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A 1H, 13C, 15N and 77Se NMR study of three organoselenium compounds
Journal of Molecular Structure, 268 (1992) 311-314 Elsevier Science Publishers B.V., Amsterdam
311
Short Communication
A ‘H, 13C, 15N and 77Se NMR study of three organoselenium compounds J. Mlochowski and L. Syper Institute of Organic and Physical Chemistry, Technical University of Wroclaw, Wroclaw (Poland)
L. Stefaniak, W. Domalewski and W. Schilf Institute of Organic Chemistry, Polish Academy of Sciences, Warsaw (Poland)
G.A. Webb Department of Chemistry, University of Surrey, Guildford, Surrey (UK) (Received9 September 1991)
INTRODUCTION
Previously we have reported multinuclear NMR studies on heteroaromatic compounds containing nitrogen, oxygen and sulphur [ 1,2]. We now turn our attention to some aromatic compounds containing nitrogen, oxygen and selenium, reporting ‘H, 13C,15Nand 77Sechemical shifts for three organoselenium compounds. The 77Sedata are found to be extremely sensitive to the molecular structure and may readily be used to distinguish between structural types. Nitrogen chemical shifts are also very useful for determining the type of structure present. In the case of 13Cchemical shifts only those adjacent to selenium and in a ring bridging position are found to provide useful structural information. EXPERIMENTAL
The compounds were prepared using previously published procedures [ 3 1. The NMR spectra were taken on a Bruker AM 500 spectrometer operating at 500 MHz for ‘H, at 125.76 MHz for 13C,at 36.142 MHz for 14N,at 50.698 MHz for 15N and at 95.383 MHz for 77Se. The compounds were studied in DMSO solutions. Correspondence to: Dr. G.A. Webb, Department of Chemistry, University of Surrey, Guildford, Surrey, UK.
0022-2860/92/$05.00
0 1992 Elsevier Science Publishers B.V. All rights reserved.
C6
C5
Cd
c3
k, c2
%=o
CH3
H6
H5
H4
H3
N-H N-CH3
Nucleus 8.7bsc 2.Bb x7.8 x7.4 zz7.3 x7.7 26.3 167.7 131.8,132.8 127.7 131.5 126.1 129.8
Chemical shift’
Compound - 278.4’ 453.6 3.3 = 7.8 x 7.6 m7.4 x8.0 30.3 166.6 139.0 127.6 127.2 131.3 125.7 125.8 - 280.0 888.1
N Se N-CH, H, H, H6
N Se
c7
G
G
Cd
C la C3e
y=o
CH3
H7
Chemical shift”
Nucleus
6-A a
5/
7
4
lII
lo
I
30
Compound
0
II
Se ’
>,CH,
c3
::
N Se
c7
C.5 C6
G
C3a
C Ia
>c=o
043
H7
H4 H6 b
N-Cl&
Nucleus
3.2 x8.2 ~7.8 z7.7 z 7.85 27.4 168.3 147.2 130.5 127.3 133.6 132.1 126.7 - 232.1 1142.7
Chemical shift’
“The ‘H and 13Cchemical shifts are reported with respect to TMS. The 15Nchemical shifts are given with respect to neat nitromethane as external standard. The 77Sechemical shifts are measured with respect to diselenium diphenyl as external standard which has a chemical shift of 460 ppm from the reporting standard. diselenium dimethyl neat liquid. b 3J(H-H) = 4.5 Hz. “J(N-H)=92.7Hz.
Compound
‘H, 13C,“N and 77Sechemical shifts for three organoselenium compounds
TABLE 1
313
RESULTS AND DISCUSSION
The results of ‘H, 13C,15Nand “Se NMR measurements are given in Table 1. The ‘H assignments were made as follows. The chemical shifts found for the N-CH3 and N-H protons are typical values for groups of this type. The ‘H signals of the aromatic rings in compounds I, II and III exhibit two doublets and approximate triplets. The doublet corresponding to the proton on the carbon adjacent to the carbonyl group is assigned by observing the carbonyl 13C signal when the proton in question is decoupled. The remaining ‘H doublet signal is thus assigned to H6 in I and to H, in II and III. ‘H-‘H COSY spectra were employed to assign the two approximate ‘H triplet signals. In compound I, H3, H4 and Hg, H6 are strongly coupled and, since H, and H6 are previously assigned to the doublet signals, the assignments of H4 and H5 are obtained. Similar arguments are used to assign the approximate triplets of H5 and H, in II and III, based upon their couplings to the previously assigned signals from H, and H, respectively. The 13C assignments of the N-CH3 and carbonyl groups are made on the basis of the typical positions observed for these signals. From the relative intensities of the ‘H decoupled 13Cspectra, and from DEPT measurements, we were able to distinguish between the quaternary and C-H carbons of the aromatic rings in compounds, I, II and III. The 13Csignals of the proton-bearing carbons are assigned by means of 13C-lH COSY measurements. In compound I, the quaternary carbon signals are not