Estimating Solid–Liquid Phase Change Enthalpies and Entropies Cite as: Journal of Physical and Chemical Reference Data 28, 1535 (1999); https:// doi.org/10.1063/1.556045 Submitted: 07 January 1999 . Published Online: 28 April 2000 James S. Chickos, William E. Acree, and Joel F. Liebman ARTICLES YOU MAY BE INTERESTED IN Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds. Sublimation, Vaporization and Fusion Enthalpies From 1880 to 2010 Journal of Physical and Chemical Reference Data 39, 043101 (2010); https:// doi.org/10.1063/1.3309507 Heat Capacities and Entropies of Organic Compounds in the Condensed Phase. Volume III Journal of Physical and Chemical Reference Data 25, 1 (1996); https://doi.org/10.1063/1.555985 Enthalpies of Vaporization of Organic and Organometallic Compounds, 1880–2002 Journal of Physical and Chemical Reference Data 32, 519 (2003); https:// doi.org/10.1063/1.1529214 Journal of Physical and Chemical Reference Data 28, 1535 (1999); https://doi.org/10.1063/1.556045 28, 1535 © 1999 American Institute of Physics and American Chemical Society. Estimating Solid–Liquid Phase Change Enthalpies and Entropies James S. Chickosa… Department of Chemistry, University of Missouri–St. Louis, St. Louis Missouri 63121 William E. Acree, Jr. Department of Chemistry, University of North Texas, Denton, Texas 76203 Joel F. Liebman Department of Chemistry and Biochemistry, University of Maryland Baltimore County, Baltimore, Maryland 21250 Received January 7, 1999; revised manuscript received July 10, 1999 A group additivity method based on molecular structure is described that can be used ⌬Tfus ⌬Tfus to estimate solid–liquid total phase change entropy ( 0 Stpce) and enthalpy ( 0 Htpce) of organic molecules. The estimation of these phase changes is described and numerous examples are provided to guide the user in evaluating these properties for a broad range of organic structures. A total of 1858 compounds were used in deriving the group values and these values are tested on a database of 260 additional compounds. The absolute average and relative errors between experimental and calculated values for these 1858 compounds are 9.9 J molϪ1 KϪ1 and 3.52 kJ molϪ1, and 0.154 and 0.17 for ⌬TfusS • • • 0 tpce ⌬Tfus and 0 Htpce , respectively. For the 260 test compounds, standard deviations of Ϯ13.0 J molϪ1 KϪ1(⌬TfusS ) and Ϯ4.88 kJ molϪ1(⌬TfusH ) between experimental • • 0 tpce 0 tpce and calculated values were obtained. Estimations are provided for both databases. Fusion enthalpies for some additional compounds not included in the statistics are also included in the tabulation. © 1999 American Institute of Physics and American Chemical Soci- ety. ͓S0047-2689͑99͒00106-3͔ Contents 4.1.1. Decachlorobiphenyl................ 1540 1. Introduction................................ 1536 4.1.2. N-acetyl-L-alanine amide. ........... 1540 1.1. Fusion Enthalpies....................... 1536 4.1.3. Trifluoroacetonitrile................ 1540 1.2. Fusion Entropies........................ 1536 4.1.4. Isoquinoline...................... 1540 2. Estimation of Total Phase Change Entropy 4.2. Cyclic and Polycyclic Hydrocarbon and Enthalpy............................... 1536 Derivatives............................. 1540 2.1. Derivation of Group Values............... 1536 4.2.1. 2-Chlorodibenzodioxin.............. 1540 3. Estimations of Hydrocarbons.................. 1538 4.2.2. 6,8,9-Trimethyladenine.............. 1540 3.1. Acyclic and Aromatic Hydrocarbons. ...... 1538 4.2.3. Lenacil.......................... 1540 3.1.1. Styrene.......................... 1538 4.2.4. Cortisone......................... 1541 3.1.2. 1-Heptene........................ 1538 4.3. Polymers.............................. 1541 5. The Group Coefficient in Cycloalkyl Derivatives.. 1541 3.1.3. Perylene......................... 1538 6. Polymorphism.............................. 1541 3.2. Nonaromatic Cyclic and Polycyclic 7. Statistics of the Correlation................... 1542 Hydrocarbons.......................... 1538 7.1. Database Compounds.................... 1542 3.2.1. 10,10,13,13-Tetramethyl-1,5- 7.2. Test Compounds........................ 1543 cyclohexadecadiyne................ 1539 8. Acknowledgments.......................... 1673 3.2.2. Bullvalene........................ 1539 9. References................................. 1673 3.2.3. Acenaphthylene................... 1539 4. Estimations of Hydrocarbon Derivatives. ........ 1539 4.1. Acyclic and Aromatic Hydrocarbon List of Tables ͑ ͒ Derivatives............................. 1540 1. a Contributions of the hydrocarbon portion of acyclic and aromatic molecules................ 1543 1. ͑b͒ Contributions of the cyclic hydrocarbon a͒ Electronic mail: [email protected] portions of the molecule..................... 