Gas phase acidities and associated equilibrium isotope effects for selected main group mono- and polyhydrides, carbon acids, and oxyacids: A G4 and W1BD study

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Abstract

Gas phase standard state (298.15 K, 1 atm) enthalpies (ΔacidH°(g)) and free energiesacidG°(g)) of acid dissociation were calculated at the Gaussian-4 (G4) and W1BD levels of theory for a range of perproteated, perdeuterated, pertritiated, and partially isotopically labeled main group mono- and polyhydrides, carbon acids, and oxyacids. Excellent agreement was obtained between the available experimental datasets and the theoretical estimates, with effectively equivalent ΔacidH°(g)acidG°(g) prediction accuracy for the G4 and W1BD methods on carbon acids and oxyacids. The W1BD level of theory provided ΔacidH°(g)acidG°(g) errors about one-half those of the G4 method on main group hydrides. G4 and W1BD predicted primary and secondary equilibrium isotope effects (EIEs) on gas phase acidity for deuterium and tritium substitution exhibit periodic trends among the main group hydrides, as well as acid strength and structure–property relationships for some groups of carbon acids and oxyacids. Primary EIEs calculated at the W1BD level for various isotopologues of the H2, LiH, CH4, NH3, SiH4, SH2, and ClH main group hydrides using the major isotopes for each non-protic element declined in magnitude with increasing atomic number due to decreasing mass differences between the respective isotopologues.

Introduction

Gas phase acidities represent intrinsic physical properties of interest and can be exploited for a variety of applications. Correlations have been developed between electronegativity (Χ) and hardness (μ) and the gas phase acidities of second and third row compounds, suggesting that both increased electronegativity and polarizability (softness) contribute to acidity. Thus, more electronegative and softer components on the conjugate base allow it to better accommodate the additional charge following deprotonation [1]. In addition to numerous works investigating gas phase acidities of isolated groups of compounds, several studies have considered more comprehensive viewpoints, often including theoretical treatments to complement and add to the experimental database and structure–property trends (see, e.g., Refs. [2], [3], [4], [5], [6], [7], [8], [9]).

Isotopic substitution, either primary (the atoms comprising the acidic bond) or secondary (other atoms in the molecule), will also play a role in the gas phase acidity. In general, secondary hydrogen–deuterium equilibrium isotope effects (EIEs) on gas phase acidities are much smaller (typically ∼<1 kJ/mol for the α-position, and ∼<0.5 kJ/mol for the β-position) than primary EIEs [10], for which the experimental database [11] shows an effect typically on the order of ∼5 to 10 kJ/mol. However, despite the broad interest in isotope effects across all disciplines of chemistry, it appears relatively few experimental or theoretical studies have investigated EIEs on gas phase acidities [10] (of interest, we also note the following EIE solution phase studies on acidity constants [12], [13], [14], [15], [16], [17], [18], [19], [20], [21]). Consequently, in the current work we examine the gas phase acidities of various main group hydrides, carbon acids, and oxyacids and representative isotopologues using high-level theoretical methods, providing comparison to experimental data where possible, and investigating potential periodic trends and other structure–property relationships.

Section snippets

Computational details

Calculations were conducted using the Gaussian-4 (G4) [22] and W1BD [23], [24] methods in Gaussian 09 [25] on the Western Canada Research Grid (WestGrid; project 100185 [K. Forest]) and the Shared Hierarchical Academic Research Computing Network (SHARCNET; project sn4612 [K. Forest]) of Compute/Calcul Canada. All calculations used the same gas phase starting geometries obtained with the PM6 semiempirical method [26] as implemented in MOPAC 2009 (http://www.openmopac.net/; v. 9.281). Molecular

Results and discussion

Gas phase standard state (298.15 K, 1 atm) enthalpies (ΔacidH°(g)) and free energies (ΔacidG°(g)) of acid dissociation were calculated at the G4 and W1BD levels for a range of perproteated main group hydrides (Table 1), carbon acids (Table 2), and oxyacids (Table 3) extending up to the basis set atomic number limits for the respective methods (G4, bromine; W1BD, chlorine). Experimental ΔacidH°(g) were available for comparison with all perproteated main group hydrides from the NIST database [11].

Acknowledgements

This work was made possible by the facilities of the Western Canada Research Grid (WestGrid: www.westgrid.ca; project 100185), the Shared Hierarchical Academic Research Computing Network (SHARCNET: www.sharcnet.ca; project sn4612), and Compute/Calcul Canada. We thank an anonymous reviewer for constructive comments, as well as suggestions for additional calculations on partial isotopic substitution, that improved the quality of the manuscript.

