A new light source has been developed which produces numerous self-reversed lines in both the first and second spectra of rare-earth elements. It consists of a pulsed arc discharge with a peak current of 75 amperes and an on-time of one millisecond per cycle. Resonance lines are nearly completely absorbed, and can be distinguished by this character. From spectrograms obtained with this light source, the ground states of Tb I and U II were determined, and those reported for Yb I, Yb II, Tm I, Tm II, and U I were confirmed.
{"title":"Light Source for Producing Self-Reversed Spectral Lines","authors":"J. Sugar","doi":"10.6028/jres.066A.032","DOIUrl":"https://doi.org/10.6028/jres.066A.032","url":null,"abstract":"A new light source has been developed which produces numerous self-reversed lines in both the first and second spectra of rare-earth elements. It consists of a pulsed arc discharge with a peak current of 75 amperes and an on-time of one millisecond per cycle. Resonance lines are nearly completely absorbed, and can be distinguished by this character. From spectrograms obtained with this light source, the ground states of Tb I and U II were determined, and those reported for Yb I, Yb II, Tm I, Tm II, and U I were confirmed.","PeriodicalId":94340,"journal":{"name":"Journal of research of the National Bureau of Standards. Section A, Physics and chemistry","volume":"363 1","pages":"321 - 324"},"PeriodicalIF":0.0,"publicationDate":"1962-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77220307","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A high pressure X-ray powder camera has been constructed. The instrument has been found to be useful for routine X-ray work, using molybdenum radiation, to pressures of approximately 60 kilobars. Previously reported transitions have been observed in silver iodide, potassium iodide, bismuth, and thallium. The high pressure forms and lattice parameters were found to be: AgI—f.c.c. (NaCl type), a0=6.067 A; KI—s.c. (CsCl type), a0 = 4.093 A; Tl—f.c.c. (NaCl type), a0 = 4.778 A; Bi structure not determined. These data confirm previous reports on the high pressure forms of AgI and KI. Data on Tl and Bi are apparently reported for the first time. The high pressure modifications were studied at the following approximate pressures which are not indicative of the point where the transition occurs: AgI—3.3 kilobars, KI—20 kilobars, Bi—28 kilobars, and Tl—60 kilobars. The pressure limit to which the unit can be used successfully has not been ascertained. It is believed to be much higher than the pressures reported. The present instrument is capable of producing powder diffraction patterns of materials of relatively high scattering power, giving data to 2θ=35°. High background on the X-ray powder patterns is believed to arise from scattering by the diamonds. This background may obscure weak diffraction rings. This effect may be reduced by screening, monochromatization, and other improvements in experimental technique.
{"title":"A Diamond Cell for X-ray Diffraction Studies at High Pressures","authors":"G. Piermarini, C. Weir","doi":"10.6028/jres.066A.033","DOIUrl":"https://doi.org/10.6028/jres.066A.033","url":null,"abstract":"A high pressure X-ray powder camera has been constructed. The instrument has been found to be useful for routine X-ray work, using molybdenum radiation, to pressures of approximately 60 kilobars. Previously reported transitions have been observed in silver iodide, potassium iodide, bismuth, and thallium. The high pressure forms and lattice parameters were found to be: AgI—f.c.c. (NaCl type), a0=6.067 A; KI—s.c. (CsCl type), a0 = 4.093 A; Tl—f.c.c. (NaCl type), a0 = 4.778 A; Bi structure not determined. These data confirm previous reports on the high pressure forms of AgI and KI. Data on Tl and Bi are apparently reported for the first time. The high pressure modifications were studied at the following approximate pressures which are not indicative of the point where the transition occurs: AgI—3.3 kilobars, KI—20 kilobars, Bi—28 kilobars, and Tl—60 kilobars. The pressure limit to which the unit can be used successfully has not been ascertained. It is believed to be much higher than the pressures reported. The present instrument is capable of producing powder diffraction patterns of materials of relatively high scattering power, giving data to 2θ=35°. High background on the X-ray powder patterns is believed to arise from scattering by the diamonds. This background may obscure weak diffraction rings. This effect may be reduced by screening, monochromatization, and other improvements in experimental technique.","PeriodicalId":94340,"journal":{"name":"Journal of research of the National Bureau of Standards. Section A, Physics and chemistry","volume":"17 1","pages":"325 - 331"},"PeriodicalIF":0.0,"publicationDate":"1962-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73592064","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
By combining appropriate geometric configuration and mathematical analysis with improved measuring techniques, the cell constant of a coaxial cylinder thermal conductivity cell was determined within 0.1 percent. An analysis of the rate of heat transfer in such a cell showed a way to treat the data so that the error contribution of experimental deviations from idealized conditions is kept small. The principal considerations are: That heat transport by convection is significantly large in a dense gas. This transport was analyzed mathematically from basic principles. The agreement of experimental results with the analysis indicated that the expressions are valid and that the convective heat transport could be accounted for with little more error than was involved in the precision of the heat transfer measurements. That the heat transfer in a vacuum corresponds to the heat transfer by radiation and solid contacts in the presence of a gas. The uncertainty was that associated with the accuracy of determining the vacuum values. That other effects were small enough to be computed and corrected for without increasing the uncertainty of the values of the thermal conductivity.
