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Molecular structure of N-methylpyrrole studied by gas electron diffraction using rotational constants and liquid–crystal NMR spectroscopy
Journal of Molecular Structure 567±568 (2001) 107±111
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Molecular structure of N-methylpyrrole studied by gas electron diffraction using rotational constants and liquid±crystal NMR spectroscopy q H. Takeuchi, K. Inoue, J. Enmi, T. Hamada, T. Shibuya, S. Konaka* Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan Received 30 May 2000; accepted 19 July 2000
Abstract The molecular structure of N-methylpyrrole has been reinvestigated by gas electron diffraction using the rotational constants of 13C- and 15N-substituted species of N-methylpyrrole and N-methyl-d3-pyrrole measured by Huber et al. [J. Mol. Struct. 413± Ê ) and /z (8)) with the estimated limits of error (3s ) are: r(N± 414 (1997) 93]. The resulting structural parameters (rz (A Cring) 1.372(6), r(N±CMe) 1.425(7), r(CyC) 1.383(9), r(C±C) 1.425(11) kr(C±H)l 1.088(4), /CNC 109.3(9), / NCC 108.2(7), /CCC 107.1(4), /NCHring 117.7(29), /HCC(N) 124.0(42), /HCH 109.1(3), where k l denotes an average value. The molecular structure, including carbon positions, of N-methylpyrrole dissolved in liquid crystal, ZLI 1167, has been determined by analyzing the 1H NMR spectrum with 13C satellites. The results show that the molecular structure in ZLI 1167 agrees with that in the gas phase within experimental uncertainties. q 2001 Elsevier Science B.V. All rights reserved. Keywords: N-Methylpyrrole; Molecular structure; Gas electron diffraction; Liquid±crystal NMR
1. Introduction As is well known, the structures of molecules dissolved in nematic liquid crystals can be determined precisely by NMR spectroscopy (liquid±crystal NMR) [1,2]. By comparing them with the gas-phase structures, it is possible to study the deformation of the molecular structures due to liquid±crystal solvents. For this purpose, it is necessary to determine molecular structures as accurately as possible. Some time ago, we determined the molecular structure of N-methylpyrrole (NMP, see Fig. 1) by gas q Dedicated to Professor Marit Trñtteberg on the occasion of her 70th birthday. * Corresponding author. Fax.: 181-11-706-2699. E-mail address: [email protected] (S. Konaka).
electron diffraction (GED) combined with ab initio calculations [3] In this study, the rotational constants, B0 and C0, of NMP reported by Arnold et al. [4] were used and the differences between some structural parameters were taken from the result of RHF/631G p calculations [3]. Recently, Huber et al. measured the rotational constants of 13C- and 15Nsubstituted species of NMP and N-methyl-d3-pyrrole (NMPD3) [5] and the rotational constants of the complexes of NMP with one or two argon atoms [6] by microwave spectroscopy (MW). The use of the rotational constants of 13C- and 15N-substituted species of NMP and NMPD3 allows us to determine a more reliable structure. Therefore, in the present study, the molecular structure of NMP is reinvestigated by a joint analysis of the GED intensities reported in [3] and these rotational constants.
0022-2860/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0022-286 0(01)00538-5
108
H. Takeuchi et al. / Journal of Molecular Structure 567±568 (2001) 107±111 Table 1 Rotational constants and vibrational corrections of N-methylpyrrole (NMP), N-methyl-d3-pyrrole (NMPD3) and their isotopic species (in MHz) a B0 b
Fig. 1. Molecular model of N-methylpyrrole.
Suryaprakash et al. [7] determined the ratios of inter-proton distances of NMP dissolved in nematic liquid crystals, ZLI 1167, MBBA and EBBA, by NMR spectroscopy. In the present study, we have measured a 1H NMR spectrum of NMP in ZLI 1167 and determined a more complete structure including carbon positions by analyzing the spectrum with 13C satellites. The resultant structure is compared with the gas-phase structure to investigate the deformation of the molecular structure in ZLI 1167.
