This document is © Elsevier Science, 1994
Presented in part at the 13th Colloquium on High Resolution Molecular Spectroscopy, 13-17 September 1993 in Riccione.
The compounds with five-membered rings include fulvene (I) and cyclopentadienone (II). They are unstable, but it is possible to obtain microwave spectra of both molecules. In the case of fulvene extensive work has been done [1] so that an almost complete rs structure is available. For cyclopentadienone the work on a reliable structure is still in progress [2].
Cross-conjugated compounds with six-membered rings are of special interest since they represent tautomeric forms
of aromatic counterparts. The oxo-compound 2,5-cyclohexadienone (IIIa) is a keto-tautomer of phenol. This is also
the reason of its high instability which has made it impossible up to now to study this molecule by microwave
spectroscopy. We were, however, able to record and assign the spectrum of the corresponding dimethyl-compound
(IIIb) [3].
In this paper we wish to present our investigations on the methylene compound 1-methylene-2,5-cyclohexadiene*
(IVa) - a tautomer of toluene. An electron diffraction paper [4] on 4,4-dimethyl-1-methylene-2,5-cyclohexadiene
(IVb) claims a non-planar ring structure with dihedral angles within the ring of about 8 degrees. One of our aims in
this work was to check this by microwave spectroscopy.
*The correct nomenclature for (IVa) would be 3-methylene-1,4-cyclohexadiene. However, for easier reference to various substituted
cyclohexadienes we will use "2,5-cyclohexadiene" as the basic unit. The unsaturated exocyclic group is referred to as position 1, the saturated
carbon atom on the opposite side of the ring is referred to as position 4.
Unless denoted otherwise whenever a value is given with error limits (in parentheses) these denote the standard
deviation or the uncertainty resulting from error propagation in units of the last digits given.
First benzoic acid (V) is hydrogenated in a Birch reduction [7]. The dihydrobenzoic acid
(VI) is then converted to
the corresponding amine by standard procedures: formation of the acid chloride
(VII) with oxalyl chloride [5]; the
acid chloride is allowed to react with dimethylamine to give the dimethylamide
(VIII) [5] which is in turn reduced
to the amine (IX) with LiAlH4 [5]. The amine is oxidized with H2O2 according to Cope et al. [8]. Thermolysis of
the amine oxide (X) finally gives methylenecyclohexadiene (IVa) and dimethylhydroxylamine [6].
The thermolysis was monitored by a quadrupole mass spectrometer. Thus it could be observed that even at
temperatures barely above room temperature a noticeable amount of the amine oxide decomposes. The main part
was, however, thermolyzed at about 65°C. The products were collected in a trap cooled with liquid nitrogen. From
this trap the pyrolysate could easily be separated by fractional sublimation. The most volatile compound was the
desired hydrocarbon. For the microwave measurements methylenecyclohexadiene could thus be passed directly
from the original cooling trap into the cell.
As long as the contents of the trap were kept cool enough so as to prevent melting of the contents, the hydrocarbon
could be handled quite easily and no significant decomposition, oligomerization or tautomerization could be
observed. However as soon as the trap was warmed enough to melt the contents, practically no
methylenecyclohexadiene could be recovered.
Due to the relatively small dipole moment first trials of assignments were made in the region between 35 and 40
GHz where the most intense transitions could be expected. Since a powerful computer (a DEC VAX 9000-410 of
the computational center of the University of Ulm) was available we tried an "automatic assignment". First we
determined reasonable ranges for each of the rotational constants by investigating the derivatives of these constants
with respect to the different molecular parameters. Using these ranges it was possible to calculate ranges for some
intense low-J-transitions for which the contributions of centrifugal distortion should be below 1 MHz. Now all lines
found in these ranges were fed into a computer program, which succesively fitted each possible combination to a
rigid rotor model. Combinations resulting in a standard deviation of less than 1.5 MHz and leaving the rotational
constants within the given ranges were printed. After some unfruitful trials we found the correct assignment for
four transitions. The rotational constants that resulted from this fit were accurate enough to assign many other
transitions within a relatively short period of time.
As expected the spectrum followed a-type selection rules and we were able to assign 63 transitions between 12 and
40 GHz with a maximum J of 60 (cf. Table 1). The least squares fit showed a standard
deviation of 23 kHz and yielded the three rotational constants and all five quartic centrifugal distortion constants
(see Table 2).