{"title":"Thermal Conductivity of Gases. I. The Coaxial Cylinder Cell","authors":"L. A. Guildner","doi":"10.6028/jres.066A.034","DOIUrl":"https://doi.org/10.6028/jres.066A.034","url":null,"abstract":"By combining appropriate geometric configuration and mathematical analysis with improved measuring techniques, the cell constant of a coaxial cylinder thermal conductivity cell was determined within 0.1 percent. An analysis of the rate of heat transfer in such a cell showed a way to treat the data so that the error contribution of experimental deviations from idealized conditions is kept small. The principal considerations are: That heat transport by convection is significantly large in a dense gas. This transport was analyzed mathematically from basic principles. The agreement of experimental results with the analysis indicated that the expressions are valid and that the convective heat transport could be accounted for with little more error than was involved in the precision of the heat transfer measurements. That the heat transfer in a vacuum corresponds to the heat transfer by radiation and solid contacts in the presence of a gas. The uncertainty was that associated with the accuracy of determining the vacuum values. That other effects were small enough to be computed and corrected for without increasing the uncertainty of the values of the thermal conductivity.","PeriodicalId":94340,"journal":{"name":"Journal of research of the National Bureau of Standards. Section A, Physics and chemistry","volume":"47 1","pages":"333 - 340"},"PeriodicalIF":0.0,"publicationDate":"1962-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91187195","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Scott, D. Scheiber, A. J. Curtis, J. I. Lauritzen, J. Hoffman
The dielectric properties of polychlorotrifluoroethylene (Tm = 224 °C, Tg = 52 °C) have been measured at temperatures between −50 and +250 °C, and at frequencies between 0.1 c/s and 8.6 kMc/s. Specimens of known crystallinities, ranging from χ = 0.80 to χ = 0.00 (pure liquid) were studied. Comprehensive tables of data are presented. The experimental techniques employed to measure the dielectric properties over these wide ranges of temperature, frequency, physical state, and sample type (disks, cylinders, and thin films), are discussed. The operation and calibration of the specimen holder, bridges, resonant circuits, and waveguide apparatus used are discussed in detail. When the dielectric loss index, ϵ″, at 1 c/s is plotted as a function of temperature for a highly crystalline specimen (χ = 0.80), where the crystallinity consists largely of lamellar spherulites, three distinct loss peaks are readily apparent. These peaks occur at about −40 °C (low-temperature process), 95 °C (intermediate-temperature process), and 150 °C (high-temperature process). The dielectric data are compared with the mechanical loss data obtained at 1 c/s by McCrum. Mechanical loss peaks at temperatures virtually identical to those in the ϵ″ versus T plot are found. The high-temperature process is attributed to the presence of well-formed chain-folded lamellar spherulites. Some evidence points to the surfaces of the lamellae as the site of the loss mechanism. The high-temperature loss peak does not appear in resolved form in non-spherulitic specimens even when the crystallinity is high. The intermediate-temperature process originates in the normal supercooled amorphous phase, and is due to the complex dipole relaxation effects involving motions of large numbers of polymer chain segments that are associated with the onset of the glass transition at Tg = 52 °C. As determined by V¯−T data, the glass transition temperature at Tg = 52 °C that is associated with this relaxation effect does not shift appreciably with increasing crystallinity. The low-temperature dielectric loss process, which is active far below Tg, originates principally in the supercooled amorphous regions, and evidently corresponds to a fairly simple motion involving a small number of chain segments. This process tends to exhibit anomalous behavior in highly crystalline specimens, particularly at low temperatures. A large dipolar contribution of the crystals to the static dielectric constant was observed. This contribution increased with increasing temperature, and corresponded to a very rapid dipole reorientation process (τ~10−11 sec at 23 °C).