Bz2B0 c
Bz d
Ba0 e
NMP B 3559.92967(19) C 2566.94415(13)
21.33(27) 20.53(11)
3558.60(27) 2566.41(11)
3558.3(7) 2566.2(6)
NMPD3 B 3129.18246(62) C 2335.44261(62)
21.31(26) 20.56(11)
3127.87(26) 2334.88(11)
3127.7(7) 2334.4(5)
2- 13C-NMPD3 B 3128.32559(94) C 2321.67619(88)
21.31(26) 20.55(11)
3127.02(26) 2321.13(11)
3126.7(7) 2320.6(6)
3- 13C-NMPD3 B 3084.03647(80) C 2305.04409(80)
21.28(26) 20.55(11)
3082.76(26) 2304.49(11)
3082.3(8) 2303.9(6)
2- 13C-NMP B 3559.60750(18) C 2550.72902(16)
21.33(27) 20.52(10)
3558.28(27) 2550.21(10)
3557.8(6) 2549.8(5)
3- 13C-NMP B 3508.04663(18) C 2533.63652(16)
21.30(26) 20.52(10)
3506.75(26) 2533.12(10)
3506.1(7) 2532.7(5)
C(methyl)-NMP B 3452.77149(28) C 2510.75327(29)
21.30(26) 20.52(10)
3451.47(26) 2510.23(10)
3451.0(7) 2510.0(6)
N-NMP B 3549.24227(73) C 2561.43451(54)
21.30(26) 20.53(11)
3547.94(26) 2560.90(11)
3547.6(7) 2560.6(6)
13
15
2. Experimental The 1H and 13C spectra of 5 M solution of NMP in CDCl3 were recorded on a JNM EX400 spectrometer at 238C to obtain indirect coupling constants. The sample dissolved at a concentration of 5 wt% in ZLI 1167 was degassed and sealed in vacuum. A 1H-NMR spectrum was recorded on the same spectrometer at 278C. External CDCl3 was used to lock the magnetic ®eld. The measured spectrum is similar to that reported in [7]. 3. Structural analysis 3.1. Gas electron diffraction The structural analysis was carried out by using the GED intensities measured at 288C [3]. The range of sÊ 21. The total intensities have values was 4.4±33.6 A
a
Parenthesized values are the estimated limits of error. Rotational constants taken from Ref. [5]. c Vibrational corrections. The limits of error were estimated to be 20% of the corrections. d Rotational constants in the zero-point average structure. e Calculated from the ra0 structure determined by a joint analysis of GED intensities and rotational constants. The estimated limits of error are 3s . b
been deposited [3] and they are also available from the corresponding author. The following assumptions were made in the data analysis: (1) molecular symmetry is Cs in the equilibrium state as shown in Fig. 1 [3,5,6]; (2) C, N and Hring atoms are on the same plane [3]; (3) the methyl group has C3v symmetry; (4) rg(C9±H1) is equal to rg(C10±H2); (5) the difference between rg(C±HMe) Ê (HF/6-31G p and rg(C±Hring) is equal to 0.012 A value [3]). Adjustable parameters were selected as
H. Takeuchi et al. / Journal of Molecular Structure 567±568 (2001) 107±111 Table 2 Indirect and direct coupling constants, Jij and Dij, of N-methylpyrrole (in Hz) a i; j
Jij
Dij
Daij
a b Dij,calc
1,2 1,3 1,4 1,5 1,9 1,10 1,13 2,3 2,5 2,9 2,10 2,13 3,9 3,10 4,9 4,10 5,6 5,9 5,10 5,13
2.57(6) 1.62(6) 1.85(2) 0.23(2) 182.33(4) 7.59(16) 0.0 3.94(3) 0.0 7.90(17) 169.72(7) 0.0 7.81(17) 3.96(7) 5.85(5) 8.15(16) 0.0 2.99(3) 0.0 138.14(6)
553.24(6) 65.35(7) 21.63(14) 255.95(4) 605.28(28) 175.24(25) 72.3(4) 75.62(13) 81.81(5) 280.0(4) 1530.76(23) 26.6(8) 42.3(5) 68.1(5) 13.0(4) 31.5(4) 21015.04(4) 86.8(6) 40.0(6) 2691.19(31)
563.6(5) 66.19(8) 21.89(14) 257.56(9) 675(4) 180.5(4) 73.0(4) 78.36(19) 81.81(5) 287.1(6) 1679(7) 26.7(8) 42.8(5) 69.0(5) 13.1(4) 31.9(4) 21055.4(20) 87.5(6) 39.9(6) 2744.2(27)
563.7 66.19 21.68 257.59 676 180.5 71.9 78.49 81.79 287.2 1676 28.2 43.2 68.8 13.3 31.4 21055.6 87.9 38.1 2743.9
a b
The numbers in parentheses are 1s . The values calculated in the ®nal analysis.
Table 3 Mean amplitudes lij and interatomic distances rg of N-methylpyrrole Ê )a (A Atom pair b
lcalc ij
lobs ij
rg
Group c
H1±C9 H2±C10 H5±C13 N8±C9 N8±C13 C9yC10 C10±C11 N8´´´C10 C9´´´C11 C9´´´C12 C9´´´C13 C10´´´C13
0.076 0.077 0.079 0.045 0.047 0.044 0.049 0.049 0.052 0.051 0.065 0.060
0.071(4) d 0.071 0.074 0.045(1) d 0.048 0.045 0.050 0.052(2) d 0.054 0.053 0.068 0.066(8) d
1.096 1.097 1.109 1.374 1.452 1.384 1.427 2.232 2.260 2.241 2.510 3.638
1 1 1 2 2 2 2 3 3 3 3 4
a The mean amplitudes of relatively important atom pairs are listed. b Non-bonded atom pairs including hydrogen atoms are omitted. c The mean amplitudes with the same number were re®ned as one group. d The numbers in parentheses are the estimated limits of error 3s , where s denotes the standard error.
