J. Phys. Chem. 1986, 90, 2569-2574 and the hydrogen halides is substantially greater than between cyclopropane and the hydrogen halides. If the site of coordination was to the edge of the ring in these complexes (as was observed for cyclopropane), a smaller shift would be anticipated since electron-withdrawing substituents lessen the basicity of the ring. Moreover, the observed product bands in the substituted cyclopropane region were all assigned to perturbed modes of the substituent. There was no hint of perturbed vibrations of the cyclopropane ring, again in contrast to the CP-HX complexes. The difference in the shifted hydrogen halide stretching modes and the nature of the perturbed modes of the base subunit suggest that the site of coordination is not to the cyclopropane ring, but to the substituent itself. This conclusion is in agreement with the gas-phase ion cyclotron resonance studies of these substituted cyclopropanes, but in disagreement with the chemistry of cyclopropylmethylcarbinol in acid solution, where attack of the ring occurred, leading to ring expansion and the formation of cyclobutanol. These results point up the strong influence of polar solvents on the course of the reaction. Spectroscopic Trends. In each complex, a perturbed mode of the substituent was observed. It is interesting to compare the position of the hydrogen halide stretch in these complexes to other complexes containing the same functional groups. The HCl stretch in the acetone-HC1 complex is observed at 2392 ~ m - ’ which ,~~ is a shift of 464 cm-I. The HCl stretch shifts 450 cm-’ in forming the HCl-CPMK complex. Clearly, the interaction between these two gases is comparable and further substantiates the proposed structure of the HCl-CPMK complex. The HCl complexes with methanol, ethanol, 2-propanol, and 2-methyl-2-propanol show shifts of 331, 352, 391, and 394 cm-’, (32) Maes, G.; Zeegers-Huyskens, Th. J . Mol. Srrucr. 1983, 100, 305.
2569
r e ~ p e c t i v e l y . ~A~shift of 446 cm-’ was observed for the HC1CPMC complexes indicating that the interaction here is somewhat stronger. The magnitude of the shift of the HCl stretch in each of the complexes examined in this study can be used to estimate the strength of the interaction between the acid and base subunits. The strength of interaction decreases as CPMK > C P M C > C N C P > BMCP > BMP, as is demonstrated in Table I. Conclusions
The matrix isolation technique has been used to successfully isolate and characterize the 1:l hydrogen-bonded complexes between HCl and HBr and cyclopropanes bearing electron-withdrawing groups as substituents. Although the basicities of these functional groups varied over a substantial range, in each case coordination was to the substituent rather than the cyclopropane ring. These conclusions were made on the basis of spectral results which showed only a perturbed hydrogen halide stretch and perturbed vibrations of the substituent. The results obtained in the work stand in sharp contrast to the H X - c y c l ~ p r o p a n e ~and -~~ HX-methyl-substituted cyclopropane” complexes where coordination was to the edge of the cyclopropane ring.
Acknowledgment. The authors gratefully acknowledge support of this research by the National Science Foundation under Grant CHE8400450. B.S.A. also acknowledges the Dreyfus Foundation for a Teacher-Scholar Grant. R e t r y NO. BCP, 4333-56-6; CNCP, 5500-21-0; BMCP, 7051-34-5; CPMK, 765-43-5; CPMC, 765-42-4; HC1,7647-01-0; HBr, 10035- 10-6; Ar, 7440-37-1; N2, 7721-37-9. (33) Barnes, A. J. J . Mol. Srrucr. 1980, 60, 343.
Vibrational Assignments and Normal-Coordinate Analyses of y-Butyrolactone and 2-Py rrolidinones Dana P. McDermott Department of Chemistry, Lafayette College, Easton, Pennsylvania 18042 (Received: September 16, 1985)
Liquid-phase mid-infrared and Raman spectra and gas-phase far-infrared spectra of y-butyrolactone, 2-pyrrolidinone-N-do and -N-d, and N-(methyl-do)- and N-(methyl-d3)-2-pyrrolidinonehave been recorded. Normal-coordinate analyses have been performed, and a virtually complete assignment of the fundamental absorptions has been made for these molecules. In particular, bands in the vicinity of 540 and 480 cm-I for each of the molecules are assigned to the in-plane and out-of-plane deformation of the carbonyl group, respectively. The N-H in-plane deformation of 2-pyrrolidinone is assigned to a band at 1370 cm-’. All of the 2-pyrrolidinones have a band at approximately 1500 cm-’ which is assigned to the amide bond stretch.
Introduction
,
The pyrrolidinones, CH2CH2CH2(C=O)-NH,
,
.
and related
compounds such as y-butyrolactone, CH2CH2CH2(C=O)-0, are of interest due to their structural similarity to cyclic peptides of biological import. Also, they are of interest for basic studies due to their being the simplest cyclic amides and cyclic ester, respectively. Some previous spectroscopic work and vibrational calculations have been done on these compounds.’” These either lacked (1) Parsons, A. E. J . Mol. Spectrosc. 1961, 6, 201. (2) Rey-Lafon, M.; Forel, M.; Lascombe, J. J. Chim. Phys. 1%7,64, 1435. (3) Durig, J. R.;Coulter, G. L.; Wertz, D. W. J . Mol. Spectrosc. 1968, 27, 285.