The dipole moment was determined from a least squares fit of 32 measurements of Stark shifts of the M
components of the transition 8(35)-7(34) and was found to be 0.8645(31) D along the a axis. The cell was
calibrated using the dipole moment of OCS [9]. The figure below shows a sample spectrum of the transition 8(35)-
7(34) along with a calculated spectrum.
Spectrum of the transition 8(35)-7(34) recorded at a static field of 825 V/cm with a modulation field of 1025 V/cm (above) and calculated
using Lorentzian line-shapes with line-widths (FWHM) of 250 kHz (below). The zero-field frequency of the transition is shown (---). The signals
are labeled with their respective values of M. The signals marked with an asterisk represent the Stark lobes.
As mentioned earlier, one of our aims was to find out whether the ring of this molecule is planar or not. When the
ring is planar the molecule possesses C2v symmetry. This would result in four pairs of identical hydrogens which
would lead to a spin weight ratio of 17:15. However such a small difference could not be ascertained with the
technique used.
The planar moment Pc was found to be 1.58785(49) amuŲ (using the conversion factor 505379.1 amuŲMHz).
This is what would be expected for a planar ring with one pair of hydrogens out of the plane. This value is also in
good agreement with the values found for planar four-membered and five-membered rings with only pairs of
hydrogen atoms out of the plane (cf. Table 3). The methylene geometry should be
suspected to change systematically when moving from four- to six-membered rings. As the C-C-C ring angle
increases the H-C-H angle gets smaller, thus reducing the planar moment. The elongation of the C-H distance that
also has to be expected has much less influence. So the planar moment per pair of hydrogens should get smaller
with increasing ring size. Taking into account the effect of out-of-plane vibrations on the planar moment - which
should be expected to be higher for six-membered rings than for five-membered rings, thus making the value of Pc
larger - this corresponds quite well with the experimental values.
However a slight bending of the cyclohexadiene ring to form a very shallow boat cannot be ruled out by the planar
moment Pc alone. If the observed value is to be reproduced the dihedral angles within the ring can be as large as
about 3 degrees if the C-H bond length and the H-C-H angle are to remain within acceptable limits (cf. figure
below). Yet, a value of almost 8 degrees, as determined by Trætteberg et al. [4] for the 4,4-dimethylated species, is
not reconcilable with these results.
Dependence of the H-C4-H angle and the C4-H distance on variation of the dihedral angles (C6-C1-C2-C3 and C2-C3-C4-C5) in the ring.
The abscissa represents the H-C-H angle in degrees, the ordinate the C-H distance in Å. For nine dihedral angles (varying between 0 degrees and
8 degrees) the data points show the possible values of the methylene geometry to reproduce the experimental planar moment Pc. The dashed lines
denote extreme values between which the parameters should be expected to lie.
For a final decision it was therefore desirable to be able to calculate the actual contribution of the two hydrogens in
position 4 to the planar moment. This can be done if their coordinates (especially the c coordinates) are known. So
we decided to synthesize and measure 4-monodeuterated 1-methylene-2,5-cyclohexadiene.
Starting from p-bromo-toluene deuteration was achieved via a Grignard compound which was treated with
deuterium oxide. The methyl group is easily oxidized by potassium permanganate. From the resulting 4-deutero-
benzoic acid (XI) the preparation of 4-deutero-1-methylene-2,5-cyclohexadiene
(IVc) was carried out as mentioned
above for the non-deuterated compound.
Purity and degree of deuteration were checked by mass spectrometry and NMR. Both methods showed that the
degree of deuteration was well over 90%.
The rotational constants that were predicted by ab initio calculations for the parent molecule were compared to the
experimental data. The relative deviation for each constant was multiplied with the corresponding constant for the
deuterated molecule obtained from the ab initio geometry (cf. Table 4). The rotational
constants thus calculated predicted rotational transitions near 39 GHz (J=9) with deviations of less than 1 MHz. So
the spectrum of the deuterated compound could be assigned with no substantial difficulties. We measured 44
transitions between 28 and 40 GHz with a maximum J of 49 (cf. Table 5). The least squares fit showed a standard
deviation of 18 kHz and yielded the rotational constants as well as all five quartic centrifugal distortion constants
(see Table 2).