109
r(N±Cring), r(N±CMe), r CyC; kr(C±H)l, /CNC, / NCC, /NCHring, /HCC(N) and /HCH, where k l denotes an average value. The analysis of GED intensities was performed by treating the methyl rotation as a large amplitude motion. The rotational angles of the methyl groups of pseudo-conformers were taken at intervals of 108. The weights of pseudo-conformers were calculated from the experimental potential function [3] by assuming a Boltzmann distribution. The mean amplitudes and shrinkage corrections, r a0 2 ra ; of pseudoconformers were calculated from the quadratic force constants reported in [3]. The rotational constant A0 is an effective one because of internal rotation of the methyl group [4,5]. Therefore, the rotational constants, B0 and C0, of several isotopomers [5] were used in the analysis. The vibrational corrections for rotational constants, B0 2 Bz and C0 2 Cz, were calculated as described in [8] using the force constants [3]. In the calculations, the methyl group was ®xed at the con®guration shown in Fig. 1. The values of rotational constants, Bz and Cz, are listed in Table 1. Isotopic effects on the bond lengths were calculated Ê 21. By by assuming the Morse parameter to be 2.0 A referring to the results, the deuterium isotopic effect on the C±HMe distance, rz(C±HMe) 2 rz(C±DMe), was Ê , while the ®xed at the calculated value of 0.002 A isotopic effects on the other bond lengths were assumed to be zero in the structural analysis. The structural parameters, index of resolution and mean amplitudes were determined by a joint analysis of the GED intensities and rotational constants. 3.2. Liquid±crystal NMR The analysis of NMR spectra of NMP in CDCl3 and ZLI 1167 was carried out with the program LCNMR [9]. Indirect coupling constants, Jij, were determined from the 1H and 13C spectra of NMP in CDCl3. The values of Jij were used to determine direct coupling constants, Dij, from the 1H-NMR spectrum and its 13C satellites of NMP in ZLI 1167. Direct coupling constants were corrected for harmonic vibrations by using the force constants [3] and converted to those in the ra structure, Dija [1,2]. The Dija 's thus obtained include the uncertainties of vibrational corrections arising from the arbitrariness
110
H. Takeuchi et al. / Journal of Molecular Structure 567±568 (2001) 107±111
Table 4 Structural parameters of N-methylpyrrole a rz(GED 1 MW) b r(N8±C9) r(N8±C13) r(C9yC10) r(C10±C11) r(H1±C9) r(H2±C10) r(H5±C13) /C9N8C12 /N8C9C10 /C9C10C11 /H1C9N8 /H1C9C10 /H2C10C9 /H2C10C11 /H5C13H6 /H5C13N8
1.372(6) 1.452(7) 1.383(9) 1.425(11) e 1.079(4) 1.081(4) e 1.100(4) e 109.3(9) 108.2(7) 107.1(4) e 117.7(29) 134.2(32) e 124.0(42) 128.9(44) e 109.1(3) 109.9(3) e
Table 5 Distance ratios and bond angles of N-methylpyrrole a
rs(MW) c 1.361 1.452 1.393 1.422
110.5 107.7 107.0
rc(ab initio) d
LCNMR
0.757(7) b 0.759(7) b 0.772(7) b 0.970(13) b 1.761(14) b 107.1(3) 134.2(32) 124.0(42) 109.1(3)
0.756(6) 0.750(7) 0.769(5) 0.966(8) 1.761(11) 106.8(2) 131.2(4) 125.8(4) 109.0(2) 2 0.0133(4) c 2 0.101(3) c
1.371 1.450 1.387 1.418 1.081 1.081 1.092 109.5 108.1 107.2 120.7
r(H1±C9)/r(C10±C11) r(H2±C10)/r(C10±C11) r(H5±C13)/r(C10±C11) r(C9yC10)/r(C10±C11) r(C9´ ´´C13)/r(C10±C11) /C9C10C11 /H1C9C10 /H2C10C9 /H5C13H6 Sxx Szz
127.1
Bond angles in degrees. The numbers in parentheses are 3s . The ratios of internuclear distances are calculated from the rz structure listed in Table 4. c Order parameters. The value of r(C10±C11) was assumed to be Ê. 1.425 A
Ê , angles in degrees. Bond lengths in A The result obtained by a joint analysis of GED intensities and rotational constants. The numbers in parentheses are the estimated limits of error 3s , where s denotes the standard error from leastsquares re®nement. The rg bond distances are listed in Table 3. The correlation coef®cients with the absolute values larger than 0.7 are: r N8±C9=r C9yC10 20:89; r(N8±C13)//C9N8C12 0.79, r(N8±C13)/N8C9C10 20.75, /C9N8C12//N8C9C10 20.93, and l1/12 0.82, where l1 and l2 denote the groups of mean amplitudes de®ned in Table 3. c Ref. [5]. d The result of MP2/6-311G(d,p) calculation [5]. e Dependent parameter. a
b
GED 1 MW
a
b
of harmonic force constants and anharmonic contributions to vibrational frequencies. In the present study, they were assumed to be 5% of vibrational corrections as suggested by Diehl [2,10]. The results are summarized in Table 2. The ratios of internuclear distances and order parameters were determined by least-squares calculations on Dija .
