Infrared and
Raman
Spectra
of
The Journal
Cyclopropene
Stigliani, W. M.; Laurie, V. W.; Li, J. C. J . Chem. fhys., 1975, 62, 1890. (8) Closs, G. L. "Advances in Alicyclic Chemistry", Hart, H.; Karabatsos, G. J., Ed., Vol. 1, Academic Press: New York, 1966; p 74. (9) Crawford, B. L., Jr.; Lancaster, J. E.; Inskeep, R. G. J. Chem. Phys., 1953, 21, 678. (IO) Pulary, P.; Meyer, W. J. Mol. Spectrosc. 1971, 40, 59; Jalsovszky, G.; Pulay, P. J . Mol. Struct. 1975, 26, 277. (1 1) Pulay, P.; Meyer, W. Mol. fhys., 1974, 27, 473. Here, a somewhat larger basis set was used.
of Physical Chemistry, Vol. 83, No. 4, 1979 501
Meyer, W.; Pulay, P. J . Chem. fhys., 1972, 56, 2109. Hariharan, P. C.; Popie, J. A. Chem. Phys. Lett. 1972, 16, 217. McKean, D. C.; Duncan, J. L., Spectrochim. Acta, 1971, 27, 1879. Schachtschneider, J. H., "Vibrational Analysis of Polyatomic Molecules", Technical Reports No. 231-64 and 57-65, Shell Development Co., Emeryville, Calif. (16) Hehre, W. J.; Lathan, W. A,; Ditchfield, R.; Newton, M. D.; Pople, J. A.; Program No. 236, Quantum Chemistry Program Exchange, University of Indiana, Bloomington, Ind.
(12) (13) (14) (15)
Infrared and Raman Spectra of Cyclopropene and of Six Deuterated Derivatives T. Y. Yum and D. F. Eggers, Jr." Department of Chemistry, University of Washington, Seattle, Washington 98 195 (Received September 7, 1978)
Cyclopropene and six distinct deuterated derivatives were prepared and purified; a key step in many of the syntheses was mercury-photosensitized decarbonylation of suitably deuterated furans. Infrared spectra are reported for the gas and solid phases, and Raman spectra for the liquid phase. Vibrational assignments are suggested for all of the spectra; these result in a choice of the fundamentals for each of the molecules studied. These fundamentals are supported by recent normal coordinate calculations of other workers. The thermodynamic properties of cyclopropene are also calculated and reported.
Introduction The vibrational spectrum of cyclopropene has been reported by Eggers et al.,l hereafter denoted ESWWJE, and also by Mitchell, Dorko, and Merritt,2 hereafter denoted MDM. Although both groups prepared deuterium derivatives, the isotopic purity was not high. At about this same time Srinivasan3 reported that the mercuryphotosensitized decomposition of furan gave a C3H4 fraction that was principally cyclopropene; more importantly, the decomposition of 2-methylfuran apparently gave only 3-methylcyclopropene with none of the 1isomer. These results suggested to us that the use of specifically deuterated furans, whose synthesis and spectroscopic properties had been reported earlier,4,5should produce cycloproperies deuterated a t specific positions in high isotopic purity. We have used such methods to prepare five different deuterated cyclopropenes in quite high isotopic purity; an additional deuterated species was prepared in somewhat lower purity by the exchange of light cycloproperie with a deuterated alcohol in alkaline medium. Infrared spectra in both gas and solid phases were obtained for these various deuterated cyclopropenes, and also for light cyclopropene. A fairly complete vibrational assignment was made, but a number of puzzling features remaineda6 The samples were stored at liquid nitrogen temperature for several years; during this time we obtained a suitable grating double monochromator, a commercial laser, and associated equipment to construct a laser Raman spectrometer. We also developed sampling techniques that permitted the irradiation of a sample at temperature approaching that of liquid nitrogen and the accurate measurement of depolarization ratios of liquid samples in this cooling apparatus. We have recently completed Raman investigations of these stored cyclopropene samples. With the aid of these new data we have achieved what appears to be a satisfactory vibrational assignment, 0022-365417912083-0501$0 1.OO/O
and it is supported by the product and sum rules. Thermodynamic properties of light cyclopropene were also calculated for inclusion here.
