1. 4-difluorobenzene structure

In this paper we present the relative energies of the isomers of the phenylenediamines, dihydroxybenzenes and difluorobenzenes from ab initio calculations using large basis sets and including correlation corrections at the MP-2 level. These calculations were done at the geometry optimized structures. We also include zero-point energy corrections based on our calculated force fields. 

Electrophilic substitution in benzo[fe]thieno- and benzo[fe]furo-[2,3-c]pyridines (2) occurs mainly at the 6-position, although when this position is blocked by Cl in a related structure 5-,7-, and 8-substituted products are formed. The usefulness of triflu-oromethanesulfonic acid as a new solvent with CFCI3 for the reaction of fluorine with aromatics has been explored. Fluorobenzene gives 1,4-difluorobenzene (31%) and 1,2-difluorobenzene (7%) instead of the addition products mainly observed when the acid is absent 1,2- and 1,3- but not 1,4-difluorobenzene undergo further substitution at appropriate acidity. 

In keeping with the simplicity of its structure, fluconazole can be synthesized in two steps from commercially available starting materials (Scheme 5.3). Metallation of 1-bromo-2,4-difluorobenzene with butyllithium in ether gave the corresponding aryllithium. 

Difluorobenzenes are isomerized under gas-phase conditions in the presence of metallosilicates, containing the structure of pentasil zeolites with isomorphic substitution of some silicon atoms by aluminum, gallium, or iron.4 A German patent describes the isomerization of l-bromo-2,4-difluorobenzene to l-bromo-3,5-difluorobenzene in pentasil-type zeolites in an autoclave at 320 C and 25 x 105 Pa for 1 h, giving 29% conversion and 73% selectivity.5... 

In closing this section, we note that although the Koopmans picture is a simplification of the ionization dynamics, it provides a very useful zeroth order picture from which to consider the TRPES results. Any potential failure of this independent electron picture can always be experimentally tested directly through variation of the photoionization laser frequency resonance structures should lead to variations in the form of the spectra with electron kinetic energy, although the effect of resonances is more likely to be prominent in PAD measurements, and indeed an observation of a shape resonance in p-difluorobenzene has been reported [153, 154]. 

Write the structural formulas for the following compounds (a) p-difluorobenzene (b) ethylbenzene ... 

Figure 7. The optimal structures (MP2/aug-cc-pVDZ) of the 7i-(H20)m clusters (D p-difluorobenzene, F fluorobenzene, B benzene, T toluene, W H2O). Note the ct to 7t transition observed in the water trimer complexes of fluorobenzene and p-difluorobenzene.

In addition to the structure of supramolecular objects, the dynamics of the building blocks themselves or molecules trapped in cages and channels is of great importance [166, 202]. For instance, the guest dynamics of dimeric capsules of tetratolyl urea calixarene filled with different aromatic guests such as benzene, fluorobenzene, and 1,4-difluorobenzene was studied. Upon inclusion, all guest moieties exhibit... 

Draw molecular structures of each of the isomers of difluorobenzene and identify all axes and mirror planes of symmetry for each case. 

Figure 6.14 (a) The structure of 1,4-difluorobenzene and (b) a suitable basis for the analysis of the C—H stretching modes of this molecule the Z-axis is perpendicular to the plane of the molecule pointing out of the page. 

This sort of analysis provides a powerful use of spectroscopy to aid in the identification of molecular structure through the application of symmetry. If we had made a sample of difluorobenzene and believed it to be a pure isomer of either the 1,4- or 1,2-form, vibrational spectroscopy would provide one way to distinguish which isomer we had made. 

Figure 3 In para-difluorobenzene, the vibrational structure of the cation was not fully resolved until the Introduction of ZEKE spectroscopy.

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