3418
J. Phys. Chem. 1996, 100, 3418-3429
Anti, Ortho, and Gauche Conformers of Perfluoro-n-butane: Matrix-Isolation IR Spectra and Calculations Bo Albinsson and Josef Michl* Department of Chemistry and Biochemistry, UniVersity of Colorado, Boulder, Colorado 80309-0215 ReceiVed: October 16, 1995; In Final Form: NoVember 17, 1995X
Nitrogen matrix-isolation IR spectra have been obtained for each of the three conformers of n-C4F10 (gauche, ortho, and anti) by trapping a hot conformer mixture on a cold CsI window and subsequent matrix annealing and spectral differencing. They were assigned by comparison with results of HF/6-31G* calculations, and the nature of the normal modes has been analyzed using the total energy distribution procedure. At the fully optimized MP2/6-31G* (frozen core) level, the CCCC dihedral angles and relative energies (kcal/mol) are 54.2° and 0.68 (gauche), 94.8° and 1.63 (ortho), and 165.5° and 0 (anti). Single-point MP2/6-311G* (frozen core) relative energies at these geometries are 0.85, 2.12, and 0 kcal/mol, respectively. Only a minute amount of the ortho conformer is trapped in nitrogen matrix, and none in other matrices that were tried. A variation of the relative intensities of IR peaks of the gauche and anti conformers as a function of the temperature of the gas before deposition yields an “average” ∆H value of about 0.9 kcal/mol, with the anti conformer more stable. The temperature range covered was too small to reveal the expected bilinear nature of the van’t Hoff plot.
Introduction Until recently, it has been generally assumed that the conformational isomerism familiar from n-alkanes is characteristic of all reasonably sterically unencumbered saturated linear chains with a backbone composed of atoms of column 14 of the periodic table, i.e., that there are (i) a racemic gauche minimum (backbone dihedral angle ω about (60°) and (ii) an achiral (ω ) 180°) or racemic (ω about (165°) anti minimum with regard to rotation around each backbone bond.1 Certain empirical and semiempirical calculations predicted the existence of a third minimum near ω of about 90° at various times in the past. However, since they sometimes did so not only for permethylated and perfluorinated but also for unsubstituted alkane and oligosilane chains,2 they have apparently not been taken very seriously by most chemists. Perhaps the best documented among these early theoretical results was the case of certain highly crowded multiply alkylated alkanes, for which molecular mechanics (MM2) predicted a splitting of the gauche minimum into two.3 Recent more accurate ab initio results for n-Si4Me10,4,5 n-C4F10,6 and (CF2)n,7 none of which is particularly sterically encumbered, and for all of which three racemic conformers were calculated, are not so easily dismissed.8,9 Also, it has been pointed out6 that the splitting of the “ordinary” gauche minimum at 60° into two at 55° and 90°, presumably due primarily to 1,4-substituent interactions, would be analogous to the splitting of the “ordinary” anti minimum at 180° into two at (165°, presumably due to 1,3-substituent interactions. Such splitting of the anti minimum in numerous alkane derivatives is well established and is commonly recognized in textbooks.10 The 6-fold nature of the rotational barrier about a C-C bond and the deviation of the most stable geometry from the perfectly staggered one has been proven experimentally in hexamethylethane11 and in certain tert-butyladamantylcarbinols.12 These skewed geometries have been traditionally viewed as reflecting a splitting of the anti minimum and have been attributed to 1,3interactions. However, due to the high symmetry of these molecules, it would be possible to view them at least formally X
Abstract published in AdVance ACS Abstracts, February 1, 1996.
