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Intramolecular π-Type Hydrogen Bonding and Conformations of 3-Cyclopenten-1-ol. 2. Infrared and Raman Spectral Studies at High Temperatures Esther J. Ocola,† Abdulaziz A. Al-Saadi,†,‡ Cornelia Mlynek,§ Henning Hopf,§ and Jaan Laane*,† Department of Chemistry, Texas A&M UniVersity, College Station, Texas 77843-3255, and Institut fu¨r Organische Chemie, Technische UniVersita¨t, D-38106 Braunschweig, Germany ReceiVed: April 15, 2010; ReVised Manuscript ReceiVed: June 8, 2010
The vapor-phase infrared and Raman spectra of 3-cyclopenten-1-ol (3CPOL) have been collected at temperatures ranging from 25 to 267 °C. These clearly show the presence of four conformations of 3CPOL with the one with intramolecular π-type hydrogen bonding being most abundant. The spectra of all four conformations have been assigned, and these agree well with the computed values from the DFT calculation. The frequency shifts observed for the different conformations are in accord with the predicted values. In the O-H stretching region the conformer A with the π-type intramolecular hydrogen bond has the lowest stretching frequency at 3623.4 cm-1 while the three higher energy conformers have frequencies 14.2, 32.0, and 36 cm-1 higher. In the CdC stretching region conformer A again has the lowest frequency at 1607.3 cm-1 while the other conformers have bands 2.1, 8.0, and 13.4 cm-1 lower. Both the O-H stretching and the CdC stretching force constants are decreased about 2% by the hydrogen bonding. Five of the other vibrations show significant predicted frequency shifts up to 193 cm-1. Analysis of intensity data at different temperatures was used to calculate the energy difference between the two most stable conformers. This was found to be 435 ( 160 cm-1, and the result agrees reasonably well with the high level ab initio results which range from 274 to 401 cm-1. Introduction 1
In the previous paper we presented our theoretical calculations for the four conformers of 3-cyclopenten-1-ol (3CPOL), including the one with the π-type intramolecular hydrogen bonding. In the present paper we present our infrared and Raman spectroscopic investigation of 3CPOL in the vapor phase at temperatures ranging from 25 to 257 °C and also in the liquid phase at room temperature. The results will confirm the presence of the four predicted conformers. Experimental Section The sample of 3CPOL was prepared in the Hopf laboratory in Germany. The procedure involved three steps. 1,3-Cyclopentadiene was initially obtained by the thermal cracking of its dimer,2 and this was then monoepoxidized to 3,4-epoxycyclopentene as described by Crandall and co-workers.3 The 3-cyclopenten-1-ol (bp 136 °C) then was obtained by LiAlH4 reduction4 and purified by Kugelrohr distillation at 50 °C and 30 Torr pressure. Better than 98% purity was verified by NMR. The infrared spectra of vapor-phase 3CPOL were recorded using a Bruker Vertex 70 instrument which was purged by a stream of nitrogen gas. Samples at 25 °C (vapor pressure of ∼3 Torr) were obtained using a 4.2 m Infrared Industries long path multireflection cell with KBr windows. Infrared spectra at temperatures up to 90° were obtained in a heatable metal 10 cm cell (Specac Storm 10 with model 4000 temperature * To whom correspondence should be addressed, laane@ mail.chem.tamu.edu. † Texas A&M University. ‡ Present address: Chemistry Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia. § Technische Universita¨t.
