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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Plant acetylenes

Chin, Clinton Gordon January 1965 (has links)
No description available.
32

Ligand shape and its stereochemical consequences

Halfpenny, M. T. January 1968 (has links)
No description available.
33

The crystal and molecular structures of some inorganic, organic, and biological compounds

Camerman, Norman January 1964 (has links)
The crystal and molecular structures of cyanodi-methylarsine (cacodyl cyanide), diiodomethylarsine, and "cacodyl disulphide" (dimethylarsi.no dimethylditbioarsinate) have been determined by x-ray diffraction of single crystals, in order to investigate the stereochemistry of arsenic. The structure of cyanodimethylarsine was determined from projections along the three crystallographic axes. The central arsenic bond angle of 105° agrees well with that found in the halogendiphenylarsines, and is considerably larger than the value assumed in an electron-diffraction investigation of the corresponding dimethyl derivatives. There is an unusually short As….N inter-molecular separation, which is indicative of charge-transfer bonding involving donation of nitrogen lone pair electrons to vacant arsenic 4d-orbitals, which probably accounts for the solidity of the compound whereas the halogendimethylarsines are all liquid at room temperature. Diiodomethylarsine, one of the few simple arsenic derivatives which are solid at room temperature, was structurally determined from partial three-dimensional data in normal and generalized projections. Though severe absorption corrections had to be applied, values of the bond distances, valency angles, and intermolecular separations were obtained. The molecular structure of "cacodyl disulphide" was determined precisely, utilizing the full three-dimensional data, and the analysis revealed the compound to be dimethylarsino dimethyldithioarsinate, an unusual structure, having one trivalent and one pentavalent arsenic atom in the molecule. The former atom has a trigonal-pyramidal configuration, while the latter is roughly tetrahedral. There is an unusually short intermolecular As[superscript III].. .As[superscript III] separation which suggests charge-transfer bonding involving donation of lone pair electrons on each As[superscript III] to vacant 4d-orbitals on the other As[superscript III]. The structure of the alkaloid cleavamine, a product of the acidification of the Vinca rosea Linn alkaloid catharanthine, was determined from a three-dimensional x-ray analysis of cleavamine methiodide. The indole system is retained in cleavamine but the rest of the molecule undergoes rearrangement via bond fission, the result: being a tetracyclic alkaloid structurally resembling the known alkaloid quebrachamine. The presence of the iodide ion prevented accurate measurements of the bond distances and angles, but, the measurements were sufficiently precise to differentiate between the different types of bonds and angles. The absolute configuration of cleavamine was also established. The crystal and molecular structure of 5-iodo-2'-deoxy-uridine, the first anti-viral agent to have proven clinical chemotherapeutic value, was elucidated by a three-dimensional x-ray investigation. The bond lengths and angles in the nucleoside were determined accurately, and indicated that, the pyrimidine base is in the di-keto form. The deoxyribose ring is puckered with C2' displaced 0.59 Å from the plane of the other four atoms; the distances and angles in the sugar ring are all normal. The most significant intermolecular distance is an I....0 (carbonyl) separation of 2.96 Å; this is considerably shorter than the usual van der Waals contact (3.55 Å) and suggests charge-transfer bonding involving donation of oxygen lone pair electrons to vacant 5d-orbitals of the iodine atom. A strong intermolecular attraction of this type may be the cause of the increase in "melting temperature" observed when 5-iodo-2'-deoxyuridine is substituted for thymidine in DNA, and hence may be the molecular basis for the compound's anti-viral activity. A preliminary x-ray investigation was carried out: on crystals of sodium thymidylyl-(53')-thymidylate-(51). The cell constants and space group of the dinucleotide were determined, and the intensities of the three-dimensional diffraction maxima were recorded, but the absence of a relatively heavy atom made attempts at: a complete structural elucidation unsuccessful. A number of crystallographic computer programmes have been written for the IBM 1620 and 7040 computers; a list of these is given in an appendix. / Science, Faculty of / Chemistry, Department of / Graduate
34