0022-3654/96/20100-3418$12.00/0
as reflecting a splitting of the gauche minimum as well. With this possible exception, we are aware of no prior experimental evidence for the splitting of the gauche minimum. Because of the fundamental importance of the conformational properties of open chains and because of their intimate relation to our work on σ-bond delocalization in oligosilanes,5 we have been interested in experimental verification of the theoretical predictions of the doubling of the gauche minimum in relatively unstrained chains. The method we have chosen in our search is matrix-isolation IR spectroscopy of conformer mixtures deposited from hot vapor onto a cold CsI window. The very rapid cooling does not permit the conformers to interconvert efficiently, and under these conditions the equilibrium concentrations present in the gas phase are believed to be trapped more or less intact.13 Once in matrix isolation, the conformers are prevented from interconverting by the rigid environment unless the temperature of the matrix is raised. After inducing interconversion by gentle annealing, the matrix can be cooled again, and difference spectra taken at leisure. Given the usually narrow spectral line widths in inert-gas matrices, one can hope to identify the IR peaks of all three conformers. This is the procedure that had been used successfully to obtain the IR spectra of the two conformers present in n-butane14 (the annealing was done with an IR beam) and more recently, n-tetrasilane.15 Unfortunately, our efforts to provide experimental evidence for the existence of all three conformers in n-Si4Me10 have so far been fruitless, presumably because the IR spectra of the gauche and the ortho conformers are predicted to differ detectably only in the far IR region, where the bands of both have extremely low intensities.5 In the hope that it might be easier to identify the ortho conformer experimentally in n-C4F10, we calculated the IR spectra of its three conformers and were pleased to see that the predicted differences among the intense peaks of the three conformers in the mid-IR region were large. Indeed, the experiment succeeded,16 and the novel ortho isomer was identified, although it was present in only minute amounts. Presently, we provide the full experimental and computational details of this work and describe our current understanding of © 1996 American Chemical Society
Conformers of Perfluoro-n-butane
J. Phys. Chem., Vol. 100, No. 9, 1996 3419
the conformers of n-C4F10 and their matrix isolation IR spectra. An investigation of the relative concentrations of the trapped gauche and anti conformers as a function of the temperature of the gas before deposition did not permit us to measure the enthalpy differences of all three conformers accurately but gave results that were compatible with the calculated value of the conformer concentration ratio. The label “ortho” for the third conformer with a dihedral angle close to 90° perhaps requires an explanation. It was proposed16 as a convenient abbreviation for what the literature seemed to avoid referring to by a name, and for what we would have otherwise had to refer to as “the one of the doubled gauche conformers that has the larger dihedral angle”. Thus, we propose to continue the use of the standard gauche, anti notation if there are only two enantiomeric pairs of conformers (one of which may collapse into a single achiral structure, as in n-butane), and to label the conformers gauche, ortho, and anti in the order of increasing dihedral angle if they occur as three enantiomeric pairs. Materials and Methods Matrix isolation experiments used nitrogen or argon gas (US Welding, 99.999% purity). The matrix gas was deposited on a polished CsI window held in an oxygen-free copper sample holder mounted on the second stage of a closed-cycle helium cryostat (Air Products Displex 202) and kept at 12 K as measured by a calibrated chromel-gold (0.07% Fe) thermocouple. In controlled warmup experiments, the cold tip of the cryostat was heated with a foil heater. n-C4F10 (Indofine Chemical Co., >97%), neat or mixed with one of the matrix gases at ratios between 1:1000 and 1:2000, was deposited slowly (1 mmol/h) onto the cold window through a quartz oven held at a constant temperature or through a glass tube fitted with a cooling mantle filled with dry ice. The temperature of the gas mixture was measured with a calibrated chromel-alumel thermocouple located a few centimeters from the cold window. Mid-IR and far-IR spectra were measured at 1 cm-1 resolution on Nicolet 800 and 20F FTIR spectrometers, respectively. The mid-IR spectrometer was equipped with a wide-range liquid nitrogen cooled MCT detector and the far-IR vacuum spectrometer with a TGS detector. Quantum mechanical calculations were done on IBM RS6000550 and 590 workstations using the Gaussian 92 program.17 The basis sets were 3-21G* 18 and 6-31G*.19 The geometries of three different conformers were fully optimized using either HF or MP2 (frozen core) calculations and each of the two basis sets. The second derivatives of the potential energy were all positive at these optimized geometries and the vibrational frequencies, IR and Raman intensities, dipole moments, and rotational constants were calculated. The second derivatives and the vibrational spectra were not calculated at the highest level of theory (MP2/6-31G*) due to technical limitations. To unravel the physical nature of the individual normal modes, the quadratic force constants calculated by the Gaussian program for the Cartesian coordinate system were transformed into a set of internal symmetry coordinates by using the program INTDER95.20 The vector q of normal coordinates is related in first order to the vector s of internal displacement coordinates by21
s ) Lq
(1)
The elements of the total energy distribution (TED) matrix are defined by
[TED]ik ) LikLki-1
(2)
Figure 1. MP2/6-31G* (frozen core) optimized geometries of the gauche (top), ortho (center), and anti (bottom) conformers of perfluoron-butane.
