Estimation of the normal boiling point of organic compounds via group contributions

The normal boiling point is a fundamental thermo-physical property, which is important in describing the transition between the vapor and liquid phases. Reliable method which can predict it is of great importance, especially for compounds where there are no experimental data available. In this work, an improved group contribution method, which is second order method, for determination of the normal boiling point of organic compounds based on the Joback functional first order groups with some changes and added some other functional groups was developed by using experimental data for 632 organic components. It could distinguish most of structural isomerism and stereoisomerism, which including the structural, cis- and trans- isomers of organic compounds. First and second order contributions for hydrocarbons and hydrocarbon derivatives containing carbon, hydrogen, oxygen, nitrogen, sulfur, fluorine, chlorine and bromine atoms, are given. The fminsearch mathematical approach from MATLAB software is used in this study to select an optimal collection of functional groups (65 functional groups) and subsequently to develop the model. This is a direct search method that uses the simplex search method of Lagarias et al. The results of the new method are compared to the several currently used methods and are shown to be far more accurate and reliable. The average absolute deviation of normal boiling point predictions for 632 organic compounds is 4.4350 K; and the average absolute relative deviation is 1.1047 %, which is of adequate accuracy for many practical applications.

Stable isotope ratios of foraminifera and sea surface temperature estimation of sediment core W2804A-14

Carbon isotopically based estimates of CO2 levels have been generated from a record of the photosynthetic fractionation of 13C (epsilon p) in a central equatorial Pacific sediment core that spans the last ~255 ka. Contents of 13C in phytoplanktonic biomass were determined by analysis of C37 alkadienones. These compounds are exclusive products of Prymnesiophyte algae which at present grow most abundantly at depths of 70-90 m in the central equatorial Pacific. A record of the isotopic compostion of dissolved CO2 was constructed from isotopic analyses of the planktonic foraminifera Neogloboquadrina dutertrei, which calcifies at 70-90 m in the same region. Values of epsilon p, derived by comparison of the organic and inorganic delta values, were transformed to yield concentrations of dissolved CO2 (c e) based on a new, site-specific calibration of the relationship between epsilon p and c e. The calibration was based on reassessment of existing epsilon p versus c e data, which support a physiologically based model in which epsilon p is inversely related to c e. Values of PCO2, the partial pressure of CO2 that would be in equilibrium with the estimated concentrations of dissolved CO2, were calculated using Henry's law and the temperature determined from the alkenone-unsaturation index UK 37. Uncertainties in these values arise mainly from uncertainties about the appropriateness (particularly over time) of the site-specific relationship between epsilon p and 1/c e. These are discussed in detail and it is concluded that the observed record of epsilon p most probably reflects significant variations in Delta pCO2, the ocean-atmosphere disequilibrium, which appears to have ranged from ~110 µatm during glacial intervals (ocean > atmosphere) to ~60 µatm during interglacials. Fluxes of CO2 to the atmosphere would thus have been significantly larger during glacial intervals. If this were characteristic of large areas of the equatorial Pacific, then greater glacial sinks for the equatorially evaded CO2 must have existed elsewhere. Statistical analysis of air-sea pCO2 differences and other parameters revealed significant (p < 0.01) inverse correlations of Delta pCO2 with sea surface temperature and with the mass accumulation rate of opal. The former suggests response to the strength of upwelling, the latter may indicate either drawdown of CO2 by siliceous phytoplankton or variation of [CO2]/[Si(OH)4] ratios in upwelling waters.

Sea surface temperature estimation of the South Tasman Rise

The Subtropical Front (STF) marking the northern boundary of the Southern Ocean has a steep gradient in sea surface temperature (SST) of approximately 4°C over 0.5° of latitude. Presently, in the region south of Tasmania, the STF lies nominally at 47°S in the summer and 45°S in the winter. We present here SST reconstructions in a latitudinal transect of cores across the South Tasman Rise, southeast of Australia, during the late Quaternary. SST reconstructions are based on two paleotemperature proxies, alkenones and faunal assemblages, which are used to assess past changes in SST in spring and summer. The north-south alignment in core locations allows reconstruction of movement of the STF over the last 100 ka. Surface water temperatures during the last glaciation in this region were ~4°C colder than today. Additional temperature changes greater in magnitude than 4°C seen in individual cores can be attributed to changes in the water mass overlying the core site caused by the movement of the front across that location. During the penultimate interglacial, SST was ~2°C warmer and the STF was largely positioned south of 47°S. Movement of the STF to the north occurred during cool climate periods such as the last marine isotope stages 3 and 4. In the last glaciation, the front was at its farthest north position, becoming pinned against the Tasmanian landmass. It moved south by 4° latitude to 47°S in summer during the deglaciation but remained north of 45°S in spring throughout the early deglaciation. After 11 ka B.P. inferred invigoration of the East Australia Current appears to have pushed the STF seasonally south of the East Tasman Plateau, until after 6 ka B.P. when it achieved its present configuration.