1 / 61

Application of Correlation-Gas Chromatography to Problems in Thermochemistry

Application of Correlation-Gas Chromatography to Problems in Thermochemistry. James S. Chickos Department of Chemistry and Biochemistry University of Missouri-St. Louis Louis MO 63121 E-mail: jsc@umsl.edu October 3, 2011. Outline. The Correlation-Gas Chromatographic Method

olympe
Télécharger la présentation

Application of Correlation-Gas Chromatography to Problems in Thermochemistry

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Application of Correlation-Gas Chromatography to Problems in Thermochemistry James S. Chickos Department of Chemistry and Biochemistry University of Missouri-St. Louis Louis MO 63121 E-mail: jsc@umsl.edu October 3, 2011

  2. Outline • The Correlation-Gas Chromatographic Method • Applications 1) Evaluation of the vaporization enthalpies of large molecules, the n-alkanes, C21 to C92. 2) Evaluation of the vaporization enthalpies of tautomeric mixtures. 3) Identifying unusual interactions in heterocyclic systems 4) Measurement of Vapor Pressure Isotope Effects

  3. 1.The Correlation-Gas Chromatographic Method A typical series of isothermal gas chromatograms as a function of temperature; the compounds in these chromatograms are hydrocarbons

  4. Fundamentals of Correlation –Gas Chromatography • tnrr: time of a non-retained reference; a measure of the time needed to travel through the column; usually the solvent or methane • ta: adjusted retention time: tanalyte – tnrr; a measure of the time the analyte spends on the column; • ta is inversely proportional to the vapor pressure of the analyte off the column • A plot of ln(to/ta) versus 1/T (K-1) results in a linear relationship with a slope equal to the enthalpy of transfer from the column to the gas phase, -gslnHm(Tm)/R; to = 1 min gslnHm(Tm) = lgHm(Tm) + slnHm(Tm) • Enthalpies of transfer values measured at Tm are found empirically to correlate linearly with the vaporization enthalpies of standards evaluated at any temperature, including T=298.15 K • Since solids do not crystallize on the column, the measurement provides the vaporization enthalpy of the solid Peacock, L. A.; Fuchs, R Enthalpy of Vaporization Measurements by Gas Chromatography, J. Am. Chem. Soc. 1977, 99, 5524-5. Lipkind, D.; Chickos, J. An Examination of the Factors Influencing the Thermodynamics of Correlation Gas Chromatography as Applied to Large Molecules and Chiral Separations, J. Chem. Eng. Data 2010, 55, 698-707.

  5. A: Determination of Vaporization Enthalpy • Experimental retention times for n-C14 to C20:

  6. Enthalpy of Transfer Determination for Hexadecane • ln(to/ta) = -gslnHm(Tm)/R*1/T + intercept • gslnHm(Tm) * 8.314 J mol-1 = 60.308 kJ mol-1

  7. Equations for the temperature dependence of ln(to/ta) for C14 to C20 where to = 1 min: ln(to/ta) = -gslnHm(Tm)/R*1/T + intercept

  8. lgHm (298.15 K) = (1.4240.019) slngHm(Tm) – (3.980.35); r 2= 0.9991 • Vaporization enthalpies (in kJ mol-1) of the n- alkanes (C14 to C20): unknown 81.4 ? 821.1

  9. Correlations between vaporization enthalpy at T = 298.15 K against the enthalpy of transfer

  10. B: Determination of Vapor Pressures • literature vapor pressure evaluated using the Cox equationa • ln (p/po) = (1-Tb/T)exp(Ao +A1T +A2T 2) po = 101.325 kPa • aRuzicka, K.; Majer, V. Simultaneous Treatment of Vapor Pressures and Related Thermal data Between the Triple Point and Normal Boiling Temperatures for n-Alkanes C5-C20. J. Phys. Chem. Ref. Data1994, 23, 1-39.