controller) with KBr windows. At 90° the vapor pressure was estimated to be ∼90 Torr. Infrared spectra of a capillary film of the neat liquid between two KBr disks were recorded on the same infrared instrument. Raman spectra of 3CPOL vapor were recorded using a Jobin-Yvon U-1000 spectrometer and a Coherent Verdi V10 laser operating at 532 nm with a power of 5 W. Samples were contained in special heatable Raman cells which we have previously described.5 Temperatures up to 257 °C with ∼600 Torr of vapor pressure were used. Raman spectra of the neat liquid contained in a cuvette were recorded using the same instrumentation. Results and Discussion The infrared and Raman spectra of both liquid- and vaporphase 3-cyclopenten-1-ol (3CPOL) were analyzed. In the vapor phase all four of the predicted conformers were clearly present and the experimental spectra agree very well with the predicted vibrational frequencies. Conformer A with the intramolecular π-type hydrogen bond produces strong spectra, but the lowerabundance conformers B, C, and D can also be clearly seen. In the liquid phase the much stronger intermolecular hydrogen bonding between hydroxyl groups on neighboring molecules is present so that little or no intramolecular hydrogen bonding is retained. Thus, the theoretical calculations of the previous paper are not applicable to the molecule in condensed phases. The vapor spectra of 3CPOL to be described result from the combination of the individual spectra of the four conformers. Table 1 lists the calculated abundance of the conformers at the different temperatures at which the spectra were recorded. The hydrogen-bonded conformer is calculated to be more than 47% abundant at the temperatures used. In addition to the overlap of the spectra from different conformers, the spectra also show a large number of hot bands
10.1021/jp103406c 2010 American Chemical Society Published on Web 06/24/2010
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TABLE 1: Calculated Abundance (%) of 3CPOL Conformers at Different Temperaturesa temp (°C) A (0 cm-1) B (274 cm-1) C (409 cm-1) D (420 cm-1) 25 90 186 257
65 58 51 47
18 20 21 22
9 12 14 16
8 11 14 15
a Based on calculated energy differences calculated using CCSD/ 6-311++G(d,p).
Figure 2. Comparison between the experimental and computed Raman spectra of conformer A of 3CPOL.
Figure 1. Comparison between the experimental and computed infrared spectra of conformer A of 3CPOL.
arising from the vibrational excited states of the low-frequency vibrations, notably the ring-puckering vibrations with frequencies below 120 cm-1. The -OH torsional vibrations near 300 cm-1 are also expected to produce a number of observed hot bands. Figures 1 and 2 show the liquid- and vapor-phase infrared (25 °C) and Raman spectra (186 °C) of the sample and compare these to the calculated (DFT: B3LYP/cc-pVTZ) spectra for conformer A. Since most of the bands from the other conformers are only shifted by a few wavenumbers, it is only necessary to show the calculated spectrum for A in these broad general views. Figure 3 compares the vapor-phase infrared and Raman spectra and illustrates how very different the infrared and Raman intensities are from each other. Table 2 presents a comprehensive listing of the vibrational assignments of the spectra for all four conformers and compares these to the scaled values from the DFT computation. The vibrational descriptions were verified utilizing GaussView 3.0 software. The agreement between the experimental and calculated values is remarkably good, especially for the predicted wavenumber shifts between the different conformations. The wavenumber shifts in the table are listed as ∆ν. All of the calculated values are listed in italics below the experimental ones. The vibrations have been numbered according to Cs symmetry for the A conformer. In some cases the numbering would change for the D conformer which also has Cs symmetry since the frequency order may change. Conformations B and C have C1 symmetry, and their usual
Figure 3. Infrared and Raman spectra of 3CPOL vapor.
vibration numbering would not be according to A′ and A′′ symmetry species. For comparison’s sake, Table 2 also lists the vibrational frequencies for cyclopentene6 along with their symmetry species according to the C2V symmetry group. As expected, many of the 3CPOL vibrations are very similar to cyclopentene in both description and frequency. Whereas the wavenumber agreement is very good between experimental and computed values, the intensities agree more poorly. This can be seen in Figures 1 and 2 and also is evident in Table 2.
