This project deals with hydrogen bonding between HCl and sp3 or sp2 oxygen acceptors such as acetone, methanol, and acetic acid. The key issue is the extent to which inert noble gas matrix environments strengthen these interactions. We have investigated these complexes with low temperature infrared spectroscopy and DFT calculations. Infrared frequency shifts for the H-X bond correspond hydrogen bond strength, and we tracked these as a function of methyl substitution as well as matrix host. Through an extensive validation study, M06, M06-2X, and M05-2X (with the aug-cc-pVTZ basis set) were found to be the optimal DFT methods that best reproduced high-level binding energies and experimental structure results for H2O-HCl. The M06 binding energies for H2O-HCl, Methanol-HCl, and DME-HCl are –5.5 kcal/mol, –6.3 kcal/mol, and –6.9 kcal/mol, respectively, illustrating that methyl substitution slightly increases hydrogen bond strength. Interestingly, we found two stable isomeric structures for the Acetic Acid-HCl complex, and the lowest energy form had the HCl hydrogen bonded to the sp3 oxygen. In addition, we compared predicted H-X frequency shifts in the systems to the published data for nitrogen and argon matrices. Neon matrix experiments are currently in progress and these results will also be discussed.

Medium effect on hydrogen bond strength in HCl–oxygen donor complexes: DFT calculations and matrix IR spectra

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