  11. Equations for the temperature dependence of ln(to/ta) for C14 to C20: ln(to/ta) = -gslnHm(Tm)/R + intercept

  12. ln(p/po) = (1.27  0.01) ln(to/ta) - (1.693  0.048); r 2 = 0.9997 • Vapor pressures of n-alkanes (C14 to C20) at T = 298.15 K: unknown -13.3 -13.3 ? po = 101.325 kPa

  13. Correlation between ln(1/ta) calculated by extrapolation to T = 298.15 K versus ln(p/po) calculated from the Cox equation for C14 to C20 (po = 101.325 kPa) ln(p/po) = (1.27  0.01) ln(to/ta) - (1.693  0.048); r 2 = 0.9997

  14. Vapor pressure -temperature dependence for hexadecane; line: vapor pressure calculated from the Cox equations for C14, circles; vapor pressures calculated by correlation treating hexadecane as an unknown and correlating ln(to/ta) with ln(p/po) for C14, C15, C17-C20. normal boiling temperature: 560.2 (expt); 559.9 (calcd)

  15. Validation of the results Compare with (Hvap) lit Vaporization. Enthalpy Sublimation Enthalpy (for cryst. solids) Compare with (Hsub) lit + Fusion Enthalpy c-GC Liquid Vapor Pressure Boiling Temperature Compare with (BT) lit Compare with (ln p/p0) lit

  16. Some Advantages and Limitations of Correlation-Gas Chromatography 1. The method works well on hydrocarbons and hydrocarbon derivatives regardless of the hydrocarbon structure 2. With hydrocarbon derivatives, standards need to be chosen with the same number and type of functional group as the compound(s) to be evaluated unless demonstrated otherwise 3. Measurements can be made on small sample sizes and purity is not generally an issue 4. Correlation of the standards needs to be documented experimentally 5. The correlation equations can be used to obtain vapor pressures as well provided vapor pressures of the standards are available and to estimate boiling temperatures. 6. The results are only as good as the quality of the standard data

  17. What if suitable standards for the compounds of interest are not available?

  18. Functional Group Contributions to Vaporization Enthalpies Functional Group Group Value Functional Group Group Value b b acid -C(=O)OH 38.8 iodide -I 18.0 alcohol -OH 29.4 ketone >C=O 10.5aldehyde -CHO 12.9 nitrile -CN 16.7 amide [mono- nitro -NO2 22.8 subst.] -C(=O)NH- 42.5 heterocyclic aromatic amine [pri.] -NH2 14.8 nitrogen =N- [12.2] amine [sec.] -NH- 8.9 sulfide >S 13.4 amine [tert.] >N- 6.6 disulfide -SS- [22.3] bromide -Br 14.4 sulfoxide >SO [42.4] chloride -Cl 10.8 sulfone -SO2- [53.0] ester -C(=O)O- 10.5 thiolester -C(=O)S- [16.9] ether >O 5.0 thiol -SH 13.9 lgHm(298.15 K)/(kJ.mol-1) = 4.69.(n-nQ) + (1.3).nQ + b + (3.0) n = number of non-quaternary carbons; nQ = number of quaternary carbons; values in brackets are tentative assignments Chickos, J. S.; Acree, Jr. W. Liebman, J. F. (Frurip, D.; Irikura, K., Editors) Computational Thermochem., Prediction and Estimation of Molecular Thermodynamics, ACS: Washington DC, 1998, pp 63-93

  19. Applications • The evaluation of vaporization enthalp[ies of large molecules

  20. 1. Applications of correlation gas chromatography for the evaluation of the vaporization enthalpies of large molecules, the n-alkanes, C21 to C92. C60 A partial GC trace of a mixture of Polywax 1000 spiked with n-alkanes C42, C50 and C60 run at T = 648 K

  21. Applications of correlation gas chromatography for the evaluation of the vaporization enthalpies of large molecules, the n-alkanes, C21 to C92. • Reliable vaporization enthalpies and vapor pressures are available up to eicosane • Using the available data from heptadecane to eicosane, vaporization enthalpies were evaluated for C21,C22, C23. These values in turn were used to evaluate the larger n-alkanes in a stepwise process up to C38, most of which are commercially available. • Additionally, a few other larger n-alkanes, C40, C42, C48, C50, and C60 are likewise commercially available. These were used in conjunction with polywax to evaluate vaporization enthalpies and vapor pressures up to C92 (even series) • Since very little experimental data was available for comparison, the results from correlation gas chromatography were compared with estimations by PERT2a and estimated Antoine Constantsb aPERT2 is a FORTRAN program written by D.L. Morgan in 1996 which includes parameters for n-alkanes from C1 to C100 and heat of vaporization and vapor pressure correlations. Morgan, D. L.; Kobayashi, R. “Extension of Pitzer CSP models for vapor pressures and heats of vaporization to long chain hydrocarbons,” Fluid Phase Equilibrium 1994, 94, 51-87. bKudchadker, A. P.; Zwolinski, B. J. “Vapor Pressures and Boiling Points of Normal Alkanes, C21 to C100,” J. Chem. Eng. Data 1966, 11, 253-55.