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TABLE 2: Observed and Calculated Vibrational Frequencies (cm-1) for the Four Conformers of 3-Cyclopenten-1-ola assignments
3-cyclopentenol conformers υ(A)
A′ υ1 O-H str. υ2 υ3 υ4 υ5 υ6 υ7 υ8 υ9 υ10 υ11 υ12 υ13 υ14 υ15 υ16 υ17 υ18 υ19 υ20 A′′ υ21 υ22 υ23 υ24 υ25 υ26 υ27 υ28 υ29 υ30 υ31 υ32 υ33 υ34 υ35 υ36
3623.4 3640.9 dCsH sym. str 3074.4 3072.3 C-H str. 2976.7 2972.7 R-CH2 antisym. str. i.p. 2933.0 2942.1 R-CH2 sym. str. i.p. 2862.6 2888.9 CdC str. 1607.3 1644.0 R-CH2 def. i.p. 1445.6 1460.4 β-CH bend/COH bend 1394.5 1405.6 R-CH2 wag i.p. 1295.1 1299.2 COH bend/β-CH bend 1274.6 1278.0 R-CH2 twist i.p. 1155.5 1157.3 dCH wag o.p in plane 1108.0 1113.8 R-CH2 rock 1047.5 1049.3 ring stretching 967.9 956.6 C-O stretching 948.3 931.0 ring stretching 832.4 819.9 ring deformation 744.6 746.3 CH i.p. bend out of 673.5 plane 680.7 CO rock 397.4 390.1 ring puckering s 119.0 dCH antisym. str. 3057 sh 3049.14 R-CH2 antisym. str. o.p. 2933.0 2941.2 R-CH2 sym. str. o.p. 2862.4 2889.3 R-CH2 def. o.p. 1446.4 1453.0 dCH wag i.p. in plane 1356 1363.8 R-CH2 wag o.p. 1283.2 1294.4 β-CH wag 1230.8 1224.9 R-CH2 twist o.p. 1151.3 1150.3 ring stretching 1034 1030.9 dCH wag o.p out of s plane 965.7 ring stretching 926.1 927.2 R-CH2 rock o.p. 862.8 861.8 ring deformation 780.7 781.6 CO wag 444.3 441.7 CdC twist 376 375.8 C-OH torsion s 322.5
cyclopentene
INT(IR, R)
υ(B)
∆υ
INT(IR, R)
υ(C)
∆υ
INT(IR, R)
υ(D)
∆υ
INT(IR, R)
41, 9 19, 554 85, 194 25, 1939 62, 23 50, 1376 202, 43 23, 1177 25, 10 33, 2365 2, 46 2, 220 17, 19 3, 163 38, 13 64, 72 18, 8 8, 32 9, 3 2, 32 100, 0.7 100, 34 4, 95 0.01, 168 54, 0.7 49, 36 2, 100 2, 100 29, 17 18, 29 51, 77 45, 116 5, 3 3, 12 97, 12 51, 37 s, 8 0.6, 10 s,s 3, 13 2, 30 8, 912 202, 43 23, 1068 28, 10 43, 738 3, 19 8, 130 s, 3 1, 6 1, 4 3, 5 5, s 10, 25 33, 0.4 2, 26 s, 0.7 0.02, 27 s, s 0.001, 5 5, 2 13, 1.2 5, 4 10, 14 1, 1 2, 11 0.5, 2 10, 6 s, 6 30, 20 s, s 72, 52