Experimental Section Light cyclopropene was prepared by the method of Closs and Krantz' from allyl chloride and sodium amide a t 80 OC. Some of this product was repeatedly bubbled through a solution of potassium tert-butoxide in tert-butyl alcohol-OD to prepare ~yclopropene-l,2-d~.~ This exchange reaction proceeded with a substantial loss of cyclopropene; it was terminated when there were still substantial cyclopropene-1-d and cyclopropene-do present. For convenience in the following discussion, these isomers will be denoted -1,2-d2,-1-d, etc., respectively. Since we also had prepared -do and -1-d in higher purity, the infrared spectrum of -1,2-d2 was obtained by placing sufficient pressures of -do and -1-d in two different cells in the reference beam of the double-beam instrument to cancel out absorptions due to the latter two substances in the sample mixture. Several of the deuterated furans were prepared by way of mercury derivatives of furan. We were not able to prepare these compounds in very high purity; 5-10% of a different derivative would often accompany the desired substance. This produced some mixing of different deuterated cyclopropenes in the final product. In most cases, however, we were again able to use a sample of the impurity a t lower pressure in the reference beam of the infrared instrument to balance out the impurity absorption. This technique was not applicable in the Raman spectra. However, the linearity of peak height with species concentration made it possible to compute, for a known percentage of impurity, the expected intensities of various impurity lines; the method appeared to be quite successful. Although we synthesized some furan-2,5-dz from mercurials, we found that furan-2,5-dz could be prepared in 0 1979 American Chemical Society
502
The Journal of Physical Chemistry, Vol. 83, No. 4,
1979
TABLE I : Major and Minor Isotopic Cydopropenes (%) in the Various Samplesa minor species major -3,3-3- -1,3,3component -do d, -d, -1-d d d, -3-d -1-d -3,3-d, -1,2-d, -1.3,3-d,
-4
I
1
1
5 9
3
2
40
20
10 1
1
1 9
' Values were obtained by combination of infrared,
mass spectra, and NMR measurements. Note: Since we had no samples of -1,3-d, or of -1,2,3-d,, we could not analyze for thpir presence. They were no doubt present to a significant extent, especially in the last three substances.
substantially higher isotopic purity by exchange of furan Furan-d4 with D20at 130 "C, catalyzed by nickel ~hloride.~ was purchased commercially. The various furans were converted to cyclopropenes in a batch process; irradiation was by germicidal mercury lamps through a Vycor tube to allow passage of 253.7-nm radiation. Further details may be found in the thesis of Yum.6 Purification was effected by fractional codistillationlo and by gas chromatography with the use of suitable liquid phases. The methylacetylene by-product was cleanly separated from the cyclopropene, but the allene was a greater problem. The major amount could be removed, but its presence in the final purified cyclopropene could still be detected as a moderate or weak band in the 1900-2000-~m~~ region of the infrared spectrum. This is the strongest band in the allene spectrum. As will be noted below, we speculate irn several instances about the possible presence of additional impurities that we could not identify. Concentrations of is0 topic impurities present in the various deuterated cyelopropenes prepared from the deuterated furans are summarized in Table I. The percentages are based on a combination of mass, infrared, and, in some cases, NMR spectra. It was found that these isotopic impurity concentrations could be quantitatively accounted for by the isotopic impurities in the precursor furans. This indicates that the photochemical reaction indeed produces neither loss of deuterium nor scrambling of its position in the molecule. Some early infrared spectra were obtained on a Perkin-Elmer Model 21 instrument with a sodium chloride prism, but most of the infrared work was done with a Perkin-Elmer 225 grating instrument. Gas samples were run in glass cells of 10-cm path length; pressures were limited t o 10 cmHg since gaseous cyclopropene tends to polymerize at room temperature under higher pressures. A few studies were carried out on -do with the use of a White-type cell having 2.5-m path. The pure solid cyclopropene was studied in conventional glass cold cells; liquid nitrogen was the coolant used. The Raman instrument was constructed from various commercial components and patterned very much after that described by Miller, Rousseau, and Leroi.'' We used a Coherent Radiation Model 52 MG laser, a Spex 1401 double grating monochromator, with 1200 grooves per mm gratings, and an RCA C31034 cooled photomultiplier. A replica plane grating between the laser and the sample area served to eliminate weak plasma lines that could otherwise give false signals. A polarization scrambler was placed immediately before the entrance slit of the monochromator, and a sheet of Polaroid, mounted between glass plates, was used to measure polarizations. In highly