0022-3654/86/2090-2569$01 .50/0
Raman studies, or were incomplete examinations of the infrared region, or based calculations upon a single set of spectral data assembled from spectra of different phases. The latter problem can cause some portions of a calculated force field to include intermolecular forces whereas other portions, for gas-phase frequencies, would not include such forces. Considerable disagreement exists amongst those previous works as to the location of modes such as the amide bond stretch, the in-plane and outof-plane deformations of the carbonyl group, and the in-plane deformation of the amide hydrogen. Similar disagreement also exists in similar work done on cis-N-alkyla~etamides.~-~~ (4) Legon, A. C. Chem. Commun. 1970, 838. (5) Warshel, A,; Levitt, M.; Lifson, S. J . Mol. Spectrosc. 1970, 33, 84. (6) Durig, J. R.; Li, Y.S.; Tong, C. C. J . Mol. Struct. 1973, 18, 269.
0 1986 American Chemical Society
2570 The Journal of Physical Chemistry, Vol. 90, No. 12, 1986 The purpose of this work was to characterize more completely the vibrational motions of the pyrrolidinones and related compounds, and to determine the magnitudes of the forces present in and about the amide group. Experimental Section
Spectra. 2-Pyrrolidinone, N-methyl-2-pyrrolidinone, and ybutyrolactone were obtained commercially, the former two from General Aniline and Film Co., the latter from Eastman Kodak. 2-pyrrolidinone-N-dl and N-(methyl-d3)-2-pyrrolidinonewere synthesized. All five compounds were distilled and used without further purification. N M R spectra of each compound showed no evidence of impurities. All mid-infrared spectra (4000-400 cm-’) were recorded with a Beckman IR-12, CsI plates, and each compound as a neat liquid film. All Raman spectra were taken with each compound as a neat liquid and using a Coherent Radiation CR-2 argon ion laser and its 5145-A green line with a Spex double monochromator. Far-infrared spectra were taken for each compound in the gas phase at an effective path length of 40 m and 20 ‘C. The spectra were obtained with a White-type multipass cell” attached to a RIIC FS-520 Michelson interferometer. Mylar beam splitters of thickness from mil to 2 mils were used to allow a total spectral range of 500-20 cm-I. Syntheses. A. 2-Pyrrolidinone-N-dl. Ten milliliters of 2pyrrolidinone (previously distilled) was mixed with 50 g of D20 (99.87%) D, Bic-Rad Laboratories, Richmond, CA). This mixture was stirred vigorously for 24 h to give a yield of approximately 75% of the deuterated compound. B. N-(MethyZ-d3)-2-pyrrolidinone. The method of Tafel and WassmuthI4 was used to prepare this compound. A 29.5-g portion of a 57% N a H dispersion (Alfa Inorganic) was placed in a flask under dry N2, and then washed with benzene to remove the mineral oil. Fresh benzene (600 mL) was then added to the washed N a H . The mixture was stirred and 25.8 mL (29.2 g) of 2-pyrrolidinonewas added over a period of 30 min. H2was evolved and the sodium salt of 2-pyrrolidinone was formed. While the mixture was being refluxed, 17.5 mL (40 g) of CD31 (99.5% D, Bio-Rad) was added and stirred in over a period of 2 h. Anhydrous ethyl ether (Mallinckrodt, Analytical Reagent) was added and the liquid filtered. The solvent was stripped off and the remaining material distilled at 90-91 “C under aspirator pressure. The yield was approximately 15 mL or 52%. N M R showed the sample to be approximately 90% d3 species. Normal-Coordinate Analyses
A. Structural Assumptions. Although some theoretical calculations have been performed on 2-pyrrolidinones and y-butyrolactone, no complete experimental determinations of their structures have ever been reported. The existing theoretical work on 2-pyrrolidinones5J5 indicates that all ring and amide group atoms are roughly coplanar with all dihedral angles being less than 5’. The existing work, both e ~ p e r i m e n t a l and ~ . ~ theoretical,I6 on y-butyrolactone indicates that the @carbon atom is out of the plane of the remaining four ring atoms, which are believed to be coplanar. Nevertheless, there is a total lack of information on dihedral angles of the ring skeleton of y-butyrolactone. Thus, (7) Miyazawa, T.; Shimanouchi, T.; Mizushima, S. J. Chem. Phys. 1958, 29, 611. (8) Miyazawa, T. Bull. SOC.Chem. Jpn. 1961, 34, 691. (9) Itoh, K.; Shimanouchi, T. Biopolymers 1967, 5 , 921. (10) Durgaprasad, G.; Sathyanarayana, D. N.; Patel, C. C.; Randhawa, H. S.; Goil, Abha; Rao, C. N. R. Spectrochim. Acta, Part A 1972,28A, 231 1. (11) Jakes, J.; Krimm, S. Spectrochim. Acta, Part A 1971, 27A, 19. (12) Reddy, T. B.; Chalapathi, V. V.; Ramiah, K. V. Indian J. Pure Appl. Phys. 1978, 16, 652. (13) Pickett, H. M.; Bradley, G. M.; Straws, H. L. Appl. Opt. 1970, 9, 2397. (14) Tafel, J.; Wassmuth, 0. Chem. Ber. 1907, 40, 2831. (15) Treschanke, L.; Rademacher, P. J . Mol. Struct.: (THEOCHEM) 1985, 122, 35. (16) Allinger, N. L.; Chang, S. H. M. Tetrahedron 1977, 33, 1561.
