摘要:

Extrusion of a stable molecular fragment (like N2, CO2, SO2, CO, etc.) is a common chemical process. Using thermodynamic additivity concepts, group values, and heat of formation data, a Relative Extrusibility Scale (ΔHex0) has been defined for these fragmentations:Twenty-four such extrusions spanning 150 kcal mol−1have been compiled. Typical values include N2(−42.0), CO2(−2.6), HCN (13.8), CO (15.4), H2CO (18.3), C2H4(32.2), and1CH2(109). Among other theoretical and mechanistic applications, this list should be useful when designing synthetic routes involving extrusion reactions.In a particularly effective illustration of the usefulness of the scale, it rationalizes, for the first time, the variety of product types obtained from thermolyses of 14 different kinds of 5-membered ring diazenes. Heat of formation data on most of these compounds do not exist and they contain such sufficiently complicated functional group arrangements that most of the thermodynamic group equivalents are also unknown. This problem can be circumvented by thermodynamic cycles based on the Relative Extrusibility Scale, suitable models, and interfragment resonance corrections. Within an error framework of less than ± 5 kcal mol−1, enthalpy estimates are sufficiently accurate to give heats of reaction capable of predicting which of the potential fragmentation routes actually occur. Formation of a 3-membered ring must be exothermic by at least 30 kcal mol−1to contribute to the products, but 3-piece fragmentation and 1,3-dipolar cycloreversion will contribute to the observed products when the process is either thermoneutral or exothermic. The unimportance of entropy is also discussed.

ISSN:0008-4042    

DOI:10.1139/v81-070

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The vacuum ultraviolet absorption spectrum oftrans-diimide (N2H2) in the gas phase has been re-examined between 1800 and 1300 Å, using diimide prepared by the thermal decomposition of sodium tosylhydrazide. Two band systems were observed, designatedand, with origins at 1727 and 1473 Å, which have been assigned to the Rydberg transitions 3pπ(bu) ← n+and 4pπ(bu) ← n+respectively. Both systems show long progressions in v2′, the N—N—H symmetric bending frequency, and short progressions in v3′, the symmetric N—N stretching frequency.Thesystem has well-resolved rotationalJtype structure in some bands, and the rotational analysis showed that the ground state is a totally symmetric singlet state ofC2hsymmetry (planartrans-N2H2isomer), and that the system arises from a1Bu ← 1Agtransition. Rotational constants obtained for the 0–0 band of the-state wereA = 15.63,B = 1.32, andC = 1.22 cm−1, and the values ofrH−N = 1.028 Å,rH−N = 1.167 Å, andwere estimated from them assuming a planartransconformation.

ISSN:0008-4042    

DOI:10.1139/v81-071

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The Cu(I) complex [Me2Ga(OCH2CH2NMe2)N2C5H7]Cu•PPh3has been synthesized and its fluxional behavior in solution probed. Attempts have been made to isolate the analogous Cu(I) carbonyl complex. Crystals of [dimethyl(3,5-dimethyl-1-pyrazolyl)(N,N-dimethylethanolamino)gallato (N(2),O,N(3))](triphenylphosphine)copper(I) are monoclinic,a = 18.871(2),b = 9.464(1),c = 18.374(2) Ā, β = 109.62(1)°,Z = 4, space groupP21/c. The structure was solved by direct methods and was refined by full-matrix least-squares procedures toR = 0.028 andRw = 0.035 for 2729 reflections withI ≥ 3σ(I). The copper atom is bonded to the phosphine and to the tridentate Me2Ga(OCH2CH2NMe2)N2C5H7−ligand resulting in a distorted tetrahedral coordination geometry. The Cu—P distance of 2.156(1) Å is unusually short. Other important bond distances (corrected for libration) are: Cu—O, 2.163(2), Cu—N(pyrazolyl), 2.025(3), Cu—N(amino), 2.144(3), Ga—O, 1.896(3), Ga—N, 2.005(3), and Ga—C, 1.972(5) and 1.987(5) Å

ISSN:0008-4042    

DOI:10.1139/v81-072

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Crystals of the title compound, C22H32O3, are monoclinic,P21/n,a = 11.832(1),b = 11.423(1),c = 14.637(1) Å, β = 98.71(2)°,Z = 4. The structure was solved by direct methods and was refined toR = 0.035 for 2052 reflexions withI ≥ 3σ(I). The X-ray study was carried out in order to determine the structures of two diastereomeric products obtained from a key step in a projected synthesis of the diterpenoids aphidicolin and stemodin. The product examined is the stemodin intermediate.

ISSN:0008-4042    

DOI:10.1139/v81-073

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The electrochemical reduction of compounds of the typehas been investigated in hydroorganic medium between pH 0 and 7. For3(R1 = R2 = R3 = C6H5), the 3,4,5-triphenylisoxazole is obtained at pH 1.3in neutral medium,1(R1 = CH3, R2 = R3 = C6H5) and2(R1 = C2H5, R2 = R3 = C6H5) lead to 4,5-dihydroxy-2-isoxazoline (only one of such compounds is described in the literature). The structure of these compounds has been determined by the usual spectroscopic methods (ir, nmr, mass spectrometry) and by radiocrystallography. A mechanism which accounts for the whole set of our results is proposed: it involves an intermediate α,β-nitrosoethylenic compound which cyclizes into a 4,5-dihydroxy-2-isoxazoline or gives an 1,3-diketone oxime upon reduction; this last compound cyclizes into an isoxazole.

