Abstract
The properties of alkanes are consequential for understanding many chemical processes in nature and industry. We use molecular dynamics simulations with the Amber force field GAFF2 to examine the structure of pure liquids at each respective normal boiling point, spanning the 15 n-alkanes from methane to pentadecane. The densities predicted from the simulations are found to agree well with reported experimental values, with an average deviation of 1.9%. The enthalpies of vaporization have an average absolute deviation from experiment of 10.4%. Radial distribution functions show that short alkanes have distinct local structures that are found to converge with each other with increasing chain length. This provides a unique perspective on trends in the n-alkane series and will be useful for interpreting similarities and differences in the n-alkane series as well as the breakdown of ideal solution behavior in mixtures of these molecules.
Highlights
Alkanes are common in nature and are frequently used in various applications in chemical industries [1]
We have found that GAFF2 with charges parameterized with RESP reproduces liquid densities at the normal boiling point of n-alkanes from methane to pentadecane within an average deviation of 2%
All deviations in density are positive but deviations in ∆Hvap are more complex. ∆Hvap is overestimated for short alkanes but the increase with chain length is too small so it is underestimated for long alkanes
Summary
Alkanes are common in nature and are frequently used in various applications in chemical industries [1]. We wish to highlight that alkanes frequently occur in heterogeneous systems, composed of many molecules and phases at a wide range of pressures and temperatures. Petroleum is composed overwhelmingly of hydrocarbons and often a significant portion are alkanes [2]. Alkanes are much more reactive than CO2 , so they have far shorter lifetimes in the atmosphere [3]. Their reactivity is important for their use in synthetic organic chemistry as well as linked to their hypothesized roles in the natural formation of complex organic molecules in abiotic conditions.
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