Random fluorinated copolymers of tetrafluoroethylene: a study of the inclusion/exclusion of defects from the crystal by conformational and packing energy calculations

A conformational analysis has been performed on the isolated chains of copolymers of tetrafluoroethylene with hexafluoropropene, chlorotrifluoroethylene or perfluoromethyl vinyl ether, in comparison with polytetrafluoroethylene. The lowest energy conformations in accordance with the chain repeating distance of polytetrafluoroethylene in the low temperature crystal phase have been used in packing energy calculations. The results of both conformational and packing energy calculations suggest that the  Cl group is easily tolerated in the crystal phase. The —CF₃ group could also be tolerated in the crystal phase but at the cost of conformational and crystal lattice deformations. On the contrary, it can be concluded that the —OCF₃ group is excluded from the crystal phase because its presence should require high energy values and wide deformations in the unit cell parameters.     

Molecular structure of trichlorophosphazo compounds from ab initio calculation and chlorine-35 NQR spectroscopy data

The molecular structures of trichlorophosphazo compounds Cl₃P=NR with R = C(CH₃)₃, C(C₂H₅)₃, C(CF₃)₃, CCl(CF₃)₂, CCl₂CF₃, CCl₃, CCl₂CCl₃, and CCl(CCl₃)₂ were analyzed by combined consideration of the results of ab initio MP2/6-31G* calculations and previously measured ³⁵Cl NQR frequencies. The conformational peculiarity of these molecules caused by the relative spatial orientations of the P-Cl and N-C bonds is reflected in the calculated geometric parameters of the Cl₃P=NC fragments and in the pattern of ³⁵Cl quadrupole resonance spectra for PCl₃ groups. For these atomic groups, the ³⁵Cl NQR frequencies were brought in correlation with the charges of the chlorine atoms found by quantum-chemical calculations.     

Vibrational relaxation and dissociation in the perfluoromethyl halides,CF3Cl,CF3Br,andCF3I

The processes of vibrational relaxation and unimolecular dissociation of the perfluoromethyl halides CF₃Cl, CF₃Br, and CF₃I have been studied in the shock tube with the laser-schlieren technique. Vibrational relaxation was resolved in pure CF₃Cl and CF₃Br (400–484 K and 400–500 K, respectively), and in the mixtures; 2% CF₃Cl/Kr (500–1000 K), 10% CF₃Cl/Kr (440–670 K), 4% CF₃Br/Kr (450–850 K), and 2% CF₃I/Kr (620–860 K). Relaxation in the pure gases is extremely rapid, but shows a well-resolved, accurately exponential decay which provides very precise relaxation times in close agreement with ultrasonic results. Relaxation times as short as 0.1 μs-atm can be resolved, showing the method has a resolution within a factor 2–3 of the best ultrasonic methods. Relaxation dilute in rare gas shows a complex double exponential behavior consistent with a two-stage series process. Rates of CF₃(SINGLEBOND)X fission in these mixtures were measured over 1800–3000 K, P<0.55 atm, for CF₃Cl; 1600–2500 K, P<0.55 atm, in CF₃Br; and 1260–2100 K, P<0.34 atm, in CF₃I. Rates for dissociation were derived from a full profile modeling using a secondary mechanism of six CF₃ reactions. RRKM analysis showed all dissociations to lie near the low pressure limit. Using literature barriers, these rates are best fit with (ΔE)_all=−270 cm⁻¹ for CF₃Cl, 〈ΔE〉_down=0.3 T for CF₃Br, and 〈ΔE〉_down=800 cm⁻¹ for CF₃F. All these transfers are on the large side, similar to those found in other halogenated methanes. © 1997 John Wiley & Sons, Inc.     

Beryllium‐Based Anion Sponges: Close Relatives of Proton Sponges

Through the use of high‐level ab initio and density functional calculations it is shown that 1,8‐diBeX‐naphthalene (X=H, F, Cl, CN, CF₃, C(CF₃)₃) derivatives behave as anion sponges, very much as 1,8‐bis(dimethylamino)naphthalene derivatives behave as proton sponges. The electron‐deficient nature of the BeX substituents, which favors strong charge transfer from the anion towards the former, results in anion affinities that are among the largest ones reported for single neutral molecules.     