3655.4 3663.5 3075.7 3072.5 2949 2946.0 2921.3 2918.0 2861.5 2892.0 1620.7 1657.0 1443.8 1457.2 1392.0 1394.0 1303.5 1311.2 1273.8 1270.5 1195 1193.7 1110.5 1114.6 1053.3 1056.9 970.2 965.6 951.8 944.2 834.1 823.9 729.9 736.4 669.7 676.3 s 408.5 s 96.1 s 3049.13 2913.8 2905.2 s 2879.8 s 1448.1 s 1365.2 1294.9 1305.5 ∼ 1217.3 1215.6 1152.7 1152.0 1022.5 1019.4 s962.8 927.5 930.2 875.0 873.3 778.3 780.5 s 421.8 368 359.6 s 281.8
32.0 22.6 1.3 0.2 -28 -26.7 -11.7 -24.1 -1.1 3.1 13.4 13.0 -1.8 -3.2 -2.5 -11.6 8.4 12.0 -0.8 -7.5 39.5 36.4 2.5 0.8 5.8 7.6 2.3 9.0 3.5 13.2 0.6 4.0 -14.7 -9.9 -3.8 -4.4 s 18.4 s -22.9 s -0.01 -19.2 -36.0 s -9.5 s -4.9 ∼0 1.4 11.7 11.1 -14.0 -9.3 1.4 1.7 -11.5 -11.5 s -2.9 1.4 3.0 12.2 11.5 -2.4 -1.1 s -19.9 -7 -16.2 s -40.7
10, 31 26, 1078 58, 26 28, 2014 3, 20 18, 1026 54, 45 44, 987 21, 10 14, 804 1, 25 3, 222 12, 18 1, 180 14, 2 5, 45 4, 2 9, 21 8, 3 59, 19 ∼1, ∼1 5, 47 3, 95 1, 174 10, 0.4 17, 44 5, 75 0.4, 11 11, 13 72, 62 5, 61 22, 116 1, 0.7 1, 15 75, 10 39, 36 s,s 11, 5 s, s 0.1, 16 s,s 9, 944 54, 18 88, 3108 s, s 67, 744 s, s 8, 108 s,s 8, 24 4, 7 5, 20 2, s 48, 54 23, 0.4 7, 11 1, 0.4 5, 29 s, s 3, 57 3, 2 23, 5 1, 1 6, 15 1, 1 5, 13 s, s 7, 5 s, 6 2, 43 s, s 143, 28
3659 3670.1 3073.5 3070.3 2940 2941.4 2929 2926.2 2849.1 2888.3 1615.3 1654.8 1457 1470.9 1392.7 1403.0 1305.3 1318.7 1273.4 1273.3 1178.8 1181.5 1111.4 1117.9 1076.0 1069.8 970.8 963.9 1016.7 1011.8 839.8 829.3 571.2 572.3 690.1 700.6 464.8 467.5 s 71.4 s 3047.2 2906.9 2898.2 s 2868.2 s 1462.1 s 1366.8 1286.1 1295.0 1251.8 1252.3 1134.4 ? 1137.9 1046.6 1043.2 s 968.3 937.6 939.6 895.5 901.8 755.5 765.3 s 369.3 s 390.6 s 275.0
36 29.2 -0.9 -2.0 -37 -31.3 -4 -15.9 -13.5 -0.6 8.0 10.8 11.4 10.5 -1.8 -2.6 10.2 19.5 -1.2 -4.7 23.3 24.2 3.4 4.1 28.5 20.5 2.9 7.3 68.4 80.8 7.4 9.4 -173.4 -174.0 16.6 19.9 67.4 77.4 s -47.6 s -1.9 -26.1 -43.0 s -21.1 s 9.1 ∼0 3.0 2.9 0.6 21.0 27.4 -16.9 -12.4 12.6 12.3 s 2.6 11.5 12.4 32.7 40.0 -25.2 -16.3 s -72.4 s 14.8 s -47.5
3, 22 33, 1144 43, 232 30, 2027 5, 22 45, 1224 1, 46 49, 1210 s, 39 41, 1166 2, 86 3, 219 19, 7 2, 197 6, 4 3, 55 3, s 12, 10 7, 3 10, 15 1, s 3, 16 2, s 1.3, 173 4, 3 72, 55 3, 56 1, 12 8, 3 0.2, 96 3, 45 0.6, 90 s, 3 53, 46 42, 1 4, 27 2,5 1.2, 23 s, s 0.7, 7 s,s 10, 950 27, 20 32, 1532 s, s 46, 1321 s, s 4, 104 s,s 12, 29 3, 6 9, 33 6, s 74, 47 1, 0.4 3, 8 35, 0.4 1, 23 s, s 69, 34 10, 2 19, 1 1, s 3, 5 1, 3 2, 21 s, s 12, 13 s, s 10, 19 s, s 134, 27