By a qualitative evaluation of the observed spectra first indications for a planar ring can be obtained. As Avirah et
al. [13] have pointed out there are several possibilities with respect to the potential function of the ring-bending
vibration (and thus to the planarity question):
A first possibility would be a double minimum potential with a high barrier (> 500 cm-1). In this case the
rotational spectrum in the ground state of the normal isotopomer would possibly show no indication of the barrier
(except the planar moment, which would be higher than expected). The 4-monodeuterated species, however, would
exist in two distinct conformers (flagpole or bowsprit deuterium) which would have different microwave spectra. It
cannot be definitely ruled out that only transitions of one of the conformers have been assigned and the others have
gone unnoticed, but the probability would be rather small, as the transitions that were predicted using rotational
constants calculated for a planar conformation were correct within 1 MHz. This would be very unlikely if the ring
were not planar. So this possibility can be ruled out.
A second possibility is a double minimum potential with a medium height barrier (~100-500 cm-1). In this case the
interaction between the two degenerate vibrational levels would become so strong that the splittings caused in the
microwave spectrum should make it impossible to fit the observed transitions to a planar model.
The third possibility is a double minimum potential with a barrier below the vibrational ground state energy. An
example of such a case is cyclobutanone [14]. Without investigation of the microwave spectrum in the excited
vibrational states such a case cannot be distinguished from the fourth possibility, a single minimum potential.
So the only potentials that would be consistent with the observed microwave spectra are either a single minimum
potential or a double minimum potential with a barrier below the vibrational ground state. In either case, however,
the vibrational ground state structure would have to be considered planar.
Preparation
1-Methylene-2,5-cyclohexadiene (IVa) has been prepared following the method of Plieninger and Maier-Borst [5]
with the modification proposed by Gajevski and Gortva [6]: Microwave Spectrum and assignment
The measurements were carried out at -30°C and about 3 Pa (0.03 mbar) using a conventional Stark spectrometer
with a 3m cell. The compound was found to be sufficiently stable for static measurements. For the aforementioned
conditions we determined a half life within the cell of about 4 hours. Ab initio and semi-empirical calculations were
very helpful for first guesses of the rotational constants. It turned out that the calculated constants deviated from the
experimentally determined ones by as few as some tenths of a percent. This is in agreement with the experiences
from 4,4-dimethyl-2,5-cyclohexadienone (IIIb) [3]. Deuteration
First we tried to deuterate the amine (IX), but it turned out that no significant exchange of deuterium for hydrogen
could be achieved. Therefore we prepared a p-deutero substituted benzoic acid
(XI) according to the following
reaction scheme:Theoretical calculations
Just as for the analogous oxo-compound 4,4-dimethyl-2,5-cyclohexadienone all ab initio and all semi-empirical
calculations predicted a planar ring for methylene-cyclohexadiene. It is a well-known fact that particularly semi-
empirical methods (we used MINDO/3 [18], MNDO [19] and AM1 [20] with the software package MOPAC [21])
are too much in favor of planar rings. But ab initio calculations with GAUSSIAN86 [22] gave the same result with
both smaller (STO-3G) and larger (6-31G*) basis sets. Rotational constants, dipole moment and the geometry of
the ring methylene group were predicted remarkably well by a RHF-SCF ab initio calculation with a 6-31G* basis
set. A survey of some of the results is given in Table 6.Geometry
If the molecule is planar it possesses C2v symmetry, the ring lying in the ab plane with a being the twofold axis
defined by the two methylene carbon atoms. The substituted hydrogen would then lie in the ac plane and the b
coordinate should be zero. Using Kraitchman's equations [23] for singly substituted molecules the b coordinate was
0.060(52) Å*. So it seemed to be justified to use the formulas that apply to atoms that lie in a plane of inertia. The
resulting a and c coordinates were identical with the previously obtained values within the error limits (a =
2.5550(12) Å, c = 0.8673(36) Å). The agreement with the ab initio calculated structure (planar) is striking (cf. Table 7). The contribution of the two hydrogens in position 4 to the planar moment Pc
can now easily be accounted for to give the pseudoinertial defect:
Dc = 2(2m(H)c² - Pc) = -0.1435(56) amuÅ
This value is definitely too low to allow for any significant non-planarity of the ring skeleton. The lowest vibration was calculated at 127 cm-1. It is an out-of-plane vibration that should give quite a large negative contribution to the pseudoinertial defect, so that possible contributions of a non-planar equilibrium structure can be ruled out.