T. Y. Yum and D.
F. Eggers
polarized bands we could often measure depolarization ratios less than 0.05; for bands that we feel fairly certain to be depolarized, we would in most cases obtain values typically 0.73-0.75. Most spectra were run at a constant mechanical slit width of 0.3 mm; since we used 514.5-nm radiation, this is a spectral slit width of 6 cm-' over the region that was scanned. For some very weak lines we employed 0.6-mm slits. The liquid sample for Raman work was contained in a quartz tube of 5-mm 0.d.; the lower end was flared slightly and a flat quartz window was sealed on. The tube was connected at the other end to Pyrex glass through a graded seal and to two bulbs of 150-mL capacity. The bulbs allowed for expansion in case the sample might warm suddenly. The laser beam entered through the flat window and passed up the axis of the sample tube; the light scattered at 90" was focused on the entrance slit of the spectrometer by a lens. Cooling was achieved by a flow of cold nitrogen gas passed through a clear Pyrex dewar with a sidearm for introduction of the cold gas. Spectra were run at a temperature just above the melting point of cyclopropene; it melts a t about 140 K. In contrast to the earlier Raman work, in which 435.8-nm mercury radiation was used,' in the present experiments we had no evidence of decomposition or polymerization of the cyclopropene samples.
Results and Discussion The microwave spectrum of cyclopropene12 is entirely consistent with the assumption of Czusymmetry for the equilibrium geometry, and we used this symmetry in analysis of the vibrational spectra. We have not found compelling evidence in the observed spectra for symmetry different from Czu. We also chose the orientations of the two reflection planes such that vibrations belonging to the Bz symmetry species have atomic displacements that are antisymmetrical with respect to reflection in a plane containing the three carbon atoms. This choice is consistent with previous work.lp2 The bond distances and angles in cyclopropene have values such that the A inertial axis is along the C2$ymmetry axis in -do and in the three deuterated species in which Czu!ymmetry is retained. For these four molecules the C inertial axis is perpendicular to the plane of the three carbon atoms. Thus, infrared bands of symmetry species AI, B1, and Bz should appear in the vapor as asymmetric rotor A-, B-, and C-type bands, respectively. In many cases the observed contours were very helpful in establishing the assignments; however, in others there were apparently substantial differences between the moments of inertia in the ground and excited vibrational states that rendered the contours less distinctive. For the isotopic derivatives -1-d and -1,3,3-d3 the symmetry becomes C, with A' vibrations having hybrid A-B contours and A" vibrations having C-type contours in the infrared. For -3-d the symmetry is also C,;here, however, the A' vibrations have hybrid A-C contours and the A" vibrations B contours. In a hybrid band, however, there is no a priori way to predict the relative strengths of the two components in the hybrid. In the Raman spectra, the CZumolecules permitted very clearcut distinction of Al vibrations by depolarization ratios. However, this was not always true in the C, molecules; some of the A' vibrations had measured p values very close to 0.75. Other criteria had to be used in making assignments of such vibrations. Since our cyclopropene spectra have been accepted by the Thermodynamics Research Center for incorporation into their publications of spectral data, no figures of spectra
Infrared and Raman Spectra of Cyclopropene
The Journal of Physical Chemistry, Vo/. 83,No. 4, 1979 503
TABLE XV: Fundamental Vibrations (cm-I ) for Various Deuterated Cyclopropenesa sym species A,
vibrn VI V? v 3 v4
v5 V6
A2
B,
”7
’
8
‘J 9 1J10
1/11 iJ12
B,
rJ, ‘J ‘J
3
14 I 5
-do 3152 2909 1653 1483 1105 905
-1,2-d2 2904 2435 1572 1460 1094 669
-3,3-d, 3151 2144 1648 1154 1050 890
-d4 2435 2142 1548 1147 1023 639
- 1-d
-3-d
-1,3,3-d3
3133 2905 2376 1607 1480 1106
3149 2963 2203 1649 1354 1102
3133 2379 2144 1593 1148 1044
(996) 815
817 737
749 640
1040 974
927 880
966 862
3116 1043 1011 769
(990) (661 1 2320 1040 880 680
3118 1014 863 710
2313 885 863 637
801 678 2994 1087
565 3117 1021 1009
770 647 2261 850
2995 1088 569
2995 1080 431
2260 863 562
2262 863 424
(991) 761 479
(817) 817 718
769 725 47 1
The designations of symmetry species apply only t o molecules of C,, symmetry.
