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• 1. [Article] Towards p-Type Conductivity in SnO2Nanocrystals through Li Doping and Its Applications in Porous Diodes for Room Temperature Chlorine Gas Detection

  This work examined electrical transport properties and Li doping in SnO2synthesized by the sol–gel method. Solid-state 7Li-NMR line shapes revealed that Li ions occupy two distinct sites with differing ...

  Citation × Citation Citation Abstract Copy Title: Towards p-Type Conductivity in SnO2Nanocrystals through Li Doping and Its Applications in Porous Diodes for Room Temperature Chlorine Gas Detection Author: Chaparadza, Allen, Rananavare, Shankar Year: 2016 This work examined electrical transport properties and Li doping in SnO2synthesized by the sol–gel method. Solid-state 7Li-NMR line shapes revealed that Li ions occupy two distinct sites with differing dynamic mobilities. The chemical exchange rate between the two sites is, however, too slow for detection on the NMR timescale. Compressed nanoparticulate films of this doped semiconductor exhibited a positive Seebeck coefficient implying a p-type conductivity. A variable-temperature direct current conductivity, over a 25–350 °C temperature range, followed an Efros–Shklovskii variable range hopping (ES-VRH) conduction mechanism (ln(ρ) versus T−1/2) at temperatures below 100 °C with a crossover to 2D Mott variable range hopping (M-VRH) (ln(ρ) versus T−1/3) conduction at temperatures above 250 °C. In a transition region between these two limiting behaviors, direct current resistivity exhibited an anomalous temperature-independent plateau. We suggest that its origin may lie in a carrier inversion phenomenon wherein the majority carriers switch from holes to electrons due to Li ion expulsion from the crystalline core and creation of oxygen vacancies generated by loss of oxygen at elevated temperatures. Using a compression technique, porous diodes consisting of n-type (antimony doped SnO2) and the p-type (lithium-doped) nano-particulate films were prepared. Typical current-voltage curves of such devices resembled the behavior of a typical diode but for one key difference; owing to the porosity of the film, areas near the p-n interface and the p- and n-regions are accessible to gaseous analytes. This access is not possible in conventional diodes fabricated through contemporary planar technology. The gas sensing properties of the diodes were investigated by using Cl2, Br2, HCl, NO, NO2, CHCl3, NH3 and H2. Of all the gases tested, the sensor had very good sensitivity to Cl2 and had a response of 80 at 400 ppb of Cl2. The response time of the sensor was ~30 s at room temperature but the recovery time was temperature dependent. At room temperature the recovery time was 80s after 400 ppb chlorine exposure. The sensors were also found to recover quickly (~ 30 s) when the junctions were biased. Reverse biasing the diode provides a controllable band-bending at a p-n junction that could influence the electron-transfer rates from the adsorbates which create intra-band localized states. As a result reverse biasing can provide a means of desorbing the analyzed species. This approach eliminates the requirement to remove adsorbates by elevating the sensor temperature and hence improves on the energy efficiency of these types of sensors. Title: Towards p-Type Conductivity in SnO2Nanocrystals through Li Doping and Its Applications in Porous Diodes for Room Temperature Chlorine Gas Detection Author: Chaparadza, Allen, Rananavare, Shankar Year: 2016 This work examined electrical transport properties and Li doping in SnO2synthesized by the sol–gel method. Solid-state 7Li-NMR line shapes revealed that Li ions occupy two distinct sites with differing dynamic mobilities. The chemical exchange rate between the two sites is, however, too slow for detection on the NMR timescale. Compressed nanoparticulate films of this doped semiconductor exhibited a positive Seebeck coefficient implying a p-type conductivity. A variable-temperature direct current conductivity, over a 25–350 °C temperature range, followed an Efros–Shklovskii variable range hopping (ES-VRH) conduction mechanism (ln(ρ) versus T−1/2) at temperatures below 100 °C with a crossover to 2D Mott variable range hopping (M-VRH) (ln(ρ) versus T−1/3) conduction at temperatures above 250 °C. In a transition region between these two limiting behaviors, direct current resistivity exhibited an anomalous temperature-independent plateau. We suggest that its origin may lie in a carrier inversion phenomenon wherein the majority carriers switch from holes to electrons due to Li ion expulsion from the crystalline core and creation of oxygen vacancies generated by loss of oxygen at elevated temperatures. Using a compression technique, porous diodes consisting of n-type (antimony doped SnO2) and the p-type (lithium-doped) nano-particulate films were prepared. Typical current-voltage curves of such devices resembled the behavior of a typical diode but for one key difference; owing to the porosity of the film, areas near the p-n interface and the p- and n-regions are accessible to gaseous analytes. This access is not possible in conventional diodes fabricated through contemporary planar technology. The gas sensing properties of the diodes were investigated by using Cl2, Br2, HCl, NO, NO2, CHCl3, NH3 and H2. Of all the gases tested, the sensor had very good sensitivity to Cl2 and had a response of 80 at 400 ppb of Cl2. The response time of the sensor was ~30 s at room temperature but the recovery time was temperature dependent. At room temperature the recovery time was 80s after 400 ppb chlorine exposure. The sensors were also found to recover quickly (~ 30 s) when the junctions were biased. Reverse biasing the diode provides a controllable band-bending at a p-n junction that could influence the electron-transfer rates from the adsorbates which create intra-band localized states. As a result reverse biasing can provide a means of desorbing the analyzed species. This approach eliminates the requirement to remove adsorbates by elevating the sensor temperature and hence improves on the energy efficiency of these types of sensors. Close