individually assigned. However from a comparison of the 13Cspectra of compounds II and III we are able to distinguish between C1, and Csasince Csahas a comparable bonding environment in both compounds while that for Ci, differs in II and III. We turn now to a consideration of the nitrogen chemical shifts reported in Table 1. For compound III the nitrogen shielding is reduced by about 50 ppm with respect to that for compounds I and II. Thus from a comparison of compounds II and III the oxidation of selenium leads to a reduction of the shielding of the nitrogen atom in the adjacent ring position. The nitrogen chemical shift of - 278.4 ppm for compound I is typical for similar amides [ 4,5] and the fact that the value for compound II is comparable is probably fortuitous. In addition, the 14N NMR spectra of compounds II and III were also obtained. A single broad resonance of about 3 KHz half width was found in each case with the same chemical shifts as in the corresponding 15Nspectra. The 77Sespectra of compounds I-II show drastically different chemical shifts (Table 1). For compound I the 77Sechemical shift is comparable with that of diphenyl diselenium (460 ppm) . A small increase in 77Seshielding occurs due to the presence of the electron donating group CH,NHCO- in the ortho position. A comparable deshielding effect on selenium is noted by para substitution with a nitro group [ 61. Comparison of the 77Seshieldings for compounds I and
314
II indicate a significant deshielding when the neighbouring atom changes from selenium to nitrogen. The oxidation of selenium (compound III) results in a further, large, selenium deshielding. As shown in Table 1 the ‘H chemical shifts of compounds II and III are very similar and thus are not particularly useful for distinguishing between these two structures. The situation with the 13C data is similar with the exception of the shielding of C1, which is sensitive to whether or not the adjacent selenium atom is oxidised. We conclude that 77Se NMR is a very sensitive technique for structural investigations. In addition nitrogen NMR distinguishes very clearly between structures II and III. Some further support may be obtained from the chemical shifts of Cl,.
REFERENCES 1 B. Kamienski, W. Schilf, J. Sitkowski, L. Stefaniak and G.A. Webb, J. Cryst. Spect. Res., 19 (1989) 1003. 2 J. Jazwinski, L. Stefaniak and G.A. Webb, Magn. Reson. Chem., 26 (1988) 1012. 3 J. Mlochowski, K. Kloc, L. Syper and A.D. Inglot, Phosphorus, Sulphur and Silicon, 59 (1991) 267. 4 G.J. Martin, J.P. Gouesnard, J. Dorie, C. Robillier and M.L. Martin, J. Am. Chem. Sot., 99 (1977) 1381. 5 G.G. Furin, A.I. Rezvukhin, M.A. Fedotov and G.G. Yakobson, J. Fluorine Chem., 22 (1983) 231. 6 M. Lardon, J. Am. Chem. Sot., 92 (1970) 1063.
311
Short Communication
A ‘H, 13C, 15N and 77Se NMR study of three organoselenium compounds J. Mlochowski and L. Syper Institute of Organic and Physical Chemistry, Technical University of Wroclaw, Wroclaw (Poland)
L. Stefaniak, W. Domalewski and W. Schilf Institute of Organic Chemistry, Polish Academy of Sciences, Warsaw (Poland)
G.A. Webb Department of Chemistry, University of Surrey, Guildford, Surrey (UK) (Received9 September 1991)
INTRODUCTION
Previously we have reported multinuclear NMR studies on heteroaromatic compounds containing nitrogen, oxygen and sulphur [ 1,2]. We now turn our attention to some aromatic compounds containing nitrogen, oxygen and selenium, reporting ‘H, 13C,15Nand 77Sechemical shifts for three organoselenium compounds. The 77Sedata are found to be extremely sensitive to the molecular structure and may readily be used to distinguish between structural types. Nitrogen chemical shifts are also very useful for determining the type of structure present. In the case of 13Cchemical shifts only those adjacent to selenium and in a ring bridging position are found to provide useful structural information. EXPERIMENTAL
The compounds were prepared using previously published procedures [ 3 1. The NMR spectra were taken on a Bruker AM 500 spectrometer operating at 500 MHz for ‘H, at 125.76 MHz for 13C,at 36.142 MHz for 14N,at 50.698 MHz for 15N and at 95.383 MHz for 77Se. The compounds were studied in DMSO solutions. Correspondence to: Dr. G.A. Webb, Department of Chemistry, University of Surrey, Guildford, Surrey, UK.
0022-2860/92/$05.00
0 1992 Elsevier Science Publishers B.V. All rights reserved.