{"title":"Dielectric Properties of Semicrystalline Polychlorotrifluoroethylene","authors":"A. Scott, D. Scheiber, A. J. Curtis, J. I. Lauritzen, J. Hoffman","doi":"10.6028/jres.066A.028","DOIUrl":"https://doi.org/10.6028/jres.066A.028","url":null,"abstract":"The dielectric properties of polychlorotrifluoroethylene (Tm = 224 °C, Tg = 52 °C) have been measured at temperatures between −50 and +250 °C, and at frequencies between 0.1 c/s and 8.6 kMc/s. Specimens of known crystallinities, ranging from χ = 0.80 to χ = 0.00 (pure liquid) were studied. Comprehensive tables of data are presented. The experimental techniques employed to measure the dielectric properties over these wide ranges of temperature, frequency, physical state, and sample type (disks, cylinders, and thin films), are discussed. The operation and calibration of the specimen holder, bridges, resonant circuits, and waveguide apparatus used are discussed in detail. When the dielectric loss index, ϵ″, at 1 c/s is plotted as a function of temperature for a highly crystalline specimen (χ = 0.80), where the crystallinity consists largely of lamellar spherulites, three distinct loss peaks are readily apparent. These peaks occur at about −40 °C (low-temperature process), 95 °C (intermediate-temperature process), and 150 °C (high-temperature process). The dielectric data are compared with the mechanical loss data obtained at 1 c/s by McCrum. Mechanical loss peaks at temperatures virtually identical to those in the ϵ″ versus T plot are found. The high-temperature process is attributed to the presence of well-formed chain-folded lamellar spherulites. Some evidence points to the surfaces of the lamellae as the site of the loss mechanism. The high-temperature loss peak does not appear in resolved form in non-spherulitic specimens even when the crystallinity is high. The intermediate-temperature process originates in the normal supercooled amorphous phase, and is due to the complex dipole relaxation effects involving motions of large numbers of polymer chain segments that are associated with the onset of the glass transition at Tg = 52 °C. As determined by V¯−T data, the glass transition temperature at Tg = 52 °C that is associated with this relaxation effect does not shift appreciably with increasing crystallinity. The low-temperature dielectric loss process, which is active far below Tg, originates principally in the supercooled amorphous regions, and evidently corresponds to a fairly simple motion involving a small number of chain segments. This process tends to exhibit anomalous behavior in highly crystalline specimens, particularly at low temperatures. A large dipolar contribution of the crystals to the static dielectric constant was observed. This contribution increased with increasing temperature, and corresponded to a very rapid dipole reorientation process (τ~10−11 sec at 23 °C).","PeriodicalId":94340,"journal":{"name":"Journal of research of the National Bureau of Standards. Section A, Physics and chemistry","volume":"13 1","pages":"269 - 305"},"PeriodicalIF":0.0,"publicationDate":"1962-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86233545","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
2-Propoxy-5-methylbenzoic acid has been synthesized by two routes from p-cresotinic acid. Synthesis of the ethyl ester of p-cresotinic acid, propylation to the ether, and subsequent hydrolysis of the ester proved to be the preferred route.
{"title":"Synthesis of 2-Propoxy-5-Methylbenzoic Acid","authors":"G. Brauer, L. Simon","doi":"10.6028/jres.066A.030","DOIUrl":"https://doi.org/10.6028/jres.066A.030","url":null,"abstract":"2-Propoxy-5-methylbenzoic acid has been synthesized by two routes from p-cresotinic acid. Synthesis of the ethyl ester of p-cresotinic acid, propylation to the ether, and subsequent hydrolysis of the ester proved to be the preferred route.","PeriodicalId":94340,"journal":{"name":"Journal of research of the National Bureau of Standards. Section A, Physics and chemistry","volume":"10 1","pages":"313 - 315"},"PeriodicalIF":0.0,"publicationDate":"1962-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78666716","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. Wyman, J. Cuthill, G. Moore, J. J. Park, H. Yakowitz
In attempting to produce superconducting wire of the niobium sheath Nb3Sn core type, it became apparent that results were generally unpredictable. Metallographic examination showed that such materials are heterogeneous and contain a number of intermediate phases. Detailed metallographic studies were made on diffusion zones in which tin had been allowed to react with porous niobium blocks, with fused niobium rod, and with niobium wires, and on a number of reacted powder mixtures. The phases produced were identified by anodizing to characteristic colors and by microspot analysis, supplemented by some hot-stage microscope and thermal analysis tests. On the basis of these observations, a tentative revised diagram is offered to illustrate the types of reactions which occur in the system. The presumably desired phase, Nb3Sn, is found to lie between the more easily formed phases Nb4Sn and Nb2Sn3, which are stable to temperatures well above the peritectoid decomposition of the Nb3Sn. At lower temperatures the compound Nb2Sn is formed. It is indicated that the high-temperature treatment to react niobium and tin should be followed either by very slow cooling or by an anneal in the 600 to 700 °C range to form Nb3Sn.
