Fluorinated derivatives calculations

Our calculations showed that the first step, cyclization of the nitrene to an azabicyclo[4.1.0]heptatriene, is rate-determining. Our calculated barriers for cyclization of four fluorinated derivatives of lb are given in Table 6.87 The CASPT2/cc-pVDZ barrier of 13.4 kcal/mol for cyclization of 2,6-difluoro-phenylnitrene (10b) is 4.1 kcal/mol higher than the barrier computed for lb -+ 2b. In contrast, the calculated barriers to rearrangement of 3,5-difluoro-phenylnitrene (lOe) and 4-fluorophenylnitrene (10c) are very similar to that computed for unsubstituted phenylnitrene (lb). These computational results are consistent with the observed reluctance of pentafluorophenylnitrene (10a) and 2,6-difluorophenylnitrene (10b) to rearrange,48 1 81 83 and with the relative ease... 

In n-hexane, a similar band with a maximum at around 384 nm was observed with a comparably fast risetime, so that one can conclude that the photoinduced charge-transfer process in this fluorinated derivative is a quasi-barrierless process in both polar and non-polar solvents. Preliminary DFT calculations indicate that in vacuum DMABN-F4 is nonplanar in the ground state in contrast to DMABN [7]. The fact that the observed CT state absorption spectrum is blue-shifted compared to that of DMABN and of the benzonitrile anion radical (Fig. 3) might be an indication that the equilibrium geometry of the CT state of DMABN-F4 is different from that of the TICT state of DMABN or might be due to the influence of the four fluorine atoms. 

Calculations at the MP2(Full)/6-31++G(d,p)//MP2(Full)/6-31+G(d) level of theory were used to investigate the SN reactions between ammonia and aziridine, aze-tidine, methylethylamine, and four fluorinated derivatives of aziridine.52 The results show that aziridine and azetidine have strain energies of 27.3 and 25.2 kcalmol-1, respectively, and that as a consequence they react 7.76 x 1023 and 2.30 x 1017 times faster with ammonia than does the methylene group of methylethylamine. However, even after subtracting the effect due to the release of ring strain, aziridine still reacts much faster than the other two substrates. This is because the electrostatic attraction of the charges in the product-like dipolar transition state are much greater for aziridine. 

In all the cases considered, the thioperoxide isomer is more stable than the corresponding sulfoxide. The energy differences ranged between 33 kJ mol-1 for the fluorine derivative up to 134 kJ mol-1 for the SiH3 substituted compound. The calculated TS barrier for the transformation of the isolated sulfoxide into the corresponding thioperoxide has been found to correlate with Taft s mesomeric constants, aR (3.3). 

Table V. Calculations for Fluorinated Derivatives of DB[a,/t]ACR-l,2-Epoxide and DB[a,/r]ACR-8,9- poxide in Figures 10 and 11...

The preferred pattern for addition of X2 (X = H, F, Cl, Br, I) to Ceo has been calculated to be 1,9- for small groups and 1,7- for bulky groups (Figure 22). Fluorine atoms are small enough for 1,9-addition to be favored and Ceo does indeed yield highly fluorinated derivatives upon careful reaction with F2 gas. Exhaustive fluorination of Ceo yields a product which exhibits a single F NMR line. This result indicates the production of a highly fluorinated species in which all... 

Compared in Table 4 are the strengths of the CH/O hydrogen bonds calculated for methane and its fluorinated derivatives in complex with water or formaldehyde. " It is noted that the proportion of the electrostatic term is comparable to the ordinary hydrogen bond, whereas contribution from the correlation energy is unimportant. Acetylene, ethylene, and ethane were shown to interact favorably with H2O and NH3. The interaction of CHs... 

The impressive development in molecular simulation stems from important improvement in both codes and computers. It made available accurate atomistic simulation of fluorine derivatives. Depiction of the SPF is most commonly achieved by quantum calculations. The major difficulty in describing interactions involving fluorine atoms actually lies in a correct description of the electrostatic effects [38]. Crystal unit cell dimensions [39,40] and the thermal behavior of fluoropolymers [41 3] were thus originally difficult to reproduce. Dihedral potential energy (Equation 6.3) that plays a central role in the backbone dynamics was also incorrectly depicted. In this section, illustrative examples of force fields specifically dedicated to fluoropolymers and more transferable force fields are reviewed. 

The equimolar copolymer of ethylene and tetrafluoroethylene is isomeric with poly(vinyhdene fluoride) but has a higher melting point (16,17) and a lower dielectric loss (18,19) (see Fluorine compounds, organic-poly(VINYLIDENE fluoride)). A copolymer with the degree of alternation of about 0.88 was used to study the stmcture (20). Its unit cell was determined by x-ray diffraction. Despite irregularities in the chain stmcture and low crystallinity, a unit cell and stmcture was derived that gave a calculated crystalline density of 1.9 g/cm. The unit cell is befleved to be orthorhombic or monoclinic (a = 0.96 nm, b = 0.925 nm, c = 0.50 nm 7 = 96%. 

A comprehensive review of the preparation, reactions, and n.m.r. spectra of phosphorus-fluorine compounds has appeared. This year s literature has been notable for the first detailed applications of ab initio SCF-MO calculations to the problems of bonding in halogenophosphines and their derivatives. - Comparison of the results of such theoretical calculations with experimental data obtained from photoelectron spectra shows a good correlation in the case of phosphorus trichloride and phosphoryl chloride, and of phosphorus trifluoride and its borane complex. ... 

Fluorine bomb calorimetry is in many aspects similar to oxygen bomb calorimetry. The experiments are carried out in isoperibol instruments, which, except for the bomb, are basically identical to those described in sections 7.1 and 7.2. The procedure used to calculate Acf/°(298.15 K) from the experimental results is also analogous to that discussed for oxygen bomb calorimetry in section 7.1. Thus, a temperature-time curve, such as the one in figure 7.2, is first acquired, and the corresponding adiabatic temperature rise, A Tad, is derived. 

Adsorbed water was observed to have a large effect on the F spin-lattice relaxation time for fluorine-doped aluminas in the dilute and intermediate concentration range of fluorine (0.3-8 wt. % F). An increase in Ti by a factor of 2 to 3 was observed in these samples when adsorbed water was removed from the solid by heating between 200-300°. The effect was completely reversible addition of oxygen-free water back to the solid resulted in recovery of the original (shorter) relaxation time. This effect was observed by the measurement of the in phase and ir/2 out of phase components of the dispersion derivative at resonance dx /6Ho at high rf power, from which effective values of Ti may be calculated 46). Values of Ti were also obtained by saturation of the resonance absorption derivative. 

---