McDermott TABLE I: Structural Parameters’ for y-Butyrolactone and 2-Pyrrolidinone y-butyrolactone r(C2-O) 1.347 r(C2=0) 1.239 r(C2-C3) 1.515 r(C3-C4) 1.529 r(C4-c5) 1.530 r(~5-o) 1.411 ~ ~ 3 ~ 2 109.7 0 LC4C3C2 102.2 LCSC4C’ 99.4 f0CSC4 105.1 LCZOCS 110.2
2-pyrrolidinone r(C2-N) 1.404 r(C2=0) 1.223 r(C2-C3) 1.532 r(C3-C4) 1.545 r(C4-C5) 1.550 r(C5-N) 1.456 LNC20 122.4 LNC2C3 107.8 LC2C3C4 105.7 LC3C4C5 106.9 LNC5C4 108.1 LC~NC~ 114.7
Distances in angstroms, angles in degrees. Numbering of atoms
according to IUPAC rules. all ring, amide group, and carbonyl group atoms were taken to be coplanar for both of the two rings in this work. The other structural parameters for the two ringsIsJ6 are given in Table I. parameters for the methyl group For N-methyl-2-pyrrolidinone, were taken from n-paraffins.” The position of the methyl group was fixed so that one of its hydrogens was eclipsed with the oxygen and coplanar with the ring, carbonyl oxygen, and methyl carbon atoms. Any other orientation would have made the molecule’s assumed symmetry to be C1,which is inconsistent with its Raman spectrum. B. Method. All analyses were camed out using the G F method of Wilson, Decius, and Cross,1aand the programs of Schactschneider.Ig The structural assumptions make all the molecules in this work to be of C, symmetry. The symmetry coordinates for all molecules were constructed using the assumed C, symmetry of the molecules and separate into two blocks: A’and A”. An A”mode or symmetry coordinate is antisymmetric with respect to the molecular plane. The normal modes for the molecules separate into the two symmetry blocks as follows: butyrolactone, 9A”; 2-pyrrolidinone, 23A’ 10A”; N-methyl-221A’ pyrrolidinone, 28A’ + 14A”. All observed frequencies used for modifying force constants were determined in the liquid phase. Low-frequency ring deformations were given a weight of zero for any modifications of force constants since these deformations are usually very anharmonic. For all of the molecules, the analyses were performed with modified Urey-Bradley force fields (MUBFF). This type of field contains valence and valence interaction force constants and Urey-Bradley constants for repulsions and attractions between nonbonded atoms. Initial force constants came from other workers’ analyses of N-methylacetamide,20 oxetanone-3,21 and N,N-dimethylacetamide.I0 For each molecule, all initial force constants were allowed to be changed and were fit to the observed frequencies by a linear least-squares fit procedure. In the cases of two isotopomers such as 2-pyrrolidinone-N-do and -N-d, the force constants were fit simultaneously to the observed frequencies of the two molecules. The same was done with N-(methyl-do)- and N-(methyl-d3)-2pyrrolidinone. The final force constants, in most cases, differed from the initial force constants by less than 12%. For all of the molecules studied in this work, the largest changes of force constants occurred for those constants involving the ester or amide group. The carbonyl stretch constant was decreased by as much as 15% for 2-pyrrolidinone-N-do and -N-d, and N-(methyl-do)and N-(methyl-d3)-2-pyrrolidinone,whereas the similar force constant was increased by 15% for y-butyrolactone. The most
+
+
(17) Schachtschneider, J. H.; Snyder, R. G. Spectrochim. Acta, Part A
1963. 19A. 5124.
(18) Wilson, Jr., E. B.; Decius, J. C.; Cross, P. C. Molecular Vibrations; McGraw-Hill: New York, 1955. (19) Schachtschneider, J. H. Vibrational Analysis of Polyatomic Molecules; Shell Development Co.: Emeryville, CA, 1962; Vol. 1-111. (20) Jakes, J.; Schneider, B. Collect. Czech. Chem. Commun. 1968, 33, 643. (21) Blackwell, C. S. Ph.D. Dissertation, Massachusetts Institute of Technology, 1971
The Journal of Physical Chemistry, Vola90, No. 12, 1986 2571
Spectra of y-Butyrolactone and 2-Pyrrolidinones TABLE II: Observed and Calculated Frequencies (em-'), Assignments, and the Potential Energy Distribution for Butyrolactone obsd Raman
IR
3000 dp, s
2990 m
2930 p, s
2920 m
1765 p, m 1488 dp, m 1464 dp, m 1425 dp, m 1378 dp, w
1770 s 1487 m 1463 m 1425 m 1378 s 1318 m 1288 m 1280 dp, w 1280 m 1245 dp, m 1240 m 1200 dp, m 1200 m 1180 dp, m 1180 m 1140 m 1085 dp, w 1085 w 1040 dp, w 1038 m 995 dp, w 994 m 933 p, s 934 m 870 p, s 870 m 805 p, s 805 m 678 p, s 675 m 638 p, m 637 m 540 dp, w 539 m 493 dp, m 492 m 205 (gas) w
170 dp, w
calcd 2986.4 2981.3 2975.7 2933.6 293 1.2 2930.9 1772.9 1484.3 1467.7 1454.4 1375.3 1336.9 1305.5 1274.6 1254.2 1233.3 1172.3 1172.7 1076.5 1030.2 977.4 920.8 879.6 836.0 682.2 631.8 527.0 490.5
TABLE III: Observed and Calculated Frequencies (cm-I), Assignments, and the Potential Energy Distribution for 2-Pyrrolidinone-N-do obsd
assignment and PED,' 7'%
v(C=O), 90.3 57.3 s, 59.4 S, 67.4 v(C'-0), 31.9; W, 14.1 W. 83.7 W, 76.5 W, 60.8; v(C-0), 24.3 T, 86.3 T, 93.8 T, 94.7 u(C-O), 43.9 R, 76.2 R, 37.8 R, 46.5 v(C-C'), 16.8; u(C-C), 11.5 u(C-C), 38.1 v(C-C), 57.6 u(C-C), 24.8 u(C-C), 12.0 6(C=O), 34.9 x(C=O), 62.8; ring bond torsions, 36.8 221.1 ring twist (0-C-C-C torsion, 59.2; C-C-C-C' torsion, 21.9; out-of-plane C=O deformation, 19.6) 101.9 ring pucker (C-C-C'-0 torsion, 79.1)
s,
' u = stretch; S, W, T, R = C H 2 scissor, wag, twist, rock; 6, x = in-plane and out-of-plane deformation; dp = depolarized; p = polarized, s = strong; m = medium; w = weak; C' = carbonyl carbon.