are included here. Some checks with calibration gases showed that the instrument scale was good to the nearest wavenumber, and this is the limit to which values are reported. Judicious choice of the feature that should be measured in the band envelope was also necessary. Tables II-’XIV13 give the measured wavenumbers for the various vibrations in the infrared and Raman spectra; isotopic impurities which were balanced out are not listed for the infrared. For the Raman, the lines of such impurities are listed and identified. Intensities in the Raman spectra were simply measured as peak heights; since depolarized lines were often observed to be somewhat broader than polarized lines, the true relative intensities (band areas) of the nontotally symmetric vibrations would probably be somewhat larger than given in the tables. Raman intensities were all reduced to a basis of 100 for the C=C stretching vibration in each molecule, but no corrections were made for varying response of the photomultiplier and spectrometer with varying wavelength. At any rate, the procedures used seem to have been reasonably successful in allowing us to correct for the presence of isotopic impurities. It will be noted that we have no Raman spectrum to report for pure -do; none of this substance remained for Raman measurements. Some of its bands could be found in the mixture of -1,2-d2,-1-d, and -do;otherwise, we made some use of the Raman spectrum reported by MDM. This was run with mercury 435.8-nm excitation on a Cary 81 instrument. For vibrations in which there is agreement between ESWWJE and MDM, the discussion given below is minimal; we concentrate on those bands in which the present work has shown the need for revised assignments. The totally symmetric vibrations of the molecules having CZusymmetry were the easiest to assign. In many cases, they showed up as well-defined A-type infrared band contours and also as strong, polarized lines in the Raman spectra. The symmetric CH stretching vibration (=C-H), involving the 1 and 2 positions of the ring, and also the symmetric C-C single-bond stretching vibration, were found to be exceedingly weak in the infrared spectrum of the gas phase. In the earlier work, ESWWJE neglected the Raman lines in the 3100-cm-l region as possibly due to impurities since they were absent from the (gas phase) infrared. In the present work, samples rigorously purified by gas chromatography still showed these Raman lines. Furthermore, they showed up strongly in the infrared spectra of the solid phase; they also had appropriate shifts upon deuteration at the 1 and 2 positions of the ring.
TABLE XVI: Product Rule Ratios of Various Deuterated Species to Cyclopropene-dOa
A
b
c d
A,
B, B,
b
c
d b c d b c d
-1-d
-3-d
-1,3,3-d,
0.5366 0.5510 2.7
0.5447 0.5586 2.5
0.2097 0.2228 6.3
-1,2-d 0.5128 0.5284 3.0 0.5596 0.5714 2.1 0.7554 0.7519 0.5
-3,3-d, 0.5128 0.5341. 4.2
-4
0.5739 0.5912 3.0
I .
0.2627 0.2693 2.5 0.4254 0.4454 4.7 0.4316 0.4464 3.4
a Missing entries correspond t o molecules for which the product rule was used to deduce a missing fundamental. b Theoretical value. Experimental value. Percent difference.
Because of the inability to observe some of these vibrations in the infrared, we have entered liquid-phase Raman values for all such vibrations in the list of fundamental vibrations in Table XV. The new data have also’led to a revision of the ESWWJE assignments foir v4 and v5 Intense and polarized Raman lines leave us no choice but those indicated in Table XV; the values previously assigned are clearly an overtone and a combination (see below). The lowest Al vibration stands out clearly in only -do and in -3,3-d2. In the other two molecules of CZusymmetry, it appears as a weak feature on top of a much stronger B-type band. ‘In the Raman of -1,2-dz, it appears as a shoulder of uncertain polarization on a strong depolarized line; in the -d4 Raman spectrum, there is apparently a coincidence with a strong depolarized line. The assignments in the AI species of -do and of -3,3-d2 are supported very well by the product rule as shown in Table XVI. Assignmentfa in the AI species of -d4 and of -1,2-d2are also supported by the product rule; we regard this as mainly confirming the location of the lowest A, frequency. The sum rule was also applied for sets of these molecules with results as shown in Table XVII. Vibrations of B2 symmetry were considered next. The CH2 and CD2 antisymmetric stretching is easily located from the infrared band contour, shift upon deuteration of the CH2 group, and from the depolarization of the Raman line. Likewise, the lowest vibration, v15, HC=CH bending out of the C3 plane, is clear from its infrared band contour
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The Journal of Physical Chemisfry, Vol. 83, No. 4, 7979
