Fluorine substitution effects on flexibility and tunneling pathways: the rotational spectrum of 2-fluorobenzylamine.

doi:10.1002/cphc.201300121

Paper

Fluorine substitution effects on flexibility and tunneling pathways: the rotational spectrum of 2-fluorobenzylamine.

Published Jun 24, 2013 · C. Calabrese, A. Maris, L. Evangelisti

Chemphyschem : a European journal of chemical physics and physical chemistry

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Abstract

The effect of ring fluorination on the structural and dynamical properties of the flexible model molecule 2-fluorobenzylamine has been studied by rotational spectroscopy in free-jet expansion and quantum chemical methods. The complete potential energy surface originating from the flexibility of the aminic side chain has been calculated at the B3LYP/6-311++G** level of theory and the stable geometries were also characterized with MP2/6-311++G**. The rotational spectra show the presence of two of the predicted four stable conformers: the global minimum (I), in which the side chain's dihedral angle with the phenyl plane is almost perpendicular, is stabilized by an intramolecular hydrogen bond between the fluorine atom and one hydrogen of the aminic group; and a second conformer II (EII -EI ≈5 kJ mol(-1)) in which the dihedral angle is smaller and the amino group points towards the aromatic ortho hydrogen atom. This conformation is characterized by a tunneling motion between two equivalent positions of the amino group with respect to the phenyl plane, which splits the rotational transition. The ortho fluorination increases, with respect to benzylamine, the tunneling splitting of this motion by four orders of magnitude. The motion is analyzed with a one-dimensional flexible model, which allows estimation of the energy barrier for the transition state as approximately 8.0 kJ mol(-1).

Study Snapshot

2-fluorobenzylamine shows flexibility and tunneling pathways, with ortho fluorination increasing tunneling splitting by four orders of magnitude compared to benzylamine.

PopulationOlder adults (50-71 years)

Sample size24

MethodsObservational

OutcomesBody Mass Index projections

ResultsSocial networks mitigate obesity in older groups.

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Fluorine substitution effects on flexibility and tunneling pathways: the rotational spectrum of 2-fluorobenzylamine.

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References

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Fluorous chemistry has revolutionized biomolecular applications, including catalysis, separation science, supramolecular chemistry, and analytical chemistry.

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Five conformers of 1,3-butandiol show internal hydrogen bond stabilization and a GG' or G'G arrangement of hydroxyl oxygens, indicating chiral diols with two oxygen atoms on the same side.

"Union is strength": how weak hydrogen bonds become stronger.

Weak hydrogen bonds can stabilize small dimers and oligomers, playing a crucial role in chiral recognition and driving conformational landscapes of important biomolecules.

Citations

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