Characterization of a Closed-Shell Fluorine−Fluorine Bonding Interaction in Aromatic Compounds on the Basis of the Electron Density (original) (raw)
Related papers
The nature, strength and directionality of C-FÁÁÁF interactions were theoretically evaluated on all symmetry unique dimers present in the CF 4 , C 2 F 4 and C 6 F 6 crystals and on CF 4 , CHF 3 , CH 2 F 2 and CH 3 F model dimers placed in two different geometries. On each dimer, the interaction energy was computed at the MP2/aug-cc-pVDZ level, and also an Atoms in Molecule analysis of the dimer electron density was done to find all intermolecular bonds. The characterization was completed by computing the energy components of the dimer interaction energy, using the SAPT method. The results show that in most dimers found in the CF 4 , C 2 F 4 and C 6 F 6 crystals, there are more than one C-FÁÁÁF intermolecular bond and sometimes even a C-FÁÁÁp intermolecular bond. By selecting dimers presenting one C-FÁÁÁF bond, the following strength can be estimated for a single C-FÁÁÁF bond: -0.21 kcal/mol in C(sp 3 ) atoms, -0.25 kcal/mol in C(non-aromatic sp 2 ), -0.41 kcal/mol in C(aromatic sp 2 ). The interaction energy of the dimer grows almost linearly with the number of C-FÁÁÁF bonds present. The relative orientation of the C-FÁÁÁF bond affects the bond strength. The SAPT calculations indicate that in collinear dimers, C-FÁÁÁF interactions are strongly dominated by the dispersion energetic component, while when in non-collinear conformations the electrostatic component can be as important as the dispersion one.
Extended Halogen Bonding between Fully Fluorinated Aromatic Molecules
ACS nano, 2015
Halogen bonding is a noncovalent interaction where an electrophilic cap on a halogen atom, the so-called σ-hole, attracts a nucleophilic site on an adjacent molecule. The polarizability of halogens relates to the strength of the σ-hole, and accordingly the halogen-halogen distance becomes shorter in the order of Cl, Br, and I. Fully fluoro-substituted aromatic molecules, on the contrary, are generally believed not to form halogen bonds due to the absence of a σ-hole. Here, we study atomic-scale in-plane F-F contacts with high-resolution force microscopy. Our ab initio calculations show that the attractive dispersion forces can overcome the electrostatic repulsion between the fluorine atoms, while the anisotropic distribution of the negative electrostatic potential leads the directional bond and even changes the gap. The coexistence of these two competing forces results in the formation of a "windmill" structure, containing three C-F···F bonds among neighboring molecules. W...
Ab initio and DFT studies of hydrogen bond interactions in difluoroacetic acid dimer
Structural Chemistry, 2010
Density functional theory (DFT) and ab initio calculations were performed for difluoroacetic acid (DFA). Eight theoretically possible conformers were considered and by using conformational analysis only three stable conformers were found. The hydrogen bonding interaction of DFA complex has been investigated using DFT and ab initio methods for cis conformers. Stabilization energies of dimers including basis set superposition error and ZPE were found in the range 8.89-13.08 kcal mol-1. It was found that EFC dimer is slightly more stable. Red shift of O-H bond in the range-226.3 to 505.7 cm-1 predicted for dimers. The natural bond orbital analysis was applied to characterize nature of the interaction. Keywords Difluoroacetic acid Á Hydrogen bonding Á Conformational analysis Á Density functional theory (DFT) Á Hartree-Fock (HF) Á Natural bond orbital (NBO)
Journal of Molecular Structure, 2012
Conformations, molecular structure, keto-enol content, and intramolecular hydrogen bonding of 1,1, 1-trifluoro-5,5-dimethyl-2,4-hexanedione (also named as (Z)-6,6,6-trifluoro-5-hydroxy-2,2-dimethylhex-4-en-3-one), known as pivaloyltrifluoroacetone, have been investigated by means of the density functional theory calculations and experimental NMR, IR and Raman spectroscopies. The geometries and the electronic energies of different cis-enol conformers of this molecule have been obtained at BLYP, B3LYP, BPW91, B3PW91, G96LYP, G96PW91 and also MP2 levels of theory, using various basis sets. The results of conformational stabilities, molecular structures, NBO atomic charges, estimated energies of intramolecular hydrogen bonding, barrier height for proton transfer, and some spectroscopic properties related to the intramolecular hydrogen bonding for stable chelated enol forms of the target molecule have been compared with each other and also with those of some similar compounds. This is suggested by the theoretical studies that this b-diketone is completely in the enol form, in the best agreement with the experimental analyses done. Also, the theoretical calculations besides the 1 H NMR and vibrational spectroscopic results indicate that the intramolecular hydrogen bond strength of this molecule is considerably weaker than that of 5,5-dimethyl-2,4-hexanedione, but stronger than that of 1,1,1-trifluoro-2,4-pentanedione.