• 2. [Article] Electrical Detection of the Temperature Induced Melting Transition of a DNA Hairpin Covalently Attached to Gold Interdigitated Microelectrodes

  The temperature induced melting transition of a self-complementary DNA strand covalently attached at the 5' end to the surface of a gold interdigitated microelectrode (GIME) was monitored in a novel, label-free, ...

  Citation × Citation Citation Abstract Copy Title: Electrical Detection of the Temperature Induced Melting Transition of a DNA Hairpin Covalently Attached to Gold Interdigitated Microelectrodes Author: Brewood, Greg P., Rangineni, Yaswanth, Fish, Daniel J., Bhandiwad, Ashwini, Evans, David R., Solanki, Raj, Benight, Albert S. Year: 2008 The temperature induced melting transition of a self-complementary DNA strand covalently attached at the 5' end to the surface of a gold interdigitated microelectrode (GIME) was monitored in a novel, label-free, manner. The structural state of the hairpin was assessed by measuring four different electronic properties of the GIME (capacitance, impedance, dissipation factor and phase angle) as a function of temperature from 25 degrees C to 80 degrees C. Consistent changes in all four electronic properties of the GIME were observed over this temperature range, and attributed to the transition of the attached single-stranded DNA (ssDNA) from an intramolecular, folded hairpin structure to a melted ssDNA. The melting curve of the self-complementary single strand was also measured in solution using differential scanning calorimetry (DSC) and UV absorbance spectroscopy. Temperature dependent electronic measurements on the surface and absorbance versus temperature values measured in solution experiments were analyzed assuming a two-state process. The model analysis provided estimates of the thermodynamic transition parameters of the hairpin on the surface. Two-state analyses of optical melting data and DSC measurements provided evaluations of the thermodynamic transition parameters of the hairpin in solution. Comparison of surface and solution measurements provided quantitative evaluation of the effect of the surface on the thermodynamics of the melting transition of the DNA hairpin. Title: Electrical Detection of the Temperature Induced Melting Transition of a DNA Hairpin Covalently Attached to Gold Interdigitated Microelectrodes Author: Brewood, Greg P., Rangineni, Yaswanth, Fish, Daniel J., Bhandiwad, Ashwini, Evans, David R., Solanki, Raj, Benight, Albert S. Year: 2008 The temperature induced melting transition of a self-complementary DNA strand covalently attached at the 5' end to the surface of a gold interdigitated microelectrode (GIME) was monitored in a novel, label-free, manner. The structural state of the hairpin was assessed by measuring four different electronic properties of the GIME (capacitance, impedance, dissipation factor and phase angle) as a function of temperature from 25 degrees C to 80 degrees C. Consistent changes in all four electronic properties of the GIME were observed over this temperature range, and attributed to the transition of the attached single-stranded DNA (ssDNA) from an intramolecular, folded hairpin structure to a melted ssDNA. The melting curve of the self-complementary single strand was also measured in solution using differential scanning calorimetry (DSC) and UV absorbance spectroscopy. Temperature dependent electronic measurements on the surface and absorbance versus temperature values measured in solution experiments were analyzed assuming a two-state process. The model analysis provided estimates of the thermodynamic transition parameters of the hairpin on the surface. Two-state analyses of optical melting data and DSC measurements provided evaluations of the thermodynamic transition parameters of the hairpin in solution. Comparison of surface and solution measurements provided quantitative evaluation of the effect of the surface on the thermodynamics of the melting transition of the DNA hairpin. Close

