title: NH+-F hydrogen bonding in a fluorinated "proton sponge" derivative: integration of solution, solid-state, gas-phase, and computational studies.
abstract: We report detailed studies on the characterization of an intramolecular NH-F hydrogen bond formed within a fluorinated "proton sponge" derivative. An ammonium ion, generated from 8-fluoro-N,N-dimethylnaphthalen-1-amine, serves as a charged hydrogen bond donor to a covalently bound fluorine appropriately positioned on the naphthalene skeleton. Potentiometric titrations of various N,N-dimethylnaphthalen-1-amines demonstrate a significant increase in basicity when hydrogen bonding is possible. X-ray crystallography reveals that NH-F hydrogen bonding in protonated 8-fluoro-N,N-dimethylnaphthalen-1-amine is heavily influenced by ion pairing in the solid state; bifurcated and trifurcated hydrogen bonds are formed depending on the counterion utilized. Compelling evidence of hydrogen bonding in the 8-fluoro-N,N-dimethylnaphthyl-1-ammonium cation is provided by gas-phase cryogenic vibrational photodissociation spectroscopy. Solution-phase infrared spectroscopy provides complementary results, and the frequencies of the N-H stretching mode in both phases are in excellent agreement with the computed vibrational spectra. NMR analysis of protonated 8-fluoro-N,N-dimethylnaphthalen-1-amine demonstrates significant H-F coupling between the N-H hydrogen and fluorine that cannot be attributed to long-range, through-bond interactions; the couplings correlate favorably with calculated values. The results obtained from these experiments are congruent with the formation of an NH-F hydrogen bond upon protonation of 8-fluoro-N,N-dimethylnaphthalen-1-amine.
authors: Department of Chemistry, New Chemistry Building, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States.
authors: Michael T
authors: MT
authors: Scerba
authors: Christopher M
authors: CM
authors: Leavitt
authors: Matthew E
authors: ME
authors: Diener
authors: Andrew F
authors: AF
authors: DeBlase
authors: Timothy L
authors: TL
authors: Guasco
authors: Maxime A
authors: MA
authors: Siegler
authors: Nathaniel
authors: N
authors: Bair
authors: Mark A
authors: MA
authors: Johnson
authors: Thomas
authors: T
authors: Lectka
mesh_terms: D018360:Crystallography, X-Ray; D005461:Fluorine / Q000737:chemistry*; D005740:Gases / Q000737:chemistry*; D054879:Halogenation; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D011522:Protons; D011789:Quantum Theory; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012996:Solutions
chemical_list: D005740:Gases; D011522:Protons; D000644:Quaternary Ammonium Compounds; D012996:Solutions; D005461:Fluorine