References (135)

  • D.W. Davis

    J. Mol. Struct.

    (1985)
  • C.L. Perrin

    Secondary equilibrium isotope effects on acidity

  • S. Rayne et al.

    J. Mol. Struct. (THEOCHEM)

    (2010)
  • G.B. Ellison et al.

    Int. J. Mass Spectrom. Ion Processes

    (1996)
  • M.J. Haas et al.

    Int. J. Mass Spectrom. Ion Processes

    (1993)
  • R.E. Carter et al.

    Adv. Phys. Org. Chem.

    (1973)
  • V.B. Luzhkov

    Chem. Phys.

    (2005)
  • N.B. Mansour et al.

    Nucl. Instrum. Methods Phys. Res. B

    (1988)
  • J.F. Gal et al.

    Int. J. Mass Spectrom. Ion Processes

    (1989)
  • R.A. Seburg et al.

    Int. J. Mass Spectrom. Ion Processes

    (1997)
  • R.F. Gunion et al.

    Int. J. Mass Spectrom. Ion Processes

    (1992)
  • F.A. Carey et al.

    Advanced Organic Chemistry, Part A: Structure and Mechanisms

    (2007)
  • F.G. Bordwell et al.

    J. Am. Chem. Soc.

    (1975)
  • P. Kebarle

    Ann. Rev. Phys. Chem.

    (1977)
  • F.G. Bordwell et al.

    J. Org. Chem.

    (1978)
  • J.E. Bartmess et al.

    J. Am. Chem. Soc.

    (1979)
  • J.E. Bartmess et al.

    J. Am. Chem. Soc.

    (1979)
  • P. Burk et al.

    Theor. Chim. Acta

    (1993)
  • J.E. Bartmess et al.

    Can. J. Chem.

    (2005)
  • T.T. Dang et al.

    Int. J. Mass Spectrom. Ion Processes

    (1993)
  • S.G. Lias, J.E. Bartmess, J.F. Liebman, J.L. Holmes, R.D. Levin, W.G. Mallard, Ion energetics data, in: P.J. Linstrom,...
  • A. Streitwieser et al.

    J. Am. Chem. Soc.

    (1963)
  • D. Northcott et al.

    J. Phys. Chem.

    (1969)
  • S.L.R. Ellison et al.

    J. Chem. Soc., Chem. Comm.

    (1983)
  • T. Pehk et al.

    J. Chem. Soc., Perkin Trans.

    (1997)
  • B.E. Lewis et al.

    J. Am. Chem. Soc.

    (2003)
  • C.L. Perrin et al.

    J. Am. Chem. Soc.

    (2003)
  • C.L. Perrin et al.

    J. Am. Chem. Soc.

    (2005)
  • C.L. Perrin et al.

    J. Am. Chem. Soc.

    (2007)
  • C.L. Perrin et al.

    J. Am. Chem. Soc.

    (2008)
  • L.A. Curtiss et al.

    J. Chem. Phys.

    (2007)
  • J.M.L. Martin et al.

    J. Chem. Phys.

    (1999)
  • S. Parthiban et al.

    J. Chem. Phys.

    (2001)
  • M.J. Frisch et al.

    Gaussian 09, Revision A.1

    (2009)
  • J.J.P. Stewart

    J. Mol. Model.

    (2007)
  • V. van Speybroeck et al.

    Chem. Soc. Rev.

    (2010)
  • R.C. Shiell et al.

    Faraday Discuss.

    (2000)
  • S.T. Pratt et al.

    Phys. Rev. Lett.

    (1992)
  • L.V. Gurvich et al.
  • K.R. Lykke et al.

    Phys. Rev. A

    (1991)
  • P.A. Schulz et al.

    J. Chem. Phys.

    (1982)
  • J.M. Oakes et al.

    J. Chem. Phys.

    (1985)
  • T.M. Ramond et al.

    J. Chem. Phys.

    (2000)
  • N.L. Allinger et al.

    J. Comp. Chem.

    (1983)
  • L.S. Bartell et al.

    J. Chem. Phys.

    (1965)
  • S. Gabbay et al.

    J. Chem. Soc. Faraday Trans. 2

    (1982)
  • B.D. Allen et al.

    J. Am. Chem. Soc.

    (2005)
  • D.J. O’Leary et al.

    J. Org. Chem.

    (2010)
  • G. Haeffler et al.

    Phys. Rev. A

    (1996)
  • M. Scheer et al.

    Phys. Rev. Lett.

    (1998)
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