  22. curvature The vaporization enthalpies at T = 298.15 for C5 to C92. N represents the number of carbon atoms. The solid line was derived using the recommended vaporization enthalpies of C5 to C20 The empty circles are values calculated values using the program PERT2 The solid circles are values evaluated from correlations of slngHm(Tm) with lgHm(298.15K). Vapor pressures and Vaporization Enthalpies of the n Alkanes from C78 to C92 at T = 298.15 K by Correlation–Gas Chromatography, Chickos, J. S.; Lipkind, D. J. Chem.Eng. Data 2008, 53, 2432–2440.

  23. The Vaporization Enthalpies of the n-Alkanes at T = 298.15 K As A Function of the Number of Carbon Atoms, N How is it possible to measure a vaporization enthalpy greater that a C-C bond strength (~335 kJmol-1)?

  24. Vapor pressures and vaporization enthalpies for C14 to C20 are known over a large temperature range. glHm(Tm) and ΔslngHm(Tm) correlate at any temperature Values of at ΔslngHm(449 K) and ΔlgHm(449 K) on an SPB-5 Column Tm = 449 K -slope/T intercept ΔslngHm(449 K) ΔlgHm(449 K) kJmol-1 kJmol-1 lit1 calcd (eq 1) tetradecane 6393.8±95 14.161±0.01 53.2±0.8 56.92 57.0±0.8 pentadecane 6787.9±73 14.597±0.01 56.4±0.6 60.71 60.6±0.8 hexadecane 7251.5±62 15.190±0.01 60.3±0.5 64.50 64.8±0.9 heptadecane 7612.6±65 15.587±0.01 63.3±0.5 68.19 68.1±0.9 octadecane 8014.8±71 16.070±0.01 66.6±0.6 72.11 71.8±1.0 nonadecane 8457.4±74 16.640±0.01 70.3±0.6 76.01 75.8±1.0 eicosane 8919.6±85 17.257±0.01 74.2±0.7 79.81 80.1±1.1 glHm(449 K)/kJmol-1 = (1.0980.0133) slngHm(449 K) - (1.390.25) r2 = 0.9993 (1) slngHm(Tm) = lgHm(Tm) + slnHm(Tm) slnHm(Tm) must be of opposite sign to lgHm(Tm) • 1Ruzicka, K.; Majer, V. Simultaneous Treatment of Vapor Pressures and Related Thermal data Between the Triple Point and Normal Boiling Temperatures for n-Alkanes C5-C20. J. Phys. Chem. Ref. Data1994, 23, 1-39.

  25. Values of at ΔslngHm(509K) and ΔlgHm(509 K) on an SPB-5 Column • -slope T intercept ΔslngHm(509 K) ΔlgHm(509 K) • kJ⋅mol-1 kJ⋅mol-1 • lit1,2 calcd • heptadecane 6108.2±78.2 12.148±0.008 50.8±0.7 62.831 62.9±0.3 • octadecane 6489.9±63.8 12.584±0.006 54.0±0.5 66.341 66.2±0.3 • nonadecane 6901.0±58.7 13.077±0.006 57.4±0.5 69.741 69.8±0.3 • eicosane 7270.0±60.5 13.496±0.006 60.4±0.5 73.071 73.1±0.3 • heneicosane 7670.9±65.3 13.974±0.006 63.8±0.5 76.662 76.6±0.3 • docosane 8064.5±71.6 14.439±0.007 67.1±0.6 80.132 80.1±0.4 • tricosane 8451.1±73.9 14.897±0.008 70.3±0.7 83.542 83.5±0.4 lgHm(509 K)/kJmol-1 = (1.0620.004) slngHm(509 K) + (8.94.020.07) r2 = 0.9999 • 1Ruzicka, K.; Majer, V. Simultaneous Treatment of Vapor Pressures and Related Thermal data Between the Triple Point and Normal Boiling Temperatures for n-Alkanes C5-C20. J. Phys. Chem. Ref. Data1994, 23, 1-39. • 2Chickos, J. S.; Hanshaw, W. Vapor pressures and vaporization enthalpies of the n-alkanes from C21-C30 at T = 298.15 K by correlation–gas chromatography, J. Chem. Eng Data 2004, 49, 77-85.

