ISSN:0008-4042    

DOI:10.1139/cjcauthor98

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Various ketoximes have been reacted with aliphatic aldehydes in the presence of oxybis(diphenylborane) in order to assess the influence of increasingly bulky residues on the nature of the products. Crystals of 5-tert-butyl-2-cyclohexylidene-3,3-diphenyl-1,4-dioxa-2-azonia-3-boratacyclopentane,4c, are monoclinic,a= 14.0647(9),b= 11.416(1),c= 14.756(1) Å, &bgr; = 115.696(4)°,Z= 4, space groupP21/c. The structure was solved by direct methods and refined by full-matrix least-squares procedures toR= 0.038 (Rw= 0.038) for 2511 reflections withI>= 3&sgr;(I). A bulky substituent at the aldehyde favors &agr;-hydroxyalkylation at the oxime oxygen atom and subsequently leads to the formation of BOCON diphenylboron chelates, whereas formaldehyde reacts byN-alkylation of the oximes, resulting in COBON diphenylboron chelates.Key words: ketoximes, organoboron compounds, crystal structur

ISSN:0008-4042    

DOI:10.1139/v98-206

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The facile reaction of 3,6-di(2-pyridyl)-1,4-dihydro-1,2,4,5-tetrazine (DPDHT) (1) with trimethylgallium has resulted in the formation of the purple crystalline product, [(DPT)(GaMe2)2] (2), via methane elimination. Crystals of [(DPT)(GaMe2)2] are orthorhombic,Pbca,a= 15.380(2),b= 21.642(4),c= 11.355(2) Å,Z= 8. The structure was solved by heavy-atom Patterson methods and refined by full-matrix least-squares procedures toR= 0.035 for 1570 reflections withI>= 3&sgr;(I) (Rw= 0.063 for all 4342 reflections). The [(DPT)(GaMe2)2] molecule is roughly planar (apart from the four methyl groups), in contrast to the folded structure of the DPDHT molecule; molecular dimensions are normal.Key words: methylgallium, crystal structure, dipyridyldihydrotetrazine

ISSN:0008-4042    

DOI:10.1139/v98-203

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Complete far-IR and Raman data (<400 cm-1) are reported for triphenyltin azide (1) as well as for adducts Ph3SnN3·L (L = hexamethylphosphoramide (HMPA), triphenylphosphine oxide, pyridine-N-oxide, 4-picoline-N-oxide, or pyridine). The small changes inv(Sn-N3) noted on going from (1) to the adducts, as well as solid-state119Sn nmr data, indicate that (1), like the adducts, has five-coordinate tin atoms. X-ray analysis shows that (1) crystallizes with two different chains of five-coordinate Ph3Sn units joined by 1,3-azide bridges. In one unit, the geometry around tin is similar to that found for the monomeric HMPA adduct (2), which hastrans-axial HMPA and azide ligands. The other unit in (1) has nonplanar -SnC3- groups connected by less symmetric 1,3-azide bridges and thus resembles the structure of isoelectronic triphenyltin isocyanate.Key words: triphenyltin azide,O- andN-donor adducts, far-IR/Raman, crystal structures.

ISSN:0008-4042    

DOI:10.1139/v98-207

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Densities and viscosities ofR[xNaSCN + (1 -x)Na2S2O3] + (1 -R)H2O systems withR= 0.05, 0.10, 0.14, and 0.18 were measured as functions of mole fraction,x(= 0.0-1.0), and temperature (293.15 <=T/K <= 323.15). A significant mixed anion effect has been observed within the temperature range of the study. The normalized viscosity isotherms were found to detect the mixed anion effect ~1.2 to 3.7 times more than the simple viscosity isotherms. The progressive replacement of S2O32-ions by SCN-ions causes the systems to be less structured and S2O32-ions polarized Na+ions more towards themselves than towards the SCN-ions. Both these effects govern the variation of the viscosity with mole fraction,x. The mixed anion effect was found to vanish at aroundR= 0.0106.Key words: mixed anion effect, sodium thiocyanate, sodium thiosulfate, viscosity.