{"title":"Intermediate Phases in Superconducting Niobium-Tin Alloys","authors":"L. Wyman, J. Cuthill, G. Moore, J. J. Park, H. Yakowitz","doi":"10.6028/jres.066A.037","DOIUrl":"https://doi.org/10.6028/jres.066A.037","url":null,"abstract":"In attempting to produce superconducting wire of the niobium sheath Nb3Sn core type, it became apparent that results were generally unpredictable. Metallographic examination showed that such materials are heterogeneous and contain a number of intermediate phases. Detailed metallographic studies were made on diffusion zones in which tin had been allowed to react with porous niobium blocks, with fused niobium rod, and with niobium wires, and on a number of reacted powder mixtures. The phases produced were identified by anodizing to characteristic colors and by microspot analysis, supplemented by some hot-stage microscope and thermal analysis tests. On the basis of these observations, a tentative revised diagram is offered to illustrate the types of reactions which occur in the system. The presumably desired phase, Nb3Sn, is found to lie between the more easily formed phases Nb4Sn and Nb2Sn3, which are stable to temperatures well above the peritectoid decomposition of the Nb3Sn. At lower temperatures the compound Nb2Sn is formed. It is indicated that the high-temperature treatment to react niobium and tin should be followed either by very slow cooling or by an anneal in the 600 to 700 °C range to form Nb3Sn.","PeriodicalId":94340,"journal":{"name":"Journal of research of the National Bureau of Standards. Section A, Physics and chemistry","volume":"62 1","pages":"351 - 363"},"PeriodicalIF":0.0,"publicationDate":"1962-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88037398","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The thermal conductivity of CO2 has been measured in a coaxial cylinder cell as a function of pressure over a range of temperatures from 3.66 to 75.26 °C. Particular attention was given to the measurements from 1 to 9 deg C above the critical temperature at pressures closely spaced to include the critical density. The thermal conductivity of CO2(g) near the critical point is very large compared to one atmosphere values around room temperature. At 1 deg C above the critical point the thermal conductivity reaches a maximum at the critical density. This maximum is greater than the maxima at higher temperatures. At 75.26 °C, 44 deg C above the critical temperature, little unusual increase at the critical density was observed. The rate of heat transport by convection in the critical region is also very large. This problem was studied carefully in order that the temperature differences used were restricted to the region of laminar flow, and that appropriate extrapolation procedures were used to find the rate of heat transfer by thermal conduction alone. Also, at densities and temperatures away from the critical region, new thermal conductivity values were obtained.
{"title":"Thermal Conductivity of Gases. II. Thermal Conductivity of Carbon Dioxide Near the Critical Point","authors":"L. A. Guildner","doi":"10.6028/jres.066A.035","DOIUrl":"https://doi.org/10.6028/jres.066A.035","url":null,"abstract":"The thermal conductivity of CO2 has been measured in a coaxial cylinder cell as a function of pressure over a range of temperatures from 3.66 to 75.26 °C. Particular attention was given to the measurements from 1 to 9 deg C above the critical temperature at pressures closely spaced to include the critical density. The thermal conductivity of CO2(g) near the critical point is very large compared to one atmosphere values around room temperature. At 1 deg C above the critical point the thermal conductivity reaches a maximum at the critical density. This maximum is greater than the maxima at higher temperatures. At 75.26 °C, 44 deg C above the critical temperature, little unusual increase at the critical density was observed. The rate of heat transport by convection in the critical region is also very large. This problem was studied carefully in order that the temperature differences used were restricted to the region of laminar flow, and that appropriate extrapolation procedures were used to find the rate of heat transfer by thermal conduction alone. Also, at densities and temperatures away from the critical region, new thermal conductivity values were obtained.","PeriodicalId":94340,"journal":{"name":"Journal of research of the National Bureau of Standards. Section A, Physics and chemistry","volume":"127 1 1","pages":"341 - 348"},"PeriodicalIF":0.0,"publicationDate":"1962-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83619537","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The distribution of gamma-radiation emitted in the decay of Ce141 nuclei alined in neodymium ethylsulfate single crystals has been remeasured for temperatures as low as 0.0162 °K and has been found to be considerably more anisotropic than previously thought. The discrepancy is explained on the basis of preferential scattering of the plane-polarized radiation in the Dewar system. Similar measurements with Ce141 nuclei oriented in a polarized cerium ethylsulfate crystal have been made. The hyperfine constant for Ce141 in the neodymium ethylsulfate lattice is deduced as A =0.0305±0.003 cm−1, and the E2/M1 ratio for the 145-kev gamma ray in Pr141 is +0.068 ±0.008.