* The error limit was determined using the relation proposed by van Eijck [24].
Based on these results the previously published data for 4,4-dimethyl-2,5-cyclohexadienone [3] (IIIb) may also be interpreted as indicative of a planar ring structure. This would be in agreement with the observations on 4-pyranone (XIIa) and its three sulfur analogs (XIIb-d) [25] as well as on 1,4-cyclohexadiene (XIII) [26] which were all found to be planar.
These results are, however, in direct conflict with the structure published by Trætteberg et al. [4] for 4,4-dimethyl-
1-methylene-2,5-cyclohexadiene (IVb). That work claims a bent ring with dihedral angles of about 8 degrees. Such
a bent ring structure can be definitely ruled out for 1-methylene-2,5-cyclohexadiene both from the pseudoinertial
defect and from the qualitative arguments discussed above. The effect of the two methyl groups should be negligible
and the investigations on the oxo-compound 4,4-dimethyl-2,5-cyclohexadienone suggest a planar structure for 4,4-
dimethylated species, too.
Acknowledgements
Financial support by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie is gratefully
acknowledged. Note added in proof
Additional information on this work is contained in the dissertation thesis of W.H. (German).
1 a) R.D. Brown, F.R. Burden and J.E. Kent, J. Chem. Phys., 49 (1968) 5542. b) P.A. Baron, R.D. Brown, F.R. Burden, P.J. Domaille and J.E. Kent, J. Mol. Spectrosc., 43 (1972) 401. c) R.D. Suenram and M.D. Harmony, J. Chem. Phys., 58 (1973) 5842. 2 a) P.A. Baron and R.D. Brown, Chem. Phys., 1 (1973) 444. b) K. Bestle and H.-K. Bodenseh, 12th Coll. High Res. Mol. Spectrosc. Dijon (1991) F12. c) R. Ruoff and H.-K. Bodenseh, 13th Coll. High Res. Mol. Spectrosc. Riccione (1993) F11. 3 W. Hutter and H.-K. Bodenseh, J. Mol. Struct., 291 (1993) 151. 4 M. Trætteberg, P. Bakken, A. Almenningen, W. Lüttke and J. Janssen, J. Mol. Struct., 81 (1982) 87. 5 H. Plieninger and W. Maier-Borst, Chem. Ber., 98 (1965) 2504. 6 J.J. Gajewski and A.M. Gortva, J. Am. Chem. Soc., 104 (1982) 334. 7 M.E. Kuehne and B.F. Lambert, Org. Synth., 43 (1963) 22. 8 A.C. Cope, T.T. Foster and P.H. Towle, J. Am. Chem. Soc., 71 (1949) 3929. 9 J.S. Muenter, J. Chem. Phys., 48 (1968) 4544. 10 J.S. Gibson and D.O. Harris, J. Chem. Phys., 52 (1970) 5234. 11 J.S. Gibson and D.O. Harris, J. Chem. Phys., 57 (1972) 2318. 12 a) C.S. Blackwell, Ph.D. Dissertation, Massachusetts Institute of Technology, June 1971. b) T.K. Avirah, R.L. Cook and T.B. Malloy, Jr., J. Mol. Spectrosc., 55 (1975) 464. 13 T.K. Avirah, R.L. Cook and T.B. Malloy, Jr., J. Mol. Spectrosc., 54 (1975) 231. 14 a) L.H. Scharpen and V.W. Laurie, J. Chem. Phys., 49 (1968) 221. b) J.L. Alonso, R. Spiehl, A. Guarnieri, J.C. López and A.G. Lesarri, J. Mol. Spectrosc., 156 (1992) 341. 15 M. Bogey, C. Demuynck and J.L. Destombes, J. Mol. Spectrosc., 132 (1988) 277. 16 T. Sakaizumi, H. Kikuchi, O. Ohashi and I. Yamaguchi, Bull. Chem. Soc. Jap., 60 (1987) 3903. 