• 3. [Image] Geological and Geophysical Analysis of Coso Geothermal Exploration Hole No. 1 (CGEH-1), Coso Hot Springs KGRA, California

  	The Coso Geothermal Exploration Hole number one (CGEH-1) was drilled in the Coso Hot Springs KGRA, California from September 2 to December 2, 1977. Chip samples were collected at ten foot intervals and ...
  	Citation × Citation Citation Abstract Copy Title: Geological and Geophysical Analysis of Coso Geothermal Exploration Hole No. 1 (CGEH-1), Coso Hot Springs KGRA, California Author: Galbraith, R.M. Year: 1978 The Coso Geothermal Exploration Hole number one (CGEH-1) was drilled in the Coso Hot Springs KGRA, California from September 2 to December 2, 1977. Chip samples were collected at ten foot intervals and extensive geophysical logging surveys were conducted to document the geologic character of the geothermal system as penetrated by CGEH-1. The major rock units encountered include a mafic metamorphic sequence and a leucogranite which intruded the metamorphic rocks. Only weak hydrothermal alteration was noted in these rocks. Drillhole surveys and drilling rate data indicate that the geothermal system is structurally controlled and that the drillhole itself was strongly influenced by structural zones. Water chemistry indicates that this geothermal resource is a hot-water rather than a vapor-dominated system. Several geophysical logs were employed to characterize the drillhole geology. The natural gamma and neutron porosity logs indicate gross rock type and the acoustic logs indicate fractured rock and potentially permeable zones. A series of temperature logs run as a function of time during and after the completion of Drilling were most Useful in delineating the zones of maximum heat flux. Convective heat flow and temperatures greater than 350/sup 0/F appear to occur only along an open fracture system encountered between depths of 1850 and 2775 feet. Temperature logs indicate a negative thermal gradient below 3000 feet Title: Geological and Geophysical Analysis of Coso Geothermal Exploration Hole No. 1 (CGEH-1), Coso Hot Springs KGRA, California Author: Galbraith, R.M. Year: 1978 The Coso Geothermal Exploration Hole number one (CGEH-1) was drilled in the Coso Hot Springs KGRA, California from September 2 to December 2, 1977. Chip samples were collected at ten foot intervals and extensive geophysical logging surveys were conducted to document the geologic character of the geothermal system as penetrated by CGEH-1. The major rock units encountered include a mafic metamorphic sequence and a leucogranite which intruded the metamorphic rocks. Only weak hydrothermal alteration was noted in these rocks. Drillhole surveys and drilling rate data indicate that the geothermal system is structurally controlled and that the drillhole itself was strongly influenced by structural zones. Water chemistry indicates that this geothermal resource is a hot-water rather than a vapor-dominated system. Several geophysical logs were employed to characterize the drillhole geology. The natural gamma and neutron porosity logs indicate gross rock type and the acoustic logs indicate fractured rock and potentially permeable zones. A series of temperature logs run as a function of time during and after the completion of Drilling were most Useful in delineating the zones of maximum heat flux. Convective heat flow and temperatures greater than 350/sup 0/F appear to occur only along an open fracture system encountered between depths of 1850 and 2775 feet. Temperature logs indicate a negative thermal gradient below 3000 feet Close

• 4. [Article] Nanosilver Rainbow: A Rapid and Facile Method to Tune Different Colours of Nanosilver Through the Controlled Synthesis of Stable Spherical Silver Nanoparticles

  A rapid and simple one-pot reaction to synthesize stable, spherically shaped silver nanoparticles (AgNps) of different sizes producing distinct optical properties in aqueous solution at ambient temperature ...