ISSN:0008-4042    

DOI:10.1139/v81-074

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The fission fragment radiolysis of CO2and the CO2–C3H8, CO2–NO2systems is studied in comparison with the γ radiolysis. Two kinds of back reactions (re-oxidation of carbon monoxide to carbon dioxide) are operative in the fission fragment radiolysis. One (a rapid back reaction) is the unidentified ionic chain reaction which proceeds at low CO concentrations, and the other (a slow back reaction) is assigned to a radical reaction (CO + O + CO2 → 2CO2 [3′]). This slow back reaction is a characteristic of the fission fragment radiolysis. The analysis of results gives an upper limit of the radius of fission fragment tracks in the reaction system,rρ < 1.04 μg cm−2.

ISSN:0008-4042    

DOI:10.1139/v81-075

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The gas-phase photolysis of 1,1-dimethylcyclopropane has been investigated using xenon (147.0 nm) and krypton (123.6 nm) resonance radiation. Major products observed in order of decreasing importance were isobutene, ethylene, hydrogen, 1,3-butadiene 2-methyl-1,3-butadiene, propylene, allene, methylacetylene, and acetylene. Radical scavengers, NO and O2, and radical interceptors, H2S/D2S and HI, were used to determine the relative importance of radical and molecular processes. CH3, C2H3, C3H5, and C4H7radical species were identified and quantified. Ten primary reaction channels were postulated, of which the elimination of methylene was the most predominant, accounting for 34% of the photo-decomposition at 147.0 nm and 39% at 123.6 nm. Although ionization was established at 123.6 nm (η = 0.10) the nature of a charge transfer or other ion-molecule reaction channel leading to the formation of 2-methyl-1-butene and 2-methyl-2-butene could not be determined.

ISSN:0008-4042    

DOI:10.1139/v81-076

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The mass spectra for thirteen symmetrical and thirty-five unsymmetrical dialkyl disulfides have been determined at 70 eV. Carbon–sulfur bond cleavage to give hydrocarbon ions was observed as well as the formation of RS+ions. Factors affecting these two processes are discussed. The most favoured decomposition pathway for the molecular ions of most of the dialkyl disulfides (RSSR′) studied was intramolecular hydrogen transfer to give RSSH and R′SSH. The effect of varying the structure of the alkyl groups on this process has been investigated.

ISSN:0008-4042    

DOI:10.1139/v81-077

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The optical absorption spectra of small particles of α-, β-, andx-form of metal-free phthalocyanine (H2Pc) and vanadyl phthalocyanine (VOPc) surrounded by a dielectric (polymers) have been studied. The true bulk absorption can be obtained by measuring the difference in transmittance of two films of identical composition but different thicknesses. This approach eliminates effectively light reflection losses. Comparison between the absorption spectra measured by direct vs. difference in transmittance revealed a number of differences: shift in the absorption frequencies, change in absorption intensities, and change in peak-to-valley ratio. These differences are due to light scattering which can be significantly minimized by using the differential transmittance method. The true peak absorption ofx-H2Pc particles located at 770 and 615 nm had an absorption coefficient of 35.3 and 34.2 μm−1, respectively. The absorption minimum occurs at 477 nm. The peak-to-valley ratio was 27.The absorption spectra of VOPc particles did not correspond to any one polymorph, but are due to a mixture of two known polymorphs. Some discrepancies between the particle absorption of α-H2Pc or β-H2Pc and the corresponding evaporated film absorption were observed. These discrepancies are attributed to the spread in particle size and also to local agglomeration of the particles.

ISSN:0008-4042    

DOI:10.1139/v81-078

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Conditional formation constants were determined at 25 °C and with a background electrolyte of 0.1 mol dm−3NaNO3for the proton, nickel(II), copper(II), and zinc(II) complexes of glycine, iminodiacetic acid, and nitrilotriacetic acid in 0, 20, 50, 80, and 95 volume percent methanol mixed with water. Similar measurements were made for triethylenetetramine in all but 95% methanol, and the formation constants so determined were used to determineKMNTAby a competitive method.The variation of all constants with solvent composition was examined from the point of view that complex formation is accompanied by solvent displacement. Accordingly it should be possible to correlate the observations by means of an over-all formation constant, valid for any solvent concentration. It was concluded that for two solvents as similar as water and methanol, both of which appear to be involved in solvation or desolvation in the reaction, the correlations sought could not very precisely fix the amounts of solvents displaced or taken up. The goodness of fit to the attempted correlations suggests that they would be useful for interpolations to solvent compositions other than those studied.

ISSN:0008-4042    

DOI:10.1139/v81-079

出版商:NRC Research Press    

年代:1981

数据来源: NRC