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Examining the PM6 semiempirical method for pKa prediction across a wide range of oxyacids

Sierra Rayne¹, Kaya Forest² & Ken J. Friesen¹

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1. University of Winnipeg
2. Okanagan College

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Document Type:

Manuscript

Date:

Received 25 March 2009 17:24 UTC; Posted 26 March 2009

Subjects:

Chemistry, Pharmacology, Earth & Environment

Tags:

• pKa prediction
• PM6 method
• oxyacids
• SPARC
• Validation

Abstract:

The pK_a estimation ability of the semiempirical PM6 method was evaluated across a broad range of oxyacids and compared to results obtained using the SPARC software program. Compound classes under consideration included acetic acids, alicyclic and aromatic heterocyclic acids, benzoic acids, boronic acids, hydroxamic acids, oximes, peroxides, peroxyacids, phenols, α-saturated acids, α-saturated alcohols, sulfinic acids, α-unsaturated acids, and α-unsaturated alcohols. PM6 accurately predicts the acidity of acetic and benzoic acids and their derivatives, but is less reliable for alicyclic and aromatic heterocyclic acids and phenols. α-Saturated acids are reliably modeled by PM6 except for polyacid derivatives with α-alcohol moieties. α-Saturated alcohols only appear to yield reliable PM6 results where an α-hydroxy or α-alkoxy moiety is absent. Carboxylic acids with simple α-alkene unsaturation are well approximated by PM6 except where alkyne α-unsaturation or α-carboxylation are also present. The PM6 and SPARC methods exhibit approximately equal pKa prediction performance for the acetic, alicyclic, and benzoic acids. SPARC outperforms PM6 on the peroxides, peroxyacids, phenols, and α-saturated acids and α-saturated alcohols. pKa values for boron, nitrogen, and sulfur oxyacids do not appear to be reliably estimated by either the PM6 or SPARC methods. The findings will help guide the potential appropriateness of results from the PM6 pK_a estimation method for waste treatment and environmental fate investigations.

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This document is licensed to the public under the Creative Commons Attribution 3.0 License

How to cite this document:

Rayne, Sierra, Forest, Kaya, and Friesen, Ken. Examining the PM6 semiempirical method for pKa prediction across a wide range of oxyacids. Available from Nature Precedings <http://hdl.handle.net/10101/npre.2009.2981.1> (2009)

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