  Citation × Citation Citation Abstract Copy Title: Nanosilver Rainbow: A Rapid and Facile Method to Tune Different Colours of Nanosilver Through the Controlled Synthesis of Stable Spherical Silver Nanoparticles Author: Mendis, Pramujitha, de Silva, Rohini M., Nalin de Silva, K. M., Wijenayaka, Lahiru A., Jayawardana, Kalana, Yan, Mingdi Year: 2016 A rapid and simple one-pot reaction to synthesize stable, spherically shaped silver nanoparticles (AgNps) of different sizes producing distinct optical properties in aqueous solution at ambient temperature has been developed. Each system contains various sizes of silver nanoparticles showing rainbow colours with the peak wavelength of the absorption spectra ranging from 400 to 750 nm. Seven different colours of nano silver were developed through the controlled synthesis of spherical silver nanoparticles using silver nitrate as the metal precursor. Sodium borohydride was used as the main reducing agent and trisodium citrate and hydrazine sulphate were used as the stabilizing and auxiliary reducing agents respectively. The colour of the solution was controlled by varying the concentrations of reagents and the optimum conditions for all the colours are reported. Characterization of silver nanoparticles was carried out using UV-visible spectrophotometry and Transmission Electron Microscopy (TEM). Factors affecting the formation of different sizes of silver nanoparticles, such as silver nitrate concentration, reducing agent concentrations, reaction temperature and reaction pH are also reported. The stability of these coloured silver colloidal solutions was also investigated at different temperatures and the most stable temperature was found to be 4 °C, while the optimum pH to synthesize distinctively coloured silver nanoparticles was found to be in the range of 7–8. The outlined procedure provides a rapid, facile and reproducible synthetic route to spherical AgNps of varying size and ensuing optical properties. Thus, this method is certain to find value in the many applications where size tunability of AgNps is desired. Title: Nanosilver Rainbow: A Rapid and Facile Method to Tune Different Colours of Nanosilver Through the Controlled Synthesis of Stable Spherical Silver Nanoparticles Author: Mendis, Pramujitha, de Silva, Rohini M., Nalin de Silva, K. M., Wijenayaka, Lahiru A., Jayawardana, Kalana, Yan, Mingdi Year: 2016 A rapid and simple one-pot reaction to synthesize stable, spherically shaped silver nanoparticles (AgNps) of different sizes producing distinct optical properties in aqueous solution at ambient temperature has been developed. Each system contains various sizes of silver nanoparticles showing rainbow colours with the peak wavelength of the absorption spectra ranging from 400 to 750 nm. Seven different colours of nano silver were developed through the controlled synthesis of spherical silver nanoparticles using silver nitrate as the metal precursor. Sodium borohydride was used as the main reducing agent and trisodium citrate and hydrazine sulphate were used as the stabilizing and auxiliary reducing agents respectively. The colour of the solution was controlled by varying the concentrations of reagents and the optimum conditions for all the colours are reported. Characterization of silver nanoparticles was carried out using UV-visible spectrophotometry and Transmission Electron Microscopy (TEM). Factors affecting the formation of different sizes of silver nanoparticles, such as silver nitrate concentration, reducing agent concentrations, reaction temperature and reaction pH are also reported. The stability of these coloured silver colloidal solutions was also investigated at different temperatures and the most stable temperature was found to be 4 °C, while the optimum pH to synthesize distinctively coloured silver nanoparticles was found to be in the range of 7–8. The outlined procedure provides a rapid, facile and reproducible synthetic route to spherical AgNps of varying size and ensuing optical properties. Thus, this method is certain to find value in the many applications where size tunability of AgNps is desired. Close

• 5. [Article] Measurement of low vapor pressures : a kinetic approach

  A kinetic model was applied to vapor pressure data obtained by a variable flow method. The vapor pressures of benzoic acid, naphthalene, benzophenone, and phenylhydrazine were measured at temperatures ...

  Citation × Citation Citation Abstract Copy Title: Measurement of low vapor pressures : a kinetic approach Author: Bliden, Samuel Bernard Year: 1984 A kinetic model was applied to vapor pressure data obtained by a variable flow method. The vapor pressures of benzoic acid, naphthalene, benzophenone, and phenylhydrazine were measured at temperatures of 293K to 307K. The data are summarized in the data table on the following page. These data were obtained by passing air over a sample of the substance in a tube. The air stream was combusted, and a flame ionization detector was used to measure the mass of CO2 so obtained. Several different flow rates were used at each temperature with each substance. Title: Measurement of low vapor pressures : a kinetic approach Author: Bliden, Samuel Bernard Year: 1984 A kinetic model was applied to vapor pressure data obtained by a variable flow method. The vapor pressures of benzoic acid, naphthalene, benzophenone, and phenylhydrazine were measured at temperatures of 293K to 307K. The data are summarized in the data table on the following page. These data were obtained by passing air over a sample of the substance in a tube. The air stream was combusted, and a flame ionization detector was used to measure the mass of CO2 so obtained. Several different flow rates were used at each temperature with each substance. Close

• 6. [Article] Study of photolytic interference on HO measurements by LIF-FAGE

  For many years there has been a great interest among the scientific community in the study of the hydroxyl radical, HO. This interest stems from the fundamental role played by this molecule in the photochemistry ...