Studies on sulfinatodehalogenation XIII. Synthesis of 2-perfluoroalkyl-2-deoxy-D-glucose,mono- and poly-O-polyfluoroalkylated-D-glucoses

Sodium dithionite-initiated addition of R_FI (1) [R_F=1a, Cl(CF₂)₄; 1b, Cl(CF₂)₆; 1c, Cl(CF₂)₆; 1d, n-C₆F₁₃; 1e, n-C₃F₁₇] to the properly protected glucose derivatives 2, 9, 12 and 15 gave polyfluoroalkylated glucose derivatives 7, 11, 14 and 17 respectively in good yields after reduction and deprotection. These compounds are strongly surface active.     

Rate constants and Arrhenius parameters for the reactions of Cl atoms with the halogenated ethers: CF3CH2OCHF2, CF3CHClOCHF2, and CF3CH2OCClF2

Rate constants have been determined for the reactions of Cl atoms with the halogenated ethers CF₃CH₂OCHF₂, CF₃CHClOCHF₂, and CF₃CH₂OCClF₂ using a relative‐rate technique. Chlorine atoms were generated by continuous photolysis of Cl₂ in a mixture containing the ether and CD₄. Changes in the concentrations of these two species were measured via changes in their infrared absorption spectra observed with a Fourier transform infrared (FTIR) spectrometer. Relative‐rate constants were converted to absolute values using the previously measured rate constants for the reaction, Cl + CD₄ → DCl + CD₃. Experiments were carried out at 295, 323, and 363 K, yielding the following Arrhenius expressions for the rate constants within this range of temperature:Cl + CF₃CH₂OCHF₂: k = (5.1₅ ± 0.7) × 10⁻¹² exp(−1830 ± 410 K/T) cm³ molecule⁻¹ s⁻¹ Cl + CF₃CHClOCHF₂: k = (1.6 ± 0.2) × 10⁻¹¹ exp(−2450 ± 250 K/T) cm³ molecule⁻¹ s⁻¹ Cl + CF₃CH₂OCClF₂: k = (9.6 ± 0.4) × 10⁻¹² exp(−2390 ± 190 K/T) cm³ molecule⁻¹ s⁻¹ The results are compared with those obtained previously for the reactions of Cl atoms with other halogenated methyl ethyl ethers. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 165–172, 2001     

NMR‐Solution Structures and Affinities for the Human Somatostatin G‐Protein‐Coupled Receptors hsst1–5 of CF3 Derivatives of Sandostatin® (Octreotide)

The previously reported (Helv. Chim. Acta 2008 , 91, 2035) derivatives of octreotide ( 1 ) with a (CF₃)‐Trp substitution, i.e., 3 , and with open‐chain structures, i.e., 2, 4 , and 5 , have been tested for their affinities to hsst_1–5 receptors and subjected to a detailed NMR analysis. Their affinities vary from 15 nM to 5 μM , as compared to 0.6 nM to 0.8 μM for octreotide itself (Table 1). This decreased bioactivity may have had to be expected for the open‐chain compounds 4 and 5 ; possible reasons for this decrease in the case of CF₃ derivative of octreotide, 3 , are discussed. NMR Analysis (Tables 2 and 3) provides evidence for increased dynamics of all new derivatives 2 – 5 . The dynamics of the octreotide molecule 1 was analyzed by (natural‐abundance) longitudinal ¹³C‐T₁‐relaxation time measurements (Table 4), from which the conclusion is drawn that the backbone of the macrocycle is rather rigid on the time scale of this method.     