Synthesis and stereochemistry of some 9, 10-disubstituted cis-decalins

Scott, William Bruce January 1965 (has links)
The application of low temperature nuclear magnetic resonance (n. m. r.) spectroscopy to the determination of the barrier heights to interconversion in compounds which contain one and two flexible six-membered rings is reviewed. Although the barrier heights in cyclohexane and its derivatives have been experimentally determined, similar studies in the cis-decalin system have (until very recently) not been successful. Consideration is given, therefore, to the preparation of a number of cis-9, 10-disubstituted decalin derivatives, which will act as model compounds for a further study in the problem of the barrier height to ring interconversion in the cis-decalin system. Various attempts to synthesize a novel model compound, tricycle [4. 4. 4. 0] tetradecane, are described. Partial success has been achieved in that a small but demonstrable amount of tricycle [4. 4.4. 0]-3, 8-tetradecadiene has been synthesized in a ten step reaction sequence, starting from acetylenedicarboxylic acid. A Diels-Alder condensation of this compound with two mole-equivalents of 1, 3-butadiene gave Δ² ⁶-hexalin-9,10-dicarboxylic anhydride. Lithium aluminum hydride reduction of this compound gave cis-9, 10-bis(hydroxymethyl)-Δ² ⁶ -hexalin, which was converted to its dimesylate derivative on treatment with methanesulfonyl chloride in pyridine. Reaction of the dimesylate derivative with sodium cyanide in N-methyl-2-pyrrolidinone gave cis-9, 10-bis(cyanomethyl)-Δ² ⁶-hexalin. Alkaline hydrolysis of the latter gave cis-9,10-bis(carboxymethyl)-Δ² ⁶-hexalin, which was converted to its dimethyl ester on treatment with diazo- methane in 1, 2-dimethoxyethane. Lithium aluminum hydride reduction of the dimethyl ester gave cis-9,10-bis(2-hydroxyethyl)Δ² ⁶-hexalin. Treatment of the dialcohol with methanesulfonyl chloride in pyridine gave cis-9, 10-bis(2-mesyl-oxyethyl)-Δ² ⁶-hexalin. Reaction of the dimesylate with sodium iodide in acetone gave cis-9, 10-bis(2-iodoethyl)-Δ² ⁶-hexalin. Treatment of this compound with n-butyllithium in diethyl ether and in heptane gave a mixture of cis-9-ethyl-10- vinyl-Δ² ⁶-hexalin and tricyclo[4. 4.4. 0]-3, 8-tetradecadiene (minor product). Attempts to improve the yield of the tricyclic compound, using zinc and magnesium as coupling reagents, were unsuccessful. The syntheses of other desired model compounds are described. Thus, cis-9, 10-dimethyl-Δ²-octalin and -Δ² ⁶-hexalin were prepared from their cis- 9, 10-bis(mesyloxymethyl)- analogs on treatment of the latter compounds with sodium iodide in N, N-dimethylformamide, followed by the treatment of the respective product diiodides with lithium aluminum hydride in 1, 2-dimethoxyethane. cis-9,10- Dimethyldecalin was prepared from cis-9, 10-dimethyl-Δ² ⁶-hexalin by catalytic hydrogenation of the latter. In addition, treatment of cis-9, 10-bis(hydroxymethyl)- decalin and -Δ²-octalin with p-toluenesulfonic acid in benzene yielded 12-oxa- tricycle [4. 4. 3. 0] tridecane and -3-tridecene, respectively. 12-Oxatricyclo [4. 4. 3. 0] -3, 8-tridecadiene was isolated as a by-product from the reaction of cis-9, 10-bis- (mesyloxymethyl)-Δ² ⁶-hexalin with sodium cyanide in N-methyl-2-pyrrolidinone, as was 12-amino-11-cyanotricyclo [4. 4. 3. 0]-3, 8, 11-tridecatriene. All of the new compounds have been characterized by means of infrared, ultraviolet, and n. m. r. spectroscopy, mass spectrometry, and microanalysis, where applicable. Preliminary investigations of the barrier heights to interconversion in cis-9, 10-dimethyldecalin and 12-oxatricyclo [4. 4. 3. 0] tridecane are described. Quantitative kinetic data could not be obtained from the low temperature (0 to -60°) n. m. r. spectra of the former, since no broadening of the ring proton resonance peak was observed. On the other hand, the latter compound gave n. m. r. spectra in which the ether ring proton resonance peak broadened considerably as the sample temperature was lowered. From these spectra a value of the energy of activation (Ea) of 8. 4 ± 2 kcal. /mole was calculated for the interconversion process in 12-oxatricyclo [4. 4. 3. 0] tridecane. / Science, Faculty of / Chemistry, Department of / Graduate
35