  Citation × Citation Citation Abstract Copy Title: Study of photolytic interference on HO measurements by LIF-FAGE Author: Martinez, Carmen Ivette Year: 1989 For many years there has been a great interest among the scientific community in the study of the hydroxyl radical, HO. This interest stems from the fundamental role played by this molecule in the photochemistry of the atmosphere, mainly as a cleansing agent of environmental pollutants. Knowing the concentration of the radical would enable scientists to corroborate current atmospheric models and to predict future trends in the atmosphere. Even though there is a great interest in the determination of atmospheric concentrations of this molecule, the task has been very difficult. This is mainly due to the lack of a method sensitive enough to detect concentrations around 106 molecules per cubic centimeter. The most accurate method presently available is the method of laser induced fluorescence using the fluorescence assay with gas expansion technique (LIF-FAGE). This method involves low pressure excitation of HO from its ground state to its lowest electronic excited state and observing the consequent fluorescence around 309 nm. The procedure is done at a pressure of 5 Torr to maximize the fluorescence lifetime of the radical and to minimize the interference of photolytic species. Background determination is achieved by chemical modulation using isobutane in a second channel of the same cell which removes the HO signal. In this study an assessment of the level of ozone interference in LIFF AGE has been done by calculating the relative population distribution of HO among its rotational levels and from this, determining its temperature. When the laser passes through the excitation detection cell it photolyses the ozone present producing in this way the highly reactive 0 1(D). When this molecule reacts with water or with isobutane it produces HO, and this is the source of interference in the actual measurements. In the determination of the relative population distributions of the different HO species, it was found that the naturally occurring HO has a thermal distribution with a temperature of about 300 K. The HO molecules produced from the reaction of 0 1(D) with isobutane also showed a thermal distribution with a temperature of about 230 K. On the other hand, the HO produced from the reaction of 0 1(D) with water did not show a thermal distribution. Two distinct temperatures were observed for this case: one around 200 K for values of K = 1 to 4, and the second one around 3000 K for values of K = 5 to 6. These values agree with previous experimental results for LIF methods by other authors except for the fact that the deviation from the first temperature determined by other authors starts at K = 6 or 7. Title: Study of photolytic interference on HO measurements by LIF-FAGE Author: Martinez, Carmen Ivette Year: 1989 For many years there has been a great interest among the scientific community in the study of the hydroxyl radical, HO. This interest stems from the fundamental role played by this molecule in the photochemistry of the atmosphere, mainly as a cleansing agent of environmental pollutants. Knowing the concentration of the radical would enable scientists to corroborate current atmospheric models and to predict future trends in the atmosphere. Even though there is a great interest in the determination of atmospheric concentrations of this molecule, the task has been very difficult. This is mainly due to the lack of a method sensitive enough to detect concentrations around 106 molecules per cubic centimeter. The most accurate method presently available is the method of laser induced fluorescence using the fluorescence assay with gas expansion technique (LIF-FAGE). This method involves low pressure excitation of HO from its ground state to its lowest electronic excited state and observing the consequent fluorescence around 309 nm. The procedure is done at a pressure of 5 Torr to maximize the fluorescence lifetime of the radical and to minimize the interference of photolytic species. Background determination is achieved by chemical modulation using isobutane in a second channel of the same cell which removes the HO signal. In this study an assessment of the level of ozone interference in LIFF AGE has been done by calculating the relative population distribution of HO among its rotational levels and from this, determining its temperature. When the laser passes through the excitation detection cell it photolyses the ozone present producing in this way the highly reactive 0 1(D). When this molecule reacts with water or with isobutane it produces HO, and this is the source of interference in the actual measurements. In the determination of the relative population distributions of the different HO species, it was found that the naturally occurring HO has a thermal distribution with a temperature of about 300 K. The HO molecules produced from the reaction of 0 1(D) with isobutane also showed a thermal distribution with a temperature of about 230 K. On the other hand, the HO produced from the reaction of 0 1(D) with water did not show a thermal distribution. Two distinct temperatures were observed for this case: one around 200 K for values of K = 1 to 4, and the second one around 3000 K for values of K = 5 to 6. These values agree with previous experimental results for LIF methods by other authors except for the fact that the deviation from the first temperature determined by other authors starts at K = 6 or 7. Close

• 7. [Article] Vibrational Sum Frequency Spectroscopic Investigations of Sulfur Dioxide Adsorption to Atmospherically Relevant Aqueous Surfaces

  xv, 108 p. : ill. (chiefly col.)

