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Si(mply) rips it apart: C-F activation of fluorobenzene has been achieved using the extremely strong silyl Lewis acids [Et3Si(X)]+ (X=PhF or Et3SiH) and [(2,6-dixylyl-C6H 3)SiMe2] + paired with the anion CHB 11Cl11-. They abstract fluoride from unactivated fluorobenzene to give arylated products, consistent with phenyl-cation-like reactivity (see scheme). © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.

Si(mply) rips it apart: C-F activation of fluorobenzene has been achieved using the extremely strong silyl Lewis acids [Et3Si(X)]+ (X=PhF or Et3SiH) and [(2,6-dixylyl-C6H 3)SiMe2] + paired with the anion CHB 11Cl11-. They abstract fluoride from unactivated fluorobenzene to give arylated products, consistent with phenyl-cation-like reactivity (see scheme). © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.

The potential energy surfaces of the van der Waals complexes benzene–Ar and p-difluorobenzene–Ar have been investigated at the second-order Møller–Plesset (MP2) level of theory with the aug-cc-pVDZ basis set. Calculations were performed with unconstrained geometry optimization for all stationary points. This study has been performed to elucidate the nature of a conflict between experimental results from dispersed fluorescence and velocity map imaging (VMI). The inconsistency is that spectra for levels of p-difluorobenzene–Ar and –Kr below the dissociation thresholds determined by VMI show bands where free p-difluorobenzene emits, suggesting that dissociation is occurring. We proposed that the bands observed in the dispersed fluorescence spectra are due to emission from states in which the rare gas atom orbits the aromatic chromophore; these states are populated by intramolecular vibrational redistribution from the initially excited level [S. M. Bellm, R. J. Moulds, and W. D. Lawrance, J. Chem. Phys. 115, 10709 (2001)]. To test this proposition, stationary points have been located on both the benzene–Ar and p-difluorobenzene–Ar potential energy surfaces (PESs) to determine the barriers to this orbiting motion. Comparison with previous single point CCSD(T) calculations of the benzene–Ar PES has been used to determine the amount by which the barriers are overestimated at the MP2 level.As there is little difference in the comparable regions of the benzene–Ar and p-difluorobenzene–Ar PESs, the overestimation is expected to be similar for p-difluorobenzene–Ar. Allowing for this overestimation gives the barrier to movement of the Ar atom around the pDFB ring via the valley between the H atoms as ⩽204 cm−1 in S0 (including zero point energy). From the estimated change upon electronic excitation, the corresponding barrier in S1 is estimated to be ⩽225 cm−1. This barrier is less than the 240 cm−1 energy of30 2, the vibrational level for which the anomalous “free p-difluoroben

Potential energy hypersurfaces (PESs) for four fluoroform complexes (with acetonitrile, ethyleneoxide, formaldehyde, and water) were explored at the HF, MP2, and B3LYP/6-311 ++G(d,p) levels of theory. Anharmonic C-H stretching vibrational frequency shifts are reported for all minima located on the studied PESs. In all cases, the lowest-energy minimum occurs for a C-H...O(N) hydrogen-bonded arrangement and is characterized by a significant C-H frequency blueshift (upshift), while additional minima [for reversed'' orientations, in which there is no direct C-H...O(N) contact] show only small C-H frequency upshifts. The large blueshifts found for the hydrogen-bonded arrangements are predominantly caused by the electronic exchange interaction, as revealed by Kitaura-Morokuma (KM) analysis, while the purely electrostatic + polarization interaction leads to C-H frequency redshifts, which was proven both by the KM analysis and the charge field perturbational (CFP) approach. The large net blueshifting effect of the exchange contribution is only possible thanks to the smallness of the redshifting electrostatic + polarization contribution, which, in turn, is a consequence of the fact that dmu((0))/dr(CH) is negative for the fluoroform molecule. In all cases the charge transfer as well as the dispersion energy contributions lead to frequency redshifts. The small C-H blueshifts for the reversed orientations are almost completely governed by the electrostatic interaction, as shown by the KM and CFP analyses. All these characteristics of blueshifting H bonds are in line with a previously outlined general model concerning standard'' and blueshifting'' H-bonding interactions, QC 20100525

