Boiling Points of the Family of Small Molecules, CHwFxClyBrz: How Are They Related to Molecular Mass?

Laing, Michael

doi:10.1021/ed078p1544

Cited by 14 publications

(15 citation statements)

References 4 publications

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“…However, this effect is generally overridden by the poor polarizability of organofluorine compounds. Polarizability expressed by the molar refraction R does indeed correlate linearly with the boiling points within the dihalomethanes, trihalomethanes, and tetrahalomethanes series …”

Section: 1 Boiling and Melting Ranges Of Polyfluoro Ethersmentioning

confidence: 88%

“…Polarizability expressed by the molar refraction R does indeed correlate linearly with the boiling points within the dihalomethanes, trihalomethanes, and tetrahalomethanes series. 140 Fluorine tends to increase volatilities also in the aromatic series. Difluoromethyl phenyl ether 22 and trifluoromethyl phenyl ether 25 distill at lower temperatures (139 and 106 °C, respectively) than anisole (155 °C).…”

Section: Boiling and Melting Ranges Of Polyfluoro Ethersmentioning

confidence: 99%

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α-Fluorinated Ethers, Thioethers, and Amines: Anomerically Biased Species

2005

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Section: 1 Boiling and Melting Ranges Of Polyfluoro Ethersmentioning

confidence: 88%

Section: Boiling and Melting Ranges Of Polyfluoro Ethersmentioning

confidence: 99%

α-Fluorinated Ethers, Thioethers, and Amines: Anomerically Biased Species

2005

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“…Empirical equations have been developed to predict boiling points (16,(28)(29)(30), but no purely theoretical treatment has been developed. Repulsive force can be added with a term of the general form, b/r n where b and n are empirical factors unique to each molecule (3).…”

Section: Acknowledgmentmentioning

confidence: 99%

A Closer Look at Trends in Boiling Points of Hydrides: Using an Inquiry-Based Approach To Teach Intermolecular Forces of Attraction

2010

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Boiling-point data are commonly used in introductory chemistry classes to illustrate the effects of intermolecular forces of attraction (IMFs) on familiar physical properties. In this article, we describe how we use boiling-point trends of group IV-VII hydrides to introduce intermolecular forces in our first-year general chemistry classes. Our approach grew out of our experience teaching with the ACS general chemistry textbook (1), which emphasizes conceptual understanding and uses an inquiry-based approach to help students understand chemical principles.A number of parameters can be used as a measure of intermolecular forces, and it could be argued that the enthalpy of vaporization is a more direct, and therefore better, indicator of the strength of these attractive forces. Boiling point is the temperature at which Gibbs energy, ΔG vap , equals zero, so that the boiling temperature, T BP , is the ratio of the enthalpy of vaporization, ΔH vap , to the entropy of vaporization, ΔS vap :Because ΔH vap depends directly on the strength of intermolecular forces, boiling points also incorporate a similar dependence. However, the boiling point also depends on ΔS vap , which theoretically could change the overall dependence of boiling point on IMFs. We explore this question and explain why we believe that it is legitimate to look at boiling-point trends, at least for the group IV-VII hydrides. We also examine the choice of variable to use on the x axis when graphing boiling point or ΔH vap and discuss why the number of electrons, although an imperfect indicator of the total molecular interaction energy, is conceptually more sound than other reasonable alternatives, especially in an introductory chemistry class. Finally, we address the common misconception that dispersion forces are the weakest of the IMFs and then use London dispersion forces to explore the nonlinearity of the boiling-point data for the group IV compounds. Discussion: Trends in Boiling Points of HydridesThe Effects of Intermolecular Forces of Attraction on Boiling PointAll general chemistry courses introduce the different types of intermolecular forces and how they help to explain a variety of physical properties. A graph of the boiling points of the group IV-VII hydrides is often used to illustrate periodic trends that relate to intermolecular forces because it is generally assumed that a higher boiling point is the result of stronger intermolecular attractions. Because the enthalpy of vaporization is a more direct measure of the strength of IMFs in a liquid and differences in IMF strength will change the magnitude of ΔH vap , there is an argument for using ΔH vap rather than boiling point to examine the role of IMFs. In our courses, IMFs are introduced early in the chemistry course, when students have not yet learned about enthalpy, and thus, it makes sense to talk instead about a property (boiling point) with which the students are familiar. To test the validity of using boiling point as an indicator of IMF strength, we compare graphs of boiling points...

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“…About the possibility to model salts with graph concepts see refs. 6,14, and15, where the concepts of purely ionic bond and purely covalent bond are reconsidered. The graphs of metal halides are deceptively simple graphs that can be represented by two connected points, that is, •——•.…”

Section: Resultsmentioning

confidence: 99%

Complete graph conjecture for inner‐core electrons: Homogeneous index case

Pogliani¹

2003

J Comput Chem

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The complete graph conjecture that encodes the inner-core electrons of atoms with principal quantum number n >or= 2 with complete graphs, and especially with odd complete graphs, is discussed. This conjecture is used to derive new values for the molecular connectivity and pseudoconnectivity basis indices of hydrogen-suppressed chemical pseudographs. For atoms with n = 2 the new values derived with this conjecture are coincident with the old ones. The modeling ability of the new homogeneous basis indices, and of the higher-order terms, is tested and compared with previous modeling studies, which are centered on basis indices that are either based on quantum concepts or partially based on this new conjecture for the inner-core electrons. Two similar algorithms have been proposed with this conjecture, and they parallel the two "quantum" algorithms put forward by molecular connectivity for atoms with n > 2. Nine properties of five classes of compounds have been tested: the molecular polarizabilities of a class of organic compounds, the dipole moment, molar refraction, boiling points, ionization energies, and parachor of a series of halomethanes, the lattice enthalpy of metal halides, the rates of hydrogen abstraction of chlorofluorocarbons, and the pED(50) of phenylalkylamines. The two tested algorithms based on the odd complete graph conjecture give rise to a highly interesting model of the nine properties, and three of them can even be modeled by the same set of basis indices. Interesting is the role of some basis indices all along the model.

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Boiling Points of the Family of Small Molecules, CHwFxClyBrz: How Are They Related to Molecular Mass?

Cited by 14 publications

References 4 publications

α-Fluorinated Ethers, Thioethers, and Amines: Anomerically Biased Species

α-Fluorinated Ethers, Thioethers, and Amines: Anomerically Biased Species

A Closer Look at Trends in Boiling Points of Hydrides: Using an Inquiry-Based Approach To Teach Intermolecular Forces of Attraction

Complete graph conjecture for inner‐core electrons: Homogeneous index case

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