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Density functional steric analysis of linear and branched alkanes
Daniel H Ess1, Shubin Liu, Frank De Proft
1Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, USA. dhe@chem.byu.edu
The Journal of Physical Chemistry. A
|November 20, 2010
Summary
Branched alkanes exhibit greater thermodynamic stability than linear alkanes due to favorable electrostatic interactions. Density functional theory (DFT) reveals that reduced steric hindrance in branched alkanes contributes to their enhanced stability.
Area of Science:
- Physical Chemistry
- Computational Chemistry
- Organic Chemistry
Background:
- Branched alkanes are thermodynamically more stable than their linear counterparts.
- This stability difference is observable in alkane bond separation energies.
Purpose of the Study:
- To elucidate the physical underpinnings of stability differences between branched and linear alkanes.
- To introduce a novel density functional theory (DFT) based definition of steric energy.
Main Methods:
- Utilized a novel DFT definition of steric energy based on the Weizäcker kinetic energy.
- Employed the M06-2X functional to partition total DFT energy into steric, electrostatic, and fermionic quantum energy terms.
- Analyzed the contributions of these energy terms to the overall stability of branched versus linear alkanes.
Main Results:
- Branched alkanes possess less destabilizing DFT steric energy compared to linear alkanes.
- A significant quantum energy term, encompassing Pauli and exchange-correlation energies, counteracts the steric effects.
- The electrostatic energy term was identified as the primary factor favoring alkane branching.
Conclusions:
- The enhanced stability of branched alkanes arises from a balance between steric and quantum energy effects, with electrostatic interactions playing a dominant role.
- DFT analysis provides a detailed molecular-level explanation for the observed thermodynamic stability of branched alkanes.
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