Theoretical Investigation of the Additivity of Structural Substituent Effects in Benzene Derivatives

The additivity of substituent effects in 1,3- and 1,4-disubstituted C₆H₄X₂, and 1,3,5-trisubstituted C₆H₃X₃ (X=F, Cl, CN, NO₂, CH₃, CF₃, NH₂, OH) benzene derivatives on the ring geometry has been investigated. The analysis is based on ab initio calculations at the MP2/6-31G** level of theory. The substituent impacts on the benzene ring are generally in good agreement with the results reported in earlier experimental and lower level theoretical studies. The impacts determined in the monosubstituted benzenes were used to estimate the ring distortions in the di- and trisubstituted derivatives. The estimated ring CC bond distances agree generally within 0.001 Å and the estimated CCC bond angles within 0.3 degree, with the optimized ones. The best agreement (deviations up to only 0.0003 Å and 0.03 deg.) between the estimated and optimized geometrical parameters was obtained for the CH₃ derivatives. Generally, the para-disubstituted derivatives showed the best compliance with additivity, somewhat poorer agreement characterized the meta derivatives while the trisubstituted derivatives showed angular distortions of up to about 0.4°.     

Structural and Conformational Aspects of Equatorial and Axial Trifluoromethyl,Difluoromethyl, and Monofluoromethyl Groups

The X‐ray crystal structures of cis‐ and trans‐1‐(indol‐3‐yl)‐4‐methyl cyclohexane and its congeners with stepwise fluorination of the methyl group are reported. The trans‐configured compounds adopted diequatorial conformations, whereas the cis analogues adopted regular cyclohexane chair conformations with the methyl group preferentially assuming the axial position, even in the case of the CF₃ group. Surprisingly, although the axial CF₃ derivative displayed distinct valence deformations in the cyclohexane moiety, the observed structural changes were relatively modest. The cis derivatives with axial mono‐ and difluorinated methyl groups exhibited conformational disorder in the crystals with significant population levels for the staggered conformations that had one fluorine atom in the endo position; their respective trans counterparts adopted unique conformations, but again with one fluorine atom in the endo position. Theoretical calculations for a series of cis‐ and trans‐1,4‐dimethyl cyclohexane model compounds with stepwise fluorination of one equatorial or axial methyl group reproduced the experimentally observed structural response patterns very well, reproduced the experimentally determined nonlinear correlation of the axial–equatorial energy difference with the degree of methyl fluorination in a satisfactory manner, and provided further insights into important conformational aspects of partially fluorinated methyl groups.     

Tailoring the Solid‐State Fluorescence Emission of BODIPY Dyes by meso Substitution

4,4‐Difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) derivatives bearing varied substituents at the meso position (i.e., CF₃, CH₃, COOR, CHO, CN, Cl, iPr) were synthesized to elucidate the structure–property relationships that give rise to emissive J‐aggregates. Several new BODIPY derivatives can be added to the previously reported 1,3,5,7‐tetramethyl‐8‐trifluoromethyl derivative to the list of those forming J‐aggregates, in addition to other dyes that are emissive in the solid state without forming J‐aggregates.     

C?X⋅⋅⋅O Halogen Bonding: Interactions of Trifluoromethyl Halides with Dimethyl Ether

The formation of weakly bound molecular complexes between dimethyl ether (DME) and the trifluoromethyl halides CF₃Cl, CF₃Br and CF₃I dissolved in liquid argon and in liquid krypton is investigated, using Raman and FTIR spectroscopy. For all halides evidence is found for the formation of C? X???O halogen‐bonded 1:1 complexes. At higher concentrations of CF₃Br, a weak absorption due to a 1:2 complex is also observed. Using spectra recorded at temperatures between 87 and 125 K, the complexation enthalpies for the complexes are determined to be ?6.8(3) kJ mol^?1 (DME?CF₃Cl), ?10.2(1) kJ mol^?1 (DME?CF₃Br), ?15.5(1) kJ mol^?1 (DME?CF₃I), and ?17.8(5) kJ mol^?1 [DME(?CF₃Br)₂]. Structural and spectral information on the complexes is obtained from ab initio calculations at the MP2/ 6‐311++G(d,p) and MP2/6‐311++G(d,p)+LanL2DZ* levels. By applying Monte Carlo free energy perturbation calculations to account for the solvent influences, and statistical thermodynamics to estimate the zero‐point vibrational and thermal influences, the ab initio complexation energies are converted into complexation enthalpies for the solutions in liquid argon. The resulting values are compared with the experimental data deduced from the cryosolutions.     