profound change was that for FNO,the Urey-Bradley repulsion constant between the nitrogen and oxygen atoms of the amide group. The initial value'0*20was 1.500, whereas the final value of FNo was 1.000 for the 2;1~yrrolidinones, and 1.154 for the N-methyl-Zpyrrolidinones. The observed and calculated frequencies, assignments, and final force constants are presented as follows: y-butyrolactone, Tables I1 and VII; and 2-pyrrolidinone-N-do and -N-d, Tables 111, IV, and VIII; N-(methyl-do)- and N-(methyl-d3)-2-pyrrolidinone, Tables V, VI, and IX.
Results and Discussion A . y-Butyrolaclone. The analysis and assignment of y-butyrolactone's spectra proved to be remarkably straightforward (Table 11). The frequencies of the various methylene group motions proved easy to calculate and their final force constants (Table VII) have values which are typical of the similar constants for the methylene modes of n-paraffins. The stretching.modes of the ester bond and the other C-O single bond are assigned to bands at 1378 and 1140 cm-I, respectively. These values aie very typical for similar modes in esters and lactones.22 Two bands at 540 and 493 cm-' were assigned to the in-plane and out-of-plane deformations, respectively, of the carbonyl group. These assignments are based on the facts that carbonyl deformation modes do not normally give strong absorptions dqd occur in this general region, and the 540-cm-' band, when observed in the gas phase, is A type, and has the width expected for a carbonyl deformation on the basis of diagrams for asymmetric rotor band ~~
~~
~
(22) Silverstein, R. M.; Bassler, G. C.; Morrill, T. C. Spectrometric Identification of Organic Compounds, Fourth Edition; Wiley: New York, 1981.
IR
Raman 3250 p, m
3250 s
2975 dp, s
2982 m
2920 p, s 2900 p, s
2930 m 2890 m
1650 p, m
1650 s
calcd 3225.3 2971.1 2966.2 2960.5 2901.8 2899.6 2898.5 1674.6
1495 p, m
1494 m
1471.0
1465 p, m 1463 m 1445 p, m 1437 m 1425 p, m 1425 m 1370 p, w 1375 w 1310 p, w 1305 s 1285 p, w 1288 s 1269 p, w 1268 s 1227 dp, m 1231 w 1195 dp, w 1193 w 1170 dp, w 1173 w 1070 dp, w 1070 m (1029)' (1029)'
1465.0 1448.3 1430.8 1353.3 1314.7 1285.1 1235.5 1212.2 1206.3 1168.1 1061.2 998.2
997 dp, m 920 p, s 895 p, s (900)b 810 p, m 687 p, m 630 p, m 545 dp, w 472 dp, m
997 m 919 w 890 w (900)b 810 m 740 m 686 m 630 m 540 w (gas) 477 s 205
180 dp, w
984.7 954.6 872.4 889.6 809.8 737.1 681.4 614.4 513.8 474.8 186.0 122.6
assignment and PED,' % t4N-H). . , 99.3 vaSym(C-H),100 uSym(C-H), 100 u(C=O), 37.3 u(C'-N), 36.7 v(C'-N), 25.1 u(C=O), 17.5 v(C'-C), 12.3 S, 67.2 S, 67.6 S, 67.5 6(N-H), 39.7; W, 39.4 W, 98.8 W, 98.5 W, 74.3 T, 94.9 T, 97.2 T, 98.0 R, 88.4 u(C-N), 63.8 6(N-H), 11.7 R,77.6 v(C'-C), 19.3 u(C-C), 45.9 R, 73.0 u(C-C), 59.3 x(N-H), 87.9 u(C-C), 17.2 u(C-N), 12.9; 6(C=O), 10.5 6(C=O), 38.5 x(C=O), 59.9; amide bond torsion, 18.5 ring twist amide bond torsion, 70.1; x(C=O), 27.2 ring pucker (NC'CC torsion, 89.2)
'Taken from Table IV. bTaken from Table V. = stretch; S, W, T , R = CHI scissor, wag, twist, rock; 6, x = in-plane and out-of-plane deformation; dp = depolarized; p = polarized; s = strong; m = medium; w = weak; c' = carbonyl carbon.