TABLE XVII: Sum Rule Checks (cm-' x sym sums of squares reaction species of fundamentals -do t -d, 3 -1,2-d, t -3,3-d, A, 4.1053 $ 4.1077 A, 2.6268 2.6277 B; 1.9695 $ 1.9700 1.6519 f 1.6490 -do + -1,2-d, 2 2(-1-d) 6.6090; 6.6055 A" 2.3873 f 2.3872 -do t -3,3-d, 2 2(-3-d) A' 6.2483 2 6.2537 A" 2.7277 2.7253 A 5.5435 2 5.5411 -d, -t -3,3-d, 2 2(-1,3,3-d,) A ' 1.4391 1.4347 -1-d t -3,3-d, 2 -do t -1,3,3-d, A' 6.5494 $ 6.5485 A ' 1.9315 f 1.9307
3
5 5
and from shifts upon deuteration at carbons one and two. Both ESWWJE and MDM chose the same values that we give here. The ~ 1 vibration, 4 principally CH2 or CDz rocking, is more of a problem. MDM identified it in -do with a weak Raman line a t 820 cm-l, using the fact that CH2rocking is almost always found in this general region. ESWWJE assigned this vibration in -do at 1046 cm-l, a feature of medium intensity on the side of the strong B-type infrared band at 1011 cm-l. We have arrived at a still different assignment for this vibration. First, we note that the vibration around 820 cm-l shows no shift upon deuteration of the CHz group; this is found both from the Raman spectrum and from the infrared band near 1390 cm-I that we assign as a combination (see below). Second, the complex structure of the infrared spectrum in -do between 800 and 1100 cm-I gives way to three well-developed bands, nicely separated from each other, in -3-d. The one at 1009 cm-l is clearly of type B and must, therefore, be of A" symmetry. The sharp Q branches at 880 and at 927 cm-I must then both be of A' symmetry. All other bands in -3-d of A' symmetry can be identified readily, so that we have a test by the product rule between -doand -3-d, in the A' species. Choice of 1088 cm-l for v i 4 in -do provides good agreement with the product rule as shown in Table XVI. The value 1046 cm-l would increase the deviation from the theoretical product rule to 6.7%. Furthermore, choice of 1046 cm-I would leave us with the problem of assigning 1088 cm-l in some other way; this turns out to be difficult. Association of the 1088-cm-' band with the CH2 group can also be seen by its persistence in the infrared spectrum of -1-d. This surprisingly high value for v i 4 is supported by the fundamentals in diazirine as assigned by Ettinger.14 He finds the value 1125 cm-I for CH2 rocking, with support from the infrared spectra of diazirine-d and diazirine-d2. Other fundaments in diazirine also show strong similarities to those of cyclopropene. We also considered the possibility that the 1088-cm-l infrared band of -do could correspond to the same fundamental that is seen in the Raman, and is polarized at about 1106 cm-l, although the liquid-gas shift would be a bit large and in the opposite direction from that usually found. Several objections can be raised. First, in -3-d the 1088-~m-~ band disappears completely, but the Raman line at 1102 cm-l remains. Second, a gas-phase value of 1106 cm-l in -do would let us explain a weak Q branch at 536 cm-I as a difference band, v5 - v16, with calculated value of 537 cm-I. If 1088 cm-l were the gas-phase value for v5, the calculated value would be 519 cm-l and in disagreement with 536 cm-l. Completing the assignment for the Bz fundamentals in the remaining CZumolecules is done with the choice of 863 cm-l in both -3,3-dz and -d4. Although a very prominent Q branch appears in the former at 889 cm-l, the Raman
T. Y. Yum and
D. F. Eggers
polarization shows that it is, at least in part, an Al vibration. The product rule is satisfied better with the somewhat lower value for ~ 1 4 as , shown in Table XVI. The product rule is also used to deduce the value in -d4, and there is some structure in the infrared spectrum at the appropriate location. Assignments in the Bl symmetry species are in general agreement with those of MDM. The antisymmetric CH stretching involving the 1and 2 positions of the ring is clear from the depolarized Raman line that shifts when these ring positions are substituted by deuterium. Two of the remaining three fundamentals in -do are very clear from the strong B-type infrared bands at 1011 and 769 cm-'. The remaining one is shown to be above 1011 cm-l by the fact that we have a strong band a t 1042 cm-' of -1,2-d2. The band type is not too clear, probably in part due to the fact that the presence of two additional cyclopropene species had to be corrected for by placing cells containing them in the reference beams. This band cannot be the v5 vibration, since we find it some 50 cm-I higher in the Raman of the liquid; furthermore, in all other cyclopropenes the v5 band is exceedingly weak or absent in the infrared of the gas. As noted for -do,and also for -3,3-d2 (see below), difference bands are fit very well by assuming the Raman liquid value for v5 applies also to the gas phase. The considerable strength of the 