SiMe(Si-t-Bu 3 ) 2 ), and the second by Sekiguchi and co-workers, who synthesized RSitSiR (2; R ) Si-i-Pr[CH(SiMe 3 ) 2 ] 2 ), which was also characterized by X-ray crystallography and NMR spectroscopy. We report the first detailed quantum-mechanical study of the 29 Si NMR chemical shifts of disilynes, RSitSiR, in particular those with R ) H, CH 3 , SiH 3 , SiMe(SiH 3 ) 2 , SiMe(SiMe 3 ) 2 , SiMe(Si-t-Bu 3 ) 2 (1), Si-i-Pr[CH(SiMe 3 ) 2 ] 2 (2). The main conclusions are as follows: (1) Small changes in geometry (i.e., in r(SitSi), in the RSiSi bond angle, and in the RSiSiR torsion angle) strongly affect the chemical shift.

Journal of the American Chemical Society, 1976

Abstract: The energies of planar vs. tetrahedral geometries of tetracoordinate organic molecules ... more Abstract: The energies of planar vs. tetrahedral geometries of tetracoordinate organic molecules have been surveyed by ab ini-tio molecular orbital calculations. Because of their 7~ acceptor and u donor character, electropositive substituents, especially lithium, are ...

Journal of the American Chemical Society, 1995

Journal of the American Chemical Society, 1998

Significant efforts have been expended to characterize and understand the electronic nature of si... more Significant efforts have been expended to characterize and understand the electronic nature of silylenes. The diaminosubstituted silylenes 1, 1 2, 2 and 3 3 enjoy a special interest, both theoretically 1,4,5 and experimentally, 2,6 because of their unusual high thermodynamic and kinetic stability. Silylene 1 can be regarded as a 6π-electron aromatic molecule, and the nature and degree of electron delocalization in this silyene has been controversial. 4-6 We report here the chemical shift tensors for 1-3 (1 δ 11 ) 284.9, δ 22 ) -16.1, δ 33 ) -43.3; 2 δ 11 ) 350.7, δ 22 ) -2.1, δ 33 ) -4.5; 3 δ 11 ) 316.4, δ 22 ) 21.1, δ 33 ) -60.0 ppm), along with theoretical calculations for model molecules, including nucleus-independent chemical shift (NICS) calculations. 7 The latter support the model that 1 and 3 are cyclically delocalized and have some "aromatic" character.