摘要:

A non classical rearrangement is observed when thiopheno[c] and [b]bishomotropones react with ethanedithiol, leading to a naphtho[1,8-bc]thiophene and (or) a benzo[b]thiophene. The structure of the products is supported by deuterium labelling,1H nmr spectra, and X-ray analysis of 5,6-diphenyl naphtho[1,8-bc]thiophene. A mechanism is proposed which implies an electronic transfer between a "soft" nucleophile and a "hard" acid, in the key step.

ISSN:0008-4042    

DOI:10.1139/v85-345

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The rate constants for deuteroxide and hydroxide catalyzed H → D and D → H exchange of benzodihydrothiophene oxide (1a) and several of its deuterated analogs1b,1c, and1dat 30.00 ± 0.05 °C are reported along with the rate constants for D → H exchange of deuterated benzyl methyl sulfoxides2band2c. Application of the steady-state assumption to schemes involving equilibrating pyramidal anions yield equations which are used to fit experimentally determined(kf/ks)H → Dand(kf/ks)D → Hratios. The analysis supports our view that exchange of the diastereotopic protons (deuterons) occurs by inversion. The inversion component contributes significantly to exchange of the "slow" proton (deuteron) of a diastereotopic pair and this accounts for the observation that(kf/ks)D → H < (kf/ks)H → D. This study establishes an upper limit of 6 kcal for the barrier to inversion of the carbanions derivable from1and2, if pyramidal anions are formed.

ISSN:0008-4042    

DOI:10.1139/v85-346

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Prefractionation procedures based on high performance liquid chromatography (hplc) and low pressure column chromatography (lpcc) were developed and applied to the separation of components in extracts of environmental samples. Effective fractionation was obtained using solvent systems based on hexane, carbon tetrachloride, dichloromethane, and ether for elution on lpcc Florisil and hplc silica columns. This facilitated the identification of over thirty compounds consisting mainly of aliphatic and polyaromatic hydrocarbons, phthalate esters, phenols, and pesticides in environmental samples extracted from water. Chromatographic background levels were minimized, and compounds whose chromatographic peaks were unresolved before fractionation were isolated into separate fractions. This afforded more highly reliable gc/ms identifications. Prefractionation also served to retard the rapid degradation of capillary columns which was caused by the injection of unfractionated samples.

ISSN:0008-4042    

DOI:10.1139/v85-347

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The crystal structures of [N(n-C4H9)4] [catechol … Cl] (1) and [N(n-C4H9)4] [catechol … Br] (2) have been determined by X-ray analysis which showed that the two structures are isomorphous, with the orthorhombic space groupPbca,Z = 8. The cell dimensions and finalR-values are: (1)a = 15.323(2),b = 16.166(2),c = 19.713(2) Å,R = 0.048 for 1361 observed reflections; (2)a = 15.432(1),b = 16.244(2),c = 19.824(1) Å,R = 0.041 for 1958 observed reflections. The crystal structures consist of discrete tetra-n-butylammonium cations and catechol halide anions. Catechol forms two strong hydrogen bonds to a single halide ion giving a pattern of hydrogen bonding unique for such systems.

ISSN:0008-4042    

DOI:10.1139/v85-348

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Three products, 2-acetonyl-2-methylsuccinic anhydride (5), 2,7-dioxa-1,5-dimethylbicyclo[3.2. 1]octane-3,6-dione (6), and 3-acetonyl-3,5-dimethyl-2(3H) furanone (7) were identified from the base-catalysed reaction of 3-methyltricarballylic acid with acetic anhydride. These compounds arise as a result of acylative decarboxylation of 3-methyltricarballylic acid.