1042-cm-l band in -1,2-d2 argues strongly that it be a fundamental, and only B1 fundamentals remain that are infrared active. An objection may be raised to the close proximity of two B1 fundamentals in -do. However, if they are considerably localized in different parts ofkhe molecule, such as in the CHz part and in the HC=CH part, their interaction and hence tendency to drive the levels further apart might be minimized. As seen in Table XVI, the product rule shows good agreement between -do and -1,2-d2in the B1 species with the assignments given above. For -d4 and -3,3-d2, it is necessary to assign a B1 and a Bz fundamental in coincidence. The product rule is then rather well satisfied; see Table XVI. Vibrations in the A2 symmetry species are forbidden in the infrared by symmetry though allowed in the Raman. There is formidable though indirect evidence for the assignment of one such mode to 815 cm-'. The band at 1385 cm-l has not been assigned as a fundamental, in contrast to ESWWJE, and MDM also assigned it as a combination. The latter workers ascribed it to ~ 1 4 ~ 1 5 necessarily , of Al symmetry. We found that a band at very nearly this value and strength remained in -3,3-d2,and this would be impossible with the ~ 1 +4 ~ 1 aasignment, 5 since ~ 1 has 4 to be principally a CHz (CD,) rocking vibration. However, the general shape of the 1385-cm-l band is quite unsymmetrical; without doing a much more complete investigation, such as with even higher resolving power and with computer calculations to attempt to reproduce the observed band contour using both A- and B-type selection rules, we cannot definitely rule out either symmetry. On the basis of isotopic shifts, we assign 815 cm-' as vg, the lower of the two Az fundamentals in -do. We believe the vibration involves principally the HC=CH part of the molecule, and it is not unreasonable that this vibration could combine strongly with ~ 1 5 that , is also probably localized mainly in that part of the molecule. Further support for this choice comes from -1-d in which molecule the selection rule becomes relaxed. We find a strong Q branch at 760 cm-l and definite indication of absorptions with spacing about 1.7 cm-l at somewhat lower frequencies; these provide good evidence for a C-type band.
+
The Journal of Physlcal Chemistry, Vol. 83, No. 4, 1078 506
Infrared and Ramen Spectra of Cyclopropene
TABLE XVIII: Calculated Thermodynamic Propertier of Cyclopropene (cal deg-' mol-') for the Ideal Gmeoue
State (1 atm Pressure)
temp, K
100 200 308 400 600 600
700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 24a0 2500
2600 2700 2800 2900 $000
3100 3200 3300 3400 3600 3600 3700 3800 3900 4000 273.15 298,15
(H' - Heo)/T
SO 7.993 9,400 18.706 16.242 19.240 21,668 23.669 26.330 26.766 27,983 29.046 29,966 30,766 31,462 82.069 32,801 33.067 83,478 33,84Q 84,161 34.446 34,700 34,927 36,131 36.315 35.480 36.640 86,766 35,890 36.003 36,106 36.200 36.287 36,367 $6.441 46.609 36.572 36,630 36.684 36.735 11,734 12,639
48,036 53,870 M0272 62.420 66,378 70,109 73,603 76.874 79.942 82,826 86.646 88,112 90,543 92,849 96.041 97,128 99,119 101.021 102.841 104,586 106.269 107,867 109.415 110.906 112,343 113.732 118.074 118,372 117,629 11 8,848 120.030 121.178 122,293 123.378 124.433 126,461 126,462 127,438 128.390 129,320 57.127 58.194
Furthermore, thern is a band generally similar to the one at 1385 cm-l in -dofound in -1-d at about 1241 cm-l; the sum of 760 and 479 cm-l agrees very closely, Other molecules show bands that tend to support this assignment. The remaining vibration of A2 symmetry was located by indirect methods. We find vibrations at 787 cm-l in -3,3-d2 and a t 749 cm-l in -dq that are difficult to assign. They remain in the Raman at low temperatures and cannot, therefore, be difference bands, They are depolarized and quite strong; this would argue against assigning them as impurities, as would the rigorous purification steps used and the almost complete absence of other lines or bands that must be ascribed to impurities. The combinationband approach used successfully in -do, in -3,3-d2,and in -1-d yields a value of about 640 cm-l for one of the A2 fundamentals of -d4, It is found that the 737- and 749-cm-l bands, if both are assigned as the other Az vibrations in -3,3-d2 and in -d4, respectively, provide good agreement with the product rule; see Table XVI. Another combination band, probably also of type B and located at about 1175 cm-l, can then be assigned as v7 vIB in -d4; other assignments for this band are much less credible, We have then obtained the other A2 fundamental of -do by the product rule, a t approximately 996 cm-l. With the large concentrations of two isotopic impurities in the eamples of the -1,2-d2isomer, it is not surprising that we found no positive evidence for either A2 fundamental.