17 T. Sakaizumi, K. Matsui, Y. Sato, M. Itatani, J. Shibano, O. Ohashi and I. Yamaguchi, Nippon Kagaku Kaishi, 1989, 1247. 18 R.C. Bingham, M.J.S. Dewar and D.H. Lo, J. Am. Chem. Soc., 97 (1975) 1285. 19 M.J.S. Dewar and W.Thiel, J. Am. Chem. Soc., 99 (1977) 4899. 20 M.J.S. Dewar, E.G. Zoebisch, E.F. Healy and J.J.P. Stewart, J. Am. Chem. Soc., 107 (1985) 3902. 21 M.J.S. Dewar, J. Mol. Struct., 100 (1983) 41. 22 M.J. Frisch, J.S. Binkley, H.B. Schlegel, K. Raghavachari, C.F. Melius, R.L. Martin, J.J.P. Stewart, F.W. Bobrowicz, C.M. Rolfing, L.R. Kahn, D.J. Defrees, R. Seeger, R.A. Whiteside, D.J. Fox, E.M. Fleuder and J.A. Pople, GAUSSIAN86, Carnegie-Mellon Quantum Chemistry Publishing Unit, Pittsburgh PA, 1984. 23 J. Kraitchman, Am. J. Phys. 21 (1953) 17. 24 B.P. van Eijck, J. Mol. Spectrosc., 91 (1982) 348. 25 J.N. Macdonald, S.A. Mackay, J.K. Tyler, A.P. Cox and I.C. Ewart, J. Chem. Soc., Faraday Trans., 2, 77 (1981) 79. 26 L.A. Carreira, R.O. Carter und J.R. Durig, J. Chem. Phys., 59 (1973) 812.
________________________________________________________________________ N J KP KO J' KP' KO' nexp. ncalc. exp.-calc. ________________________________________________________________________ 1 3 0 3 2 0 2 12.429251 12.429252 -0.000001 2 51 18 33 51 18 34 14.715834 14.715845 -0.000011 3 4 1 4 3 1 3 15.460635 15.460645 -0.000010 4 54 19 35 54 19 36 15.572041 15.572044 -0.000003 5 4 0 4 3 0 3 16.005919 16.005928 -0.000009 6 8 2 6 8 2 7 16.283481 16.283494 -0.000013 7 37 13 24 37 13 25 16.362626 16.362610 0.000016 8 57 20 37 57 20 38 16.426237 16.426213 0.000024 9 60 21 39 60 21 40 17.278182 17.278140 0.000042 10 4 2 3 3 2 2 17.333277 17.333276 0.000001 11 26 9 17 26 9 18 17.356299 17.356290 0.000009 12 40 14 26 40 14 27 17.574459 17.574477 -0.000018 13 18 6 12 18 6 13 17.741738 17.741684 0.000054 14 4 3 2 3 3 1 17.776629 17.776620 0.000009 15 4 3 1 3 3 0 17.919963 17.919899 0.000064 16 13 4 9 13 4 10 18.181990 18.181925 0.000065 17 4 1 3 3 1 2 18.746576 18.746577 -0.000001 18 43 15 28 43 15 29 18.780095 18.780092 0.000003 19 4 2 2 3 2 1 18.800557 18.800524 0.000033 20 5 1 5 4 1 4 19.118405 19.118380 0.000025 21 5 0 5 4 0 4 19.446452 19.446470 -0.000018 22 46 16 30 46 16 31 19.979716 19.979698 0.000018 23 44 15 29 44 15 30 27.187218 27.187203 0.000015 24 6 3 3 5 3 2 27.773132 27.773151 -0.000019 25 6 2 4 5 2 3 28.661582 28.661586 -0.000004 26 47 16 31 47 16 32 28.778581 28.778626 -0.000045 27 8 1 8 7 1 7 29.796033 29.796035 -0.000002 28 8 0 8 7 0 7 29.830023 29.830003 0.000020 29 50 17 33 50 17 34 30.358727 30.358765 -0.000038 30 20 6 14 20 6 15 30.499962 30.499953 0.000009 31 7 3 5 6 3 4 31.013539 31.013501 0.000038 32 7 5 3 6 5 2 31.234962 31.234983 -0.000021 33 7 5 2 6 5 1 31.249771 31.249780 -0.000009 34 7 4 4 6 4 3 31.378332 31.378296 0.000036 35 7 4 3 6 4 2 31.671998 31.672038 -0.000040 36 53 18 35 53 18 36 31.928011 31.928056 -0.000045 37 28 9 19 28 9 20 32.178425 32.178411 0.000014 38 7 2 5 6 2 4 33.214239 33.214227 0.000012 39 8 1 7 7 1 6 33.627072 33.627073 -0.000001 40 42 14 28 42 14 29 