as the products of the element for mode k and internal coordinate i and the inverse of the element for mode i and internal coordinate k of the L matrix.22 They are similar to the more commonly used potential energy distribution (PED). The sum of all TEDs for a specific mode is 1, but individual elements can occasionally be less than 0, when a small positive diagonal force constant is associated with a negative coupling constant. Results Calculations. We have optimized the geometries of the three stable conformers of n-C4F10 at four levels of approximation: HF and MP2 with both the 3-21G* and the 6-31G* basis set. The three local minima found by varying the CCCC dihedral angle are located near 165° (anti), 95° (ortho), and 54° (gauche). The fully optimized structures of the three conformers (Figure 1) are listed in Table 1, along with their energies, dipole moments, and rotational constants. Except for the dihedral angle, most geometrical parameters are very similar for all three species. As has been noted before,6 the twist of the trifluoromethyl end groups [ω(CF3)] is in the opposite direction in the ortho conformer than in the anti and gauche conformers. The predicted relative energies are anti < ortho < gauche using the 3-21G* basis set and anti < gauche < ortho using the 6-31G* basis set. At the highest level of theory used for full geometrical optimization (MP2/6-31G* with frozen core) the gauche conformer is 0.7 kcal/mol and the ortho conformer is 1.6 kcal/mol above the global anti minimum. A single-point MP2/6-311G* calculation at these geometries (Table 2) changes these numbers to 0.9 and 2.1 kcal/mol, respectively. These energies are small enough to expect measurable quantities of the less stable conformers to be present at equilibrium at room
ortho
Albinsson and Michl a The sign of the twist of the trifluoromethyl groups is defined with reference to the adjoining CCC plane. A value smaller than 180° means that the twist is in the same direction as the CCCC helix (anti and gauche), and a value larger than 180° means that the twist is in the opposite direction (ortho). b Directed along the C2 symmetry axis, pointing in the same direction as the sum of the vectors C(2)F2 f C(1)F3 and C(3)F2 f C(4)F3. c C2 denotes the rotational constant that corresponds to rotation around the C2 symmetry axis. d Angle in the plane perpendicular to the C2 symmetry axis between the principal axis with smallest moment of inertia and the C(2)C(3) bond.
