摘要:

TheT1's, linewidths (T2's), and chemical shifts of119Sn nuclei in a variety of tin compounds have been surveyed using pulse Fourier transform techniques. The results span the very large chemical shift range for tin-119 (∼2000 ppm), and indicate rather shortT1values with widely variedT2relaxation times. Possible mechanisms are discussed for bothT1andT2relaxation times. Our results show an approximate correlation betweenT1(119Sn) and the paramagnetic contribution to the observed shielding of the119Sn nucleus, indicating that apart from a large scalar contribution in Sn(IV) iodides and bromides, the dominant119SnT1mechanism is spin rotation interaction.

ISSN:0008-4042    

DOI:10.1139/v77-130

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Nitric oxide reduces the production of hydrogen in irradiated HCl and leads to ClNO formation. The results can be interpreted on the basis of a competition between HCl and NO for H atoms and (HCl)x−negative ion intermediates. The yield of (HCl)x− = 2.4 ± 0.3 per 100 eV is similar to that found from experiments with chlorine, as was the total yield of scavengable H atoms plus electrons,ge + gH. From analyses of the competition kinetics for experiments both with and without added SF6, the ratio of the termolecular rate constant for reaction of H with NO in the presence of HCl as third body to that for reaction of H with HCl was estimated to be 6.3 ± 0.8 × 10−19 cm3molecule−1at 298 K.

ISSN:0008-4042    

DOI:10.1139/v77-131

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Nucleoside analogs, namely 6-chloro-9-(4-benzoyl-1-oxa-4-azacyclohexan-2-yl)-9H-purine6and 6-chloro-9-(4-benzoyl-1-thia-4-azacyclohexan-2-yl)-9H-purine7, were obtained by treatment of 4-benzoyl-2-hydroxy-1-oxa-4-azacyclohexane13and 4-benzoyl-2-hydroxy-1-thia-4-azacyclohexane18, respectively, with 6-chloropurine, methyldiphenylphosphine, and diethyl azodicarboxylate in refluxing tetrahydrofuran. Compounds13and18were obtained byO-deacetylation of the corresponding 2-acetoxy derivatives11and16with a catalytic amount of sodium methoxide in chloroform. 2-Acetoxy-4-benzoyl-1-oxa-4-azacyclohexane11was obtained from 4-benzoyl-1-oxa-4-azacyclohexane10by treatment withtert-butyl peracetate, cuprous chloride, and benzene, whereas 2-acetoxy-4-benzoyl-1-thia-4-azacyclohexane16was prepared by a Pummerer reaction with 4-benzoyl-1-thia-4-azacyclohexane 1-oxide15. The13C nmr spectra of all the compounds are reported; the spectra provided unambiguous proof of structure.

ISSN:0008-4042    

DOI:10.1139/v77-132

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The rotational barrier in 4-benzoyl-1-thia-4-azacyclohex-2-ene has been investigated by total line-shape analysis of variable temperature1H nmr spectra in acetonitrile-d3. Separate treatment of the vinyl and methylene signals yielded sets of values for activation parameters which were in excellent agreement. Assignment of the major and minor rotational isomers was made from chemical-shift data derived from the13C nmr spectrum at 243 K in acetonitrile-d3.

ISSN:0008-4042    

DOI:10.1139/v77-133

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Crystals ofL-prolinatodiphenylboron are monoclinic,a = 5.9427(5),b = 14.4633(7),c = 8.9654(4) Å, β = 98.423(8)°,Z = 2, space groupP21. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to a finalRof 0.037 andRwof 0.053 for 1477 reflections withI ≥ 3σ(I). The proline ring exhibits conformational disorder. The crystal structure consists of discrete molecules linked by N—H … O hydrogen bonds (N … O = 2.893(3) Å) along the shortaaxis. Intramolecular N—B coordination occurs to form a system of two fused five-membered rings. Bond lengths (corrected for libration) are: N—B, 1.630(3), O—B, 1.529(3), O—C, 1.219(3) and 1.300(3), N—C, 1.506(3) and 1.507(3),C(sp3)–C(sp3), 1.525(4),C(sp2)—C(sp3), 1.517(3), and mean C—C(phenyl), 1.394 Å.

ISSN:0008-4042    

DOI:10.1139/v77-134

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Flash thermolysis of 11,12-epoxy-9,10-dihydro-9,10-ethanoanthracene (dibenzobarrellene oxide) (2) gave 5H-dibenzo[a,d]cycloheptene-5-carboxaldehyde (3). At higher temperatures the products included 5H-dibenzo[a,d]cycloheptene-10-carboxaldehyde (4), 5H-dibenzo[a,d] cycloheptene (5), and fluorene (6). Flash thermolysis of dimethyl 3-oxatricyclo[3.2.2.02,4]nona-6,8-diene-6,7-dicarboxylate (the oxide of barrellene-2,3-dicarboxylic acid dimethyl ester) (16) gave a compound considered to be either dimethyl 3-methanoyl-1,3,5-cycloheptatriene-1,2-dicarboxylate (17) or dimethyl 1-methanoyl-1,3,5-cycloheptatriene-2,3-dicarboxylate (18), while at higher temperatures dimethyl 1-methanoyl-1,3,5-cycloheptatriene-6,7-dicarboxylate (19) was obtained.16also yielded small amounts of ketene, which was detected by low-temperature infrared spectroscopy. The mechanistic significance of these results is discussed.

ISSN:0008-4042    

DOI:10.1139/v77-135

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Flash thermolysis of dimethyl 3-oxatricyclo[3.2.2.02,4]nona-6,8-diene-6,7-dicarboxylate (the oxide of barrellene-2,3-dicarboxylic acid dimethyl ester) (2) at 700 °C gave methyl isocoumarin-7-carboxylate (3) as a major component of the thermolysate. The rearrangement is discussed in terms of sigmatropic shifts in cycloheptatrienes and their norcaradiene tautomers.

ISSN:0008-4042    

DOI:10.1139/v77-136

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The photochemistry of methyl 1-methyl-2-phenylcyclopropene-3-carboxylate has been examined in both the racemic and optically active forms. In the excited singlet the cyclopropene is converted to 2-methoxy-5-methyl-4-phenylfuran whereas the triplet state dimerizes to a tricyclohexane derivative. Experiments with optically active cyclopropene ester demonstrate that photochemical racemization occurs about 2.5 times as fast as conversion to the furan product indicating that there is an intermediate vinyl carbene on the singlet surface. No racemization is observed in the triplet state.

ISSN:0008-4042    

DOI:10.1139/v77-137

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The relative contributions of nuclear repulsion and electronic attraction to conformational rotational potentials have been analysed for several types of systems. It is shown that decomposition of a computed total energy into these two components provides a diagnostic tool for the evaluation of the reliability of such computations. It is also pointed out that Hartree–Fock theory is sufficient to reproduce experimental stereochemical observations, provided that one is aware of the accuracy needed to compute the molecular electronic wave function. This accuracy is predetermined by the nuclear or electronic dominance of the process.

ISSN:0008-4042    

DOI:10.1139/v77-138

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

A non-iterative approximation to the method of steepest descent is given for the evaluation of state density in a molecular system. Test calculations on 'large' and 'small' model molecules consisting of harmonic oscillators and rigid rotors show excellent agreement with the 'exact' first-order steepest-descent solutions, but are almost an order of magnitude faster in computing times.

ISSN:0008-4042    

DOI:10.1139/v77-139

出版商:NRC Research Press    

年代:1977

数据来源: NRC