Fig. 2. Experimental (solid line) radial distribution curve of N-methylpyrrole: Df r f rexp 2 f rtheor : An arti®cial damping function, exp(20.002s 2), is used.
H. Takeuchi et al. / Journal of Molecular Structure 567±568 (2001) 107±111
4. Results and discussion The results of the joint analysis of GED intensities and rotational constants are listed in Tables 3 and 4. The radial distribution curve is shown in Fig. 2. The differences between experimental and theoretical curves are slightly smaller than those in [3]. Table 5 compares the ratios of internuclear distances and bond angles of NMP in ZLI 1167 with those in the gas phase. In the previous study on the gas-phase structure [3], the values of /NCHring, /CyCH and the difference between two N±C bond lengths, Dr N±C rg N±CMe 2 rg N±Cring ; were taken from the RHF/6-31G p calculations. In the present study, however, these structural parameters could be determined independently by the joint analysis as shown in Table 4. The values of the structural parameters are consistent with the previous ones [3] but the experimental uncertainties of the parameters relating to hydrogen atoms are smaller than those in the previous study. The value of Dr(N±C) obtained in the present Ê , is in good agreement with the value study, 0.078(9) A Ê assumed previously [3] and the MP2/6of 0.080 A Ê [5]. The bond lengths 311G(d,p) value of 0.079 A and bond angles given by MP2/6-311G(d,p) calculations [5] agree with the rz values within experimental uncertainties. The differences between the bond lengths in the rz and rs structures are larger for the bonds related to the C9 atom, N8±C9 and C9yC10, than for N8±C13 and C10±C11 bonds. The rs value of /C9N8C12 is larger than the corresponding rz value by 1.28. These differences are ascribed to the fact that the a coordinate of C9 has not been determined precisely in the microwave spectroscopic study [5]. Table 5 shows that the values of /H1C9C10 and / H2C10C9 are determined by liquid±crystal NMR more precisely than by the joint analysis of GED intensities and rotational constants. The ratios of internuclear distances and bond angles of NMP in ZLI 1167 are in good agreement with those in the gas phase, indicating that the structural deformation of NMP by the solvent is small. This is consistent with the calculation of molecular deformation [11]: the changes of internuclear distance ratios and bond angles after deformation corrections are smaller than 0.007 and 0.28, respectively. (Resulting structure and
111
corrections to Dij are available from the corresponding author.) In the case of pyrrole in ZLI 1167, however, VaÈaÈnaÈnen et al. [12] found a large structural deformation. From the comparison between theoretical and experimental order parameters and the large variation of chemical shifts, they ascribed it to the formation of hydrogen bonding between the N±H proton and the solvent. On the other hand, NMP does not form such a hydrogen bond. This is considered to make the structural deformation of NMP much smaller than that of pyrrole.
Acknowledgements This work was supported by the Grant-in-Aid for Scienti®c Research (08454168). We thank the HighResolution NMR laboratory, Faculty of Science, Hokkaido University, for the measurement of NMR spectra. Numerical computations were carried out on a Hitachi Model MP5800/160 at the Hokkaido University Computing Center.
References [1] J.W. Esmley, J.C. Lindon, NMR Spectroscopy Using Liquid Crystal Solvents, Pergamon Press, Oxford, 1975. [2] P. Diehl, in: J.W. Emsley (Ed.), Nuclear Magnetic Resonance of Liquid Crystals, Reidel, Dordrecht, 1985 (Chapter 7). [3] N. Kurai, H. Takeuchi, S. Konaka, J. Mol. Struct. 318 (1994) 143. [4] W. Arnold, H. Dreizler, H.D. Rudolph, Z. Naturforsch. Teil A 23 (1968) 301. [5] S. Huber, T.-K. Ha, A. Bauder, J. Mol. Struct. 413±414 (1997) 93. [6] S. Huber, J. Makarewicz, A. Bauder, Mol. Phys. 95 (1998) 1021. [7] N. Suryaprakash, A.C. Kunwar, C.L. Khetrapal, Chem. Phys. Lett. 107 (1984) 333. [8] K. Kuchitsu, M. Nakata, S. Yamamoto, in: I. Hargittai, M. Hargittai (Eds.), Stereochemical Applications of Gas-phase Electron Diffraction, VCH, New York, 1988 (Chapter 7, Part A). [9] M. Nakagawa, S. Konaka, Unpublished work, 1989. [10] P. Diehl, in: A. Domenicano, I. Hargittai (Eds.), Accurate Molecular Structure, Oxford University Press, Oxford, 1992 (Chapter 12). [11] R. Wasser, M. Kellerhals, P. Diehl, Magn. Reson. Chem. 27 (1989) 335. [12] T. VaÈaÈnaÈnen, J. Jokisaari, A. KaÈaÈriaÈinen, J. Lounila, J. Mol. Struct. 102 (1983) 175.
