摘要:

SiF2produced by the quartz tube reaction has been reacted with ethylene and six methyl-substituted ethylenes. All major products (polymers, disilacyclobutanes, disilacyclohexanes, and open chain compounds) have been characterized by a combination of19F,1H,13C, and29Si nmr spectroscopy. While polymer is always formed in highest yield, the relative proportions of other products vary significantly from alkene to alkene.Key observations concerning structures and stereochemistries and product yields are summarized. Consideration of this evidence leads to a mechanism involving attack of SiF2on the olefin to form an excited silirane which either ring opens or relaxes to its ground state, followed in either case by further reaction.

ISSN:0008-4042    

DOI:10.1139/v80-067

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Polymers produced by the reaction of SiF2with olefins have been characterized by13C and29Si nmr spectroscopy and have been found to have a regular head-to-tail structure with isolated SiF2groups between olefin units. Only minor proportions of Si2F4units are formed. The open chain organosilicon derivatives formed in the reaction are, with one exception, isomers of 1,2-disilacyclohexanes. The 1,2-disilacyclobutanes are formed stereospecifically with retention of alkyl stereochemistry.19F chemical shifts can be predicted by additive chemical shift parameters for the effect of alkyl substitution.

ISSN:0008-4042    

DOI:10.1139/v80-068

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

1,2-Disilacyclohexanes are generally formed as products in the reaction of SiF2with alkenes. Unsymmetric methyl-substituted alkenes yield disilacyclohexanes with greater methyl substitution at C(2). Often two (or more isomeric) products are formed, and the reaction proceeds by a mechanism which allows isomerization of the methyl configurations. The disilacyclohexanes exist in distorted chair conformations and the chair-to-chair interconversion can be observed at low temperature in many cases. Consideration of the variable temperature19F spectra and the effect of methyl groups on average and individual19F chemical shifts allows assignment of configurations and preferred conformations of all disilacyclohexane derivatives.

ISSN:0008-4042    

DOI:10.1139/v80-069

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Treatment of dehydrosaussurea lactone4and costunolide1withN-bromosuccinimide (NBS) in aqueous acetone at room temperature furnished bromolactones6,7, and8. Structural evidence for these bromolactones rests upon spectral data and transformation to the hydrogenated bromolactones9,10, and11. The latter were found identical with the corresponding products obtained by the brominative cyclization of dihydrocostunolide2.

ISSN:0008-4042    

DOI:10.1139/v80-070

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Allyl-tert-butyl peroxide decomposes thermally in toluene withkd = 1013.8exp (−33200/θ) (s−1). Product studies show the reaction to be a mixture of homolysis and radical-induced decomposition, the latter involving both radical addition to C=C and allyl hydrogen abstraction by alkoxy radicals. Computer modelling of the system gives good agreement with the experimental results and suggests that the overall decomposition is about 50% homolysis.

ISSN:0008-4042    

DOI:10.1139/v80-071

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

An excitation spectrum of the triplet–singlet band system of CS2vapor has been measured in the range 365–378 nm using a tunable laser source. Overall intensity is relatively insensitive to pressure in the range (150 m Torr – 340 Torr) tested in these observations. The results indicate that collisions with ground state molecules of CS2are efficient in promoting intersystem crossing to the ground state, and that the spontaneous emission observed is primarily resonance emission from the state populated by the radiation.

ISSN:0008-4042    

DOI:10.1139/v80-072

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Earlier work on the photochemistry of α-sulfonyloxyketones uncovered their propensity to form the corresponding α-keto carbonium ions on photolysis. Typical reactions such as intramolecular cyclizations, carbonium ion rearrangements, and solvent trapping were found. This paper describes an attempt to extend this reaction to a general synthetic technique for polyene cyclizations. During the course of this work two other major reaction pathways were found. The first is an α-keto carbonium ion to acylium ion rearrangement and the second is a photoreduction–elimination process that leads to an α-keto radical rather than the corresponding cation.

ISSN:0008-4042    

DOI:10.1139/v80-073

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The thermolysis ofR-(+)-laurolenal (1) producesR-(+)-1,2,3-trimethylcyclopentene in high optical purity. The alcohol3, at 297 °C, similarly produces the alkeneR-(+)-4, but with mechanistic complications in that the formaldehyde produced oxidizes the alcohol3to the corresponding aldehyde1. The alcohol3-d2was used to show the extent of aldehyde conversion by virtue of the formation of4-d1. Comparison of the decarboxylation of the acid, decarbonylation of the aldehyde, and demethanalation of the alcohol gives relative rates of 9:2:1 at 297 °C.

ISSN:0008-4042    

DOI:10.1139/v80-074

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The free energy of activation for hindered rotation about the C—N exocyclic bond in someN,N-dimethylaminopyrimidine hydrochlorides has been determined by1H and13C nmr line-shape analysis.Monoprotonation ofN,N-dimethylaminopyrimidines induces a large increase of the free energy of activation (from 14 to 24 kJ mol−1). This increase is larger for the 4-dimethylamino group than for the 2-dimethylamino group due to the predominance of the monoprotonated (N-1 H) form. Consequently, the difference of conjugation of the 4- and 2-dimethylamino groups with the pyrimidine ring is more pronounced in the monoprotonated species.

ISSN:0008-4042    

DOI:10.1139/v80-075

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The geminal and vicinal13C—31P coupling constants for the 3′- and 5′-monophosphates and 3′,5′-diphosphates of thymidine and its isomer 6-methyl-2′-deoxyuridine have been obtained for aqueous solutions at varions pH values. Since the thymine base isantiand the 6-methyluracil base issyn, the data provide information about the influence of the orientation about theN-glycosyl linkage on the conformation about theandbonds. The3J(C4′—P5′) couplings reveal a preference for theconformer of the 5′-nucleotidyl units, in agreement with previous measurements of1H—31P coupling constants. The3J(C4′—P3′) and3J(C2′—P3′) couplings are consistent with a preference for theconformer for both thesynandanti3′-nucleotidyl units. The response of these couplings to secondary ionization of the phosphate is different for the thymine and 6-methyluracil derivatives and suggests a phosphate–phosphate interaction for thesyn, but not theanti, 3′,5′-diphosphates. A correlation between the sugar-pucker and theorientation is revealed. The2J(C5′—P5′) and2J(C3′—P3′) are relatively insensitive to the ionization state of the phosphate as well as to other structural features of the deoxyribose phosphate backbone.

ISSN:0008-4042    

DOI:10.1139/v80-076

出版商:NRC Research Press    

年代:1980

数据来源: NRC