3637.6 3645.9 ∼3073 3069.2 2949 2951.9 2939 2939.6 2845.8 2865.3 1609.4 1650.5 1457 1469.7 1394.1 1404.1 1303.9 1312.3 1272.8 1276.2 1134.4 ? 1139.8 s 1117.8 1085.0 1074.4 968.8 961.6 1011.3 1009.8 833.0 823.0 551.6 561.9 688.1 695.6 s 455.7 s 92.7 s 3046.4 2918.9 2930.0 2844.6 2864.7 s 1461.3 s 1363.9 s 1307.5 s 1271.4 1134.4 ? 1131.5 1063.0 1066.1 s 969.8 939.5 940.6 s 898.4 751.3 759.2 s 383.3 s 394.5 s 255.0
14.2 5.0 -1 -3.1 -28 -20.8 6 -2.5 -16.8 -23.6 2.1 6.5 11 9.3 -0.4 -1.5 8.8 13.1 -1.8 -1.8 -21.1 -17.5 s 4.0 37.5 25.1 0.9 5.0 63.0 78.8 0.6 3.1 -193 -184.4 14.6 14.9 s 65.6 s -26.3 s -2.7 -14.1 -11.2 -17.8 -24.6 s 8.3 ∼0 0.1 s 13.1 s 46.5 16.9 -18.8 29 35.2 s 4.1 13.4 13.4 s 36.6 -29.4 -22.4 s -58.4 s 18.7 s -67.5
7, 3 18, 720 27, 28 30, 2044 3, 20 59, 1686 s, 23 45, 1071 s, 24 58, 2369 1, 75 2, 237 19, 7 2, 204 36, 4 74, 54 3, 2 1, 27 3, 3 16, 37 ∼1,s 17, 76 s, s 7, 155 9, 4 161, 48 1, s 0.7, 11 1, 1 1, 93 ∼10, s 2, 76 s, 4 63, 40 26, 1 5, 37 s,s 1, 25 s,s 2, 12 s,s 9, 933 23, 28 3, 748 28, s 37, 690 s, s 5, 107 s,s 0.1, 11 s, s 1.1, 12 s, s 7, 16 1, 0.4 2, 7 3, s 5, 11 s, s 12, 13 6, 2 18, 1 s, s 3, 4 0.6, 3 3, 22 s, s 3, 20 s, s 30, 12 s, s 92, 37
υ
3078
SYM
A1
2963/2903 B2/A2 2933
B2
2860
A1
1623
A1
1445
A1
s 1290
A1
s
s
1211
B2
1101
A1
s
B2
962
A1
1047
B2
900
A1
593
A1
695
B2
s
s
127
B2
3068
B1
2955
A2
2873
B1
1438
B1
1353
B1
1297
B1
s
B1
1268
A2
1047
B2
933
A2
1037
B1
878
A2
906
B1
s
A2
390
A2
s
s
a The first line for each vibration presents experimental data. The second line in italics presents calculated values using the B3LYP/cc-pVTZ basis set. The scaling factors for the wavenumbers are 0.985 for numbers above 1800 cm-1 and 0.961 for those below 1800 cm-1. The relative intensities were determined from peak heights from absorbance for infrared and counts for Raman. Abbreviations: i.p. ) in-phase; o.p. ) out-of-phase. The frequency shifts are relative to the conformer A value.