-1 148.067 36 0.68 1.534 1.540 1.338 1.357 109.2 117.4 54.2 169.4 0.277 1.051 0.625 (C2) 0.561 -19.6 -1 148.068 45 0.00 1.538 1.537 1.340 1.356 109.1 114.4 165.5 169.5 0.0479 1.249 0.521 0.504 (C2) -41.2 -1 145.862 88 2.00 1.536 1.552 1.311 1.327 108.8 115.9 96.1 187.8 0.105 1.160 0.570 (C2) 0.549 -31.3 -1 145.864 15 1.21 1.533 1.542 1.311 1.327 109.0 118.1 56.1 170.4 0.278 1.088 0.627 (C2) 0.563 -19.6 -1 145.866 08 0.00 1.536 1.538 1.311 1.327 109.0 115.0 169.1 172.3 0.0381 1.301 0.525 0.506 (C2) -40.9 -1 141.196 20 1.12 1.525 1.536 1.368 1.388 109.1 113.6 98.5 190.1 -0.0129 1.091 0.570 (C2) 0.551 -33.4 -1 141.194 29 2.32 1.522 1.523 1.368 1.388 109.3 115.7 58.0 168.0 0.208 1.026 0.629 (C2) 0.568 -21.4 -1 141.197 99 0.00 1.527 1.526 1.368 1.386 109.3 112.8 154.7 164.4 0.0343 1.196 0.528 0.514 (C2) -42.1 -1 139.664 77 1.28 1.512 1.525 1.338 1.356 109.0 113.7 99.1 189.9 -0.0099 1.134 0.583 (C2) 0.564 -33.4 -1 139.662 26 2.86 1.509 1.513 1.338 1.357 109.2 116.2 59.0 168.6 0.190 1.067 0.641 (C2) 0.579 -21.5 -1 139.666 82 0.00 1.514 1.514 1.338 1.355 109.1 113.1 156.1 165.0 0.0261 1.247 0.540 0.524 (C2) -41.9
ortho HF
gauche anti
total energy (au) rel energy (kcal/mol) r(C(1)C(2))/Å r(C(2)C(3))/Å r(CF3)/Å r(CF2)/Å θ(FCF)/deg θ(CCC)/deg ω(CCCC)/deg ω(CF3)/dega dipole momentb (D) rotational A constantsc B (GHz) C R/degd
MP2
gauche anti
HF MP2
anti
gauche
ortho
anti
gauche
ortho
6-31G* 3-21G*
TABLE 1: Computed Properties of Gauche, Ortho, and Anti Conformers of Perfluoro-n-butane at HF and MP2 Optimized Geometries
-1 148.065 84 1.63 1.538 1.550 1.340 1.357 109.0 115.8 94.8 189.1 0.120 1.120 0.565 (C2) 0.543 -31.2
3420 J. Phys. Chem., Vol. 100, No. 9, 1996
TABLE 2: 6-311G* Energies of Gauche, Ortho, and Anti Conformers of Perfluoro-n-butane at MP2/6-31G* Optimized Geometries HF/6-311G*
MP2/6-311G*
conformer
total energy (au)
rel energy (kcal/mol)
total energy (au)
rel energy (kcal/mol)
gauche ortho anti
-1 146.153 622 4 -1 146.152 515 3 -1 146.155 759 6
1.34 2.04 0
-1 148.724 221 1 -1 148.722 192 6 -1 148.725 576 7
0.85 2.12 0
temperature and even more so, at higher temperatures (9% ortho and 30% gauche at 600 K, assuming negligible entropy differences among the conformers). The IR spectra of the three conformers were computed in the double harmonic approximation at the HF/6-31G* level of theory. Using the symmetry coordinates defined in Table 3,23 the normal modes were classified according to the nature of the motions involved (Tables 4-6). Here, the total energy distribution matrix proved invaluable, since the local motions are mixed very heavily and visual inspection provides little useful information. All three conformers are computed to be nearly symmetric prolate tops, but the almost centrosymmetric anti conformer has its largest moment of inertia along the C2 symmetry axis and possesses a relatively small dipole moment, whereas the gauche and ortho conformers have the second largest moment of inertia along their C2 symmetry axes and their dipole moments are larger. IR Spectra of the Matrix Isolated Conformers. IR spectra of n-C4F10 in N2 matrix at various stages of annealing to higher temperatures are shown in Figures 2-4. Panel A shows the initial appearance of the spectrum after deposition of the matrix onto a CsI window at 12 K. Panel B shows the difference spectrum between a sample annealed to 14 K and the initial spectrum of panel A. Only minor changes are observed in most peak shapes due to the usual matrix site effects. However, a set of very weak peaks labeled o shows a large and irreversible relative intensity decrease. By the time the matrix temperature reached 16 K, all the peaks in the o set have disappeared. The frequencies at which the peaks of this set appear