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Molecular structure of N-methylpyrrole studied by gas electron diffraction using rotational constants and liquid±crystal NMR spectroscopy q H. Takeuchi, K. Inoue, J. Enmi, T. Hamada, T. Shibuya, S. Konaka* Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan Received 30 May 2000; accepted 19 July 2000
Abstract The molecular structure of N-methylpyrrole has been reinvestigated by gas electron diffraction using the rotational constants of 13C- and 15N-substituted species of N-methylpyrrole and N-methyl-d3-pyrrole measured by Huber et al. [J. Mol. Struct. 413± Ê ) and /z (8)) with the estimated limits of error (3s ) are: r(N± 414 (1997) 93]. The resulting structural parameters (rz (A Cring) 1.372(6), r(N±CMe) 1.425(7), r(CyC) 1.383(9), r(C±C) 1.425(11) kr(C±H)l 1.088(4), /CNC 109.3(9), / NCC 108.2(7), /CCC 107.1(4), /NCHring 117.7(29), /HCC(N) 124.0(42), /HCH 109.1(3), where k l denotes an average value. The molecular structure, including carbon positions, of N-methylpyrrole dissolved in liquid crystal, ZLI 1167, has been determined by analyzing the 1H NMR spectrum with 13C satellites. The results show that the molecular structure in ZLI 1167 agrees with that in the gas phase within experimental uncertainties. q 2001 Elsevier Science B.V. All rights reserved. Keywords: N-Methylpyrrole; Molecular structure; Gas electron diffraction; Liquid±crystal NMR
1. Introduction As is well known, the structures of molecules dissolved in nematic liquid crystals can be determined precisely by NMR spectroscopy (liquid±crystal NMR) [1,2]. By comparing them with the gas-phase structures, it is possible to study the deformation of the molecular structures due to liquid±crystal solvents. For this purpose, it is necessary to determine molecular structures as accurately as possible. Some time ago, we determined the molecular structure of N-methylpyrrole (NMP, see Fig. 1) by gas q Dedicated to Professor Marit Trñtteberg on the occasion of her 70th birthday. * Corresponding author. Fax.: 181-11-706-2699. E-mail address: [email protected] (S. Konaka).
electron diffraction (GED) combined with ab initio calculations [3] In this study, the rotational constants, B0 and C0, of NMP reported by Arnold et al. [4] were used and the differences between some structural parameters were taken from the result of RHF/631G p calculations [3]. Recently, Huber et al. measured the rotational constants of 13C- and 15Nsubstituted species of NMP and N-methyl-d3-pyrrole (NMPD3) [5] and the rotational constants of the complexes of NMP with one or two argon atoms [6] by microwave spectroscopy (MW). The use of the rotational constants of 13C- and 15N-substituted species of NMP and NMPD3 allows us to determine a more reliable structure. Therefore, in the present study, the molecular structure of NMP is reinvestigated by a joint analysis of the GED intensities reported in [3] and these rotational constants.
0022-2860/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0022-286 0(01)00538-5
108
H. Takeuchi et al. / Journal of Molecular Structure 567±568 (2001) 107±111 Table 1 Rotational constants and vibrational corrections of N-methylpyrrole (NMP), N-methyl-d3-pyrrole (NMPD3) and their isotopic species (in MHz) a B0 b
Fig. 1. Molecular model of N-methylpyrrole.
Suryaprakash et al. [7] determined the ratios of inter-proton distances of NMP dissolved in nematic liquid crystals, ZLI 1167, MBBA and EBBA, by NMR spectroscopy. In the present study, we have measured a 1H NMR spectrum of NMP in ZLI 1167 and determined a more complete structure including carbon positions by analyzing the spectrum with 13C satellites. The resultant structure is compared with the gas-phase structure to investigate the deformation of the molecular structure in ZLI 1167.