34.918624 34.918620 0.000004 41 59 20 39 59 20 40 35.035341 35.035315 0.000026 42 8 3 6 7 3 5 35.215607 35.215638 -0.000031 43 8 7 2 7 7 1 35.527630 35.527617 0.000013 44 8 6 3 7 6 2 35.650366 35.650315 0.000051 45 8 6 2 7 6 1 35.652343 35.652326 0.000017 46 14 4 11 14 2 12 35.734408 35.734440 -0.000032 47 8 5 4 7 5 3 35.838096 35.838062 0.000034 48 8 5 3 7 5 2 35.894886 35.894940 -0.000054 49 8 4 5 7 4 4 35.940927 35.940899 0.000028 50 9 2 8 8 2 7 36.640094 36.640108 -0.000014 51 8 4 4 7 4 3 36.665233 36.665244 -0.000011 52 10 1 10 9 1 9 36.830340 36.830337 0.000003 53 10 0 10 9 0 9 36.836095 36.836085 0.000010 54 21 6 15 21 6 16 36.837313 36.837282 0.000031 55 45 15 30 45 15 31 36.952841 36.952889 -0.000048 56 26 8 18 26 8 19 36.975724 36.975698 0.000026 57 9 1 8 8 1 7 36.984799 36.984803 -0.000004 58 8 2 6 7 2 5 37.394574 37.394562 0.000012 59 8 3 5 7 3 4 38.185981 38.185974 0.000007 60 48 16 32 48 16 33 38.968831 38.968813 0.000018 61 15 4 12 15 2 13 39.019105 39.019136 -0.000031 62 9 8 2 8 8 1 39.955112 39.955133 -0.000021 63 9 7 3 8 7 2 40.067614 40.067563 0.000051 ________________________________________________________________________Standard deviation: 23 kHz.
______________________________________________________________ parent molecule 4-d-molecule ______________________________________________________________ A 5177.8216(37) MHz 5139.5303(23) MHz B 2613.1518(10) MHz 2518.7678(14) MHz C 1755.8422(09) MHz 1716.9106(14) MHz DJ 0.1384(65) kHz 0.1159(78) kHz DJK 0.135(16) kHz 0.128(15) kHz DK 1.074(50) kHz 1.030(53) kHz dJ 0.0440(11) kHz 0.04111(68) kHz dK 0.333(24) kHz 0.273(12) kHz k -0.4989 -0.5314 Ia 97.604577(70) amuŲ 98.331766(44) amuŲ Ib 193.398290(74) amuŲ 200.64536(11) amuŲ Ic 287.82716(15) amuŲ 294.35376(24) amuŲ m 0.8645(31) D
______________________________________________________________ Molecule Number of pairs of hydrogen Pc/n Reference n (uŲ) ______________________________________________________________ 2 1,643 [10] 2 1,639 [11] 2 1,699 [12] 2 1,652 [13] 3 1,663 [14] 1 1,551 [15] 1 1,523 [16] 1 1,520 [16] 1 1,531 (35Cl) [17] 1 1,583 (37Cl) [17] 1 1,588 This work _________________________________________________________________________
___________________________________________ distances angles ___________________________________________ C1=C7 1.32820 C2-C1-C7 122.2037 C1-C2 1.47336 C2-C1-C6 115.5927 C2=C3 1.32291 C1-C2=C3 122.4289 C3-C4 1.50310 C2=C3-C4 123.3792 C2-H 1.07639 C3-C4-C5 112.7911 C3-H 1.07697 C3=C2-H 120.2803 C4-H 1.09030 C2=C3-H 119.8276 C7-H 1.07548 H-C4-H 105.0704 H-C7-H 116.6545
_______________________________________________________________________ N J KP KO J' KP' KO' nexp. ncalc. exp.