+
7,964 8,224 9,139 10,480 11.943 13.368 14,701 16.928 17.054 18,087 19,036 190909 20,714 21,458 22,145 22,783 28.374 23,924 24.487 24,916 26,362 26.781 26.174 26,643 26.890 27.217 27.526 27,818 28,094 28,356 28.608 28.840 29.066 29.278 29,482 29.676 29,862 30,039 80.209 30.371 8.836 9.117
( G o- H o o ) / T
40,081 46,646 49.133 81.940 54.436 66.740 58.902 60.946 62.888 64,739 66.608 68.203 69.829 71,391 72,898 74,846 7Ea785 77,096 78A04 79,669 80*896 82.086 88,240 84.362 85.454 860514 87.847
_ I
-
88.884
89.686 90,491 91,425 92.337 93,228 94.099 94.951 98,784 96.600 97.398 98,181 98.948 48.291. 49.076
We have estimated the values from a combination of the product rule and the Bum rule; the results are given in parentheses in Table XV. In the three molecules of C, symmetry, we have also employed the product rule to deduce fundamentals for which there seemed to be no experimental information, Such values are given in parentheses in Table XV. For the -3-d molecule we thought at one time that two of its A" fundamentals, v12and ~ 1 3were , not clearly observed in either the infrared or the Raman spectra, Our first choice was to have the A" vEa vibration accidentally coincident with the A' one at 880 cm-l; this leads to an estimate for v12 of 964 cm-l by the product rule. However, these two values differ markedly from those calculated (see below), We have revised the assignment to have ulg accidentally coincident with v14 at 817 cm-l, even though both tbese vibrations are of the same symmetry. The product rule then gives a value of 1026 cm-l for the other miesing fundamental, and this is close to a weak Raman line observed at 1021 cm"l, Our final choice is then to have v11 a t 1021 crn-l, v l 2 a t 1009 cm-l from the infrared spectrum, and vI3 at 817 cm-l. This gives very good agreement with the product rule, The Raman spectra do show some lines that we fell; had to be ascribed to impurity. In -1-d, there is a polarized line at 1058 cm-l with intensity about 4% of the 1599 cm-l C=C stretching vibration, In the equilibrium mixture of -1,2-dz,-1-d, and -do,with the -1-d compound comprising
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The Journal of Physical Chemistry, Vol. 83, No. 4, 1979
somewhere near 40% of the total, the 1058-cm-' line is definitely missing in a clear region of the spectrum. This latter sample was prepared by a method that did not involve a mercury-photosensitized decarbonylation of furan, and it is possible that a trace of allene-d is responsible for the 1058-cm-' line. The Raman spectrum of this isotope of allene seems not to have been reported. It is also interesting that the cyclopropene -3-d Raman spectrum shows a polarized line a t 1057 cm-l, and allene-d would also be produced as a by-product in the synthesis. Essentially all of the observed vibrations in the infrared and Raman spectra, see Tables 11-XIV, can be explained in terms of the various fundamentals listed in Table XV. These values have been communicated to Professor Wiberg, and he has used them in normal coordinate calculations. Several force fields were found, and they gave good agreement with these experimental values;15 this lends substantial additional support to the assignments that we have suggested here. Since these assignments appear to be essentially correct, we have also calculated the thermodynamic properties of cyclopropene. The results are given in Table XVIII. Acknowledgment. This work was supported in part by the National Science Foundation.