Bz2B0 c
Bz d
Ba0 e
NMP B 3559.92967(19) C 2566.94415(13)
21.33(27) 20.53(11)
3558.60(27) 2566.41(11)
3558.3(7) 2566.2(6)
NMPD3 B 3129.18246(62) C 2335.44261(62)
21.31(26) 20.56(11)
3127.87(26) 2334.88(11)
3127.7(7) 2334.4(5)
2- 13C-NMPD3 B 3128.32559(94) C 2321.67619(88)
21.31(26) 20.55(11)
3127.02(26) 2321.13(11)
3126.7(7) 2320.6(6)
3- 13C-NMPD3 B 3084.03647(80) C 2305.04409(80)
21.28(26) 20.55(11)
3082.76(26) 2304.49(11)
3082.3(8) 2303.9(6)
2- 13C-NMP B 3559.60750(18) C 2550.72902(16)
21.33(27) 20.52(10)
3558.28(27) 2550.21(10)
3557.8(6) 2549.8(5)
3- 13C-NMP B 3508.04663(18) C 2533.63652(16)
21.30(26) 20.52(10)
3506.75(26) 2533.12(10)
3506.1(7) 2532.7(5)
C(methyl)-NMP B 3452.77149(28) C 2510.75327(29)
21.30(26) 20.52(10)
3451.47(26) 2510.23(10)
3451.0(7) 2510.0(6)
N-NMP B 3549.24227(73) C 2561.43451(54)
21.30(26) 20.53(11)
3547.94(26) 2560.90(11)
3547.6(7) 2560.6(6)
13
15
2. Experimental The 1H and 13C spectra of 5 M solution of NMP in CDCl3 were recorded on a JNM EX400 spectrometer at 238C to obtain indirect coupling constants. The sample dissolved at a concentration of 5 wt% in ZLI 1167 was degassed and sealed in vacuum. A 1H-NMR spectrum was recorded on the same spectrometer at 278C. External CDCl3 was used to lock the magnetic ®eld. The measured spectrum is similar to that reported in [7]. 3. Structural analysis 3.1. Gas electron diffraction The structural analysis was carried out by using the GED intensities measured at 288C [3]. The range of sÊ 21. The total intensities have values was 4.4±33.6 A
a
Parenthesized values are the estimated limits of error. Rotational constants taken from Ref. [5]. c Vibrational corrections. The limits of error were estimated to be 20% of the corrections. d Rotational constants in the zero-point average structure. e Calculated from the ra0 structure determined by a joint analysis of GED intensities and rotational constants. The estimated limits of error are 3s . b
been deposited [3] and they are also available from the corresponding author. The following assumptions were made in the data analysis: (1) molecular symmetry is Cs in the equilibrium state as shown in Fig. 1 [3,5,6]; (2) C, N and Hring atoms are on the same plane [3]; (3) the methyl group has C3v symmetry; (4) rg(C9±H1) is equal to rg(C10±H2); (5) the difference between rg(C±HMe) Ê (HF/6-31G p and rg(C±Hring) is equal to 0.012 A value [3]). Adjustable parameters were selected as
H. Takeuchi et al. / Journal of Molecular Structure 567±568 (2001) 107±111 Table 2 Indirect and direct coupling constants, Jij and Dij, of N-methylpyrrole (in Hz) a i; j
Jij
Dij
Daij
a b Dij,calc
1,2 1,3 1,4 1,5 1,9 1,10 1,13 2,3 2,5 2,9 2,10 2,13 3,9 3,10 4,9 4,10 5,6 5,9 5,10 5,13
2.57(6) 1.62(6) 1.85(2) 0.23(2) 182.33(4) 7.59(16) 0.0 3.94(3) 0.0 7.90(17) 169.72(7) 0.0 7.81(17) 3.96(7) 5.85(5) 8.15(16) 0.0 2.99(3) 0.0 138.14(6)
553.24(6) 65.35(7) 21.63(14) 255.95(4) 605.28(28) 175.24(25) 72.3(4) 75.62(13) 81.81(5) 280.0(4) 1530.76(23) 26.6(8) 42.3(5) 68.1(5) 13.0(4) 31.5(4) 21015.04(4) 86.8(6) 40.0(6) 2691.19(31)
563.6(5) 66.19(8) 21.89(14) 257.56(9) 675(4) 180.5(4) 73.0(4) 78.36(19) 81.81(5) 287.1(6) 1679(7) 26.7(8) 42.8(5) 69.0(5) 13.1(4) 31.9(4) 21055.4(20) 87.5(6) 39.9(6) 2744.2(27)
563.7 66.19 21.68 257.59 676 180.5 71.9 78.49 81.79 287.2 1676 28.2 43.2 68.8 13.3 31.4 21055.6 87.9 38.1 2743.9
a b
The numbers in parentheses are 1s . The values calculated in the ®nal analysis.
Table 3 Mean amplitudes lij and interatomic distances rg of N-methylpyrrole Ê )a (A Atom pair b
lcalc ij
lobs ij
rg
Group c
H1±C9 H2±C10 H5±C13 N8±C9 N8±C13 C9yC10 C10±C11 N8´´´C10 C9´´´C11 C9´´´C12 C9´´´C13 C10´´´C13
0.076 0.077 0.079 0.045 0.047 0.044 0.049 0.049 0.052 0.051 0.065 0.060
0.071(4) d 0.071 0.074 0.045(1) d 0.048 0.045 0.050 0.052(2) d 0.054 0.053 0.068 0.066(8) d
1.096 1.097 1.109 1.374 1.452 1.384 1.427 2.232 2.260 2.241 2.510 3.638
1 1 1 2 2 2 2 3 3 3 3 4
a The mean amplitudes of relatively important atom pairs are listed. b Non-bonded atom pairs including hydrogen atoms are omitted. c The mean amplitudes with the same number were re®ned as one group. d The numbers in parentheses are the estimated limits of error 3s , where s denotes the standard error.