  26. Enthalpies of Condensation: -slngHm(T), - lgHm(T) and slnHm(T) as a Function of Temperature -ΔslngHm(449 K) -ΔlgHm(449 K) (lit) ΔslnHm(449 K) kJ⋅mol-1 tetradecane -53.2±0.8 -56.92 3.7±0.8 pentadecane -56.4±0.6 -60.71 4.3±0.6 hexadecane -60.3±0.5 -64.5 4.2±0.5 heptadecane -63.3±0.5 -68.19 4.9±0.5 octadecane -66.6±0.6 -72.11 5.5±0.6 nonadecane -70.3±0.6 -76.01 5.7±0.6 eicosane -74.2±0.7 -79.81 5.6±0.7 -ΔslngHm(509 K) -ΔlgHm(509 K) (lit) ΔslnHm(509 K) kJ⋅mol-1 heptadecane -50.8±0.7 -62.83 12.0±0.7 octadecane -54.0±0.5 -66.34 12.3±0.5 nonadecane -57.4±0.5 -69.82 12.4±0.5 eicosane -60.4±0.5 -73.07 12.7±0.5 heneicosane -63.8±0.5 -76.66 12.9±0.5 docosane -67.1±0.6 -80.13 13.0±0.6 tricosane -70.3±0.7 -83.54 13.2±0.7 gslnHm(Tm) = lgHm(Tm) + slnHm(Tm)

  27. Figure. The effect of temperature, 450, 509, 539 K, on the magnitude of slnHm(T/ K). ■, eicosane; ●, nonadecane.

  28. Conclusions: • The enthalpy of interaction of analyte with the column is endothermic and a function of temperature; this allows access to the measurement of large vaporization enthalpies • This may also help focus GC peaks and oppose diffusion broadening • The overall enthalpy of condensation on the column is still highly exothermic, just less so then might have been imagined

  29. 2. An Application of Correlation-Gas Chromatography to a Tautomeric Mixture 0.186 0.814 The enthalpy of formation of the equilibrium mixture of the pure liquid, (-425.5±1.0)kJ·mol-1, has been reported by Hacking and Pilcher. Acetylacetone forms a number of metal complexes whose enthalpies of formation have been used to determine metal oxygen bond strengths. • Hacking, J.M.; Pilcher, G. J. Chem. Thermodyn. 1979, 11, 1015-1017. Irving, R.J.; Wadso, I. Acta Chem.Scand. 1970, 24, 589-592

  30. Table. Summary of all enthalpy differences between 2,4-pentanedione and (Z)-4-hydroxy-3-penten-2-one in the liquid and gas phase available to Hacking and Pilcher, and Irving and Wadso. Enthalpy differences measured by the temperature dependence of the equilibrium constant.

  31. Vaporization Enthalpy of the Pure Enol at T = 298.15 K ∆Hk/e = +0.67 kJ mol-1 C5H8O2(gas, 93.3%enol) C5H8O2(gas, 100%enol) ∆lgHm(298.15K) = (41.8 ± 0.2) kJmol-1 measured calorimetrically ∆lgHm(298.15K) = (43.2 ± 0.2) kJ mol-1 C5H8O2(liquid, 81.4%enol) C5H8O2(liquid, 100%enol) ∆Hk/e = -2.1 kJ mol-1 • A trace of concentrated sulfuric acid was used by Irving and Wadso to rapidly equilibrate the diketo and enol forms. Since the enol is more volatile, it was assumed that tautomerization of the diketo form to the enol contributed –2.1 kJ mol-1during vaporization.. It was also assumed that the composition in the gas phase was the equilibrium concentration. ∆lgHm(298.15K) = (41.8 ± 0.2) –( -2.1 - 0.67) = (43.2 ± 0.2) kJmol-1

  32. gas, 100% diketo (–374.4  1.3) diketo/enolHm(g)=(–10.0  0.8) gas,100% enol (–384.4  1.3) fHm(298.15K) / kJ mol–1 lgHm(298.15K) = (43.2  0.2) liquid,100% diketo (–416.3  1.1) liquid, 81.4% enol 18.6% diketo (-425.5  1.0) diketo/enolHm(l)=(–11.3  0.4) (–427.6  1.1) liquid,100% enol 0 0.814 1 x(enol) The thermochemical scheme to calculate the enthalpy of formation of (Z)-4-hydroxy-3-pentene-2-one and 2,4-pentanedione scheme used by Hacking and Pilcher in 1979

  33. The enthalpy difference of the two tautomers in the gas phase was measured by infrared spectroscopy in 1951 Gas Phase FT-IR spectrum of 2,4-pentanedione, Aldrich Chemical Co.