The Journal of Physical Chemistry A, 1999
Highly correlated ab initio calculations with large basis sets are reported for formyl fluoride, OCHF; difluorocarbene, CF 2 ; monofluoromethylene, CHF, and difluoromethane, CH 2 F 2. Based on CCSD(T)/cc-pVQZ results (including a correction for the effect of diffuse functions on fluorine and oxygen), equilibrium structures are derived. These structures are compared to experimental results, when available, and to those of similar molecules; and their accuracy is discussed.
The Journal of Physical Chemistry A, 2011
The conformational manifolds, scenarios of protonation, and hydrogen bond propensity of methyl formate and its mono and difluoro derivatives, which possess two oxygen atoms with different basicities, are studied at the B3LYP/6-311++G(3df,3pd) computational level. The optimized geometries of the title molecules, their energetics, and relevant harmonic vibrational frequencies, mainly of the ν(CH) mode of the HÀCdO group, are of a primary focus. The Natural Bond Orbital analysis is invoked to obtain the second-order intra-or intermolecular hyperconjugation energies, occupations of antibonding orbitals, and hybridization of the carbon atoms. It is demonstrated that the Z conformers (and their rotamers) of the three title molecules are characterized by a higher stability compared to the E ones. The stabilities depend on the intramolecular hyperconjugative interaction and on the attraction or repulsion nonbonded interaction. The proton affinity of the carbonyl oxygen exceeds, by 15À20 kcal 3 mol À1 , that of the methoxy oxygen. Fluorine substitution causes a moderate lowering of the proton affinity of the oxygens. Protonation on the oxygen atoms yields a contraction of the CÀH bond and large concomitant blue shift of the ν(CH) vibration. These changes are mainly determined by a lowering of the occupation of the corresponding σ*(CH) orbitals. The esters under consideration are probed on the interaction with the HF molecule. The complexes that are formed under this interaction on the oxygen of the HÀCdO group are stronger than those formed on the oxygen belonging to the methoxy one. It is deduced that the hydrogen bond energies show a linear dependence on the proton affinities of the corresponding oxygen atoms. Hydrogen-bonded complexes of moderate strength are also formed, while HF interacts with the fluorine atoms of the fluorinated esters.
Physical Chemistry Chemical Physics, 2013
The rotational spectra for the normal isotopic species and for six 13 C singly substituted isotopologues (in natural abundance) of the fluorobenzeneÁ Á Áacetylene (C 6 H 5 FÁ Á ÁHCCH) weakly bound dimer have been measured in the 6.5-18.5 GHz region using chirped-pulse Fourier-transform microwave spectroscopy. The HCCH molecule interacts with the fluorobenzene via a CHÁ Á Áp contact and is determined to lie almost over the center of, and approximately perpendicular to, the aromatic ring, with an HÁ Á Áp distance (perpendicular distance from the H atom to the ring plane) of around 2.492(47) Å; a slight tilt of HCCH towards the para carbon atom of the fluorobenzene is evident. Binding energies of this complex and related benzene and fluorobenzene dimers obtained from the pseudodiatomic approximation are compared and indicate that fluorobenzeneÁ Á Áacetylene lies among the more weakly bound of the complexes exhibiting some type of CHÁ Á Áp interaction.
Magnetic Resonance in Chemistry, 2012
Flavonoids are useful compounds in medicinal chemistry and exhibit conformational isomerism, which is ruled by intramolecular interactions. One of the main intramolecular forces governing the stability of conformations is the hydrogen bond. Hydrogen bond involving fluorine covalently bonded to carbon has been found to be rare, but it appears in 2 0 -fluoroflavonol, although the FÁÁÁHO hydrogen bond cannot be considered the main effect governing the conformational stability of this compound. Because 19 F is magnetically active and suitable for NMR studies, the 1h J F,H(O) coupling constant can be used as a probe for such an interaction in 2 0 -fluoroflavonol. In fact, the 1h J F,H(O) coupling was computationally analyzed in this work, and the FÁÁÁHO hydrogen bond was found to be its main transmission mechanism, which modulates this coupling in 2 0 -fluoroflavonol, rather than overlap of proximate electronic clouds, such as in 2-fluorophenol.