摘要:

The He(I) photoelectron spectra of propenal and the propenoyl halides, CH2=CHCOX, X = H, F, Cl, Br, were measured and interpreted with the aid of semi-empirical MO calculations, comparison with results for structurally related species, and a sum-rule for the out-of-plane orbital energies. Information concerning the identities and relative energies of the higher occupied molecular orbitals of the neutral molecules could be deduced from the spectra.

ISSN:0008-4042    

DOI:10.1139/v87-116

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Reaction of 8-aminoquinoline with pyridine-2-carboxaldehyde (2), pyridine-3-carboxaldehyde (3), pyridine-4-carboxaldehyde (4), and benzaldehyde (5) yields the corresponding aminals or Schiff's bases according to reaction conditions; analogous results are obtained from the reaction of 1-amino-naphtalene with pyridine-2-carboxaldehyde (6). On the other hand, reaction of 8-aminoquinoline with thiophene-2-carboxaldehyde or pyrrole-2-carboxaldehyde yields neither the aminal nor the Schiff's base. Crystals of4(C24H19N5) belong to the triclinic space group. Cell dimensions area = 11.547(3),b = 11.759(2),c = 15.687(5) Å, α = 98.50(2)°, β = 101.61(2)°, γ = 107.28(2)°,V = 1942.6(9) Å3. FinalR = 0.077 andRw = 0.064; 3160 reflections were observed. The ir,1H nmr of2–6, the mass spectra of4and5and the X-ray analysis of4are described and discussed. Preparative features, ir,1H nmr, analyses and crystal structure indicate that the formation of2–6are governed mainly by the nucleophilicity at the aldehyde carbon atom and the existence of the hydrogen bonds in the aminal.

ISSN:0008-4042    

DOI:10.1139/v87-117

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The title trisaccharide,13c, was synthesized, as well as its two component disaccharides,10cand11c. Four disaccharides,3c,4c,5c, and7c, were also prepared to serve as model compounds for the investigation of the 3-dimensional structure of more complex oligosaccharides. The β-1,3 linkage was formed in 75% yield by coupling 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl bromide (9) with trideuteriomethyl 2-O-benzoyl-4,6-benzylidene-β-D-galactopyranoside (2a), using silver trifluoromethanesulphonate as a promoter in the presence of the base 2,6-di-tert-butyl-4-methylpyridine. Using a silver zeolite as a promoter under a variety of conditions, both α-1,3 and β-1,3 linkages were formed. The β-1,6 linkages were prepared in high yield using9and silver zeolite with either trideuteriomethyl 2,3-di-O-benzoyl-β-D-galactopyranoside (8b) or trideuteriomethyl 2-O-benzoyl-3-O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl)-β-D-galactopyranoside (11b). 2,3,4-Tri-O-benzyl-α-L-fucopyranosyl bromide (1b) was used in the halide ion catalyzed fucosylation of2aor its 3-O-benzoyl isomer2b. The glycosylations of 3,6-di-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-2-deoxy-2-phthalimido-β-D-glucopyranosyl bromide (6b) and 4-O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-2,3,6-tri-O-acetyl-α-D-glucopyranosyl bromide (5a) by heptadeuterioisopropanol used silver zeolite as promoter.

ISSN:0008-4042    

DOI:10.1139/v87-118

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

A synthesis of the civet constituent, (+)-(S,S)-(cis-6-methyltetrahydropyran-2-yl)acetic acid, is described, in which the key stereochemistry of the chiral starting material is set by an enantiotopically selective, porcine pancreatic lipase-catalyzed, hydrolysis of amesodiester.