  34. The enthalpy difference of the two tautomers in the gas phase was re-measured by gas phase 1H NMR spectroscopy in 1985. 5.3 ppm enol vinyl 1H 3.3 ppm keto methylene 1H 1.9 ppm enol methyl 1H 2.0 ppm keto methyl 1H Folkendt, M.M.J.et.al. Phys. Chem. 1985, 89, 3347-3352

  35. Table. A summary of all the enthalpy differences measured between 2,4-pentanedione and (Z)-4-hydroxy-3-penten-2-one in the liquid and gas phase. Enthalpy differences measured by the temperature dependence of the equilibrium constant. The gas phase and condensed phase enthalpies are different, suggesting tautomer interaction

  36. If the pure enol form( 0.814 mol) is mixed with the pure keto form (0.186 mol) at the equilibrium concentrations, will ∆H = 0 ? Is ∆Hmix = 0 ? If ∆Hmix ≠ 0 • If the solution heats up when the pure diketo and enol are mixed at their equilibrium concentration, it will take more energy to vaporize the two liquids as a mixture at T= 298.15 K ; • If the solution cools down, it will take less heat to vaporize the two liquids as a mixture at T = 298.15 K. • Since Hdiketo/enol(liq) ≠ Hdiketo/enol(gas),we decided to measure lgHm(298.15K)

  37. Correlation Gas Chromatography: an ideal method for determining the vaporization enthalpy of a pure material even though the material of interest may be present in the mixture provided all components can be separated Gas Chromatograph of acetylacetone

  38. Table. Enthalpy of transfer and vaporization enthalpy obtained for (Z)-4-hydroxy-3-penten-2-one. lgHm(298.15 K)/kJ mol–1 = (0.734±0.021) slngHm(359 K) + (28.21±0.32) r2 = 0.997

  39. Table. Enthalpy of Transfer and Vaporization Enthalpies obtained for 2,4-pentanedione lgHm(298.15 K)/kJ mol–1 = (1.283±0.1) slngHm(328 K) + (5.21±1.1) r2 = 0.989

  40. (Z)-4-hydroxy-3-penten-2-one ∆lgHm(298.15K)/kJ.mol-1(corr- gas chromatography)=(50.8±0.6) kJ mol-1 ∆lgHm(298.15K)/kJ mol-1(measured as a mixture) = (43.2 0.2) kJ.mol–1a a Measured as a mixture but calculated for the pure material ∆Hmix = (50.8±0.6) - (43.2 ±0.2) = 7.6±0.6 kJ.mol-1 ∆Hketo-enoltautomerism observed = ∆Hketo-enoltautomerism real +∆Hmix ∆Hketo-enoltautomerism real = (-11.3)-(+7.6±0.6) = -18.9±0.6 kJ mol-1 Since the vaporization enthalpy at T = 298.15 K is approximately the same for 2,4-pentanedione and (Z)-4-hydroxy-3-penten-2-one, the difference in the gas phase between the two tautomers is also ~ -18.9 kJ mol-1

  41. gas, diketo (–358.9±2.5) kJ mol-1 ∆diketo/enol Hm(g) = (-19.3±2.8) kJ mol-1 (-19.5)kJ mol-1 Folkendt,M. et al. gas, 100% enol (–378.2±1.2) kJ mol-1 ΔlgHm=(51.2±2.2) kJ mol-1 lgHm= (50.8±0.6) kJ mol-1 liquid, diketo (–410.1±1.2) kJ mol-1 ∆diketo/enol Hm(l)= -18.9 kJ mol-1 (–429.0±1.0)kJ mol-1 liquid, 100% enol 0 0.814 1 x(enol) The enthalpies of formation of the tautomers of acetylacetone in the liquid phase and in the gas phase

  42. Table. Summary of Standard Molar Enthalpies at T = 298.15 K of the Two Acetylacetone Tautomers ∆fHm (T = 298.15 K, liquid, 81.4% enol and 18.6% diketo) = -425.5±1.0 kJ mol-1. values in the brackets are the previous accepted values. Temprado, M.; Roux, M. V.; Umnahanant, P.; Zhao, H.; Chickos, J. S. J. Phys. Chem. B.2005; 109, 12590-12595.