Stereochemistry of nitrate esters of polyols

Livingstone, David James January 1965 (has links)
The solution infrared spectra and proton magnetic resonance (PMR) spectra of several series of polyol nitrates have been examined in order to assess the potential of these two spectroscopic methods for the study of the stereochemistry of nitrate esters in solution. This thesis reports the first systematic study of the solution infrared spectra of nitrate esters. Correlations of the frequencies of the three principal nitrato group bands with structure and stereochemistry were observed for 1, 4:3, 6-dianhydrohexitol, benzocycloalkane, cyclohexane, sugar, 1, 2-diphenylethane, and polyhydric alcohol nitrates. The frequencies of the Ʋa(NO₂) and Ʋ (ON) bands were clearly dependent on molecular structure while that of the Ʋs(NO₂) band exhibited a marked steric dependence. On the basis of their solution infrared spectra, configurations were assigned to several 1,4:3,6-dianhydrohexitol mononitrates which were consistent with other properties of these compounds. A rationale of certain aspects of the spectral correlations is presented. Examination of the PMR spectra of the nitrate esters and of other esters of polyhydric alcohols revealed a relationship between molecular symmetry and the multiplicity of methylene resonances. The PMR spectrum of glycerol trinitrate could be classified as that of an (AB)₂X system and a complete spectral assignment was possible for both the methine and methylene resonances. The effect of solvent and substituent on the methylene chemical shifts of pentaerythritol derivatives has been studied on a qualitative basis and the application of PMR spectroscopy to the elucidation of the structure of previously unreported 1,2-O-isopropylidene- α-D- glucofuranose- 3, 5, 6-trinitrate, for which a complete PMR spectral assignment was possible, is described. Thin-layer chromatography (TLC) has been successfully applied to the polyol nitrates and for several groups of these a dependence of Rf value upon stereochemistry has been noted. A stereoselective detection has been found for the 1, 4:3, 6-dianhydrohexitol nitrates and a preliminary study (by TLC) of the reactions of a homologous series of twelve polyhydric alcohol nitrates with pyridine indicated large differences between the rates of reaction of homologues but not of diastereoisomers. The p-toluenesulfonate and p- bromobenzenesulfonate esters of 1, 4:3, 6-dianhydro-D- glucitol- 5-nitrate, 1, 2- O-isopropylidene-α-D- glucofuranose-3, 5, 6-trinitrate, pentaerythritol trinitrate p-bromobenzene sulfonate, allitol hexabenzoate, L-threitol tetrani-trate, L-iditol hexanitrate, and D-talitol hexanitrate are reported for the first time. / Science, Faculty of / Chemistry, Department of / Graduate
36

Stereochemistry of olefin formation in the pyrolysis of 3-carbomethoxy pyrazolines