envelopes.23 The in-plane carbonyl deformation occurs perpendicular to the calculated principal axis, A . These results for the carbonyl deformation modes are in agreement with those of Durig et al.3 Other workers' assignments have placed these motions at frequencies as high as 800 cm-' and as low as 420 cm-' for It should be noted that y-butyrolactone and 2-pyrrolidinone~.'~~~~J the results of this work for the carbonyl deformation modes of the 2-pyrrolidinones (Tables 111-VI) are about the same as for y-butyrolactone for the same reasons including band type and width of the in-plane carbonyl deformation. The bands at 205 cm-' (gas phase) and 170 cm-I are assigned as the ring twisting and puckering modes, respectively. These results are also in agreement with suggestions of Durig et aL3s6 and the-205 cm-I band, which is primarily due to a twisting a b u t the ester bond, is strikingly similar in frequency to the same mode in acyclic esters.22 B . 2-Pyrrolidinone-N-do and -N-d. The methylene group modes were assigned on the basis of spectral similarities t o ybutyrolactone (Tables 11-IV). Only the lowest frequency methylene rock mode of y-butyrolactone and 2-pyrrolidinone proved to be significantly different. For 2-pyrrolidinone, that mode's frequency was about 900 cm-I, about 100 cm-' lower than that ~
~
~~
(23) Ueda, T.; Shimanouchi, T. J . Mol. Spectrosc. 1968, 28, 350.
2572 The Journal of Physical Chemistry, Vol. 90, No. 12, 1986 TABLE I V Observed and Calculated Frequencies (cm-I), Assignments, and the Potential Energy Distribution for 2-Pyrrolidinone-N-d
obsd Raman 2990 dp, s 2931 dp, s
IR
calcd
2450 p, m 1650 p, m 1498 p, m
2971.1 2966.2 2960.5 2900 s 2901.7 2899.6 2895.5 2450 s 2378 1650 s 1659.8 1500 m 1465.4
1466 p, m 1445 p, m 1422 p, s 1313 p, w 1290 p, w 1270 p, w 1235 dp, m 1195 dp, w 1170 dp, w 1070 dp, w 1029 p, m
1467 m 1443 m 1424 m 1313 s 1290 s 1270 s 1232 w 1195 w 1172 m 1070 m 1030 w
1459.3 1437.1 1427.7 1314.9 1285.8 1262.6 1212.2 1206.2 1167.4 1057.8 1045.3
lOOOdp, w
997 m 944 m 924 w 894 w (900)" 808 m 689 m 643 m 580 m 545 m 474 m
981.8 961.6 876.1 826.2 887.4 791.3 674.0 612.0 599.3 508.7 458.6 175.7
2900 p, s
947 dp, m 920 p, w 891 p, s (900)' 805 p, m 686 p, m 641 p, m 540 p, w 472 dp, m 200 dp, w
2980 s
122
assignment and PED,b % U , , ~ ~ ( C H Z99.0 ), U,,~,(CHZ), 99.3 Y,,,,,,(CHZ), 99.8 u,,,(CHZ), 99.1 u,,,(CH~), 98.9 u,,,(CH~), 99.4 u(N-D), 96.6 u(C=O), 42.0; u(C'-N), 36.2 u(C'-N), 21.8; u(C=O), 19.0; u(C'-C), 13.6 S, 82.7 S , 88.1 S , 81.7 W, 98.3 W, 99.9 W, 97.7 T, 99.8 T, 97.2 T, 98.3 R, 90.5 6(N-D), 26.0; u(C-N), 24.8; u(C'-C), 10.6 R, 79.1 6(N-D), 47.6 u(C-C), 49.8 u(C-C), 37.9; x(N-D), 28.0 R, 61.2 x(N-D), 31.2; u(C-C), 11.4 u(C-C), 15.1 u(C-N), 10.8; 6(C=O), 10.1 x(N-D), 90.6 6(C=O), 64.1; u(C-N), 10.5 x(C=O), 59.1; x(N-D), 16.0 ring twist (out-of-planedeformation of N-D, 16.2; out-of-plane deformation of C=O, 29.2; amide bond torsion, 26.3)
ring pucker (out-of-planedeformation of C=O, 18.2; NC'CC torsion, 30.0; NCCC', 17.1)
'Taken from Table V. = stretch; S , W, T, R = CHI scissor, wag, twist, rock 6, x = in-plane and out-of-planedeformation; dp = depolarized; p = polarized; s = strong; m = medium; w = weak; C' = carbonyl carbon. of y-butyrolactone (Tables I1 and 111). For both compounds, the lowest frequency methylene rock was calculated to be that of the @-methylenegroup. The state of the literature on the amide bond stretch is equivocal. Many workers have placed the amide bond stretch of cis amides in the vicinity of either 1370 or 1420 cm-1.2,5,7J1Examining Tables 11-IV and VI, one can see. that butyrolactone has methylene scissors modes at 1487, 1463, and 1425 cm-', 2-pyrrolidinone has bands a t 1494, 1463, 1437, and 1425 cm-l, and N-(methyld3)-2-pyrrolidinonehas bands at 1500, 1465, 1439, and 1427 cm-'. There are similar bands for N-(methyl-do)-2-pyrrolidinone(Table V), the highest of which has a frequency of 1505 cm-I. The calculations show the bands around 1500 cm-I in the 2pyrrolidinones to be most likely due to the amide bond stretch. There is a band at 1370 cm-I for 2-pyrrolidinone-N-do, but that band disappears upon deuteration to give the N-d, compound. Also, N-methyl-2-pyrrolidinone does not have a band in the vicinity of 1370 cm-' (Table V). As stated in the Introduction, previous workers have had disagreements over the in-plane deformation of the amide hydrogen. The 2-pyrrolidinone-N-do band at 1370 cm-l is assigned to that mode. Upon deuteration, the 1370-cm-' band disappears completely, and a band at 944 cm-', assigned as the in-plane N-D deformation, appears. All absorptions within 500 cm-l of the 1370 cm-' band of 2-pyrrolidinone-N-do remain essentially unchanged