ISSN:0008-4042    

DOI:10.1139/v98-201

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

At lower temperatures stabilized ylides react with unsymmetrically substituted phthalic anhydrides to give two acyclic adducts. When the reactions are allowed to proceed at higher temperature enol lactones are formed. Identification of the acyclic intermediates was necessary to understand the mechanism of these Wittig reactions. The transient species trapped in the reaction with trimethyloxonium tetrafluoroborate were unambiguously identified by crystallographic methods. The crystal structures of the tetrafluoroborate salt of methyl(triphenylphosphoranyl idene)- acetate (8), methyl(3-methoxy,2-methoxycarbonylbenzoyl)triphenylphosphoranylideneacetate (6&bgr;), and methyl(2-methoxycarbonyl,6-nitrobenzoyl)triphenylphosphoranylideneacetate (7&agr;) were studied by X-ray diffraction. The ionic salt (8) is monoclinic,P21c,a= 12.640(5),b= 13.945(9),c= 14.825(6) Å, &bgr; = 125.32(3)°,Z= 4, andR= 0.065 (F>5.4 &sgr;(F)). Crystal6&bgr; is monoclinic,P21c,a= 16.391(16),b= 9.029(6),c= 19.835(19) Å, &bgr; = 116.60(6)°,Z= 4, andR= 0.070 (F> 4.6 &sgr;(F)), while crystal7&agr; is also monoclinic,P21c,a= 9.513(5),b= 9.361(3),c= 30.908(13) Å, &bgr; = 98.42(3)°,Z= 4, andR= 0.057 (F>5 &sgr;(F)). In the BF 4-salt (12), the four P-C distances are equal (1.791(5)-1.801(7) Å) with identical tetrahedral angles. For the two triphenylphosphoranylideneacetate compounds, the fourth P-C(1) bond is shorter (1.762(6)-1.734(5) Å) than the three P-C(Ph) bonds (avg. 1.809(5) Å). The angles C(1)-P-C(Ph) are also larger (avg. 112.9(2)° for6&bgr; and 111.9(2)° for7&agr;) than the C(Ph)-P-C(Ph) angles (avg. 105.8(2)° for 6 &bgr; and 106.9(2)° for7&agr;). These values suggest a multiple nature for the P-C(1) bond. In the nitro derivative, the nitro and the ester groups are disordered equally in positions 2 and 6.Key words: Wittig reactions, cyclic anhydrides, stabilized ylide, phosphoranylidenes, crysta

ISSN:0008-4042    

DOI:10.1139/v98-211

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

4-Methoxybenzyl cations bearing &agr;-(N,N-dimethylcarbamoyl) and &agr;-(N,N-dimethylthiocarbamoyl) substituents have been generated photochemically upon irradiation of precursors with pentafluorobenzoate or 4-methoxybenzoate leaving groups. The ions have been observed with flash photolysis in 40:60 acetonitrile:water and in 50:50 methanol:water, and rate constants were measured for their decay in solvent alone and for their capture by azide ion. The cations so studied and their lifetimes in 40% acetonitrile are6, ArC+H-CONMe2, 0.6 &mgr;s;2, ArC+H-CSNMe2, 7 ms; and4, ArC+(CH3)-CSMe2,6 ms, where Ar = 4-MeOC6H4. The cation4reacts with solvent by elimination of a proton from the &agr;-methyl group, and the rate constant for solvent addition must be less than 1 s-1. The CSNMe2substituted cations are 105-107-fold longer lived than analogs where the thioamide group has been replaced with an &agr;-methyl. The UV-visible absorption spectra of these two cations also show significant differences from those of typical 4-methoxybenzyl cations. Thus, both the lifetimes and spectra point to a strong interaction of the benzylic centre with the thioamide group.Key words: flash photolysis, thiocarbamoyl stabilized carbocation, photosolvolysis.

ISSN:0008-4042    

DOI:10.1139/v98-225

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Calculations at the HF-DFT hybrid Becke3LYP level of theory have been undertaken on protonated 2-exo- and 2-endo-norbornanols as model substrates for 2-exo- and 2-endo-norbornyl brosylates to explore the source of the experimentally determined deuterium secondary kinetic isotope effects (KIEs). Calculations on protonated alcohols as models reproduce the "normal" behaviour of 2-endosubstrate5. The observedendo&ggr;-KIE in the 7-unsubstituted 2-exosystem4is shown to arise from internal return, while those in the 7-chloro substituted 2-exosubstrates1and2can be explained with competing 1,3 (6,2)-elimination.Key words: deuterium secondary kinetic isotope effects, 2-norbornyl cation, Becke3LYP.

ISSN:0008-4042    

DOI:10.1139/v98-234

出版商:NRC Research Press    

年代:1998

数据来源: NRC

ISSN:0008-4042    

DOI:10.1139/v98-243

出版商:NRC Research Press    

年代:1998

数据来源: NRC