NH+鈥揊 Hydrogen Bonding in a Fluorinated 鈥淧roton Sponge鈥?Derivative: Integration of Solution, Solid-State, Gas-Phase, and Computational Studies
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- 作者：Michael T. Scerba ; Christopher M. Leavitt ; Matthew E. Diener ; Andrew F. DeBlase ; Timothy L. Guasco ; Maxime A. Siegler ; Nathaniel Bair ; Mark A. Johnson ; Thomas Lectka
- 刊名：Journal of Organic Chemistry
- 出版年：2011
- 出版时间：October 7, 2011
- 年：2011
- 卷：76
- 期：19
- 页码：7975-7984
- 全文大小：1151K
- 年卷期：v.76,no.19(October 7, 2011)
- ISSN：1520-6904
文摘
We report detailed studies on the characterization of an intramolecular NH鈥揊 hydrogen bond formed within a fluorinated 鈥減roton sponge鈥?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鈥揊 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鈥揌 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鈥揊 coupling between the N鈥揌 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鈥揊 hydrogen bond upon protonation of 8-fluoro-N,N-dimethylnaphthalen-1-amine.