摘要:

The effect of electron-withdrawing substituents,meta- orpara-cyano, on the reactivity of the radical cation of arylalkenes and alkanes has been determined. The radical cations were generated by single electron transfer (set) to an electron-accepting photosensitizer. Three reactions were studied: (i) the addition of nucleophile to the radical cation of arylalkenes, (ii) cleavage of the benzylic carbon–carbon bond of the radical cation of arylalkanes; and (iii) the deprotonation of the benzylic carbon–hydrogen bond of the radical cation of arylalkanes. The radical cations of 4-(1-phenylethenyl)benzonitrile (1b), 3-(1-phenylethenyl)benzonitrile (1c), 4-(2-methoxy-1-phenylethyl)benzonitrile (2b), 3-(2-methoxy-1-phenylethyl)benzonitrile (2c),cis- andtrans-5-cyano-2-methoxy-1-phenylindane (6b-cisand -trans), and 6-cyano-3-phenylindene (7b) were generated, by single electron transfer to the lowest excited singlet state of 1,4-dicyanobenzene (3), in acetonitrile–methanol. The radical cations of1b,1c, and7breact with methanol to yield theanti-Markovnikov adducts (2b,2c, and6b-cisand6b-trans). The radical cations of2b,2c, and6b-transcleave at the benzylic carbon–carbon bond to give products derived from the radical and carbocation fragments. The radical cation of6b-cisdeprotonates from the benzylic position with subsequent formation of the diastereomer,6b-trans. This behaviour can be explained/predicted on the basis of the proposed mechanisms for these reactions. Molecular orbital calculations (AM1) support the conclusions.Keywords: photosensitized, electron transfer, radical ions, radicals, molecular orbital calculations (AM1).

ISSN:0008-4042    

DOI:10.1139/v95-042

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The usefulness of the Pariser–Parr–Pople molecular orbital method for the identification of near-infrared absorbing pigment candidates for photogenerator applications is outlined. Several pigments based on the well-known class of photogeneratorsN,N′-dialkyl-3,4,9,10-perylenetetracarboxylic diimides were investigated and pigments of the dibenzoperylene, bisanthene, and zethrene classes were identified as the most promising candidates of the series. On the basis of the predictions, 7,8,15,16-dibenzo[a,j]perylenetetracarboxylic diimide was prepared and the validity of the calculations was verified.Keywords: photoconductor, near-infrared, Pariser–Parr–Pople calculations, polycyclic aromatic hydrocarbon, aceanthrene green.

ISSN:0008-4042    

DOI:10.1139/v95-043

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The reported structure of aceanthrene green, a pigment prepared by potassium hydroxide fusion of 1,9-anthracenedicarboxylic imide, was found to be incorrect. The structure of the pigment is reassigned to 7,8,15,16-dibenzo[a,j]perylenetetracarboxylic diimide on the basis of COSY, NOESY, and inversion–recovery1H NMR experiments.N-Alkyl- orN-phenyl-1,9-anthracenedicarboxylic imides, aceanthryleno[1,2-b]quinoxaline, and a benzimidazole derivative of 1,9-anthracenedicarboxylic anhydride were found to give the same dibenzo[a,j]perylene structure when reacted in potassium hydroxide. The electronic spectra of these derivatives is reported and it is shown that, as predicted by Pariser–Parr–Pople calculations, they absorb in the near-infrared. Finally, a mechanistic outline for the fusion is proposed on the basis of AM1 and frontier molecular orbital calculations.Keywords: photoconductor, near-infrared, aceanthrene green, alkalifusion, polycyclic aromatic hydrocarbon.

ISSN:0008-4042    

DOI:10.1139/v95-044

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The N,C-dilithiated derivatives of theN-tert-butoxycarbonyl-2-alkylthiomethylanilines5a–cand theN-tert-butoxycarbonyl-2-alkoxycarbonylmethylanilines11a,bwere converted into theN-tert-butoxycarbonyl-oxindole-2-thiones(thiols)7a–cand14a,b, respectively, by sequential reaction with carbon disulfide and methyl iodide. Compound7bwas converted into10d, the sulfur analog of MK886.Keywords:N-tert-butoxycarbonyl-2-alkylthiomethylanilines, dilithiation,N-tert-butoxycarbonyl-2-alkoxycarbonylmethylanilines,N-tert-butoxycarbonyloxindole-2-thiones.

ISSN:0008-4042    

DOI:10.1139/v95-045

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

A new and efficient preparation of diversely protected 2-azido-2-deoxyglycopyranosides from the corresponding glycals is described. The glycals are first transformed into protected phenyl 2-azido-2-deoxy-selenoglycopyranosides by azido-phenylselenylation. Two procedures were employed according to the protecting groups present: sodium azide and diphenyldiselenide in the presence of (diacetoxyiodo)benzene for peracetylated glycals (Procedure A) or trimethylsilyl azide and tetra-n-butylammonium fluoride in the presence ofN-phenylselenophthalimide for perbenzylated glycals (Procedure B). Agluco–mannomixture (90%) is obtained from protected d-glucal whereas only thegalactoisomer is formed from protected d-galactal (75%). The compatibility of the second procedure with one free hydroxyl group and a variety of protecting groups was verified with 1,5-anhydro-2-deoxy-3,4-O-isopropylidene-d-lyxo-hex-1-enitol and its 6-O-acetyl, 6-O-allyl, 6-O-benzyl, and 6-O-tert-butyldimethylsilyl derivatives as well as with 1,5-anhydro-4,6-O-benzylidene-2-deoxy-d-lyxo-hex-1-enitol and its 3-O-acetyl and 3-O-benzyl derivatives, which were transformed into phenyl 2-azido-2-deoxy-α-d-selenogalactopyranoside derivatives in good yield. In the second step, hydrolysis of these selenoglycosides afforded diversely protected glycopyranoses in high yield. Peracetylated derivatives were hydrolyzed in the presence ofN-iodosuccinimide, whereas mercury trifluoroacetate was employed for 3,4-O-isopropylidene, 4,6-O-benzylidene, and perbenzylated derivatives. In some cases the two steps can be carried out without isolation of the intermediate selenoglycoside.Keywords: glycals, 2-azido-2-deoxygalactopyranose, 2-azido-2-deoxyglucopyranose, selenoglycosides.