  Citation × Citation Citation Abstract Copy Title: Vibrational Sum Frequency Spectroscopic Investigations of Sulfur Dioxide Adsorption to Atmospherically Relevant Aqueous Surfaces Author: Ota, Stephanie Tomoko, 1978- Year: 2011 xv, 108 p. : ill. (chiefly col.) Title: Vibrational Sum Frequency Spectroscopic Investigations of Sulfur Dioxide Adsorption to Atmospherically Relevant Aqueous Surfaces Author: Ota, Stephanie Tomoko, 1978- Year: 2011 xv, 108 p. : ill. (chiefly col.) Close

• 8. [Image] Evaluation and Targeting of Geothermal Energy Resources in the Southeastern United States Progress Report, Apr 1, 1977--Jun 30, 1977

  	The objective of this research is to develop and apply targeting procedures for the evaluation of low-temperature radiogenically-derived geothermal resources in the eastern United States utilizing geological, ...
  	Citation × Citation Citation Abstract Copy Title: Evaluation and Targeting of Geothermal Energy Resources in the Southeastern United States Progress Report, Apr 1, 1977--Jun 30, 1977 Author: Costain, J.K. Year: 1977 The objective of this research is to develop and apply targeting procedures for the evaluation of low-temperature radiogenically-derived geothermal resources in the eastern United States utilizing geological, geochemical, and geophysical data. Detailed study of the Winnsboro complex, South Carolina, is continuing as part of a broader project to provide insight into the behavior of uranium and thorium in syn- and postmetamorphic granitic plutons Title: Evaluation and Targeting of Geothermal Energy Resources in the Southeastern United States Progress Report, Apr 1, 1977--Jun 30, 1977 Author: Costain, J.K. Year: 1977 The objective of this research is to develop and apply targeting procedures for the evaluation of low-temperature radiogenically-derived geothermal resources in the eastern United States utilizing geological, geochemical, and geophysical data. Detailed study of the Winnsboro complex, South Carolina, is continuing as part of a broader project to provide insight into the behavior of uranium and thorium in syn- and postmetamorphic granitic plutons Close

• 9. [Article] Alumina-catalyzed Cope rearrangement

  The alumina-catalyzed Cope rearrangements of meso- and dl-3,4-diphenylhexa-1,5-diene were examined in detail, following up a preliminary observation by H. Berg at Portland State University. Commercial ...