McDermott TABLE V: Observed and Calculated Frequencies (cm-I), Assignments, and the Potential Energy Distribution for
N-(MethyI-dn)-2-pyrrolidinone obsd Raman IR calcd 2982 dp, s 2960 dp, s 2923 p, s 2889 p, s 1673 p, m 1505 p, m 1476 p, 1471)" 1458 p, 1438 p, 1427 p, 1402 p, 1300 p,
m
3008.4 2991.3 2982.0 2975.1 2968.2 2945 s 2915.8 2914.6 2909.8 2890 s 2884.7 1670 vs 1639.7 1508 s 1489.0 2980 s
1255)b 1226 dp, m 1217 dp, m 1175 dp, w (1160)" 11 16 dp, w
1475 s (1471)' 1465 s 1445 s 1432 s 1405 s 1300 vs 1270 s (1255)* 1230 m 1217 w 1175 w (1160)' 11 15 s
1485.0 1478.2 1459.6 1445.2 1418.2 1397.3 1291.4 1280.4 1247.7 1225.8 1221.7 1187.8 1157.3 1147.9
(1085)' 1070 dp, w 1025 p, m
(1085)" 1075 w 1025 w
1078.0 1069.5 1090.0
984 p, m 930 p, s 900 p, w 851 p, s 748 p, s 662 dp, m 619 p, s 567 p, w 412 dp, m
988 s 930 m 900 w 855 m 750 m 658 s 619 w 570 m 472 m
994.2 894.3 903.3 856.2 802.0 649.1 634.0 495.9 474.2
310 (3) dp, m
310 m
302.5 298.0
150 dp, w
154
s
s s
m m
assignment and PED,C% u , , , ~ ( C H ~ )99.2 , U,,~,(CH~),99.1 Y,,~,,,(CH~),99.0 U,,~,(CH~),99.3 Y,,,,,,(CHZ), 99.8 U,,,(CHZ), 99.8 U~,,(CH~),98.2 u,,,(CH~), 98.3 U,~,(CH~), 97.4 u(C=O), 51.4; u(C'-N), 24.8 u(C'-N), 28.3; 6,,,(CH3), 19.0; S , 11.3 basY,(CH3), 91.6 6,,,(CH3), 72.5 S,90.5 S , 87.0 S , 89.3 sym deformation (CH,), 58.3 W, 90.2 W, 80.8 W, 77.0 T, 89.1 T, 98.3 T, 89.6 asym rock (CH,), 56.7 u(C-N), 28.2; u(CH~)-N), 26.4; sym rock (CH,), 11.9 sym rock (CH,), 85.2 R, 86.4 u(C-C'), 20.1; u(C-N), 16.2; sym rock (CH,), 15.3 R, 76.3 u(C-C), 30.3 R, 73.9 u(C-C), 30.3 u(C-C), 36.9; u(CH3-N), 19.1 u(C-N), 16.5 u(CH,-N), 19.9 6(C=O), 21.9 x(C=O), 33.9; x(N-CH3), 20.7 6(N-CH,), 70.5 x(N-CH,), 29.4; x(C=O), 20.8
133.7 ring twist 65.0 ring pucker
Taken from Jakes and Schneider's study of N-methylacetamide.2' = stretch; S , W, T, R = C H 2 scissor, wag, bTaken from Table VI. twist, rock; 6, x = in-plane and out-of-plane deformation; dp = depolarized; p = polarized; s = strong; m = medium; w = weak; C' = carbonyl carbon. by deuteration (Tables 111 and IV). The 740-cm-I band was assigned as the out-of-plane deformation of the amide hydrogen because it was not observed in the Raman spectrum. That inactivity has been noted to be a characteristic of all amides." The 740-cm-' band shifted to 580 cm-' (Tables 111 and IV) upon deuteration and remained Raman-inactive. In the calculations there was considerable mixing between the out-of-plane deformations of both the amide hydrogen and the carbonyl group, which gave a very poor calculated shift for the N-H deformation. To obtain a good calculated shift of the N-H bond required placing a repulsive valence interaction constant of value, 0.100 (Table VIII), between the N-H and C=O outof-plane deformations. That reduced the mixing of the two modes. A similar treatment was applied to N-methyl-2-pyrrolidinone. In-plane ring deformations were assigned as such on the basis of their general location in the spectrum, and particularly on the basis of their Raman peaks being strong and polarized. The ring twisting and puckering modes are assigned to bands at 205 and 180 cm-I, respectively, for which the frequencies of
Spectra of y-Butyrolactone and 2-Pyrrolidinones TABLE VI: Observed and Calculated Frequencies (em-’), Assignments, and the Potential Energy Distribution for N-(Methyl-d 3 )-2-pyrroldmone obsd Raman
IR
2973 dp, s 2928 p, s
2970111 2926 m
2896 p, s 2145 p, s 2116 dp, s 2075 p, s 1671 p,m s 1500 p. m 1465 p, m 1439 p, s 1427 p. s 1299 p, m 1266 p, m 1255 p, m 1227 dp, s 1217 dp, m 1175 dp, w 1125 p, w
2890 m 2150 w 2115 w 2073 w 1672 vs 1500s 1464s 1438s 1429 s 1299s 1270 m 1255 m 1229 w 1220 w 1170 w 1120w
assignment and PED.b 9%