-calc. _______________________________________________________________________ 1 37 12 25 37 12 26 27.988563 27.988565 -0.000002 2 23 7 16 23 7 17 28.114744 28.114796 -0.000052 3 40 13 27 40 13 28 28.938139 28.938129 0.000010 4 18 5 13 18 5 14 29.401027 29.401030 -0.000003 5 43 14 29 43 14 30 29.784465 29.784461 0.000004 6 26 8 18 26 8 19 30.130810 30.130793 0.000017 7 46 15 31 46 15 32 30.532730 30.532734 -0.000004 8 49 16 33 49 16 34 31.187715 31.187716 -0.000001 9 29 9 20 29 9 21 31.989909 31.989942 -0.000033 10 8 3 6 7 3 5 34.179731 34.179758 -0.000027 11 8 7 2 7 7 1 34.383956 34.383915 0.000041 12 14 4 11 14 2 12 34.388253 34.388214 0.000039 13 8 6 2 7 6 1 34.491518 34.491497 0.000021 14 15 5 11 15 3 12 34.542001 34.542008 -0.000007 15 8 5 4 7 5 3 34.656267 34.656286 -0.000019 16 8 5 3 7 5 2 34.695873 34.695903 -0.000030 17 8 4 5 7 4 4 34.772776 34.772796 -0.000020 18 24 7 17 24 7 18 34.913316 34.913309 0.000007 19 19 5 14 19 5 15 35.026986 35.027051 -0.000065 20 35 11 24 35 11 25 35.277119 35.277113 0.000006 21 8 4 4 7 4 3 35.331438 35.331427 0.000011 22 10 1 10 9 1 9 35.994871 35.994876 -0.000005 23 10 0 10 9 0 9 36.002813 36.002795 0.000018 24 9 1 8 8 1 7 36.155225 36.155214 0.000011 25 17 4 13 17 4 14 36.303803 36.303810 -0.000007 26 8 2 6 7 2 5 36.332733 36.332733 0.000000 27 16 5 12 16 3 13 36.663570 36.663576 -0.000006 28 38 12 26 38 12 27 36.720779 36.720764 0.000015 29 8 3 5 7 3 4 36.792976 36.792945 0.000031 30 27 8 19 27 8 20 37.396433 37.396426 0.000007 31 41 13 28 41 13 29 38.039685 38.039691 -0.000006 32 22 6 16 22 6 17 38.331662 38.331675 -0.000013 33 9 8 1 8 8 0 38.670260 38.670279 -0.000019 34 17 6 12 17 4 13 38.698089 38.698104 -0.000015 35 9 6 4 8 6 3 38.918640 38.918631 0.000009 36 9 6 3 8 6 2 38.924479 38.924492 -0.000013 37 9 5 5 8 5 4 39.132139 39.132137 0.000002 38 9 4 6 8 4 5 39.153041 39.153041 0.000000 39 44 14 30 44 14 31 39.239351 39.239348 0.000003 40 9 5 4 8 5 3 39.254453 39.254462 -0.000009 41 17 5 13 17 3 14 39.331922 39.331910 0.000012 42 11 1 11 10 1 10 39.430066 39.430069 -0.000003 43 11 0 11 10 0 10 39.433323 39.433348 -0.000025 44 18 6 13 18 4 14 39.705167 39.705155 0.000012 _______________________________________________________________________ Standard deviation: 18 kHz.
___________________________________________________________________________ GAUSSIAN86 MOPAC exptl. 6-31G* STO-3G MNDO MINDO/3 AM1 ___________________________________________________________________________ A 3338.80 3276.33 3260.03 3306.67 3370.32 3332.16 B 1205.23 1178.95 1165.69 1151.86 1197.24 1193.07 C 1092.49 1067.37 1061.41 1050.04 1084.41 1082.21 m 4.8 2.9 3.6 4.3 4.2 4.45 ___________________________________________________________________________ A 5194.16 5100.61 5167.73 5181.18 5254.50 5177.82 B 2645.64 2634.15 2559.82 2523.76 2621.14 2613.15 C 1771.38 1755.56 1730.68 1714.79 1768.96 1755.84 |a| 2.538 2.543 2.567 2.600 2.541 2.555 |c| 0.865 0.872 0.892 0.873 0.904 0.867 m 0.8 0.6 0.1 0.1 0.5 0.86
__________________________________________________________________________ "general" case H in plane of inertia error* calculated (6-31G*) __________________________________________________________________________ a 2.5551 2.5550 0.0012 2.538 b 0.060 0.0 0.052** 0.0 c 0.8673 0.8673 0.0036 0.865* according to van Eijck [24]
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