V. F. Kalasinsky, 13. E. Powers, and W. C. Harris
Supplementary Material Available: Tables 11-XIV contain the observed infrared and Raman vibrations for all of the cyclopropenes, along with suggested assignment,s (19 pages). See any current masthead page for ordering information. References and Notes (1) D. F. Eggers, J. W. Schultz, K. B. Wiberg, E. L. Wagner, L. M. Jackman, and R. L. Erskine, J . Chem. Phys., 47, 946 (1967). (2) R. W. Mitchell, E. A. Dorko, and J. A. Merritt, J . Mol. Spectrosc., 26, 197 (1968). (3) R. Srinivasan, Pure Appl. Chem., 16, 64 (1968). (4) B. Bak, L. Hansen, and J. Rastrup-Andersen, Discuss. Faraday Soc., 19, 30 (1955). (5) M. Rico, M. Barrachina, J. M. Orza, and G.Michel, J. Mol. Spectrosc., 24, 133 (1967). (6) T. Y. Yum, Dissertation, University of Washington, 1969. (7) G. L. Closs and K. D. Krantz, J , Qrg. Chem , 31, 638 (1966). (8) E. A. Dorko and R. W. Mitchell, Tetrahedron Lett., 27, 341 (1968). (9) G. E. Calf arid J. L. Garnett, Austr. J . Chem., 21, 1221 (1968). (10) D. P. Siewarth and 6.H. Cady, Anal. Chem., 31, 618 (1959). (11) R. E. Miller, D. L. Rousseau, and G. E. Leroi, Technical Report No. 22, ONR Contract 1858 (27), May 1967, DDC acquisition No. AD 651646. (12) P. H. Kasai, R. J. Myers, D. F. Eggers, and K. B. Wiberg, J . Chern. Phys., 30, 512 (1959). (13) See paragraph at end of text regarding supplementary material. (14) R. Ettinger, J. Chem. Phys., 40, 1693 (1964). (15) K. B. Wiberg and J. J. Wendoloski, J. Phys. Chom., preceding article in this issue.
Vibrational Spectra and Conformations of Cyclopropylamine V. F. Kalasinsky," Department of Chemistty, Mississippi State University, Mississippi State, Mississippi 39762
D. E. Powers, and W. C. Harris* Department of Chemistry, Furman University, Greenville, South Carolina 296 13 (Received August 14, 1976) Pubiication costs assisted by Mississippi State University and the Petroleum Research Fund
The infrared (4000-150 cm-l) and Raman (4000-50 cm-') spectra of gaseous, liquid, and solid cyclopropylamine have been recorded along with the infrared spectra of matrix-isolated samples. The vibrational spectra of all phases are consistent with the predominance of a conformer having the NH2group trans to the ring C-C bonds as suggested by previous microwave studies. The torsional mode for trans-cycloprapylamine has been ohserved at, 254 cm-l, and hot bands associated with this low-frequency fundamental are apparent throughout the spectra of the vapor phase. There are a number of weak bands which can be attributed to a second conformer, and the assignment of torsional transitions for gauche-cyclopropylamine has allowed the calculation of a suitable potential function for internal rotation, The derived value for AH is 592 cm-I, and this is consistent with variable temperature studies carried out for the liquid and vapor states. The internal rotational isomerism is discussed in terms of the bonding schemes which are applicable to cyclopropyl ring compounds.
Introduction Cyclopropane and its derivatives are of considerable interest as a result of the particularly strained bonding of the ring. Various theoretical models have been developed to account for the structure and reactivity of these species. Notably, the Walsh modell and its more recent revision by Hoffman2 suggest a hybridization model in which there exists an electron-deficient, three-center bond within the ring and three electron-rich bonds external to the ring. This model would predict very specific substituent effects, and experimental results concerning conformational 0022-3654/79/2083-0506$0 1.OO/O
problems can be used to test the models. For an electron-rich substituent such as an m i n o group, a trans conformation allows overlap between the nitrogen lone pair and the electron deficient inner orbitals of the ring. In fact, absorption lines associated with transcy~lopropylamine~~~ and trans-cycl~propylphosphine~ have been identified in microwave studies. No evidence for a gauche conformer was found in either case, but recent theoretical studies have indicated that a gauche conformer may be on the order of 3 kcal/mol less stable than the This sharply contrasts results for alkylarninesa Q 1979 American Chemical Society
