摘要:

On the basis of complexation induced15N chemical shift changes, the nucleoside inosine is shown to protonate preferentially at the N-7 site. This nitrogen is also favoured by Zn+2and Hg+2ions.199Hg shifts support the notion that the binding of the first equivalent of Hg+2is site selective.

ISSN:0008-4042    

DOI:10.1139/v83-422

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Under the influence of the very strong base, the sodium salt of 1,2-diaminoethane in 1,2-diaminoethane, 2-tetradecynoic acid is converted to 3-tetradecynoic acid (35%) and a novel dimer3. Compound3((Z)-2-(1-dodecynyl)-3-undecyl-pent-2-en-1,5-dioic diacid) is isolated as the monomethyl ester1after treatment of the crude product with methanolic HCl. The structures of1and3are deduced from an X-ray crystallographic analysis of the dimethyl ester2obtained by reaction of1with diazomethane. The dimer3is thought to arise from Michael addition of the dianion4of 3-tetradecynoic acid with the sodium salt of 2-tetradecynoic acid.

ISSN:0008-4042    

DOI:10.1139/v83-423

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

At 30 °C in 50% v/v dioxane in water, the reaction ofo-dinitrobenzene with hydroxide ion to formo-nitrophenolate anion is very slow but it proceeds much more rapidly when H2O2is also present. Although the phenolate product absorbs strongly in the visible region, standard kinetic analysis of the spectral data fails for both the peroxide-free and the peroxide-accelerated reactions. A more thorough examination of the spectral evidence reveals that, for the peroxide-accelerated reaction, a reasonably stable intermediate is first formed so that the overall reaction is in fact a two-step sequence. We have used a computer modelling technique to determine rate constants for the two steps and we find that both rate constants are dependent on [H2O2]. Several possible structures for the intermediate are discussed, with the radical anion being preferred.

ISSN:0008-4042    

DOI:10.1139/v83-424

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Using a simple model available from podocarpic acid, a method to synthesize the Ring A and B chromophore of coleon B (6b) was elaborated. When applied to the correctly substituted starting ketone8, this reaction sequence afforded the first synthesis of coleon B, as the tetra-O-methyl ether15a.

ISSN:0008-4042    

DOI:10.1139/v83-425

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

A new α-oxoaldehyde reagent, 2,2-bis(ethylthio)ethanal1, has been prepared in high yield from ethanedial. Alkylation of the potassium salt of the enamines of1with various alkylating agents followed byinsituhydrolysis of the intermediate imine afforded high yields of the alkylation products of1. This new reagent was used in the synthesis of a chiral potential precursor of the macrocyclic fragment of cytochalasins A, B, and F, as well as in the syntheses of the physiologically active diolides pyrenophorin and norpyrenophorin.

ISSN:0008-4042    

DOI:10.1139/v83-426

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

A comparative1H and13C nmr study of allylic derivatives of the IV-A group elements, of the type R3ECH2CH=CH—CH31E,Zand R3ECH(CH3)CH=CH2,2, was performed (R = —C6H5, —CH3, E = C, Si, Ge, Sn, Pb). The present paper dealing with the allylic moiety concerns both the chemical shifts, δ1H and δ13C, and the homonuclearJ(H—H) and heteronuclear couplings1J(13C—H),nJ(13C—E),n = 1 to 4,nJ(E—C—H),n = 2 and 5. The spectra are consistent with a σ-allylic structure. In order to obtain an inductive order for the groups G(E) = —E(C6H5)3a coherent group electronegativity scale was established. The intrinsic group electronegativities, without appreciable change, obey the following sequence:Both the changes along the series, in spectroscopic parameters, δ1H, δ13C, and the unusually large heteronuclear couplings,2J(E—C—H),5J(E—C—H),4J(E—13C) (E = Sn, Pb), are interpreted in terms of an electronic mesomeric donating effect for the substituent σ, R3ECH2— and R3ECH(CH3)—, by σ–π hyperconjugation. Factors intrinsic to the main-group element control the chemical shifts δ1Hαand δ13Cα. Thes-character of the bond Cα—Hαappears to control the1J(13Cα—Hα) couplings; no correlation with a σ → π hyperconjugation could be established.

