摘要:

Efficient synthetic routes to the chiral sesquiterpenes (+)-α-eudesmol (7) and (−)-α-selinene (9) from a thujone-derived intermediate (2) are described.

ISSN:0008-4042    

DOI:10.1139/v84-239

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

X-ray crystallographic determinations of 3-phenyl- and 3-cyclohexyl-thiazolidine-2-thiones are reported as a method for finding the origin of the discrepancy between13C andR-(Lambert) methods of determining the puckering in the ring. It is found that in the solid state, the puckering angles are 23.2° and 7.5° for the 3-phenyl and 3-cyclohexyl derivatives, respectively. The comparison of intramolecular and intermolecular distances for both compounds strongly suggests that these values are a fair representation of what is going on in solution. Therefore it is deduced that the puckering angle in these systems is probably better obtained by the13C nmr shift approach than by theR-Lambert method (in agreement with the most recent Lambert results). Both thiazolidine-2-thiones display a common property – S(1)C(2)S(2)N(3) lie in the same plane. N substitution is, however, different; all of the atoms of either the N-phenyl or of the N-cyclohexyl substituent are not in the S(1)C(2)S(2)N(3) plane. Only the C(6) atom of the N-cyclohexyl group is in the plane and the C(6) atom of the N-phenyl moiety is 0.12 Å out of this plane.

ISSN:0008-4042    

DOI:10.1139/v84-240

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

The ultraviolet absorption spectrum of oxalic acid vapor has been studied for the first time. Low-resolution spectra show a moderately weak (ϵmax = 25 M−1 cm−1at 277 nm) banded absorption system beginning at about 310 nm and extending to 250 nm where a stronger absorption begins. Medium-resolution spectra show a complex vibrational fine-structure at wavelengths above about 287 nm, with many sharp line-like R-branch heads, each corresponding to a different vibrational transition. A vibrational analysis was completed for12C2O4H2,12C2O4D2, and13C2O4H2, and electronic origins were estimated to be at 31903.2, 31970.2, and 31949.4 cm−1, respectively (about 313 nm). Strong features were assigned to progressions inthe C=O and C—O stretching vibrations, with prominent sequences in ν10, the C—C torsional vibration, running to the blue, implying that.This absorption system has been assigned to the first excited singlet state, designatedÃ, corresponding to a π* ← n+,1Au ← 1Agtransition of planartrans-oxalic acid. High-resolution spectra of several bands show rotational fine-structure, and a partial analysis was carried out on the, andbands of12C2O4H2, based on apparently-simple diverging P-branches.

ISSN:0008-4042    

DOI:10.1139/v84-241

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Inosine-5′-monophosphate disodium salt (5′-IMPNa2) reacts withcis-dichlorodiammineplatinum(II) (cis-DDP) and itstrans-isomer (trans-DDP) to give complexes of the typecis- andtrans-Pt(NH3)2(IMPNa2)nCl2•xH2O,n = 1 or 2 and Pt(IMPNa2)nCl2•xH2O, wheren = 1, 2, or 3 andx = 0–6. In the 1:2 platinum complexes the nucleotide binds only to the N7-atom of the purine ring system, while in the 1:1 metal complexes there is indication for Pt–carbonyl interaction (bridging or chelation) in addition to the N7-bonding at neutral pH values withcis-DDP.Solution FT-ir studies (H2O and D2O) showed that the 1:1 species formed withcis-DDP at neutral pH's behaved differently from those withtrans-DDP. The carbonyl stretching vibration of the free base at 1685 cm−1(H2O) and 1670 cm−1(D2O) exhibited marked spectral changes in intensity, shifting, and shape upon complexation, whereas the reaction with thetrans-isomer produced only slight perturbations in the above region.