ISSN:0008-4042    

DOI:10.1139/v87-119

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The relaxation pathways of excitedtrans-N,N′-diacylindigo dyes (trans-1–trans-4) and of the rigidtrans(5) andcis(6) indigo analogues have been studied by nanosecond flash photolysis and steady state measurements. In fluid solution thetranstocisphotoisomerization of1–4occurs via a singlet excited state mechanism on direct excitation, and the triplet state appears to be reached only by sensitized reaction. The lower quantum yield fortrans → cisisomerization of2–4at room temperature, as compared to1, is due to a thermally activated internal conversion step leading to thetransground state. This pathway competes with fluorescence and twisting of the molecule around the central double bond in the excited singlet state. Increasing the viscosity of the medium decreases the twisting of the flexible molecules and, as a consequence, increases the population of the lowest triplet state. A triplet transient, the intensity of which increases with the viscosity of the medium, could be characterized at low temperature under direct excitation. A transient species, which can be assigned to a triplet state on the basis of quenching experiments and on the fact that the same transient could be found under sensitized conditions, also has been observed at room temperature for the rigid5and6molecules. Quenching measurements of triplet sensitizers by5,trans-1, andtrans-2enables the localization of the triplet energy at around 40 kcal/mol.

ISSN:0008-4042    

DOI:10.1139/v87-120

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The fast atom bombardment mass spectra of selected 1,2-dihydro-1,3-disubstituted-2-oxo-pyrimidinium salts are presented. Loss of N-substituents from the solute cation is the principal fragmentation observed in the positive ion spectra. Several concentration dependent features of the spectra are identified; these are thought to result from the interaction of the solute cation with bombardment-induced matrix fragments. Cluster ions are observed in both positive and negative ion spectra. In a mixed solute system cluster ions resulting from extensive cation and anion mixing are observed; the concentration dependence of these mixed cluster ion peaks can be approximately described in terms of conventional solution equilibria.

ISSN:0008-4042    

DOI:10.1139/v87-121

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Dissociation constants of 2,4,6-trinitrophenol (picric acid) in 2-methoxyethanol and 1,2-ethanediol were measured by a conductance method at temperatures ranging from −10 to 80 °C. The determined constants in the two solvents are discussed and are compared on the basis of the physical properties of the solvents, which have been measured at the various temperatures. The dissociation constants show different behaviour with the temperature in the investigated range and they are fitted by equations of the type lnK = A + BT + C/T + DlnT. Furthermore, the thermodynamic functions have been evaluated and discussed.

ISSN:0008-4042    

DOI:10.1139/v87-122

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Methyllithium reacted with oxyberberine, affording on alkaline work-up a compound with an exomethylene group at C-8 that was transformed in acidic media into an 8-methylberberinium salt. The iminium salt was reduced to a mixture of racemic α- and β-8-methylcanadine. 5,6-Dihydro-8H-isoquino[2,1-b][2,7]naphthyridin-8-ones were similarly transformed into 8-exo-methylene and 8-methyl derivatives, which were subjected to further reduction. These reactions have been employed in a synthesis of theAlangiumalkaloid, (±)-alamaridine.

ISSN:0008-4042    

DOI:10.1139/v87-123

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Determination of common eigenvalues by embedding smaller subgraphs onto larger ones is illustrated. A nearly universal expression of the sixth coefficient of the characteristic polynomial valid for all conjugated hydrocarbon polyenes is presented. Its use in a graph theoretical determination of the Hückel MO characteristic polynomial of molecular graphs possessing heteroatoms is detailed.

ISSN:0008-4042    

DOI:10.1139/v87-124

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The transition metal carboxylates M(O2CR)n(M = Cr, R = C2H5, C6H5,n = 3; M = Mn, Fe, Ni, R = CH3, C2H5, C6H5,n-C7H15,n = 2, not all combinations) have been prepared by oxidising suitable metal anodes electrochemically in solutions of RCOOH in acetonitrile. With Co and Cu, a wide range of carboxylic acids (R = C2H5,c-C3H5,c-C5H9, C6H5,n-C4H9,n-C7H15, 2-ethylhexanoic, oleic, linoleic) has been used successfully to give M(O2CR)2. The advantages of the method are discussed. The preparation of Cu(O2CR)2involves the prior formation of CuO2CR at the anode, followed by oxidation by the solvent.

ISSN:0008-4042    

DOI:10.1139/v87-125

出版商:NRC Research Press    

年代:1987

数据来源: NRC