calcd
2982.0 2975.1 2968.2 2915.8 2914.6 2909.8 2253.0 2229.4 2058.0 1637.2 1480.2 1476.2 1445.6 1410.6 1311.1 1284.2 1253.0 1222.2 1221.7 1184.3 1145.5
vasym(CHz), 99.0 ~asym(CH2)r99.4 ~asym(CH2)g99.7 ~sym(CH2),98.3 Vsym(CH*), 98.3 Usym(CHz), 98.3 ulym, out-of-phase
(CD,), 98.0
vasym(CD3)r 98.0 uSymrin-phase (CD,), 97.0 v(C=O), 52.9; u(C’-N), 24.4 p. s u(C’-N), 22.9 S, 70.0 S, 70.4 s, 58.5 W, 91.1 W, 99.8 W, 86.4 T, 97.2 T, 97.7 T, 99.3 u(CN), 25.3; u(CD~-N),25.6; u(CC), 10.2 1078.6 R, 84.4 1090 dp, w 1057 p, m 1056 w 1058.5 1057 dp, m 1056 w 1067.5 1030 p, m 1030111 971.2 1105.1 1020 p, m (988)O (988)’ 1002.0 934 p, s 933 w 893.5 u(C-C), 31.4; u(C-C), 10.1 909 dp, w 905 w 909.3 R, 75.2 883 dp, w 881 w 877.4 CD, asym rock, 67.0 850 p, s 850 w 864.3 u(C-C), 48.6 827 p, w 829 m 798.0 CD, sym rock, 29.0; u(C-C), 27.2; u(C-C), 10.2 737 p, s 740w 778.8 CD, sym rock, 71.2 652 p, w 652m 645.2 v(CN), 18.4; in-plane ring mode 603 p, s 605 w 619.9 u(CDI-N), 20.1; b(C=O), 14.6 572 w 480.3 8(C=O), 19.2; v(CDS-N), 12.6 562 p, w 460 dp, w 462 w 469.8 x(C=O), 35.1; x(N-CD,), 18.6 280 dp, m 280111 283.8 G(N-CD,), 70.4 290.9 x(N-CD,), 29.4; x(C=O), 19.6 132.9 ring twist 62.3 ring Ducker 140 dp, w 140
“Frequency taken from Table V. = stretch; S, W, T, R = CH2 scissor, wag, twist, and rock; 8, x = in-plane and out-of-plane deformation; dp = depolarized; p = polarized; s = strong; m = medium; w = weak; C’ = carbonyl carbon.
TABLE VII: Force Constants of Butyrolactone“
4.700 0.046 10.300 5.500 5.200 2.200 3.025 0.690 0.490 0.537
HCCC HCCC Hcc.0 HCQC H-4 H-+ X
C
T~~~~
T~~~~~ T~~~~
~
0.537 0.700 0.537 0.537 0.750 0.800 0.250 0.250 0.200 0.120
0.150 0.200 1.300 F m Fwc 0.700 0.300 FCC 0.600 Fco 0.350 Fee, 0.450 C-0 with HCO 0.300 C-C with HCC CC=O with HCC -0.140 CCC with HCC -0.120 T C C ~ T C ~ T
“C’ denotes the carbonyl carbon; 0’ denotes the carbonyl oxygen; K = stretch; H = bend; F = repulsion; x = out-of-plane wag; T = torsion. Force constants are in (mdyn/A; mdyn/rad; mdyn(A/rad2)).
the analogous modes of butyrolactone (Table 11) are almost identical. The 205-cm-* band was observed in the gas phase at an effective path of 40 m. The 180-cm-’ mode was observed via the Raman and was completely depolarized. Warshel et al.5 calculated 220 cm-’ as the frequency for the ring twisting mode. I t is of interest that 205 cm-’ is the same frequency of the amide
The Journal of Physical Chemistry, Vol. 90, No. 12, 1986 2573 TABLE VIII: Force Constants of 2-Pyrrolidinone-N-doand -N-d “
4.650 0.046 5.681 7.137 6.420 KCN 3.716 Kcc 2.200 Kcc, 3.025 HHCC,HCN0.690 HHCH 0.510 HNCC 0.700 Hccc 0.700 Hccct 0.750 Hccw 0.786 Kr FR KNH Kc.4 KCLN
Hcwc 0.750 H H N C 0.455 H H N - C ~0.460 Hoc!+ 0.955
HOCXN-H
xcj4 TNC~CC TCCCC, TCCCN TCCNCT
TCNC~C
FON
0.744 0.280 0.290 0.250 0.120 0.120 0.250 0.300 1.000
FOC Fcc
Fee, FCN
x(N-H) with x(C=O) CN with HCN CC with HCC CNC’ with HCN CC’O with HCC HNC with HCN CCN with HCC CC’N with HCC CCC with HCC
0.500 0.450 0.450 0.600 0.100 0.450 0.300 0.06 0.003 0.100 -0.120 -0.120 -0.120
“C’ denotes the carbonyl carbon; K = stretch; H = bend; F = repulsion; x = out-of-plane wag; T = torsion. Force constants are in (mdyn/A; mdyn/rad; mdyn(A/rad2)). TABLE I X Force Constants of N-(Methyl-do)- and N-(Methyl-d3)-2-pyrrolidinone’ Kr(CH3) 4.704 Hccc. 0.500 FCC Kr(CH2)
FR(cH~) FR(CH2)
Kcc
HHCH(CHz) HNCC
Hccc
4.670 Hccw 0.500 Feet 0.039 H C H , , , 0.800 FcN 0.046 HCH,NC 0.800 ~ ( N x H , ) with X(C+), 0.489 Hoc” 0.900 CN with HCN ((332)
0.450 0.450 0.700 0.130 0.450
0.900 CC with HCC 0.160 CCN with HCC
0.300 -0.140
0.200 0.250 0.200 0.200
-0.120 -0.120 -0.120 0.289
CC’N with HCC CCC with HCC C’CC with HCC CH,NC’ with HfJCN(CH3) 0.250 CH,NC with H0CN(CH3) 0.300 0.100 HCH with HCH (CH?) 0.490 F C H ~ 0.100 HCN with HCH (CH,) 0.500 FNO 1.154 CH,NC with HCN(CH3) 0.500 FOC 0.900 CH3N with HCN(CH3)
-0.289 -0.010 0.050 0.06 0.426
