alexa On the Stability of Branched Hydrocarbons | OMICS International
ISSN: 2161-0398
Journal of Physical Chemistry & Biophysics
Like us on:
Make the best use of Scientific Research and information from our 700+ peer reviewed, Open Access Journals that operates with the help of 50,000+ Editorial Board Members and esteemed reviewers and 1000+ Scientific associations in Medical, Clinical, Pharmaceutical, Engineering, Technology and Management Fields.
Meet Inspiring Speakers and Experts at our 3000+ Global Conferenceseries Events with over 600+ Conferences, 1200+ Symposiums and 1200+ Workshops on
Medical, Pharma, Engineering, Science, Technology and Business

On the Stability of Branched Hydrocarbons

Lawrence S. Bartell*
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
Corresponding Author : Lawrence S. Bartell
Department of Chemistry, University of Michiga
Ann Arbor, Michigan 48109, United States
Tel: 734-764-7375
E-mail: [email protected]
Received February 17, 2014; Accepted May 16, 2014; Published May 19, 2014
Citation: Bartell LS (2014) On the Stability of Branched Hydrocarbons. J Phys Chem Biophys 4:140. doi:10.4172/2161-0398.1000140
Copyright: © 2014 Etsuro I, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Visit for more related articles at Journal of Physical Chemistry & Biophysics

Abstract

Nearly a half-century ago I published a paper which successfully calculated the relative stabilities of a large number of hydrocarbons. Calculations were based on empirical atom-atom potential energies I had introduced in 1960, which had been deliberately biased to take into account the differences between branched and u n b r a n c h e d hydrocarbon molecules. Little controversy arose until quite recently when Gronert revived this old work and entered into what evolved into a bitter controversy with the Grimme, Wiberg, and Schleyer accounts of stabilities of branched vs. unbranched hydrocarbons. Gronert invoked 1-3 nonbonded interactions to reproduce successfully the relative stabilities of the various hydrocarbons. His opponents carried out careful quantum computations including electron correlation energies (not feasible to calculate in 1960 when the empirical interaction potentials were formulated). The purpose of this paper is to resolve the controversy by showing that while the two approaches differ in verbal explanations; they are equivalent in concrete results.

Introduction
To get to the heart of what is involved, consider the fact that the relative stabilities of isomers are built into the force-fields of the molecules concerned. Molecular-mechanics computations based on the force-fields yield both the structures and energies of the molecules. Note that the primary difference between normal and iso potential energies in hydrocarbons can be expressed as [1]
Vnormal-Viso=2 VC-H - (VC-C+VH-H)     (1)
Where Vij ‘s are the potential energies of the i,j (1-3) interactions evaluated at their appropriate geminal nonbonded distances. First of all, the idea that that geminal distances (bond angles) around a central atom are based on a 1960 model [2] invoking the close packing of repelling ligands, rather than by presumed effects of hybridization or even by the interactions proposed by the popular VSEPR model. This account has since been confirmed in detail by the author of the VSEPR papers, and his colleagues [3-13]. What is it then that causes the geminal potential energies in Eq.1 to make branched hydrocarbons to be more stable than unbranched ones?
Empirical Approach
One answer is that it doesn’t matter as long as computations correctly account for experimental results. To get quickly to the point of the present argument, the Gronert force field [14], based closely on Bartell’s empirical field of 1960 [2], incorporated nonbonded interactions, which inserted into Eq. 1, deliberately biased them to make the C-H interactions more repulsive than the sum of the C-C and H-H interactions. This stratagem successfully accounted for observations of a large number of unbranched, singly, and multiplies branched hydrocarbons [1]. No explanation was advanced to account for this bias except that it was needed to account for the extra stability of branched molecules.
A More Fundamental Approach
Once it became feasible to include accurate electron correlation energies in quantum chemical computations, Wiberg [15,16], Grimme [17] and Schleyer [18-20] found electron correlation to be essential to account for experimental results. They showed that simple steric interactions between ligands (as yielded by Hartree-Fock computations) were incapable of reproducing experimental isomeric differences. As Grimme [16] showed by partitioning the electron correlation energies, the stabilizing energies were greater for C-C and H-H interactions than for the C-H. Accordingly, this accounted for the imbalance of terms in Eq. 1. Therefore, the extra stability of branched hydrocarbons is explained by Wiberg, Grimme, and Schleyer at a more fundamental level than by Gronert’s model.
Conclusion
Both the Gronert and the Wiberg-Grimme-Schleyer treatments account for what Schleyer calls protobranching stability. It cannot be denied that electron correlation energies are responsible for the extra stability of branched hydrocarbons. But that fact in no way implies that Gronert’s approach is wrong. Except for explanations, the two approaches are equivalent in content if not in the words used to describe them.
Acknowledgements
This research was supported by funds from the Social Security Administration.
References
Select your language of interest to view the total content in your interested language
Post your comment

Share This Article

Recommended Conferences

Article Usage

  • Total views: 11546
  • [From(publication date):
    April-2014 - Feb 18, 2018]
  • Breakdown by view type
  • HTML page views : 7781
  • PDF downloads : 3765
 

Post your comment

captcha   Reload  Can't read the image? click here to refresh

Peer Reviewed Journals
 
Make the best use of Scientific Research and information from our 700 + peer reviewed, Open Access Journals
International Conferences 2018-19
 
Meet Inspiring Speakers and Experts at our 3000+ Global Annual Meetings

Contact Us

Agri & Aquaculture Journals

Dr. Krish

[email protected]

1-702-714-7001Extn: 9040

Biochemistry Journals

Datta A

[email protected]

1-702-714-7001Extn: 9037

Business & Management Journals

Ronald

[email protected]

1-702-714-7001Extn: 9042

Chemistry Journals

Gabriel Shaw

[email protected]

1-702-714-7001Extn: 9040

Clinical Journals

Datta A

[email protected]

1-702-714-7001Extn: 9037

Engineering Journals

James Franklin

[email protected]

1-702-714-7001Extn: 9042

Food & Nutrition Journals

Katie Wilson

[email protected]

1-702-714-7001Extn: 9042

General Science

Andrea Jason

[email protected]

1-702-714-7001Extn: 9043

Genetics & Molecular Biology Journals

Anna Melissa

[email protected]

1-702-714-7001Extn: 9006

Immunology & Microbiology Journals

David Gorantl

[email protected]

1-702-714-7001Extn: 9014

Materials Science Journals

Rachle Green

[email protected]

1-702-714-7001Extn: 9039

Nursing & Health Care Journals

Stephanie Skinner

[email protected]

1-702-714-7001Extn: 9039

Medical Journals

Nimmi Anna

[email protected]

1-702-714-7001Extn: 9038

Neuroscience & Psychology Journals

Nathan T

[email protected]

1-702-714-7001Extn: 9041

Pharmaceutical Sciences Journals

Ann Jose

[email protected]

1-702-714-7001Extn: 9007

Social & Political Science Journals

Steve Harry

[email protected]

1-702-714-7001Extn: 9042

 
© 2008- 2018 OMICS International - Open Access Publisher. Best viewed in Mozilla Firefox | Google Chrome | Above IE 7.0 version