{"title":"The Gamma-Ray Distribution From Oriented Cerium-141","authors":"J. Schooley, D. D. Hoppes, A. T. Hirshfeld","doi":"10.6028/jres.066A.031","DOIUrl":"https://doi.org/10.6028/jres.066A.031","url":null,"abstract":"The distribution of gamma-radiation emitted in the decay of Ce141 nuclei alined in neodymium ethylsulfate single crystals has been remeasured for temperatures as low as 0.0162 °K and has been found to be considerably more anisotropic than previously thought. The discrepancy is explained on the basis of preferential scattering of the plane-polarized radiation in the Dewar system. Similar measurements with Ce141 nuclei oriented in a polarized cerium ethylsulfate crystal have been made. The hyperfine constant for Ce141 in the neodymium ethylsulfate lattice is deduced as A =0.0305±0.003 cm−1, and the E2/M1 ratio for the 145-kev gamma ray in Pr141 is +0.068 ±0.008.","PeriodicalId":94340,"journal":{"name":"Journal of research of the National Bureau of Standards. Section A, Physics and chemistry","volume":"76 1","pages":"317 - 320"},"PeriodicalIF":0.0,"publicationDate":"1962-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82673344","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Rates of oxidation of aldoses with bromine have been reappraised and interpreted in the light of present concepts of conformation and reaction mechanism. It is suggested that differences in the rates of oxidation of the α and β anomers are largely determined by differences in the free energy required by the reactants for passing from the ground state to the complex in the transition state. Structures for the aldoses in the ground states and in the transition states are postulated, and factors affecting the energy required for reaching the transition states from the ground states are discussed. The relative rates of oxidation are in accordance with the hypothesis that each of the aldoses in the ground state has the conformation predicted by Reeves, and, in the transition state, has a conformation in which the oxygen atom of the C1-hydroxyl group lies in the plane formed by the ring oxygen atom, C1, C2, and C5. Presumably, this conformation is stabilized by resonance involving the oxygen atom of the ring. For aldoses having high stability in one chair conformation, the rates of oxidation of the anomers differ widely; in each instance, the anomer in which the C1-hydroxyl group is axial is oxidized more slowly than the anomer in which this group is equatorial. For aldoses having less stability in a chair conformation, the rates of oxidation of the anomers differ less widely, but, nevertheless, show a definite correlation with the angular position of the C1-hydroxyl group relative to the plane of the ring. For aldoses for which the stability in both chair conformations is so low that they probably exist in a variety of conformations, the rates of oxidation of the anomers show little difference and no particular correlation with the angular position of the C1-hydroxyl group. The presence or absence of an oxygen atom in the ring is used to account for the large differences between the rates of bromine oxidation of the aldoses and those of derivatives of cyclohexanol. Differences in conformation in the transition state, associated with the presence or absence of this oxygen atom, likewise account for the fact that the relative rates of oxidation of the axial and equatorial isomers in the two classes of compound are reversed. Because of uncertainty as to the anomeric configurations commonly assigned to some of the aldoses, the configurations of 22 aldoses were reappraised. Advantage was taken of the principle that the anomer preponderating in the equilibrium solution has trans hydroxyl groups at C1 and C2. Except for crystalline d-glycero-d-ido-heptose, the assignments of configuration based on this principle agree with the configurations generally accepted. Classification of crystalline d-glycero-d-ido-heptose as an α-d-pyranose necessitates correction of earlier records in which this sugar was considered to be a β-d-pyranose. In accordance with the author’s earlier formulation, oxidation of the axial anomer is believed to take place by two courses: (1)