‘C’ denotes the carbonyl carbon; K = stretch; H = bend; F = repulsion; x = out-of-plane wag; T = torsion; a = HCH bend (CH,) for H out-of-plane; aa = HCH bend (CH,) for H in-plane; 0 = HCN bend (CH,) for H out-of-plane; Bo = HCN bend (CH,) for H in-plane. Force constants units are in (mdyn/A; mdyn/rad; mdyn(A/rad2)). bond torsional mode for N-methylacetamide and polyglycine I (the antiparallel chain extended conf~rmation).~ C. N-(Methyl-do)- and N-(Methyl-d3)-2-pyrrolidinone. For the analysis, the frequencies of some unobserved modes had to be assumed as noted in Tables I V and V. Unobserved methyl mode frequencies were taken from Jakes et al.3 results for Nmethylacetamide.20 The methylene modes, amide bond stretch, carbonyl modes, and the in-plane and out-of-plane ring deformations were assigned mostly on the basis of their similarity in frequency to modes of 2-pyrrolidinone with the Raman spectra serving to distinguish between A’and A”modes (Tables 111-VI). The methyl deformational modes were calculated to be in the vicinity of 300 cm-I. N-(methyl-do)- and N-(methyl-d,)-2pyrrolidinone each have three peaks in their Raman spectra (Tables V and VI) around 310 and 280 cm-I, respectively. The third peak in each case is assigned to the ring twisting mode. Peaks at 154 and 140 cm-’ were assigned to the ring-puckering modes respectively of N-(methyl-do)- and N-(methyl-d3)-2-pyrrolidinone, (Tables V and VI). Conclusions The aim of this work was to characterize the d y n a m i c s and intramolecular forces of y-butyrolactone, 2-pyrrolidinone, and
2574
J. Phys. Chem. 1986, 90, 2574-2580 frequency for the similar mode. The difference is most likely due to the ring strain which one would expect to find in the 2pyrrolidinones. The normal-coordinate analyses thus demonstrate that the vibrations associated with the carbonyl groups for all of the molecules and with the amide groups of the 2-pyrrolidinones are dissimilar in comparison with many other amides.
N-methyl-2-pyrrolidinone.The force constants for the methylene and methyl groups are, with some slight differences, similar to those for n-paraffin~.'~Other force constants such as those for ring angle bends, torsions, and in-plane deformations are higher, reflecting the ring strain and the partial rigidity imposed upon the ring by the partial double bond character of the amide bond. The carbonyl in-plane and out-of-plane deformational modes were found to be at approximately 540 and 480 cm-', respectively, for all molecules examined in this work. The N-H in-plane deformation of 2-pyrrolidinone was found to be at 1370 an-'.For all of the 2-pyrrolidinones, the amide bond stretch was found to have a frequency a t or near 1500 cm-I, in contrast to simple, acyclic cis amides for which 1370 cm-' has been given as the
Acknowledgment. Considerable thanks are due to Professor H. L. Strauss of the Berkeley Chemistry Department and the National Science Foundation who provided the facilities and support for much of this work. I am also indebted to Jim Scherer of USDA, Albany, CA, who ran all of the Raman spectra reported in this paper.
Photoelectron Spectroscopy of SO2-, Sa-, and S20Mark R. Nimlos and G. Barney Ellison* Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309 (Received: October 9, 1985)
We have studied the photoelectron spectroscopy of SO2-, S;, and SzO-and found the following electron affinities: EA(SOZ) = 1.107 f 0.008 eV, EA&) = 2.093 f 0.025 eV, EA(S20) = 1.877 f 0.008 eV. The heats of formation of the negative ions were determined to be AHf0298(S0;) = -98.0 0.2 kcal/mol, AHf0298(s3-) = -18.0 0.6 kcal/mol, AHfo298(S20-) = -57.5 f 0.3kcal/mol. From a Franckcondon analysis of the photoelectron spectra, we obtained the following geometrical parameters: rs-&O;) = 1.523 0.020 A, a&sa(SOz-) = 115.6 f 2.0°, rs-s(S3) = 1.90 0.05 R, rs-s(SzO-)= 2.010 0.020 A.
*
*
*
Introduction Sulfur oxides are thought to be important as possible intermediates in the oxidation of organosulfur compounds.' Their corresponding negative ions are crucial species in a number of solution and solid-phase s y s t e m d In this paper, photoelectron spectroscopy is used to probe SOz-, S3-,and S20- and their resulting neutral molecules. From the spectra, electron affinities (EA) of the neutral molecules and vibrational frequencies of the neutral molecules and negative ions can be obtained. We also report heats of formation of these ions. These ions and their corresponding neutral molecules provide an interesting comparison to O3and O