ISSN:0008-4042    

DOI:10.1139/v95-046

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

X-ray crystallography and NQR spectroscopy have been jointly used to study CCl3X-hexakis(phenylthio)benzene (HPTB) (X=Cl, Br, CH3, CN, NO2, H) clathrates. The crystal of the non-clathrated HPTB is triclinic,a = 9.5614(7),b = 10.2088(13),c = 10.6193(11) Å, α = 68.45(1)°, β = 76.98(1)°, γ = 65.62(1)°,Z = 1; crystals of the clathrates with CCl3CH3, CCl3Br, CCl3NO2, and CCl3CN are isostructural and trigonal,a = 14.18–14.32,c = 20.47–20.62 Å,Z = 3. The trigonal host cavity of HPTB clathrates contains two CCl3X guest molecules, and the X group occupies either the axial or one of the equatorial positions and thus undergoes a molecular order/disorder depending upon its nature. Dipole–dipole interactions between host and guest molecules are considered here to explain this order/disorder effect quantitatively.Keywords: clathrates, crystal structures, NQR, hexakis(phenylthio)benzene.

ISSN:0008-4042    

DOI:10.1139/v95-047

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The electrochemical behavior ofN,N-dimethyl-N′-phenylformamidine hydrochloride was studied on a platinum electrode. The oxidation peak at +0.90 V vs. Ag/Ag+0.01 M (in CH3CN −0.1 M LiClO4) was assigned to the oxidation of the chloride anion.N,N-Dimethyl-N′-(4-chlorophenyl)formamidine andN,N-dimethyl-N′-(2-chlorophenyl)formamidine were isolated from the preparative electrolysis of this amidine hydrochloride. The electrochemical behavior ofN-phenylbenzamidine hydrochloride andN-phenylcyclohex-3-enecarboxamidine hydrochloride was also studied at platinum and at vitreous carbon. Cyclic voltammetry of a number of amidines was performed. OnlyN-arylbenzamidines showed a reduction peak at potentials less negative than −3.0 V vs. Ag/Ag+0.01 M (discharge potential of the medium at vitreous carbon). Preparative electrooxidations of all amidines studied were unsuccessful because of strong and rapid passivation of the anode.Keywords: amidine, electrochemical oxidation, chloride, amidine hydrochloride.

ISSN:0008-4042    

DOI:10.1139/v95-048

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Excess molar volumesVE, at 288.15 and 308.15 K and normal atmospheric pressure, are reported for the binary mixtures tetrahydropyran + n-alkanes (C7–C9). From the results, the differential coefficient (∂VE/∂T)pwas estimated over the entire range of mole fractions. The Prigogine–Flory–Patterson theory and its applicability in predictingVEis tested.Keywords: Excess molar volumes, digital densimeter, tetrahydropyran,n-heptane,n-octane,n-nonane, Prigogine–Flory–Patterson theory.

ISSN:0008-4042    

DOI:10.1139/v95-049

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The reactions between Bu4todit and I2in CHCl3solution have been investigated by spectrophotometry at different temperatures. Evidence for the stepwise formation of the 1:1 and 1:2 charge-transfer complexes has been obtained by computer analysis of the experimental data. The stability constants of both complexes and the corresponding standard enthalpy and entropy changes have been calculated. The 1:2 complex has been characterized in the solid state by an X-ray structural study: the crystals of Bu4todit 2I2are monoclinic, space groupC2/c,a = 16.352(6),b = 9.376(5),c = 23.470(7) Å, β = 99.78(2)°,Z = 4,R = 0.0579. The molecular structure shows that the two thionic sulfur atoms coordinate two diiodine molecules, the bond distances and angles being similar to those observed previously in Et4todit•2I2. On the contrary, the solution studies disagree with the previous investigations on Et4todit and Ph4todit, where the absorbance data were explained assuming the formation of the 1:1 complex only. A new calculation procedure for the least-squares minimization of spectrophotometric data, based on Powell's direct search method, has been developed. This procedure allows for the refinement of the standard enthalpy and entropy changes from a set of absorbance data at different temperatures. Convergence has been attained for the reaction of diiodine with Bu4todit and Me4todit (new data) and also for Et4todit and Ph4todit (old data).Keywords: equilibrium constants, charge-transfer complexes, Fourier transform – Raman, X-ray, I2-thioamides.

ISSN:0008-4042    

DOI:10.1139/v95-050

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The mobility μeof solvated electrons in liquidtert-butanol was estimated from the measured rate constant of the diffusion-controlled reactioncombined with the measured molar conductivities of perchloric acid and ammonium perchlorate solutions;T = 300–330 K. The values μe = 4.1 × 10−8 m2V−1s−1at 300 K and Eμ = 41 kJ mol−1indicate that electrons migrate by a hopping mechanism in liquidtert-butanol. This contrasts with the ion-like diffusion mechanism ofin methanol and ethanol.Keywords:tert-butanol, solvated electron, activation energy, mobility.

ISSN:0008-4042    

DOI:10.1139/v95-051

出版商:NRC Research Press    

年代:1995

数据来源: NRC