The majority of vibrations, as shown in Table 2, show wavenumber differences of only a few cm-1 for the different conformers reflecting that the vibrations themselves are little
changed. Those vibrations that do show changes, however, are of greatest interest as they provide insight into the bonding differences between the four conformers. Figure 4 shows the
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Figure 5. Infrared and Raman spectra of vapor-phase 3CPOL in the CdC stretching region.
Figure 4. Infrared and Raman spectra of vapor-phase 3CPOL in the O-H stretching region.
OH stretching region for 3CPOL vapor. All four conformers are clearly observed in both infrared and Raman spectra although conformer C appears as a shoulder in both spectra. Conformer A, as expected, with its intramolecular hydrogen bond has the lowest O-H stretching frequency and the strongest infrared band. The frequencies for B, C, and D are 32, 36, and 14 cm-1 higher, respectively. Table 3 summarizes the frequency shifts for the seven vibrational modes of greatest significance, including ν1, and compares these to the calculated shifts. Figures 5 and 6 show the infrared and Raman spectra in the regions for two of the other modes, the CdC stretching region and CH out-of-plane bending region, respectively. As shown in Table 3, the experimentally observed trend in frequency shifts is confirmed for each of these vibrations, and the actual calculated shift agrees to within a few cm-1. The poorest agreements are for the ν15 shifts of conformer D (78.8 vs 63.0 cm-1) and ν1 for conformer B (22.6 vs 32.0 cm-1). Nonetheless, we find the computed shifts to be remarkably accurate. It is noteworthy that upon examination of Table 3, the A and B conformations have similar vibrational frequencies for many of the vibrations. This is also true for C and D. However, vibrations ν15, ν17, and ν19 show big differences between the two pairs reflecting strong vibrational coupling between these modes. The ν17 ring deformation shifts dramatically, -173.4 cm-1 for C and -193 cm-1 for D, as compared to that for A while ν15, the C-O stretching,
Figure 6. Infrared and Raman spectra of vapor-phase 3CPOL for ν18, CH out-of-plane bending.
increases 68.4 and 63.0 cm-1 for C and D, respectively. At the same time ν19, the C-O rock, increases 67 cm-1 for C and
TABLE 3: Observed and Calculateda Frequency (cm-1) Shifts between the Conformers νA
∆νB
∆νC
∆νD
vibration
obsvd
calcd
obsvd
calcd
obsvd
calcd
obsvd
calcd
ν1 O-H str. ν6 CdC str. ν15 C-O str. ν17 ring deformation ν18 CH i.p. bend out of plane ν27 β-CH wag ν29 ring stretching
3623.4 1607.3 948.3 744.6 673.5 1230.8 1034
3640.9 1644.0 931.0 746.3 680.7 1224.9 1030.9
32.0 13.4 3.5 -14.7 -3.8 -14.0 -11.5
22.6 13.0 13.2 -9.9 -4.4 -9.3 -11.5
36 8.0 68.4 -173.4 16.6 21.0 12.6
29.2 10.8 80.8 -174.0 19.9 27.4 12.3
14.2 2.1 63.0 -193 14.6
5.0 6.5 78.8 -184.4 14.9 46.5 35.2
a
B3LYP/cc-pVTZ basis set. Scaling factor: 0.985 for numbers above 1800 cm
-1
and 0.961 for those below.
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(IB/IA) ) 2(RB/RA) exp(-∆EAB /kT)
(4)
ln(IB/IA) ) ln(2RB/RA) - ∆EAB /kT
(5)
and
Figure 7. Vapor-phase infrared and Raman spectra of 3CPOL in the 600-1200 cm-1 region.