1543 ©1999 by the U.S. Secretary of Commerce on behalf of the United States. 2. ͑a͒ Contributions of the functional group portion All rights reserved. This copyright is assigned to the American Institute of Physics and the American Chemical Society. of the molecule............................. 1544 Reprints available from ACS; see Reprints List at back of issue. 2. ͑b͒ Contributions of functional groups as part of Õ Õ Õ Õ Õ 0047-2689 99 28„6… 1535 139 $71.001535 J. Phys. Chem. Ref. Data, Vol. 28, No. 6, 1999 1536 CHICKOS, ACREE, AND LIEBMAN a ring..................................... 1546 lecular motion. Others, such as liquid crystals exhibit noniso- 3. Estimations of total phase change entropies and tropic molecular motion in the liquid phase.4 Both have as- enthalpies of hydrocarbons.................... 1547 sociated with these phenomena, additional phase transitions 4. Estimations of total phase change entropies and that attenuate the enthalpy and entropy associated with fu- enthalpies sion. A large positive discrepancy in the difference between A. Substituted aromatic and aliphatic molecules; estimated and experimentally measured fusion enthalpy is a B. substituted cyclic molecules................. 1547 good indication of this behavior. 5. Experimental and calculated total phase change enthalpy and entropy of database............... 1548 6. Experimental and calculated total phase change 1.2. Fusion Entropies enthalpies and entropies of fusion of polymers.... 1641 7. Calculated and experimental phase change Very few general techniques have been developed for di- enthalpies and entropies of test solids........... 1645 rectly estimating fusion enthalpies, in part, as a consequence 8. References to Tables 5, 6, and 7............... 1668 of the complex phase behavior exhibited by some com- pounds. Fusion enthalpies have been most frequently calcu- List of Figures lated from fusion entropies and the experimental melting 1. Fusion entropy of the n-alkanes as a function of temperature of the solid Tfus . One of the earliest estimation the number of methylene groups.. ............ 1537 techniques is the use of Walden’s Rule.5 The application of 2. Total phase change entropies of the n-alkanes as Walden’s Rule provides a remarkably good approximation of ⌬ a function of the number of methylene groups.. 1537 fusHm , if one considers that the estimation is independent 3. A comparison of calculated and experimental of molecular structure and based on only two parameters. ⌬Tfus 6,7 0 Stpce of 1858 database compounds.......... 1542 Recent modifications of this rule have also been reported. 4. A histogram illustrating the distribution of errors Walden’s Rule: T ⌬ fus Ϫ Ϫ in estimating Stpce of the database ⌬ ͒ Ϸ 1 1 0 fusHm͑Tfus /Tfus 13 cal K mol compounds................................. 1542 • • Ϫ Ϫ 5. A comparison of calculated and experimental ϭ54.4 J mol 1K 1. ͑1͒ ⌬Tfus 0 Stpce of 260 test compounds............... 1542 A general method for estimating fusion entropies based on 6. A histogram illustrating the distribution of errors the principles of group additivity has been reported ⌬Tfus 8–10 in estimating 0 Stpce of 260 test compounds.... 1542 recently. This method has been developed from the as- sumption that unlike fusion enthalpy and entropy, the total 1. Introduction phase change entropy associated in going from a rigid solid at0Ktoanisotropic liquid at the melting point, Tfus ,isa 1.1. Fusion Enthalpies group property and that this property can be estimated by Fusion enthalpy is an important physical property of the standard group additivity techniques. The total phase change solid state. The magnitude of the fusion enthalpy influences entropy has been defined as the sum of the entropy associ- solute solubility in both an absolute sense and in its tempera- ated with all the phase changes occurring in the condensed ture dependence. This property plays an important factor in phase prior to and including melting. The assumption that determining molecular packing in crystals and can be useful the total phase change entropy is a more reliable group prop- in correcting thermochemical data to a standard state when erty than fusion entropy is readily apparent from an exami- combined with other thermodynamic properties. nation of these two properties as a function of the number of The discrepancy in numbers between the many new or- methylene groups for the n-alkanes. This is illustrated in ganic solids prepared and the few thermochemical measure- Figs. 1 and 2. Many alkanes have additional phase transitions ments reported annually has encouraged the development of with significant entropy components that influence the mag- empirical relationships that can be used to estimate proper- nitude of the fusion entropy.