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  • Print publication year: 2013
  • Online publication date: February 2013

9 - Structure–property relationships among hydrocarbons


Intermolecular interactions

Virtually all substances of interest in fuel chemistry consist of covalently bonded molecules. Many are hydrocarbons in the literal sense of the word – compounds containing only hydrogen and carbon atoms. Others contain one or more heteroatoms, i.e. atoms of oxygen, nitrogen, or sulfur. Physical properties of fuels have numerous important roles in fuel technology and utilization, e.g. boiling point, because distillation is commonly used for separations; density, because the amount of fuel that can be carried on vehicles or aircraft is limited by volume and not by mass; and viscosity, because we need fluids to flow, or to be pumped, from place to place. An understanding of how chemical composition and molecular structure influence physical properties shows that the properties of substances do not come about by some haphazard chance but rather because of fundamental links between composition, structure, and properties. Further, such links provide useful guidelines or rules of thumb for estimating expected properties from composition, or vice versa.

The most noticeable property of most substances is their physical state: solid, liquid, or gaseous. The first point of inquiry becomes that of why molecules form solids or liquids at all. Why isn't everything a gas? To exist in a condensed phase, i.e. as a liquid or solid, there must be attractive forces among molecules strong enough to hold them in proximity.

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Pauling, L.The Nature of the Chemical Bond. Cornell University Press: Ithaca, 1960; Chapter 3. (Might as well go straight to the fount.)
Recommended reading
Harvey, R.G.Polycyclic Aromatic Hydrocarbons. Wiley-VCH: New York, 1997. Unfortunately, most introductory textbooks of organic chemistry seldom mention aromatic hydrocarbons larger than naphthalene (or sometimes even larger than benzene). This monograph is a useful source of information on a large number of compounds of this kind.
Lide, D.R.Handbook of Chemistry and Physics. CRC Press: Boca Raton, FL, 2009. There are many useful compilations, in print and on the web, of data on the physical and thermochemical properties of hydrocarbons and the related heteroatomic compounds. This book in particular is an excellent resource.
Reid, R.C., Prausnitz, J.M., and Poling, B.E.The Properties of Gases and Liquids. McGraw-Hill: New York, 1987. This book is an excellent source of methods for calculating or estimating properties of liquids from fundamental information. It treats many of the properties discussed in this chapter, and a great many more besides.
Smith, M.B. and March, J.March's Advanced Organic Chemistry. Wiley: Hoboken, NJ, 2007. Chapter 3 provides an in-depth discussion of weak interactions such as hydrogen bonding and π–π interactions, with numerous references to the primary literature.
Szmant, H. Harry. Organic Chemistry. Prentice-Hall: Englewood Cliffs, NJ, 1957. Though this is now a rather elderly textbook, Chapter 24 provides a good discussion of the physical properties of organic compounds, much more so than many modern introductory organic texts.
Twain, M. Life on the Mississippi. Numerous editions of this classic are available. In Chapter XVII, Twain extrapolates data accumulated over 176 years to “prove” that the Mississippi River must once have been 1 300 000 miles long. This chapter should be required reading for all scientists and engineers.