ISSN:0008-4042    

DOI:10.1139/v84-242

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Rate and equilibrium constants have been measured for the hydration and retroaldol reactions of cinnamaldehyde. The equilibrium constant for the 1,4-addition of water to cinnamaldehyde is 4.42 × 10−3. The rate constants for hydroxide catalyzed reaction, extrapolated to zero hydroxide concentration (to correct for the addition of hydroxide to the aldol carbonyl), are:;; and. The rate of the formation reaction was measured by adding small amounts of acetaldehyde to alkaline solutions of benzaldehyde:andKoverall = 1480 M−1. The course of the synthetically useful reaction of acetaldehyde with benzaldehyde is discussed in the light of these results.

ISSN:0008-4042    

DOI:10.1139/v84-243

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Nitration ofo-cresol and some mono-, di-, and trimethyl derivatives in acetic anhydride at −60 °C gives 6-methyl-6-nitrocyclohexa-2,4-dienones. The dienones are more labile than the isomeric 4-methyl-4-nitrocyclohexa-2,5-dienones and, if the 2-position of the dienone is not blocked, undergo regiospecific rearrangement to 6-nitro-o-cresols. 2,3,6-Trimethyl- and 2,3,5,6-tetramethylphenol also give a 2,5-dienone with nitro attached to a secondary carbon.

ISSN:0008-4042    

DOI:10.1139/v84-244

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Five analysis methods were compared for the determination of boron in heavy water moderator: isotope dilution mass spectrometry, spectrophotometry, neutron activation, inductively coupled plasma – atomic emission spectrometry, and ion selective electrode potentiometry. Ten samples were analysed by each method; the results showed close agreement between all of the methods. Only mass spectrometry achieved the required precision (<1% rsd) for samples taken during initial reactor operation, but all of the methods achieved sufficient precision (<10% rsd) for samples taken during normal operation. For samples for which the10B concentration must be determined, only mass spectrometry and neutron activation are applicable.

ISSN:0008-4042    

DOI:10.1139/v84-245

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Cyclohexene skeletal isomerization, in a microcatalytic pulse reactor, was investigated using Al2O3and AlPO4–Al2O3as catalysts. Apparent rate constants and apparent activation energies were calculated according to the kinetic model of Bassett–Habgood. Selectivity studies concluded that 1-MCP and 3-MCP were competitive products with a first-order kinetics. The rate constants as well as the selectivity at 1-MCP increase with an increase in the number and strength of stronger acid sites, measured by means of the irreversible adsorption of aniline in cyclohexane, at 298 K, using a spectrophotometric method. The parallel reaction pathway, proposed for AlPO4catalysts, agrees with both the observed rates and selectivities using Al2O3and AlPO4–Al2O3catalysts.

ISSN:0008-4042    

DOI:10.1139/v84-246

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

A model system of rhodopsin consisting of a dienylidene Schiff base and different halogeno acids has been studied in two solvents, chloroform and methanol, by uv and 400-MHz nmr spectroscopies. The uv results indicate that in chloroform, a nonpolar solvent, monohalogenoacetic acids can protonate the Schiff base only partially, while nmr data show that the aldimine hydrogen is slightly affected by acids and that the acidic proton is moving rapidly between the donor and the acceptor. In methanol, data indicate a leveling effect. In relation with rhodopsin, our results imply that, depending on the environment surrounding the chromophore, the state of protonation of the Schiff base could be strongly affected. Finally, our model shows experimental evidence that Nakanishi's external point charge could be operating in visual pigments.

ISSN:0008-4042    

DOI:10.1139/v84-247

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

At the 3-21G (3-21G*) computational level, the intrinsic barriers associated with proton transfer between XCH2−and CH3X have been found to be essentially constant (ca. 10 kcal/mol) for X = H, F, SH, Cl. According to the Marcus rate-equilibrium treatment of proton transfer reactions, this result means that transition states should not exist for gas phase reactions, when the energy change exceeds 20 kcal/mol. This prediction has been confirmed for two cases (X = H, F) in which the energy change is less than 20 kcal/mol, and two cases (X = SH, Cl) in which the energy change is greater than 20 kcal/mol.

ISSN:0008-4042    

DOI:10.1139/v84-248

出版商:NRC Research Press    

年代:1984

数据来源: NRC