摘要:

Traces of nickel (II) are determined by measurement of light absorption in the solid state after co-precipitation with a large excess of α-benzildioxime. The detection limit is 0.2 µg Ni and nickel can be recovered even from 1000 ml sample volumes (i.e. < 1 ng/ml can be determined). Only a few foreign ions interfere.

ISSN:0008-4042    

DOI:10.1139/v75-043

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Reaction of triphenylvinyl bromide, labeled at C-2 with14C or13C (1—Br-2-14C or1—Br-2-l3C), with HOAc–AgOAc gave an isotopically rearranged product,1—OAc-x-14C or1—OAc-x-13C. After conversion of the product to 1,2,2-triphenylethanol (2—x-14C or2—x-13C),14C assays after degradation to benzophenone, or analyses by FT c.m.r. and by13C satellites of p.m.r. in the FT or CW mode all gave results that were in reasonable agreement, indicating 6.8 ± 0.9% scrambling of the label from C-2 to C-1. The work shows that while the c.m.r. technique eliminates the need for degradation, the tracer method, with appropriately high specific activities, is capable of giving higher precision.

ISSN:0008-4042    

DOI:10.1139/v75-044

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The product from the reaction of trianisylvinyl-2-13C bromide (3—Br-2-13C) with HOAc–AgOAc or with CF3COOH–CF3COOAg was converted to 1,2,2-trianisylethanol-x-13C (4—x-13C) and examined for isotopic scrambling by the use of relative intensity ratios in the c.m.r. spectra with the CH3O absorption as the internal standard, or by the intensities of the13C satellites in the p.m.r. spectra. About 20 and 50% rearrangements of the13C-label from C-2 to C-1 were found, respectively, for the acetolysis and trifluoroacetolysis. The results are in accord with the suggestion that there may be a competition between 1,2-aryl shifts in the triarylvinyl cation or ion-pair and the reaction of the ion with solvent to give product.

ISSN:0008-4042    

DOI:10.1139/v75-045

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Halogen redistribution in the sparingly soluble boron trihalide adducts of Me3P, Me3PO, and Me3PS gives mixed boron trihalide adducts of these bases. Only small proportions of the fluorine-containing mixed boron trihalide adducts are present at equilibrium in the Me3PS adduct system, in accord with previous studies of adducts of other sulfur donors. The effects of the donor on F,Cl and F,Br halogen redistribution are discussed.

ISSN:0008-4042    

DOI:10.1139/v75-046

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The thermal rearrangement of α-substituted silanes (R3SiCHXR′), in which there is exchange of X and R between the silicon atom and the adjacent carbon atom, has been studied. Kinetic parameters for two compounds (Me3SiCBrPh2and Ph3SiCHOAcPh) have been measured. Migratory aptitudes of both X and R have been examined. A mechanism involving initial migration of X to silicon, to form an "inverse ylid"is proposed.

ISSN:0008-4042    

DOI:10.1139/v75-047

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The spin–lattice relaxation time (T1) data for a number of androstane and cholestane derivatives is presented. TheNT1value of carbon-3 in several of the compounds is found to be shorter than the averageNT1value for the other ring carbons which is interpreted in terms of anisotropic motion with the long steroid axis being the preferred axis of rotation. As this effect is only observed for carbon-3, an effective molecular correlation time can be calculated from the averageNT1value for all other CH and CH2carbons. The correlation time (τi) for internal rotation of a methyl group is shown to depend on the number of 1,3 diaxial methyl group – hydrogen interactions. Thus τi(C-19) is shorter than τi(C-18) for androstane, τi(C-19) is shorter fortrans-cholestanol than for eithercis-cholestanol or cholesterol. The effects of substituents and conformational changes on τias well as the effect of solvent onT1are discussed.

ISSN:0008-4042    

DOI:10.1139/v75-048

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The preparation of 2′,4′-dihydroxy- and 2′,6′-dihydroxybiphenyl-2-carboxylic acid lactones (3and4) is described. Grignard addition to or direct boron trifluoride etherate – sodium borohydride reduction of these lactones yields respectively these 6,6-substituted (e.g.6) or the 6,6-unsubstituted (13a) 6H-dibenzo[b,d]pyrans. Evidence that the reductive route proceeds without ring cleavage is presented.

ISSN:0008-4042    

DOI:10.1139/v75-049

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The Friedel–Crafts acetylation of 3-hydroxy-6H-dibenzo[b,d]pyrans (1) with acetic acid in the presence of boron trifluoride is described. Representatives unsubstituted at C-1 acylate exclusively at C-2. A methyl or methoxyl substituent at C-1 directs acylation to the C-4 position. The identities of the individual isomers are established primarily on the basis of n.m.r. spectral interpretations.

ISSN:0008-4042    

DOI:10.1139/v75-050

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Treatment of 1,3,5-triphenyl-4-aza-1,3-pentadiene under selected basic conditions leads to either isomerization among the azapentadienes or to cyclization. Analysis of the products from reaction under aprotic conditions (LiTMP in THF) suggested that the open-chain delocalized carbanion exists in both the W and sickle forms. The open-chain anions were observed to electrocyclize in a nonstereospecific manner to produce a 1:1 mixture ofcis- andtrans-2,4,5-triphenyl-1-pyrrolines. Reaction in protic media (methanol andtert-butyl alcohol) produced a 1,5-proton transfer as well as cyclization. The details of the 1,5-proton transfer reaction were elucidated using methanol-O-dand the collapse preferences and intramolecularity in this medium were determined.

ISSN:0008-4042    

DOI:10.1139/v75-051

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The ditertiary arsine (CH3)2AsCH2CH(C(CH3)3)CD2As(CH3)2(L–L) forms 'tetrahedral' (L–L)Ni(CO)2and square planar (L–L)NiOC(CF3)2C(CF3)2O. In both complexes the conformations of the chelate rings are locked with thet-butyl groups equatorial. The dihedral angles are very similar in spite of the anticipated differences in angles at the central atom. The square planar complexes (L–L)′PtbipyCl2and (L–L)2′PtCl2and their palladium analogs ((L–L)′ = H2NCH2CH(C(CH3)3)CD2NH2) also have their chelate rings in locked chair conformations. This results in the identification of isomers in the case of (L–L)2′M2+. The3JH–Hcouplings indicate that the dihedral angles are similar in the group VIII complexes with a degree of puckering which could be less than in related complexes of L–L. The3JPt–Hcouplings indicate changes in the puckering about the N … N axis.

ISSN:0008-4042    

DOI:10.1139/v75-052

出版商:NRC Research Press    

年代:1975

数据来源: NRC