C6
C5
Cd
c3
k, c2
%=o
CH3
H6
H5
H4
H3
N-H N-CH3
Nucleus 8.7bsc 2.Bb x7.8 x7.4 zz7.3 x7.7 26.3 167.7 131.8,132.8 127.7 131.5 126.1 129.8
Chemical shift’
Compound - 278.4’ 453.6 3.3 = 7.8 x 7.6 m7.4 x8.0 30.3 166.6 139.0 127.6 127.2 131.3 125.7 125.8 - 280.0 888.1
N Se N-CH, H, H, H6
N Se
c7
G
G
Cd
C la C3e
y=o
CH3
H7
Chemical shift”
Nucleus
6-A a
5/
7
4
lII
lo
I
30
Compound
0
II
Se ’
>,CH,
c3
::
N Se
c7
C.5 C6
G
C3a
C Ia
>c=o
043
H7
H4 H6 b
N-Cl&
Nucleus
3.2 x8.2 ~7.8 z7.7 z 7.85 27.4 168.3 147.2 130.5 127.3 133.6 132.1 126.7 - 232.1 1142.7
Chemical shift’
“The ‘H and 13Cchemical shifts are reported with respect to TMS. The 15Nchemical shifts are given with respect to neat nitromethane as external standard. The 77Sechemical shifts are measured with respect to diselenium diphenyl as external standard which has a chemical shift of 460 ppm from the reporting standard. diselenium dimethyl neat liquid. b 3J(H-H) = 4.5 Hz. “J(N-H)=92.7Hz.
Compound
‘H, 13C,“N and 77Sechemical shifts for three organoselenium compounds
TABLE 1
313
RESULTS AND DISCUSSION
The results of ‘H, 13C,15Nand “Se NMR measurements are given in Table 1. The ‘H assignments were made as follows. The chemical shifts found for the N-CH3 and N-H protons are typical values for groups of this type. The ‘H signals of the aromatic rings in compounds I, II and III exhibit two doublets and approximate triplets. The doublet corresponding to the proton on the carbon adjacent to the carbonyl group is assigned by observing the carbonyl 13C signal when the proton in question is decoupled. The remaining ‘H doublet signal is thus assigned to H6 in I and to H, in II and III. ‘H-‘H COSY spectra were employed to assign the two approximate ‘H triplet signals. In compound I, H3, H4 and Hg, H6 are strongly coupled and, since H, and H6 are previously assigned to the doublet signals, the assignments of H4 and H5 are obtained. Similar arguments are used to assign the approximate triplets of H5 and H, in II and III, based upon their couplings to the previously assigned signals from H, and H, respectively. The 13C assignments of the N-CH3 and carbonyl groups are made on the basis of the typical positions observed for these signals. From the relative intensities of the ‘H decoupled 13Cspectra, and from DEPT measurements, we were able to distinguish between the quaternary and C-H carbons of the aromatic rings in compounds, I, II and III. The 13Csignals of the proton-bearing carbons are assigned by means of 13C-lH COSY measurements. In compound I, the quaternary carbon signals are not individually assigned. However from a comparison of the 13Cspectra of compounds II and III we are able to distinguish between C1, and Csasince Csahas a comparable bonding environment in both compounds while that for Ci, differs in II and III. We turn now to a consideration of the nitrogen chemical shifts reported in Table 1. For compound III the nitrogen shielding is reduced by about 50 ppm with respect to that for compounds I and II. Thus from a comparison of compounds II and III the oxidation of selenium leads to a reduction of the shielding of the nitrogen atom in the adjacent ring position. The nitrogen chemical shift of - 278.4 ppm for compound I is typical for similar amides [ 4,5] and the fact that the value for compound II is comparable is probably fortuitous. In addition, the 14N NMR spectra of compounds II and III were also obtained. A single broad resonance of about 3 KHz half width was found in each case with the same chemical shifts as in the corresponding 15Nspectra. The 77Sespectra of compounds I-II show drastically different chemical shifts (Table 1). For compound I the 77Sechemical shift is comparable with that of diphenyl diselenium (460 ppm) . A small increase in 77Seshielding occurs due to the presence of the electron donating group CH,NHCO- in the ortho position. A comparable deshielding effect on selenium is noted by para substitution with a nitro group [ 61. Comparison of the 77Seshieldings for compounds I and
314
II indicate a significant deshielding when the neighbouring atom changes from selenium to nitrogen. The oxidation of selenium (compound III) results in a further, large, selenium deshielding. As shown in Table 1 the ‘H chemical shifts of compounds II and III are very similar and thus are not particularly useful for distinguishing between these two structures. The situation with the 13C data is similar with the exception of the shielding of C1, which is sensitive to whether or not the adjacent selenium atom is oxidised. We conclude that 77Se NMR is a very sensitive technique for structural investigations. In addition nitrogen NMR distinguishes very clearly between structures II and III. Some further support may be obtained from the chemical shifts of Cl,.
REFERENCES 1 B. Kamienski, W. Schilf, J. Sitkowski, L. Stefaniak and G.A. Webb, J. Cryst. Spect. Res., 19 (1989) 1003. 2 J. Jazwinski, L. Stefaniak and G.A. Webb, Magn. Reson. Chem., 26 (1988) 1012. 3 J. Mlochowski, K. Kloc, L. Syper and A.D. Inglot, Phosphorus, Sulphur and Silicon, 59 (1991) 267. 4 G.J. Martin, J.P. Gouesnard, J. Dorie, C. Robillier and M.L. Martin, J. Am. Chem. Sot., 99 (1977) 1381. 5 G.G. Furin, A.I. Rezvukhin, M.A. Fedotov and G.G. Yakobson, J. Fluorine Chem., 22 (1983) 231. 6 M. Lardon, J. Am. Chem. Sot., 92 (1970) 1063.