  Citation × Citation Citation Abstract Copy Title: Alumina-catalyzed Cope rearrangement Author: Wang, Paul Jhy-Shing Year: 1974 The alumina-catalyzed Cope rearrangements of meso- and dl-3,4-diphenylhexa-1,5-diene were examined in detail, following up a preliminary observation by H. Berg at Portland State University. Commercial column-chromatography grade alumina was employed, and was further activated before use.by heating at 650-700° for four hours. Using a ratio of 20 mg of dl-3,4-diphenylhex-l,5-diene to 1 g of alumina in heptane, the Cope rearrangement was complete within 15 minutes at room temperature to give exclusively trans,trans-1,6-diphenylhexa-1,5-diene. This was identified.by melting point, infrared spectroscopy and vapor phase chromatography The catalyzed rearrangement of meso-3,4-diphenylhexa-l,5-diene was run using the same diene to alumina ratio. It was found that 31% of the meso-diene was converted to cis,trans- and trans,trans-l,6-diphenylhexa-1,5-diene at room temperature in four hours. Product iso-merization appeared to take place; the initial ratio of cis,trans-diene to trans,trans-diene was estimated to be 73:27. Another run was carried out at 60°, where the problem of isomerization of cis,trans-diene to trans,trans-diene was more pronounced. The rearrangement gave cis, trans-diene and trans,trans-diene in a ratio of 58:42, as estimated by extrapolation of the product ratio to zero time. Approximately 95% of meso-diene had reacted in one hour at this temperature. The extent of conversion of mes-diene was calculated by quantitative infrared spectroscopy, and the isomeric distribution of products was determined by vapor phase chromatography. The product distribution in the alumina-catalyzed rearrangements parallels that of the thermal Cope rearrangement, where dl-diene gives exclusively trans,trans-diene at 80° with a half-life of eight hours and meso-diene gives 63% cis,trans-diene and 27% trans,trans-diene at 120° with a half-life of 15 hours. Title: Alumina-catalyzed Cope rearrangement Author: Wang, Paul Jhy-Shing Year: 1974 The alumina-catalyzed Cope rearrangements of meso- and dl-3,4-diphenylhexa-1,5-diene were examined in detail, following up a preliminary observation by H. Berg at Portland State University. Commercial column-chromatography grade alumina was employed, and was further activated before use.by heating at 650-700° for four hours. Using a ratio of 20 mg of dl-3,4-diphenylhex-l,5-diene to 1 g of alumina in heptane, the Cope rearrangement was complete within 15 minutes at room temperature to give exclusively trans,trans-1,6-diphenylhexa-1,5-diene. This was identified.by melting point, infrared spectroscopy and vapor phase chromatography The catalyzed rearrangement of meso-3,4-diphenylhexa-l,5-diene was run using the same diene to alumina ratio. It was found that 31% of the meso-diene was converted to cis,trans- and trans,trans-l,6-diphenylhexa-1,5-diene at room temperature in four hours. Product iso-merization appeared to take place; the initial ratio of cis,trans-diene to trans,trans-diene was estimated to be 73:27. Another run was carried out at 60°, where the problem of isomerization of cis,trans-diene to trans,trans-diene was more pronounced. The rearrangement gave cis, trans-diene and trans,trans-diene in a ratio of 58:42, as estimated by extrapolation of the product ratio to zero time. Approximately 95% of meso-diene had reacted in one hour at this temperature. The extent of conversion of mes-diene was calculated by quantitative infrared spectroscopy, and the isomeric distribution of products was determined by vapor phase chromatography. The product distribution in the alumina-catalyzed rearrangements parallels that of the thermal Cope rearrangement, where dl-diene gives exclusively trans,trans-diene at 80° with a half-life of eight hours and meso-diene gives 63% cis,trans-diene and 27% trans,trans-diene at 120° with a half-life of 15 hours. Close

• 10. [Article] Structure and Phase Transitions of the 6, 6-Cyclopropane Isomer of C_ {61} H_ {2}

  We have used x-ray powder diffraction and differential scanning calorimetry to study the crystalline structures and thermal behavior of the 6,6-cyclopropane isomer of C61H2. At room temperature, the C61H2 ...

  Citation × Citation Citation Abstract Copy Title: Structure and Phase Transitions of the 6, 6-Cyclopropane Isomer of C_ {61} H_ {2} Author: Stetzer, M. R., Heiney, Paul A., Stephens, Peter W., Dinnebier, R. E., Zhu, Q., McGhie, Andrew R., Strongin, Robert M., Brandt, B. M., Smith, Amos B., III Year: 2000 We have used x-ray powder diffraction and differential scanning calorimetry to study the crystalline structures and thermal behavior of the 6,6-cyclopropane isomer of C61H2. At room temperature, the C61H2 cyclopropane molecules, like those of the 6,5-annulene isomer and C60O epoxide, are orientationally disordered and crystallize on a face-centered-cubic lattice such that their methylene groups are statistically disordered among the octahedral voids. Unlike 6,5−C61H2 and C60O, the low-temperature structure is not Pa3¯, but rather a low-symmetry orthorhombic lattice in which a≈b Title: Structure and Phase Transitions of the 6, 6-Cyclopropane Isomer of C_ {61} H_ {2} Author: Stetzer, M. R., Heiney, Paul A., Stephens, Peter W., Dinnebier, R. E., Zhu, Q., McGhie, Andrew R., Strongin, Robert M., Brandt, B. M., Smith, Amos B., III Year: 2000 We have used x-ray powder diffraction and differential scanning calorimetry to study the crystalline structures and thermal behavior of the 6,6-cyclopropane isomer of C61H2. At room temperature, the C61H2 cyclopropane molecules, like those of the 6,5-annulene isomer and C60O epoxide, are orientationally disordered and crystallize on a face-centered-cubic lattice such that their methylene groups are statistically disordered among the octahedral voids. Unlike 6,5−C61H2 and C60O, the low-temperature structure is not Pa3¯, but rather a low-symmetry orthorhombic lattice in which a≈b Close