109
r(N±Cring), r(N±CMe), r CyC; kr(C±H)l, /CNC, / NCC, /NCHring, /HCC(N) and /HCH, where k l denotes an average value. The analysis of GED intensities was performed by treating the methyl rotation as a large amplitude motion. The rotational angles of the methyl groups of pseudo-conformers were taken at intervals of 108. The weights of pseudo-conformers were calculated from the experimental potential function [3] by assuming a Boltzmann distribution. The mean amplitudes and shrinkage corrections, r a0 2 ra ; of pseudoconformers were calculated from the quadratic force constants reported in [3]. The rotational constant A0 is an effective one because of internal rotation of the methyl group [4,5]. Therefore, the rotational constants, B0 and C0, of several isotopomers [5] were used in the analysis. The vibrational corrections for rotational constants, B0 2 Bz and C0 2 Cz, were calculated as described in [8] using the force constants [3]. In the calculations, the methyl group was ®xed at the con®guration shown in Fig. 1. The values of rotational constants, Bz and Cz, are listed in Table 1. Isotopic effects on the bond lengths were calculated Ê 21. By by assuming the Morse parameter to be 2.0 A referring to the results, the deuterium isotopic effect on the C±HMe distance, rz(C±HMe) 2 rz(C±DMe), was Ê , while the ®xed at the calculated value of 0.002 A isotopic effects on the other bond lengths were assumed to be zero in the structural analysis. The structural parameters, index of resolution and mean amplitudes were determined by a joint analysis of the GED intensities and rotational constants. 3.2. Liquid±crystal NMR The analysis of NMR spectra of NMP in CDCl3 and ZLI 1167 was carried out with the program LCNMR [9]. Indirect coupling constants, Jij, were determined from the 1H and 13C spectra of NMP in CDCl3. The values of Jij were used to determine direct coupling constants, Dij, from the 1H-NMR spectrum and its 13C satellites of NMP in ZLI 1167. Direct coupling constants were corrected for harmonic vibrations by using the force constants [3] and converted to those in the ra structure, Dija [1,2]. The Dija 's thus obtained include the uncertainties of vibrational corrections arising from the arbitrariness
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H. Takeuchi et al. / Journal of Molecular Structure 567±568 (2001) 107±111
Table 4 Structural parameters of N-methylpyrrole a rz(GED 1 MW) b r(N8±C9) r(N8±C13) r(C9yC10) r(C10±C11) r(H1±C9) r(H2±C10) r(H5±C13) /C9N8C12 /N8C9C10 /C9C10C11 /H1C9N8 /H1C9C10 /H2C10C9 /H2C10C11 /H5C13H6 /H5C13N8
1.372(6) 1.452(7) 1.383(9) 1.425(11) e 1.079(4) 1.081(4) e 1.100(4) e 109.3(9) 108.2(7) 107.1(4) e 117.7(29) 134.2(32) e 124.0(42) 128.9(44) e 109.1(3) 109.9(3) e
Table 5 Distance ratios and bond angles of N-methylpyrrole a
rs(MW) c 1.361 1.452 1.393 1.422
110.5 107.7 107.0
rc(ab initio) d
LCNMR
0.757(7) b 0.759(7) b 0.772(7) b 0.970(13) b 1.761(14) b 107.1(3) 134.2(32) 124.0(42) 109.1(3)
0.756(6) 0.750(7) 0.769(5) 0.966(8) 1.761(11) 106.8(2) 131.2(4) 125.8(4) 109.0(2) 2 0.0133(4) c 2 0.101(3) c
1.371 1.450 1.387 1.418 1.081 1.081 1.092 109.5 108.1 107.2 120.7
r(H1±C9)/r(C10±C11) r(H2±C10)/r(C10±C11) r(H5±C13)/r(C10±C11) r(C9yC10)/r(C10±C11) r(C9´ ´´C13)/r(C10±C11) /C9C10C11 /H1C9C10 /H2C10C9 /H5C13H6 Sxx Szz
127.1
Bond angles in degrees. The numbers in parentheses are 3s . The ratios of internuclear distances are calculated from the rz structure listed in Table 4. c Order parameters. The value of r(C10±C11) was assumed to be Ê. 1.425 A
Ê , angles in degrees. Bond lengths in A The result obtained by a joint analysis of GED intensities and rotational constants. The numbers in parentheses are the estimated limits of error 3s , where s denotes the standard error from leastsquares re®nement. The rg bond distances are listed in Table 3. The correlation coef®cients with the absolute values larger than 0.7 are: r N8±C9=r C9yC10 20:89; r(N8±C13)//C9N8C12 0.79, r(N8±C13)/N8C9C10 20.75, /C9N8C12//N8C9C10 20.93, and l1/12 0.82, where l1 and l2 denote the groups of mean amplitudes de®ned in Table 3. c Ref. [5]. d The result of MP2/6-311G(d,p) calculation [5]. e Dependent parameter. a
b
GED 1 MW
a
b
of harmonic force constants and anharmonic contributions to vibrational frequencies. In the present study, they were assumed to be 5% of vibrational corrections as suggested by Diehl [2,10]. The results are summarized in Table 2. The ratios of internuclear distances and order parameters were determined by least-squares calculations on Dija .