65.6 cm-1 (calculated) for D. Both the experimental spectra and the calculations confirm these large changes. To provide additional perspective on the spectra, Figure 7 shows the vapor-phase infrared and Raman spectra in the 600-1220 cm-1 region. The many Q branches in the infrared spectra arise both from the presence of the four conformers and from hot bands originating mostly from the vibrational excited states of the ring puckering. Energy Difference between Conformers. Since both the Raman and infrared vapor-phase spectra were recorded at different temperatures, it is possible to estimate the energy difference between conformers from the observed intensity changes. As the temperature is increased the populations of the higher energy conformers are increased as shown in Table 1 which assumed calculated energy difference values. For the calculations we have that the intensity I (infrared absorbance or Raman intensity) is given by
I ) RP
(1)
where R is a proportionality constant based on the Raman cross section or infrared absorption constant as well as instrumental and/or sampling methods and P is the molecular population. The relative intensity of bands from conformers A and B can then be written as
(IB/IA) ) (RB/RA)(PB/PA)
(2)
If we assume A to be the lowest energy π-bonded conformer, the population ratio is given by
(PB/PA) ) gB exp(-EB - EA)/kT ) 2 exp(-∆EAB /kT) (3) where EA and EB are the molecular energies of the two conformers and where the degeneracy gB ) 2 for the two equivalent B conformations. Then
Thus, since we have data for IB/IA for different vibrations as a function of temperature, we can graph ln(IB/IA) vs (kT)-1 to obtain the slope which is ∆EAB, the energy difference between conformers A and B. We have done this only for these two conformers since the intensity data for the higher energy C and D conformers are not as reliable. Even for the A and B data there are fairly large uncertainties in measuring IB/IA (typically about 10%) and temperature (up to (5 °C) so that the calculated EAB value will be somewhat approximate. For these calculations we have used the Raman and infrared data for ν1 and the infrared data for ν18. Only two data points were available for each of the infrared calculations while the Raman data were collected at three different temperatures. The calculations gave the energy difference EAB between conformers A and B to be 435 ( 160 cm-1 where the uncertainty is given as twice the standard deviation (2σ). This value is not very accurate due to the uncertainties in the intensity measurements, but it is not inconsistent with the higher level ab initio results ranging from 274 to 401 cm-1 as reported in the previous paper. Conclusions The infrared and Raman spectral data recorded at four different temperatures agree remarkably well with the DFT computed values for all four conformers. This is especially true for the frequency shifts between the conformers for the same vibrational modes. The O-H stretching bond for conformer A with the weak π-type intramolecular hydrogen bond was observed at 3623.4 cm-1 whereas the conformers without hydrogen bonding have higher frequency bands at 3655.4 (B), 3659 (C), and 3637.6 (D) cm-1. The wavenumber difference between conformers A and B implies that the O-H stretching force constant is reduced by 1.8% due to the hydrogen bonding. The CdC stretching frequencies for A and B are 1607.3 and 1620.7 cm-1, respectively, implying that this stretching force constant is reduced by 1.7% due to the hydrogen bonds. Thus the effects on the OsH and CdC bonds are not great. Nonetheless, the intramolecular hydrogen bonding is large enough to give conformer A sufficiently lower energy to make it the dominant species. Acknowledgment. The authors wish to thank the Robert A. Welch Foundation (Grant A-0396) for financial support. A. AlSaadi wishes to thank King Fahd University of Petroleum and Minerals for its financial support. References and Notes (1) Al-Saadi, A. A.; Ocola, E. J.; Laane, J. J. Phys. Chem. A DOI: 10.1021/jp103404e. (2) Moffett, R. B. Organic Synthesis; Wiley & Sons.: New York,1963, Collect. Vol. 4, p 238. (3) Crandall, J. K.; Banks, D. B.; Colyer, R. A.; Watkins, R. J.; Arrington, J. P. J. Org. Chem. 1968, 33, 423. (4) Healy, E. F.; Lewis, J. D.; Minniear, A. B. Tetrahedron Lett. 1994, 35, 6647. (5) Haller, K.; Chiang, W.-Y.; del Rosario, A.; Laane, J. J. Mol. Struct. 1996, 379, 19. (6) Al-Saadi, A. A.; Laane, J. J. Mol. Struct. 2007, 830, 46.
JP103406C