Kinetic study of the reaction of chlorine atoms with CF3I and the reactions of CF3 radicals with O2, Cl2 and NO at 296 K

The kinetics of the gas-phase reaction of Cl atoms with CF₃I have been studied relative to the reaction of Cl atoms with CH₄ over the temperature range 271–363 K. Using k(Cl + CH₄) = 9.6 × 10^?12 exp(?2680/RT) cm³ molecule^?1 s^?1, we derive k(Cl + CF₃I) = 6.25 × 10^?11 exp(?2970/RT) in which E_a has units of cal mol^?1. CF₃ radicals are produced from the reaction of Cl with CF₃I in a yield which was indistinguishable from 100%. Other relative rate constant ratios measured at 296 K during these experiments were k(Cl + C₂F₅I)/k(Cl + CF₃I) = 11.0 ± 0.6 and k(Cl + C₂F₅I)/k(Cl + C₂H₅Cl) = 0.49 ± 0.02. The reaction of CF₃ radicals with Cl₂ was studied relative to that with O₂ at pressures from 4 to 700 torr of N₂ diluent. By using the published absolute rate constants for k(CF₃ + O₂) at 1–10 torr to calibrate the pressure dependence of these relative rate constants, values of the low- and high-pressure limiting rate constants have been determined at 296 K using a Troe expression: k₀(CF₃ + O₂) = (4.8 ± 1.2) × 10^?29 cm⁶ molecule^?2 s^?1; k_∞(CF₃ + O₂) = (3.95 ± 0.25) × 10^?12 cm³ molecule^?1 s^?1; F_c = 0.46. The value of the rate constant k(CF₃ + Cl₂) was determined to be (3.5 ± 0.4) × 10^?14 cm³ molecule^?1 s^?1 at 296 K. The reaction of Cl atoms with CF₃I is a convenient way to prepare CF₃ radicals for laboratory study. © 1995 John Wiley & Sons, Inc.     

Preferred spatial arrangement of the aromatic side chains in linear oligopeptides containing tyrosine.

¹H-NMR. studies of the protected linear tetrapeptides CF₃CO-Gly-Gly-L -Tyr-L -Ala-OCH₃, CF₃CO-Gly-L -Ala-L -Tyr-L -Ala-OCH₃ and CF₃CO-Gly-L -Ala-L -Tyr-Gly-OCH₃ showed that the side chain of the tyrosyl residue was in all three peptides preferentially oriented towards the amino terminus of the peptide chain. This preferred spatial arrangement of the aromatic side chain was manifested in the chemical shifts of the amino acid residue preceding tyrosine and in the vicinal spin-spin coupling constants ³J_HCαCβH of tyrosine.     

Vibrational analysis of the 1,1,1-trifluoroethyl halides

Normal coordinate calculations have been carried out for CF₃CH₂Cl using a 30-parameter valence force field. The resulting force constants for the CF₃ group have been transferred to CF₃CH₂F, CF₃CH₂Br and CF₃CH₂I with excellent results. Previous vibrational assignments have been revised, the calculations showing that several of the normal modes are highly mixed.     

Studies on sulfinatodehalogenation: IX. Synthesis and reaction of secondary perfluoroalkyl iodides

Several derivatives of secondary perfluoroalkyl iodides such as CF₃CFI(CF₂)₂O(CF₂)₃SO₂F (3), CF₃CFI(CF₂),O(CF₂)₂SO₃Na (4), CF₃CFI(CF₃)_n Cl (n=2, 7a; n=4, 7b) and CF₃(CF2)₂-OCFICF₃ (8) were synthesized using known methods, their reaction with sodium dithionite was studied and various olefins were added into the reaction system as radical traps to yield the 1:1 radical adducts.     

Conformational analysis of fluorinated copolymers of tetrafluoroethylene

Conformational analysis of fluorinated copolymers of tetrafluoroethylene (TFE) is performed by taking into account only intramolecular effects (isolated-chain model). In particular, variations of the chain conformation, which are induced by incorporating different side groups, such as –Cl, –CF₃, –OCF₃, –OCF₂CF₃, and –OCF(CF₃)₂, are investigated and discussed with respect to qualitative correlations between conformation, crystal structure, and supramolecular morphology.     