ISSN:0008-4042    

DOI:10.1139/v85-349

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The absolute rate constants for the addition of H atoms to C2H3F, 1,1-C2H2F2, C2HF3, C2H3Cl, 1,1 -C2H2Cl2, C2HCl3, and C2H3Br have been determined at 298 ± 2 K over the pressure range 0.70–1.35 Torr. For each of the compounds, the rate constants are found to undergo a modest increase with pressure. At 1.00 Torr the values determined for the rate constants are: C2H3F, (8.86 ± 1.12) × 10−14; 1,1-C2H2F2, (8.16 ± 0.66) × 10−14; C2HF3, (6.21 ± 0.53) × 10−14; C2H3Cl, (27.0 ± 0.5) × 10−14; 1,1-C2H2Cl2, (59.6 ± 3.4) × 10−14; C2HCl3, (10.4 ± 0.8) × 10−14; C2H3Br, (27.8 ± 2.5) × 10−14; in units of cm3molecule−1s−1.

ISSN:0008-4042    

DOI:10.1139/v85-350

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The effect of cholesteric liquid crystalline solvents on the energetics of rotational thermalcis–transisomerization of olefins has been examined. Rate constants have been obtained over a 70-degree temperature range for isomerization oftrans-1,2-di-(4-cyanophenyl)-1,2-diphenylethylene in two isotropic solvents and three cholesteric liquid crystals and the Arrhenius parameters determined. The rates of isomerization are found to be consistently slower in the liquid crystalline phases compared to the isotropic solvents. The Arrhenius parameters for isomerization of the olefin in the isotropic solvents (Ea = 34.8 ± 0.3 kcal/mol; ΔS≠ = −1.5 ± 0.5 e.u.) compare favourably with reported values for its isomerization in benzene solution. In the cholesteric phases,Eais consistently 1–1.5 kcal/mol higher and ΔS≠slightly more positive than the corresponding values for the isotropic solvents. The results are tentatively rationalized in terms of disruption of liquid crystalline order as the olefin twists from its pseudo-planar, ground state geometry through the globular, twisted transition state. The magnitude of this effect is proposed to depend on both the difference in steric bulk of the ground and transition states and the "tightness" of the solvation shell seen by the isomerizing molecule. It is believed that in the present case the observed effects are somewhat truncated as a result of rather poor solvation of the bulky olefin in the liquid crystalline phases.

ISSN:0008-4042    

DOI:10.1139/v85-351

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The synthesis ofN-acyl derivatives ofN-hydroxyaspartic acid was achieved by use ofN-benzyloxyaspartic acid esters as starting material. The preparation ofN-benzyloxyaspartic acid is described.

ISSN:0008-4042    

DOI:10.1139/v85-352

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Low temperature13C nuclear magnetic resonance spectroscopy has been employed to obtain the chemical shifts and to examine the conformational equilibria of the four chlorohydrins and bromohydrins of 3-methoxycyclohexene. The corresponding acetates and the unsubstituted halohydrins have also been examined. The observed chemical shifts were compared with those calculated from additivity considerations. Limitations of this approach are discussed. Relative peak area measurements have been used to obtain conformational free energies in favourable cases.

ISSN:0008-4042    

DOI:10.1139/v85-353

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The synthesis of a variety of nucleoside analogs involving modifications in the carbohydrate ring is described. In particular, 6-substituted purin-9-yl derivatives of 1-oxa-4-thiacyclohexane and 1,4-dioxacyclohexane have been synthesized. A number of 6-chloropurin-9-yl derivatives of substituted 1-oxa-4-thiacyclohexane have also been derived from the parent compounds by way of a Pummerer rearrangement. A route to nucleoside analogs of 1-oxa-4-thiacyclohexane from naturally occurring nucleosides is illustrated for the case of inosine. A route to nucleoside analogs in which the carbohydrate moiety is replaced by an acyclic moiety bearing α,β-unsaturated esters is also illustrated for the case of uridine. The results of biological screening of these analogs and others previously synthesized in our program against leukemia L-1210 cells in vitro are presented; some of these compounds showed marginal antitumor activity. The screening results of selected compounds against the human HeLa cell line in vitro are also presented; none of the compounds that were tested showed significant inhibitory activity of cell growth.

ISSN:0008-4042    

DOI:10.1139/v85-354

出版商:NRC Research Press    

年代:1985

数据来源: NRC