Fluorine Protons

Fluorine Protons: Insights from Recent Research

Fluorine Protonation in Nitrogen Fluoride

The study of fluorine protonation in nitrogen fluoride reveals the existence of two distinct isomers: F3NH+ and F2N-FH+. High-level GAUSSIAN-1 ab initio MO studies and mass-spectrometric techniques show that the fluorine-protonated isomer F2N-FH+ is more stable by 6.4 kcal mol-1 compared to its nitrogen-protonated counterpart F3NH+. This highlights the preference for fluorine over nitrogen in the protonation process of nitrogen fluoride in the gas phase.

Proton Affinities and Ionization Energies in Fluorobenzenes

Fluorine's role as both an electron-withdrawing and pi-electron donating group significantly affects the proton affinities and ionization energies of fluorobenzenes. High-resolution photoelectron spectroscopy and an additivity model describe these effects, showing linear correlations between ionization energies and proton affinities. The presence of fluorine atoms in different positions (ipso, ortho, meta, or para) relative to the site of ionization or protonation creates distinct correlation lines, influenced by the ability of hydrogens at the protonation site to act as pi-electron acceptors.

NMR Spectra of Fluorine-Containing Compounds

HBF2

Proton and fluorine NMR spectra of HBF2 reveal temperature-independent spin-coupling constants JHF, J11B-H, and J11B-F. The chemical shifts indicate significant downfield movement for both proton and fluorine resonances compared to similar compounds, reflecting the influence of boron's orbital hybridization on coupling constants.

Benzoyl Fluoride Derivatives

High-resolution proton and fluorine magnetic resonance spectra of various benzoyl fluoride derivatives show that spin-spin coupling constants between sidechain fluorine-19 and ring protons are sensitive to substituent perturbations. These couplings provide insights into conformational preferences and the nonplanarity of certain compounds, such as the 2-fluoro-6-chloro derivative.

Hypofluorous Acid (HOF)

NMR studies of hypofluorous acid (HOF) indicate that the hydrogen and fluorine atoms carry charges of approximately +0.5e and -0.5e, respectively. This charge distribution is consistent across both liquid and gas phases, as evidenced by the measured chemical shifts.

Proton Conductive Channels and Fluorination

Molecular dynamics simulations of hydrated protons in fluorinated carbon nanotubes reveal that fluorination leads to an ordered hydrogen bonding structure near the channel surface. This fluorination also lowers the free energy barrier for hydronium movement, promoting unidirectional proton transfer along the channel. The confinement within the nanotube weakens bifurcated hydrogen bonds, affecting the overall hydrogen bonding network.

Selective Protonation and Carbon-Fluorine Bond Activation

Selective protonation at a C-F bond in the presence of an iridium-methyl bond results in diastereoselective activation of the C-F bond and formation of a new C-C bond. This process occurs with complete selectivity, without protonation at the Ir-CH3 group, offering a novel pathway to create carbon stereocenters bearing fluorine atoms.

NH+-F Hydrogen Bonding in Proton Sponges

Detailed studies on a fluorinated "proton sponge" derivative show the formation of an intramolecular NH-F hydrogen bond. This bond significantly increases the basicity of the compound and is influenced by ion pairing in the solid state. NMR analysis demonstrates significant H-F coupling, supporting the presence of an NH-F hydrogen bond upon protonation.

Unimolecular Hydrogen Fluoride Loss from Protonated Fluorobenzene

The loss of hydrogen fluoride from protonated fluorobenzene involves three distinct pathways, as revealed by chemical ionization mass spectrometry and ab initio MO calculations. These pathways include direct HF loss from the fluorine-protonated molecule and 1,1- and 1,2-elimination processes from ring-protonated isomers.

Fluorine NMR in Protein Studies

Fluorine NMR is a powerful tool for studying protein structure and dynamics, offering high sensitivity to subtle structural changes. This technique is particularly useful in multicomponent systems and can provide unique insights into enzyme mechanisms, protein-ligand interactions, and structural alterations due to mutations. Fluorine labeling allows for detailed NMR studies even in complex biological systems, such as intact cells and whole organisms.

Conclusion

The research on fluorine protons spans various fields, from gas-phase protonation and NMR spectroscopy to molecular dynamics simulations and protein studies. These studies collectively enhance our understanding of fluorine's unique chemical behavior and its interactions in different molecular environments.

Summary

Not a yes or no question