{"title":"Oxidation of Aldoses With Bromine","authors":"H. Isbell","doi":"10.6028/jres.066A.023","DOIUrl":"https://doi.org/10.6028/jres.066A.023","url":null,"abstract":"Rates of oxidation of aldoses with bromine have been reappraised and interpreted in the light of present concepts of conformation and reaction mechanism. It is suggested that differences in the rates of oxidation of the α and β anomers are largely determined by differences in the free energy required by the reactants for passing from the ground state to the complex in the transition state. Structures for the aldoses in the ground states and in the transition states are postulated, and factors affecting the energy required for reaching the transition states from the ground states are discussed. The relative rates of oxidation are in accordance with the hypothesis that each of the aldoses in the ground state has the conformation predicted by Reeves, and, in the transition state, has a conformation in which the oxygen atom of the C1-hydroxyl group lies in the plane formed by the ring oxygen atom, C1, C2, and C5. Presumably, this conformation is stabilized by resonance involving the oxygen atom of the ring. For aldoses having high stability in one chair conformation, the rates of oxidation of the anomers differ widely; in each instance, the anomer in which the C1-hydroxyl group is axial is oxidized more slowly than the anomer in which this group is equatorial. For aldoses having less stability in a chair conformation, the rates of oxidation of the anomers differ less widely, but, nevertheless, show a definite correlation with the angular position of the C1-hydroxyl group relative to the plane of the ring. For aldoses for which the stability in both chair conformations is so low that they probably exist in a variety of conformations, the rates of oxidation of the anomers show little difference and no particular correlation with the angular position of the C1-hydroxyl group. The presence or absence of an oxygen atom in the ring is used to account for the large differences between the rates of bromine oxidation of the aldoses and those of derivatives of cyclohexanol. Differences in conformation in the transition state, associated with the presence or absence of this oxygen atom, likewise account for the fact that the relative rates of oxidation of the axial and equatorial isomers in the two classes of compound are reversed. Because of uncertainty as to the anomeric configurations commonly assigned to some of the aldoses, the configurations of 22 aldoses were reappraised. Advantage was taken of the principle that the anomer preponderating in the equilibrium solution has trans hydroxyl groups at C1 and C2. Except for crystalline d-glycero-d-ido-heptose, the assignments of configuration based on this principle agree with the configurations generally accepted. Classification of crystalline d-glycero-d-ido-heptose as an α-d-pyranose necessitates correction of earlier records in which this sugar was considered to be a β-d-pyranose. In accordance with the author’s earlier formulation, oxidation of the axial anomer is believed to take place by two courses: (1) ","PeriodicalId":94340,"journal":{"name":"Journal of research of the National Bureau of Standards. Section A, Physics and chemistry","volume":"61 1","pages":"233 - 239"},"PeriodicalIF":0.0,"publicationDate":"1962-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88477368","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Absorption bands of carbon disulfide have been measured with high resolution in the regions of 2180 and 2900 cm−1. Bands have been observed due to several isotopic species. By combining the observed bands with those previously measured, a set of harmonicity constants for 12C32S2 has been obtained in cm−1 as follows: X11, −1.070; X22, 0.126; X33, −6.54; X12, 0.860; X13, −7.86; X23, −6.45; g22, 0.656.
{"title":"High Resolution Investigation of Some Infrared Bands of Carbon Disulfide","authors":"D. Agar, E. K. Plyler, E. D. Tidwell","doi":"10.6028/jres.066A.027","DOIUrl":"https://doi.org/10.6028/jres.066A.027","url":null,"abstract":"Absorption bands of carbon disulfide have been measured with high resolution in the regions of 2180 and 2900 cm−1. Bands have been observed due to several isotopic species. By combining the observed bands with those previously measured, a set of harmonicity constants for 12C32S2 has been obtained in cm−1 as follows: X11, −1.070; X22, 0.126; X33, −6.54; X12, 0.860; X13, −7.86; X23, −6.45; g22, 0.656.","PeriodicalId":94340,"journal":{"name":"Journal of research of the National Bureau of Standards. Section A, Physics and chemistry","volume":"15 1","pages":"259 - 264"},"PeriodicalIF":0.0,"publicationDate":"1962-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74554103","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：