Fluorobenzene-methanol

The nucleophilic substitution reaction in clusters has been observed by Brutschy and coworkers (Awdiew et al. 1990 Brutschy 1989, 1990 Brutschy et al. 1988, 1991, 1992) for the fluorobenzene-methanol system. 

Figure 4-19. Resonance-enhanced two-photon ionization spectra of ions issued from fluorobenzene/methanol d4/helium clusters, measured by scanning the laser near the 00 transition of fluorobenzene [0]. Bands [4-6] are due to the FB+(CD3OD)2 precursor which totally fragments, either by evaporation of one methanol-d4 molecule or reaction leading to anisole + DF + CD3OD. Bands [7-9] are due to the 1-3 precursor also losing one CD3OD molecule or reacting. Bands [1-3] are more likely attributed to the 1-1 complex (isomer( ) [1], hot band [2], 0q [3]) (from Brutschy et al. 1991).

From these data it can be pointed out that for a given size of the clusters the proton affinity of water is smaller than for the other solvents consequently, for fluorobenzene/methanol or para-difluorobenzene/water systems, a proton affinity of 205/215 kcal mol-1 seems to be the limit of the reaction process (it is reached for two molecules of methanol and three molecules of water). 

The case of a very weakly re-hydrogen bonded fluorobenzene-methanol complex. A gradient-corrected density functional and MP2 study of the ground electronic state potential energy surface118... 

There are ionic reactions where site seleaive chemistry has been studied by this technique using a one colour resonant two photon ionization [3]. For example in the fluorobenzene methanol (( ) complex the first photon selects one isomer in the Sq S transition. The second photon ionizes the complex, and depending which isomer is selected the ionic complex or the anisole ion is observed. 

Streitweiser et al.597 have also measured second-order rate coefficients for hydrogen exchange of fluorobenzenes with sodium methoxide in methanol, Table 182. Nucleophilic displacement of fluoride ion by methoxide ion accompanies... 

The lack of a substrate isotope effect suggests very extensive internal return and is readily explained in terms of the fact that conversion of the hydrocarbon to the anion would require very little structural reorganisation. Since koba = k 1k 2/(kLl+k 2) and k 2 is deduced as > k2, then kobs = Kk 2, the product of the equilibrium constant and the rate of diffusion away of a solvent molecule, neither of the steps having an appreciable isotope effect. If the diffusion rates are the same for reactions of each compound then the derived logarithms of partial rate factors (above) become pAT differences between benzene and fluorobenzene hydrogens in methanol. However, since the logarithms of the partial rate factors were similar to those obtained with lithium cyclohexylamide, a Bronsted cor-... 

The small effect on reaction rates of the addition of crown ethers to the lower alcohols was also observed in the reaction of potassium acetate with 1-bromobutane in ethanol (Hirao et al., 1978a,b). The displacement of fluorine in either o-nitro- or p-nitro-fluorobenzene by a methoxy group, by reaction with potassium methoxide in methanol was hardly influenced by the presence of dicyclohexyl-18-crown-6 (Del Cima et al., 1973). Mariani et al. (1978), too,... 

The time-of-flight mass spectrum recorded for an expansion of fluorobenzene (FB) with deuterated methanol presents mass peaks corresponding to deuterated anisole+—evidence of an intracluster nucleophilic substitution reaction. In the clusters, the two decay channels of FB(CD3OD) are ... 

Two years later, Marko et al. reported an improved catalytic system which only required 0.25 equivalent of potassium carbonate instead of 2 equivalents (89). The oxidation reaction described above is dramatically influenced by the nature of the solvent. Thus, if the reaction was performed in fluorobenzene, total conversion of undecan-2-ol to undecan-2-one could be reached with 0.25 equivalent K2CO3, whereas 2 equivalents of base were necessary in toluene to convert 90% of this secondary aliphatic alcohol (Table VI). These optimized conditions were applied to a variety of functionalized alcohols and the results are reported in Table VII. The catalyst tolerates both sulphur and nitrogen substituents on the substrate. Indeed, (thiophen-2-yl)methanol, N-protected (S)-valinol or (S)-prolinol could be oxidized to the corresponding aldehydes with very good yields. In addition, no racemization was detected for the two P-amino alcohols as well as for (2S,5i )-2-isopropyl-5-methylcyclohexanol. The hindered endo- and exo-borneol are both converted to camphor with similar reaction rates, despite their distinctly different steric properties. 

Fluorobenzene and p-difluorobenzene microsolvated by methanol An infrared spectroscopic and ab initio theoretical investigation ""... 

The titrimetric determination of amine and carboxyl groups is very sensitive to the presence of extraneous bases and adds. Since samples are usually fractionated or at least reprecipitated before measurement, often in an acid medium, the traces of acid not removed by wadiing are the most frequent source of errors. Garmon and Gibson have developed a method free of this kind of error They titrated the amine groups with 2,4-dinita)fluorobenzene, which is insensitive to strong bases carboxyl groups were esterified with labelled methanol ( C) and determined by the scintillation method. The results were pradically identical with those obtained by the most frequently used classical titrimetric method of Waltz and Taylor ... 

Calibration Internal standards Toluene-d8, fluorobenzene, 4-bromofluorobenzene, 1,2-dichloroethane-d4 Solvent for all standard solutions is methanol... 

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