US EPA

1492924 

Journal Article 

NH+-F Hydrogen Bonding in a Fluorinated "Proton Sponge" Derivative: Integration of Solution, Solid-State, Gas-Phase, and Computational Studies 

Scerba, MT; Leavitt, CM; Diener, ME; Deblase, AF; Guasco, TL; Siegler, MA; Bair, N; Johnson, MA; Lectka, T 

2011 

Yes 

Journal of Organic Chemistry
ISSN: 0022-3263
EISSN: 1520-6904 

76 

19 

7975-7984 

English 

21888333 

10.1021/jo2015328 

WOS:000295302300034 

https://www.scopus.com/inward/record.uri?eid=2-s2.0-80054118874&doi=10.1021%2fjo2015328&partnerID=40&md5=7509d2b258bb7b135286d47c75142fa1
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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.