35Cl NQR Spectra and ab initio Calculations of gem-Substituted 1-Chlorocyclohexane Derivatives

The ³⁵Cl NQR spectra of gem-substiutted 1-chlorocyclohexane derivatives C₆H₁₀XCl (X = H, CH₃, CH₃O, Cl) at 77 K were measured. Ab initio RHF/6-31G(d) calculations of their conformers, and also of conformers of monosubstituted cyclohexanes were performed. Based on the calculation results, the NQR lines were assigned and the conformational energies of the substituents were evaluated. The relative conformational energies of the Cl atom and CH₃O group disagree with previous data.     

Some aspects of the chemistry of chlorofluoro-olefins which contain allylic chlorine atoms

Routes to perflouroallyl chloride, CF₂:CF.CF₂Cl, and to $\text{cis}$-and $\text{trans}$-1-chloro-hexafluoro-2-trifluoromethyl(but-2-ene), (CF₂Cl)(CF₃)C:CF.CF₃ are reported, and their susceptibility to attack by nucleophiles discussed; the allylic chlorine atoms in these olefins are the controlling factor in determining the products obtained.The conversion of 3-chloropentafluoropropene into a series of perfluoroallyl derivatives of general formula R.CF₂.CF:CF₂ [R = (CF₃)₃C-, CF₃O-, C₆F₅-, l-, MeO-, etc.] is described, and the further chemistry of 3-chloropentafluoropropene and its derivatives outlined.Water reacts rapidly with (CF₂Cl)(CF₃)C:CF.CF₃ to give CF₂:C(CF₃).CFCl.CF₃ or CF₃.CO.CH₂.CF₃. Methanol affords CF₂:C(CF₃).CFOMe.CF₃ and (MeOCF₂)(CF₃)C:CF.CF₃ as initial products, with subsequent secondary products such as CF₃.CFOMe.CH(CF₃).CF₂OMe, (CF₃)(MeO)C:C(CF₃).CF₃OMe, MeO.CF:C(CF₃).CFOMe.CF₃, (CF₃)(MeO)CF.CH(CF₃).CO₂Me, and (CF₃)(MeO)C:C(CF₃).CO₂Me. The influence of allylic chlorine and of reaction time on the formation of these products, and mechanistic pathways for their formation are considered.     

Fluorohalogeno compounds. II. Sonochemical approach to 3,3,3-trifluoropropionic acids

Fluoropropionic acids of the general formula CF₃CXYCO₂H ( X = F, Cl, Br ; Y = F, Cl, Br, H ) were obtained by the sonochemically promoted reaction of fluorohalogenoethanes CF₃CXYZ ( Z = Cl, Br ) with zinc and carbon dioxide. Penta- and tetrafluoroethanes ( X = Y = F and X = F, respectively ) gave good yields ( 35 – 47 % ) of the acids; with trifluoro derivatives the yields were substantially lower. Hydrogenolysis of the CCl and CBr bonds in CF₃CFClCO₂H and CF₃CFBrCO₂H afforded 2,3,3,3-tetrafluoropropionic acid.     

NEW CYCLIC AND POLYMERIC PHOSPHAZENES DERIVED FROM N-SILYLPHOSPHORANIMINES

Silicon-nitrogen-phosphorus compounds of the type Me ₃ SiN═PR(R′)X(X= Cl, Br, OCH₂CF ₃ , OPh), known as N-silylphosphoranimines,are useful precursors to both cyclic and polymeric phosphazenes.Depending on the leaving group (X), thermolysis reactions afford either cyclic trimers, [N═PR(R′)] ₃ (when X = Cl, Br), or linear polymers,[N═PR(R′)]_n (when X = OCH ₂ CF ₃ or OPh). Treatment of the P-trifluoroethoxy and P-phenoxy derivatives, Me ₃ SiN═PR(R′)X (X = OCH ₂ CF ₃ , OPh), with alcohols at lower temperature usually results in the formation of cyclic phosphazene trimers via silyl ether elimination. Recently, we have applied these synthetic methods to the preparation of some new phosphazene systems including a series of 4-aryl-functionalized trimers and polymers and a variety of non-geminal, mixed-substituent cyclic trimers. Representative examples of the synthesis, structural characterization, and reactivity of these new phosphazenes and their Si─N─P precursors are reported here.