ISSN:0008-4042    

DOI:10.1139/v83-427

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

The vacuum ultraviolet photolysis of gas phase bromoethane at 193.1 nm (6.42 eV) was studied over the pressure range of 1.1–303.2 Torr at room temperature using a carbon atom lamp. The pressure effect with and without inert gas, i.e., He or N2, was investigated. A scavenger effect of the reaction was also observed by adding NO as a radical scavenger. The principal reaction products were C2H6, C2H4, 1,1-C2H4Br2, andn-C4H10. The quantum yields of C2H4and C2H6were found to increase slightly with the reactant pressure. When the pressure of He or N2was varied at a constant pressure of C2H5Br, however, the quantum yields of C2H4and C2H6were found to be pressure independent. Addition of NO completely suppressed the formation of C2H6, C2H4Br2, and C4H10, and partially reduced that of C2H4. These results were interpreted in terms of two channel competition between the molecular elimination and the formation of radicals. Two different decomposition modes were 82% radical reaction and 18% molecular elimination.

ISSN:0008-4042    

DOI:10.1139/v83-428

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

The reactions of Pt(PPh3)4with elemental sulfur in ratios S/Pt = 3, 4, 5, and 6 give a mixture of compounds identified as [PtS(PPh3)2]2and PtS4(PPh3)2; PtS2(PPh3)2is not detected. The dimeric complex also forms on reaction of PtS4(PPh3)2with 3 mol of Pt(C2H4)(PPh3)2. It is alkylated at one bridging sulfido ligand by CH2Cl2and CHCl3to give cations [Pt2(μ-S)-(μ-SR)(PPh3)4]+, R = CH2Cl and CHCl2, respectively, which are characterized as their hexafluorophosphate salts. The cations give extreme AA′BB′X31Pmr spectra since theircis-phosphorus atoms (A,B) have very similar chemical shifts but different coupling constants to195Pt(X); spectral features are broadened by thiolate inversion processes. Reactions of bridging sulfido ligands with other electrophiles are discussed.

ISSN:0008-4042    

DOI:10.1139/v83-429

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

The crystal structures of 2,2-diphenyl-1,3-dioxa-3a-azonia-2-borataindan,6a, and 4-cyclohexyl-6-methyl-2,2-diphenyl-1,3-dioxa-3a-azonia-2-borataindan,6b, reported here represent the first crystallographic examples of coordination complexes of the anionic ligand derived from 2-hydroxypyridineN-oxide. Crystals of6aare monoclinic,a = 11.5210(13),b = 10.2860(8),c = 12.7354(15) Å, β = 101.878(5)°,Z = 4, space groupP21/c; and those of6bare monoclinic,a = 8.5047(8),b = 15.6603(14),c = 16.0501(18) Å, β = 104.776(5)°,Z = 4, space groupP21/n. Both structures were solved by direct methods and were refined by full-matrix least-squares procedures to finalRvalues of 0.039 and 0.042 for 1440 and 1750 reflections withI ≥ 3σ(I), respectively. Both molecules feature tetrahedrally coordinated boron atoms incorporated into five-membered OBOCN chelate rings which have B-envelope conformations. The observed molecular geometries indicate that the ligand may be classed as a hybrid of the 2-hydroxypyridineN-oxide and 1-hydroxy-2-pyridinone tautomers of the parent alcohol. Important bond lengths (corrected for libration) are: O—B = 1.557(3)−1.580(3), mean C—B = 1.600(4), C—O = 1.316(3), and N—O = 1.389(3) Å.

ISSN:0008-4042    

DOI:10.1139/v83-430

出版商:NRC Research Press    

年代:1983

数据来源: NRC

摘要:

Potential energy curves for the two lowest electronic statesX2A″ andA2A′(2Π in linear geometry) of HNF are calculated employing configuration interaction. A vibrational analysis of theA2A′—X2A″ transition is undertaken; stretching and bending modes are treated separately but vibronic coupling and large-angle bending is taken into consideration explicitly. The various vibronic levels including their K-type structure are compared with measured data wherever available and the results indicate that the prediction of vibronic spectra in small molecules on the basis of purelyabinitiodata is now within reach.

ISSN:0008-4042    

DOI:10.1139/v83-431

出版商:NRC Research Press    

年代:1983

数据来源: NRC