are quite different from those of the peaks that are not disappearing, and they are clearly due to a separate metastable conformer of n-C4F10, present in a small amount, and not to a different matrix site for one of the more abundant conformers. At higher temperatures another irreversible gradual change sets in as the g set of peaks decreases in intensity and the a set increases. Panel C in Figures 2-4 shows the difference between the spectrum taken after annealing to 18 K and the initial spectrum. The intensity changes are attributed to thermal conversion of conformer g into conformer a. Once again, the difference in their peak positions is such that the possibility that they might be just two different matrix sites of the same guest molecule can be safely ruled out. The gradual change continues until at 25 K all peaks of the g set have disappeared and the spectrum is that of pure species a. Structural assignment of the species o, g, and a is based on comparison with the calculated IR spectra of the anti, ortho and gauche forms of n-C4F10 at the HF/6-31G* level of theory, shown in panel D. Inspection of the region between 1100 and 900 cm-1 (Figure 3) permits an unequivocal assignment of peaks belonging to the observed a, o, and g sets to the calculated spectra of the anti, ortho, and gauche conformers, respectively. A detailed discussion of the assignments of the IR spectra of the three conformers is deferred to a later section. The sets of peaks that belong to each of the conformers have been sorted out by careful examination of the spectral changes
Conformers of Perfluoro-n-butane
J. Phys. Chem., Vol. 100, No. 9, 1996 3421
TABLE 3: Symmetry Coordinates for Perfluoro-n-butane speciesa
approximate description
symmetry coordinateb
ag
CF3 antisym stretch CF2 sym stretch CF3 sym stretch CF3 antisym def CF2 scissoring CF3 sym def CF2 wag CF3 rock CC stretch CC stretch CCC bend CF3 antisym stretch CF2 antisym stretch CF3 antisym def CF2 twist CF3 rock CF2 rock -CF3 torsion CCCC torsion CF3 antisym stretch CF2 antisym stretch CF3 antisym def CF2 twist CF2 rock CF3 rock -CF3 torsion CF3 antisym stretch CF2 sym stretch CF3 sym stretch CF3 antisym def CF2 scissoring CF3 sym def CF2 wag CF3 rock CC stretch CCC bend
S1 ) 2r1 - r2 - r3 + 2r8 - r9 - r10 S2 ) r4 + r5 + r6 + r7 S3 ) r1 + r2 + r3 + r8 + r9 + r10 S4 ) 2R1 - R2 - R3 + 2R4 - R5 - R6 S5 ) 4γ1 - θ1 - θ2 - θ3 - θ4 + γ2 - θ5 - θ6 - θ7 - θ8 S6 ) R1 + R2 + R3 - β1 - β2 - β3 + R4 + R5 + R6 - β4 - β5 - β6 S7 ) θ1 + θ2 - θ3 - θ4 + θ5 + θ6 - θ7 - θ8 S8 ) 2β1 - β2 - β3 + 2β4 - β5 - β6 S9 ) R1 + R3 S10 ) R2 S11 ) 5η1 - γ1 - θ1 - θ2 - θ3 - θ4 + 5η2 - γ2 - θ5 - θ6 - θ7 - θ8 S12 ) r2 - r3 + r9 - r10 S13 ) r4 - r5 + r6 - r7 S14 ) R2 - R3 + R5 - R6 S15 ) θ1 - θ2 - θ3 + θ4 + θ5 - θ6 - θ7 + θ8 S16 ) β2 - β3 + β5 - β6 S17 ) θ1 - θ2 + θ3 - θ4 + θ5 - θ6 + θ7 - θ8 S18 ) τ2 + τ3 S19 ) τ1 S20 ) r2 - r3 - r9 + r10 S21 ) r4 - r5 - r6 + r7 S22 ) R2 - R3 - R5 + R6 S23 ) θ1 - θ2 - θ3 + θ4 - θ5 + θ6 + θ7 - θ8 S24 ) θ1 - θ2 + θ3 - θ4 - θ5 + θ6 - θ7 + θ8 S25 ) β2 - β3 - β5 + β6 S26 ) τ2 - τ3 S27 ) 2r1 - r2 - r3 - 2r8 + r9 + r10 S28 ) r4 + r5 - r6 - r7 S29 ) r1 + r2 + r3 - r8 - r9 - r10 S30 ) 2R1 - R2 - R3 - 2R4 + R5 + R6 S31 ) 4γ1 - θ1 - θ2 - θ3 - θ4 - γ2 + θ5 + θ6 + θ7 + θ8 S32 ) R1 + R2 + R3 - β1 - β2 - β3 - R4 - R5 - R6 + β4 + β5 + β6 S33 ) θ1 + θ2 - θ3 - θ4 - θ5 - θ6 + θ7 + θ8 S34 ) 2β1 - β2 - β3 - 2β4 + β5 + β6 S35 ) R1 - R3 S36 ) 5η1 - γ1 - θ1 - θ2 - θ3 - θ4 - 5η2 + γ2 + θ5 + θ6 + θ7 + θ8
au
bg
bu
a Symmetry species in the C point group for the hypothetical planar C F molecule. The a and a blocks and the b and b blocks combine 2h 4 10 g u g u to form the a and b blocks, respectively, for the actual anti, ortho and gauche conformers. b Not normalized.