In this paper we put forward the idea that the various improper, blue-shifting hydrogen bond systems discussed in the literature are all of essentially the same nature and occur because of three necessary circumstances: (i) the presence of a negative dipole moment derivative, dmu(0)/dr(XH), for the isolated H-bond donor molecule; (ii) the interaction between such a molecule and any electron density concentration on the H-bond acceptor ( pi-system density, lone-pair density, ionic charge,...) which at large intermolecular distances gives rise to a field-dominated, modest vibrational blue shift; (iii) an additional blue shift due to electronic exchange overlap. The negative dipole moment derivative is a necessary but not sufficient condition for the formation of a blue-shifted H-bond: thus, the blue-shifting CH4, F3CH, and Cl3CH molecules and their relatives can also give rise to normal, red-shifted H-bonds. This is a logical extension of the blue-shifting property and occurs when the electric field from the acceptor is sufficiently strong at the intermolecular equilibrium distance (e.g., for F- and Cl- acceptors)., QC 20100525

Mass spectra obtained by colliding singly-charged benzene, benzene, benzene-d and fluorobenzene and singly- and doubly-charged buckminsterfullerene with self-assembled monolayer films are reported These surfaces were prepared by the spontaneous assembly of C2 C3, C4, C10, and C18, n-hydrocarbon thiols, perdeuteroeicosanethiol and 2-(perfluorooctyl)-ethanethiol on both gold foil and vapor-deposited gold are reported and discussed. The fluorinated surface provides the highest internal energy deposition; more extensive fragmentation of doubly-charged buckminsterfullerene could be observed on the other surfaces. Chemical reactions, such as H and CH3 additions, as well as the analogue F and CF3 additions, between benzene and fluorobenzene molecular ions and-the monolayer films have been proved. These processes, ab initio 6-31G //6-31G SCF total energies and experimental heats of formation were used for the characterization of the surface-projectile interactions., Prepared for publication in the Journal of Physical Chemistry.

In the course of studying new superacid system in nitration we evaluated the nitric-tetratriflatoboric acid system HNO3-HB(O3SCF3)4 for its nitrating ability of aromatics. Tetratriflatoboric acid, HB(O3SCF3)4 was conveniently prepared in situ from triflic acid (excess) and boron trichloride and could be used without any workup. Nitration of benzene, toluene, fluorobenzene, chlorobenzene, anisole and naphthalene was studied with HNO3-HB(O3SCF3)4 in methylene chloride solution at -30 deg C and at room temperature. the new superacidic nitration of toluene gave very low (1%) meta nitration both at - 30 deg C and at room temperature. At the same time the ortholpara isomer ratio is also lower than in most studied nitronium ion nitrations, indicating ion pairing or association with bulky tetratriflatoborate anion. Similarly high regio(positional) selectivity was found in nitration of the other aromatics.

He(I) ultraviolet photoelectron (UV-PES) spectra are reported for several bis(arene)chromium compounds. The arenes concerned are m-trifluoro-methylbenzotrifluoride, p-fluorobenzetrifluoride, p-difluorobenzene, m-dichlorobenzene, fluorobenzene, chlorobenzene, methylbenzoate, p-chlorotoluene, diphenyl ether, toluene, o-xylene, trimethylsilylbenzene, isobutylbenzene, 1,2,3-trimethylbenzene, 1,3,5-trimethylbenzene, and 1,2,4,5-tetremethylbenzene. The spectra have been interpreted using a qualitative perturbation molecular orbital model. The two major findings of the work are: (1) the ionizations from the metal-localized a sub 1g and e sub 2g molecular orbitals are governed primarily by ligand electronegativity, but there is some evidence for the operation of conjugative effects, and (2) the ionization energies of the free and coordinated arenes are quite similar. (Author)

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