  43. Application 3: Identifying unusual interactions in heterocyclic systems 1,2-Diazines Unknowns: • s-triazine • Pyrimidines • Pyridazines Standards: • Pyrazines • Pyridines

  44. A Comparison of calculated vaporization enthalpies and normal boiling temperatures with literature values s-triazine 50.0±0.3 lgHm (298.15 K)/kJ.mol-1 = (0.9410.07) slngHm(358 K) - (13.10.59), (r2 = 0.9865) a Literature boiling temperatures from SciFinder Scholar A Examination of the Vaporization Enthalpies and Vapor Pressures of Pyrazine, Pyrimidine, Pyridazine and 1,3,5-Triazine. Lipkind D., Chickos J. S. Structural Chemistry 2009, 20, 49-58

  45. Unknowns Standards Top, from left to right : phthalazine, benzo[c]cinnoline, quinazoline, quinoxaline. Standards: phenazine, 2,6-dimethylquinoline, acridine, 4,7-phenanthroline, 7,8-benzoquinoline, Lipkind, D.; Chickos, J. S. Study of the Anomalous Thermochemical Behavior of 1,2-Diazines by Correlation-Gas Chromatography J. Chem. Eng. Data 2010, 55, 698-707

  46. Since all of the compounds studied are crystalline solids, the following equations were used to adjust sublimation and fusion enthalpies to T = 298.15 K and evaluate the vaporization enthalpy Sublimation: crgHm(298.15 K)/(kJ·mol-1)=crgHm(Tm)+[0.75+0.15Cp(cr)/(J·mol-1·K-1)][Tm/K-298.15 K]/1000 Fusion: crlHm(298.15 K)/(kJ·mol-1)=crlHm(Tfus)+[(0.15Cp(cr)-0.26 Cp(l))/(J·mol-1·K-1)-9.83)][Tfus/K-298.15]/1000 Vaporization: lgHm(298.15 K) = crgHm(298.15 K) - crlHm(298.15 K) where Cp(cr), Cp(l) refer to the heat capacity of the crystal and liquid, respectively Acree, Jr.; W.; Chickos, J. S. Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds. Sublimation, Vaporization and Fusion Enthalpies From 1880 to 2009, J. Phys. Chem. Ref Data 2010, 39, 1-942.

  47. A summary of the vaporization enthalpies for diazines at T = 298 K 58.71.456.52.0-2.22.4 59.61.4 61.11.1 1.51.8 Vap. Enth. Calc, kJmol-1 : Vap. Enth. Lit, kJmol-1 : Difference, kJmol-1 : 67.31.6 711.9 3.72.5 46.42.0 53.50.4 7.12.0 79.7±1.3 78.4±2.0 -1.02.4 Vap. Enth. Calc, kJmol-1 : Vap. Enth. Lit, kJmol-1 : Difference, kJmol-1 : 76.70.7 78.82.2 2.12.3 81.90.8 89.22.3 7.32.4 Difference in the strength of intermolecular interactions between 1,2-diazines and their isomeric counterparts is approximately6-7 kJmol-1 Lipkind, D.; Chickos, J. S. Study of the Anomalous Thermochemical Behavior of 1,2-Diazines by Correlation-Gas Chromatography J. Chem. Eng. Data 2010, 55, 698-707

  48. Vaporization Enthalpies Using Pyridine Derivatives as Standards 1-EthylIMI What structural factors influence this behavior ? A Study of the Vaporization Enthalpies of Some 1-Substituted Imidazoles and Pyrazoles by Correlation-Gas Chromatography, Lipkind, D.; Plienrasri, C. Chickos, J. S. J. Phys. Chem. B 2010, 114, 16959–16967

  49. Unknowns: Standards Set 1 Standards Set 2

  50. Vaporization Enthalpies as a Function of Standards Used All the compounds whose vaporization enthalpy is in red are planar in the solid state; all are reproduced using various pyridazines and imidazole derivatives as standards The Vaporization Enthalpies of 2- and 4-(N,N-Dimethylamino)pyridine, 1,5-Diazabicyclo[4.3.0]non-5-ene, 1,8-Diazabicyclo[5.4.0]undec-7-ene, Imidazo[1,2-a]pyridine and 1,2,4-Triazolo[1,5-a]pyrimidine by Correlation –Gas Chromatography, Lipkind, D.; Rath, N.; Chickos, J.S. Pozdeev, V. A.; Verevkin, S. J. Phys. Chem. 2010, 55, 1628-35.

More Related