induced by annealing and, for the anti and gauche conformers, also by monitoring IR peak intensities as a function of the temperature of the gas mixture before deposition. By using these assignment criteria, we believe we have identified a few of the fundamental vibrations of the ortho form, and most of the fundamentals of the anti and gauche forms in the region between 1500 and 150 cm-1 (Tables 4-6). IR Spectrum of Neat n-C4F10. Figures 5 and 6 show the IR spectra of neat n-C4F10 matrices. The deposited amount is approximately 10 times larger in Figure 6 than in Figure 5 and also in the magnified inserts in Figure 5. No ortho conformer peaks were detected. The spectrum of the deposited neat sample (panel A) has the same overall appearance as the spectrum in nitrogen matrix, but larger bandwidths preclude observation of the separate conformers in the regions with large overlap. Some weak bands of the anti conformer appear to be intensified, for instance, the bands at 1109 and 1448 cm-1, both of which correspond to weak calculated transitions with gerade symmetry in the hypothetical planar anti conformer. Raising the temperature of the matrix induces similar changes as observed for the nitrogen matrix, and the difference spectrum (30 vs 12 K) in panel B shows negative bands for the gauche conformer and positive bands for the anti conformer. The intensified bands of the anti conformer grow upon annealing to 30 K, in contrast to those of the gauche conformer. At 60 K (panel C), all the gauche conformer is transformed into the anti conformer, and the intensified bands have lost most of their extra intensity. This latter behavior could be due to a minor phase change that takes place upon annealing to 60 K, but we have not studied it further.
Temperature Dependence of the Anti-Ortho-Gauche C4F10 Equilibrium. The amounts of the anti and gauche conformers trapped in the matrix vary systematically with the temperature of the gas mixture, and more of the gauche form is trapped relative to anti at higher temperatures. In puzzling contrast, the amount of the ortho conformer trapped does not depend on the temperature of the gas mixture, and the same relative intensity is observed for the o peaks when the gas mixture is deposited from room temperature and when it first passes through a 870 K oven. If the temperature of the deposition window is slightly higher (15 K), no o peaks are observed at all. It seems quite clear that the o conformer anneals with supreme ease into one of the others, presumably into the structurally quite close g conformer. We have used argon and xenon as matrix materials and also made measurements with neat n-C4F10 itself in the hope that the ortho conformer would be more efficiently trapped in these environments. The spectra of the gauche and anti forms are very similar to those measured in the nitrogen matrix, but none of these other matrices trapped any ortho conformer at all. All of the