Wu, Weh-Sai January 1966 (has links)
The thermal decomposition of cis- and trans-3-methyl-4-ethyl-3-carbo-methoxy-Δ¹-pyrazoline (cis- implies that the methyl and ethyl groups are cis) and trans-3-methyl-4-ethyl-3-carbomethoxy- Δ¹-pyrazoline gave a mixture which contained cyclopropane products, cis- and trans-1-methyl-2-ethyl-1-carbo-methoxycyclopropane; α, β-unsaturated ester products, methyl cis- and trans-2,3-dimethyl-2-pentenoate (cis and trans refer the two methyl groups); and the β, у-unsaturated ester, methyl 2-methyl-3-ethyl-3-butenoate. The α,β-unsaturated esters are formed stereospecifically since cis-3-methyl-4-ethyl-3-carbomethoxy-Δ¹-pyrazoline gave only methyl trans-2,3-dimethyl-2-pentenoate (56% in the liquid phase and 28% in the vapor phase). Similarly in the pyrolysis of trans-3-methyl-4-ethyl-3-carbomethoxy- Δ¹-pyra-zoline methyl cis-2,3-dimethyl-2-pentenoate (13% in the liquid phase and 6% in the vapor phase) was obtained while only a trace of methyl trans-2,3-dimethyl-2-pentenoate was found in both the liquid and vapor phase pyrolysis. The cyclopropane products formed from pyrolysis of cis- and trans-3-methyl-4-ethyl-3-carbomethoxy- Δ¹-pyrzaoline have shown some degree of stereo-specificity with a predominance of the isomer having the same stereochemistry as the starting pyrazoline being obtained. The results of the above experiments suggest that the mechanism of thermal pyrolysis of pyrazolines requires that the nitrogen leaves from the same side as the ethyl group, i.e. trans to the hydrogen which is migrating. The photolysis of cis- and trans-3-methyl-4-ethyl-3-carbomethoxy- Δ¹-pyrazoline has been found to be stereospecific in cyclopropane formation with the absence of isomeric olefin products. A small amount of the olefin corresponding to loss of CH₂N₂ was also found having the same stereochemistry as the pyrazolone. Since the products from photolysis are different from that of pyrolysis, a modified mechanism is required. Insufficient evidence is available to clearly define that mechanism. / Science, Faculty of / Chemistry, Department of / Graduate
37

The isomerization and stereochemistry of some iridium hydride complexes /

Yorke, William John. January 1979 (has links)
No description available.
38

The stereochemistry of nickel(II) and cobalt(II) complexes which contain cyclic tetradentate ligands /

Warner, Larry George January 1968 (has links)
No description available.
39

The Stereochemistry of Silenes and Alpha-Lithio Silanes

Bates, Tim Frank 05 1900 (has links)
When E- or Z-l-methyl-l-phenyl-2-neopentylsilene was generated by the retro-Diels-Alder vacuum-sealed tube thermolysis of its corresponding anthracene adduct, in the presence of various alkoxysilanes, only one diastereomeric adduct was formed in each case, showing that the reactions are stereospecific. An x-ray crystal structure of the methoxytriphenylsilane adduct of the E-silene confirmed its relative configuration as (R,S) or (S,R). This demonstrated that the addition of alkoxysilanes to silenes is stereospecific and syn. The relative configurations of similar alkoxysilane and alkoxystannane adducts to E- and Z-l-methyl-l-phenyl-2-neopentylsilene were assigned based on a combination of xray structures and *3C NMR data. A strong, nonbonded oxygen-metal interaction is apparent in all of those compounds studied. Treatment of the alkoxystannane adducts with alkyl lithium reagents results in tin-lithium exchange in some cases. The results indicate that the resulting <x-lithio alkoxysilanes are not configurationally stable in either THF or hydrocarbon solvents. The reaction of tert butyl lithium with a-trimethylsilylvinylmethylphenylchlorosilane in hydrocarbon solvents yields E- and Z-l-methyl-l-phenyl-2-neopentyl-2-trimethylsilylsilene. In the absence of any traps these silenes undergo a novel tert butyl lithium catalyzed rearrangement to 2-phenyl-3-trimethylsilyl-5,5-dimethyl-2-silahex-3-ene. These silenes were also trapped as their [4+2] cycloadducts with anthracene. The Z-isomer of the anthracene adduct was separated and its stereochemistry confirmed by an x-ray crystal structure. The anthracene adducts of both E- and Z-l-methyl-1-phenyl-2-neopentyl-2-trimethylsilylsilene undergo a facile, stereospecific decomposition at temperatures as low as 190°C to regenerate their respective silenes, the mildest stereospecific route to a silene yet reported. The E- and Z-silenes react stereospecifically with methanol under vacuum-sealed tube conditions. The stereochemistry of the addition is syn and a common mechanism is proposed for the addition of alcohols and the addition of alkoxysilanes to silenes.
40

Structural studies of deoxyribonucleic acids using diffraction and spectroscopic methods

Boote, Craig January 1999 (has links)
No description available.

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