Theoretical Study On The Bonding Nature And Rule Of Organic Fluorine Hydrogen Bond Forming By Small Fluorine-containing Organic Compounds

Organic fluorine hydrogen bonds are major topics among the hydrogen bondresearches, which plays an important role in biological, atmospheric and crystalengineering (particularly drugs) fields. Numerous complexes containing the organicfluorine hydrogen bonds, in which some interesting puzzles on organic fluorinehydrogen bonds still attract much attention. There are two main hotspots in theresearch field about organic fluorine hydrogen bond. The first one is some study ofthe organic fluorine hydrogen bonding in the crystal engineering. The second one is abasic question as to whether organic fluorine can form a hydrogen bond. Thefragment of C-F can act as hydrogen bond acceptor in the formation of organicfluorine hydrogen bonds, in which fluoride ion is a very strong hydrogen bondacceptor. Nevertheless, there are some other objections about the organic fluorinewhich can act as a hydrogen bond acceptor. The capability of the C-F fragment as anacceptor has been widely studied. In Anzahaee’s report, C-F···H-C hydrogen bond hadbeen studied in aqueous solutions and provided experimental evidence abouthydrogen bond can be formed by organic fluorine. In2012, Robert E. Rosenbergconfirmed that organic fluorine hydrogen bond existed in the compound formed byfluoromethane with water in theory. Therefore, organic fluorine to form hydrogenbond has been comfirmed.For this kind of the organic fluorine hydrogen bonds, Gaussian09programs wereused to perform all the calculations in this thesis. The experimental results werereproduced with the MP2method, which was the most commonly used for thedescription of these complexes, especially when accurate binding energies arerequired. Therefore, in this paper the geometrical structures of the monomers and complexes were studied at the ab initio MP2/6-311++G**level. We also carried outB97D/6-311++G**level on all systems. The accuracy of B97D for describing theweak interactions has been well established. The main work and the conclusions areas follows:The existence of C–H···F–C hydrogen bonds in this thesis has beenexperimentally proven by Caminati and co-workers. This study presents a theoreticalinvestigation on these C–H···F–C hydrogen bonds at B97D/6-311++G**andMP2/6-311++G**levels, in terms of C–H vibrational frequency shifts, atoms inmolecules characteristics, and the bonding feature of C–H···F–C hydrogen bonds. It isfound that in three important aspects, there are significant differences in propertiesbetween C–H···F–C and conventional hydrogen bonds. The C–H···F–C hydrogenbonds show a blueshift in the C–H vibrational frequencies, instead of the X–H normalredshift in X–H···Y conventional hydrogen bonds. The natural bond orbital (NBO)analyses show thatσandptypes of lone pair orbitals of the F atom to an antibondingσ H–C orbital form a dual C–H···F–C hydrogen bond. Such a dual hydrogen bondingleads to the proton acceptor directionality of the C–H···F–C hydrogen bond softer.Our studies also show that the Laplacian of the electron density (▽2ρBCP) is notalways a good criterion for hydrogen bonds. Therefore, we should not recommend theuse of the Laplacian of the electron density as a criterion for C–H···F–C hydrogenbonds.