following results deal with nitrogen matrices alone. Figure 7 shows the ratio of intensities of the gauche and the anti IR peaks as a function of the temperature of the entering nitrogen-rich gas mixture between -40 and 600 °C. Several peaks in the spectra of the anti and gauche conformers are separated enough to be used to calculate the relative trapped abundance of these conformers. The sum of the integrated areas of the gauche peaks at 1356.7, 1065.2, 959.2, 766.9, and 738.7 cm-1 was divided by a similar sum for the anti peaks at 1311.5,
3422 J. Phys. Chem., Vol. 100, No. 9, 1996
Albinsson and Michl
TABLE 4: Vibrations of anti-n-C4F10 obsd calcd ν˜
HF/6-31G* mode
approximate label
ν˜ c (cm-1)
intd (km mol-1)
TEDe (%)
nitrogen
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
CCCC torsion -CF3 torsion -CF3 torsion CCC bend CCC bend CF2 rock CF2 twist CF3 rock CF3 rock CF3 rock CF2 wag CF2 twist CF2 sciss CF2 sciss CF3 asym def CF3 asym def CF3 asym def CF3 asym def CF3 asym def CF2 sciss CF2 rock CF2 sym stretch CF3 sym def CF3 sym stretch CF3 sym stretch CF3 sym stretch
a b a b a a a b b a a b b a a b b a a b b a b a b a
21.5 59.4 71.7 121.4 181.6 198.0 230.7 232.2 284.3 286.9 319.4 329.8 355.7 374.6 416.8 497.6 516.9 534.0 576.3 582.5 612.4 681.4 717.2 757.0 903.6 1117.8
0.00 0.04 0.01 0.81 0.02* 6.7 0.01 0.03 8.7 0.01* 0.01* 0.09* 0.02 0.00* 3.1 1.4 21.6 0.05* 3.8 30.0 1.2* 0.24* 115.3 0.18* 219.5 3.3*
u g u u g u u g u g g g u g u g u g u u g g u g u g
58S19, 41S18 90S26, 6S36 60S18, 41S19 77S36, 12S34, 5S26 54S11, 22S8, 9S9 59S17, 40S16 72S15, 12S17, 12S16 50S25, 20S23, 20S24, 8S26 50S34, 32S33, 6S36, 4S30 42S8, 19S10, 18S9, 10S6 51S7, 17S9, 15S10, 11S6 63S23, 21S25, 12S22 26S31, 25S35, 16S32, 13S34 62S5, 14S8, 9S4, 5S10 44S14, 24S16, 17S15, 15S17 53S22, 21S24, 10S23, 8S21 66S30, 18S31, 8S27 69S4, 12S1, 8S5 47S14, 18S12, 16S16, 8S17 38S31, 16S32, 15S28, 7S35 32S24, 18S21, 17S22, 14S25 32S2, 19S11, 14S6, 12S5 39S32, 25S29, 18S33, 5S34 42S3, 28S6, 12S2, 9S9 41S29, 29S33, 19S35, 5S27 37S3, 17S7, 17S6, 15S2
27 28 29 30 31 32 33 34 35 36
CF2 sym stretch CF2 asym stretch CF2 asym stretch CF3 asym stretch CF3 asym stretch CF3 asym stretch CF3 asym stretch CC sym stretch CC asym stretch CC sym stretch
b a b a b b a a b a
1159.3 1237.1 1239.8 1266.6 1278.6 1290.4 1296.0 1352.8 1353.9 1430.9
282 94.0 1.6* 0.01* 482.3 19.3* 834.6 0.06* 314.2 0.46*
u u g g u g u g u g
68S28, 10S31, 8S29, 5S32 78S13, 6S16, 6S12 68S21, 12S24, 12S20 69S1, 7S10, 7S2, 6S4 63S27, 11S20, 7S30, 4S29 60S20, 9S24, 9S27, 7S22 72S12, 14S13, 8S14 36S10, 19S2, 13S7, 9S8 39S35, 20S29, 17S32, 9S28 39S9, 15S3, 13S6, 12S2
a
Ramanb
IR (cm-1) argon
neat
intf
ν˜ (cm-1)
nitrogen
neat 35 bg 186 ag
209 289 293 ag
385 ag 528.2
528.5
423 506 529
4 547 ag
594.7
594.6
586 595 622
5 620 bg 693 ag
727.7
728.4
728
32
900.6 1109.3 1140.4g 1149.4 1169.6 1195.7 1219.8 1230.8 1238.1 1252.7
899.8
900 1109 1142g 1147 1187
770 ag
1311.5
1229.6
1218
1251.1
1224
35