Fig. 2. Experimental (solid line) radial distribution curve of N-methylpyrrole: Df r f rexp 2 f rtheor : An arti®cial damping function, exp(20.002s 2), is used.
H. Takeuchi et al. / Journal of Molecular Structure 567±568 (2001) 107±111
4. Results and discussion The results of the joint analysis of GED intensities and rotational constants are listed in Tables 3 and 4. The radial distribution curve is shown in Fig. 2. The differences between experimental and theoretical curves are slightly smaller than those in [3]. Table 5 compares the ratios of internuclear distances and bond angles of NMP in ZLI 1167 with those in the gas phase. In the previous study on the gas-phase structure [3], the values of /NCHring, /CyCH and the difference between two N±C bond lengths, Dr N±C rg N±CMe 2 rg N±Cring ; were taken from the RHF/6-31G p calculations. In the present study, however, these structural parameters could be determined independently by the joint analysis as shown in Table 4. The values of the structural parameters are consistent with the previous ones [3] but the experimental uncertainties of the parameters relating to hydrogen atoms are smaller than those in the previous study. The value of Dr(N±C) obtained in the present Ê , is in good agreement with the value study, 0.078(9) A Ê assumed previously [3] and the MP2/6of 0.080 A Ê [5]. The bond lengths 311G(d,p) value of 0.079 A and bond angles given by MP2/6-311G(d,p) calculations [5] agree with the rz values within experimental uncertainties. The differences between the bond lengths in the rz and rs structures are larger for the bonds related to the C9 atom, N8±C9 and C9yC10, than for N8±C13 and C10±C11 bonds. The rs value of /C9N8C12 is larger than the corresponding rz value by 1.28. These differences are ascribed to the fact that the a coordinate of C9 has not been determined precisely in the microwave spectroscopic study [5]. Table 5 shows that the values of /H1C9C10 and / H2C10C9 are determined by liquid±crystal NMR more precisely than by the joint analysis of GED intensities and rotational constants. The ratios of internuclear distances and bond angles of NMP in ZLI 1167 are in good agreement with those in the gas phase, indicating that the structural deformation of NMP by the solvent is small. This is consistent with the calculation of molecular deformation [11]: the changes of internuclear distance ratios and bond angles after deformation corrections are smaller than 0.007 and 0.28, respectively. (Resulting structure and
111
corrections to Dij are available from the corresponding author.) In the case of pyrrole in ZLI 1167, however, VaÈaÈnaÈnen et al. [12] found a large structural deformation. From the comparison between theoretical and experimental order parameters and the large variation of chemical shifts, they ascribed it to the formation of hydrogen bonding between the N±H proton and the solvent. On the other hand, NMP does not form such a hydrogen bond. This is considered to make the structural deformation of NMP much smaller than that of pyrrole.
Acknowledgements This work was supported by the Grant-in-Aid for Scienti®c Research (08454168). We thank the HighResolution NMR laboratory, Faculty of Science, Hokkaido University, for the measurement of NMR spectra. Numerical computations were carried out on a Hitachi Model MP5800/160 at the Hokkaido University Computing Center.
References [1] J.W. Esmley, J.C. Lindon, NMR Spectroscopy Using Liquid Crystal Solvents, Pergamon Press, Oxford, 1975. [2] P. Diehl, in: J.W. Emsley (Ed.), Nuclear Magnetic Resonance of Liquid Crystals, Reidel, Dordrecht, 1985 (Chapter 7). [3] N. Kurai, H. Takeuchi, S. Konaka, J. Mol. Struct. 318 (1994) 143. [4] W. Arnold, H. Dreizler, H.D. Rudolph, Z. Naturforsch. Teil A 23 (1968) 301. [5] S. Huber, T.-K. Ha, A. Bauder, J. Mol. Struct. 413±414 (1997) 93. [6] S. Huber, J. Makarewicz, A. Bauder, Mol. Phys. 95 (1998) 1021. [7] N. Suryaprakash, A.C. Kunwar, C.L. Khetrapal, Chem. Phys. Lett. 107 (1984) 333. [8] K. Kuchitsu, M. Nakata, S. Yamamoto, in: I. Hargittai, M. Hargittai (Eds.), Stereochemical Applications of Gas-phase Electron Diffraction, VCH, New York, 1988 (Chapter 7, Part A). [9] M. Nakagawa, S. Konaka, Unpublished work, 1989. [10] P. Diehl, in: A. Domenicano, I. Hargittai (Eds.), Accurate Molecular Structure, Oxford University Press, Oxford, 1992 (Chapter 12). [11] R. Wasser, M. Kellerhals, P. Diehl, Magn. Reson. Chem. 27 (1989) 335. [12] T. VaÈaÈnaÈnen, J. Jokisaari, A. KaÈaÈriaÈinen, J. Lounila, J. Mol. Struct. 102 (1983) 175.