skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Unconventional hydrogen bonding to organic ions in the gas phase: Stepwise association of hydrogen cyanide with the pyridine and pyrimidine radical cations and protonated pyridine

Abstract

Equilibrium thermochemical measurements using the ion mobility drift cell technique have been utilized to investigate the binding energies and entropy changes for the stepwise association of HCN molecules with the pyridine and pyrimidine radical cations forming the C{sub 5}H{sub 5}N{sup +·}(HCN){sub n} and C{sub 4}H{sub 4}N{sub 2}{sup +·}(HCN){sub n} clusters, respectively, with n = 1–4. For comparison, the binding of 1–4 HCN molecules to the protonated pyridine C{sub 5}H{sub 5}NH{sup +}(HCN){sub n} has also been investigated. The binding energies of HCN to the pyridine and pyrimidine radical cations are nearly equal (11.4 and 12.0 kcal/mol, respectively) but weaker than the HCN binding to the protonated pyridine (14.0 kcal/mol). The pyridine and pyrimidine radical cations form unconventional carbon-based ionic hydrogen bonds with HCN (CH{sup δ+}⋯NCH). Protonated pyridine forms a stronger ionic hydrogen bond with HCN (NH{sup +}⋯NCH) which can be extended to a linear chain with the clustering of additional HCN molecules (NH{sup +}⋯NCH··NCH⋯NCH) leading to a rapid decrease in the bond strength as the length of the chain increases. The lowest energy structures of the pyridine and pyrimidine radical cation clusters containing 3-4 HCN molecules show a strong tendency for the internal solvation of the radical cation by the HCNmore » molecules where bifurcated structures involving multiple hydrogen bonding sites with the ring hydrogen atoms are formed. The unconventional H-bonds (CH{sup δ+}⋯NCH) formed between the pyridine or the pyrimidine radical cations and HCN molecules (11–12 kcal/mol) are stronger than the similar (CH{sup δ+}⋯NCH) bonds formed between the benzene radical cation and HCN molecules (9 kcal/mol) indicating that the CH{sup δ+} centers in the pyridine and pyrimidine radical cations have more effective charges than in the benzene radical cation.« less

Authors:
; ; ;  [1]
  1. Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia)
Publication Date:
OSTI Identifier:
22419995
Resource Type:
Journal Article
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 141; Journal Issue: 5; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-9606
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; BENZENE; BINDING ENERGY; CATIONS; EFFECTIVE CHARGE; ENTROPY; HYDROCYANIC ACID; HYDROGEN CYANIDES; MOLECULES; PYRIDINE; PYRIMIDINES; RADICALS; SOLVATION

Citation Formats

Hamid, Ahmed M., El-Shall, M. Samy, E-mail: mselshal@vcu.edu, Hilal, Rifaat, Elroby, Shaaban, and Aziz, Saadullah G. Unconventional hydrogen bonding to organic ions in the gas phase: Stepwise association of hydrogen cyanide with the pyridine and pyrimidine radical cations and protonated pyridine. United States: N. p., 2014. Web. doi:10.1063/1.4890372.
Hamid, Ahmed M., El-Shall, M. Samy, E-mail: mselshal@vcu.edu, Hilal, Rifaat, Elroby, Shaaban, & Aziz, Saadullah G. Unconventional hydrogen bonding to organic ions in the gas phase: Stepwise association of hydrogen cyanide with the pyridine and pyrimidine radical cations and protonated pyridine. United States. https://doi.org/10.1063/1.4890372
Hamid, Ahmed M., El-Shall, M. Samy, E-mail: mselshal@vcu.edu, Hilal, Rifaat, Elroby, Shaaban, and Aziz, Saadullah G. 2014. "Unconventional hydrogen bonding to organic ions in the gas phase: Stepwise association of hydrogen cyanide with the pyridine and pyrimidine radical cations and protonated pyridine". United States. https://doi.org/10.1063/1.4890372.
@article{osti_22419995,
title = {Unconventional hydrogen bonding to organic ions in the gas phase: Stepwise association of hydrogen cyanide with the pyridine and pyrimidine radical cations and protonated pyridine},
author = {Hamid, Ahmed M. and El-Shall, M. Samy, E-mail: mselshal@vcu.edu and Hilal, Rifaat and Elroby, Shaaban and Aziz, Saadullah G.},
abstractNote = {Equilibrium thermochemical measurements using the ion mobility drift cell technique have been utilized to investigate the binding energies and entropy changes for the stepwise association of HCN molecules with the pyridine and pyrimidine radical cations forming the C{sub 5}H{sub 5}N{sup +·}(HCN){sub n} and C{sub 4}H{sub 4}N{sub 2}{sup +·}(HCN){sub n} clusters, respectively, with n = 1–4. For comparison, the binding of 1–4 HCN molecules to the protonated pyridine C{sub 5}H{sub 5}NH{sup +}(HCN){sub n} has also been investigated. The binding energies of HCN to the pyridine and pyrimidine radical cations are nearly equal (11.4 and 12.0 kcal/mol, respectively) but weaker than the HCN binding to the protonated pyridine (14.0 kcal/mol). The pyridine and pyrimidine radical cations form unconventional carbon-based ionic hydrogen bonds with HCN (CH{sup δ+}⋯NCH). Protonated pyridine forms a stronger ionic hydrogen bond with HCN (NH{sup +}⋯NCH) which can be extended to a linear chain with the clustering of additional HCN molecules (NH{sup +}⋯NCH··NCH⋯NCH) leading to a rapid decrease in the bond strength as the length of the chain increases. The lowest energy structures of the pyridine and pyrimidine radical cation clusters containing 3-4 HCN molecules show a strong tendency for the internal solvation of the radical cation by the HCN molecules where bifurcated structures involving multiple hydrogen bonding sites with the ring hydrogen atoms are formed. The unconventional H-bonds (CH{sup δ+}⋯NCH) formed between the pyridine or the pyrimidine radical cations and HCN molecules (11–12 kcal/mol) are stronger than the similar (CH{sup δ+}⋯NCH) bonds formed between the benzene radical cation and HCN molecules (9 kcal/mol) indicating that the CH{sup δ+} centers in the pyridine and pyrimidine radical cations have more effective charges than in the benzene radical cation.},
doi = {10.1063/1.4890372},
url = {https://www.osti.gov/biblio/22419995}, journal = {Journal of Chemical Physics},
issn = {0021-9606},
number = 5,
volume = 141,
place = {United States},
year = {Thu Aug 07 00:00:00 EDT 2014},
month = {Thu Aug 07 00:00:00 EDT 2014}
}