Theoretical vibrational spectroscopy and the structure of nitrosubstituted glucopyranosides

Journal of Molecular Structure 556 (2000) 157–172 www.elsevier.nl/locate/molstruc

Theoretical vibrational spectroscopy and the structure of nitrosubstituted glucopyranosides M.V. Korolevich*, R.G. Zhbankov Institute of Physics, National Academy of Sciences of Belarus, Minsk 220072, Belarus Dedicated to Professor Lou Allinger in recognition of his significant contributions to the field of molecular mechanics Received 22 December 1999; accepted 28 April 2000

Abstract Coupled calculations have been carried out of normal vibration frequencies from the point of view of the valence-force field scheme and of absolute IR band intensities by the CNDO/2 method for the 2,3-di-O-nitro-methyl-b-d-glucopyranoside and 2,3,6-tri-O-nitro-methyl-b-d-glucopyranoside molecules. A good agreement with experiment has been achieved. A detailed interpretation of the observable IR spectra of both the nitro-glucopyranosides compounds considered is given. Regularities of formation of complex absorption bands of characteristic vibrations of nitro-groups have been established. 䉷 2000 Elsevier Science B.V. All rights reserved. Keywords: Glucopyranoside nitrates; IR spectra; Normal coordinate analysis; Absolute IR intensities; CNDO/2 calculations

1. Introduction The use of computational methods of classical vibrational spectroscopy and quantum chemistry is very efficient in studying the structure of monosaccharide-based materials. As is known, the spectra of monosaccharides are of a complex diffuse form, which results from the overlap of a great number of closely spaced absorption bands [1–4]. The experimental assignment of the majority of frequencies remains very problematic even when selective deuteration and cooling of samples to liquid helium temperature are used. The substitution of the hydroxyl groups in the pyranose rings for the nitrate groups has a very pronounced * Corresponding author. Tel: ⫹375-172-841098; fax: ⫹375-172840879. E-mail address: [email protected] (M.V. Korolevich).

effect on the general view of the spectrum. But in spite of the apparent simplification of the spectra and pronounced changes in the spectra arising on selective nitrosubstitution, the detailed interpretation of the spectra of monosaccharide nitrates presents a very complex problem. The full and highly reliable interpretation of the observed spectra of these compounds can be obtained only from a complete theoretical analysis including a calculation of band intensities of the vibrational spectra of these molecules. Because of a great number of degrees of freedom and normal vibrations in the considered molecules, there is a sufficiently great probability of random coincidence of the experimental and theoretical frequencies in the case of calculation of only the frequencies of vibrations. Moreover, in a number of cases the sensitivity of the IR spectra of monosaccharides to different structural transformations manifests itself as a change in the intensity of absorption bands, while the frequencies of vibrations remain unchanged.

0022-2860/00/$ - see front matter 䉷 2000 Elsevier Science B.V. All rights reserved. PII: S0022-286 0(00)00661-X

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There are numerous works devoted to theoretical calculations of vibrational spectra of mono- and disaccharides [5–17]. Apart from the work of Longhi et al. [11], all the works deal with the calculations only of frequencies and forms of normal vibrations. The authors of [11] have considered only the intensities of CH- and CD- stretchings using the charge flow model. We apply our software program technique [18–20] for the calculation of IR spectra of monosaccharides, their derivatives, as well as some other simpler compounds [18–30], which permits combining the classical analysis of normal vibrations with the quantum-chemical intensity estimation. The results obtained are strong evidence for the efficiency of application of such an approach in the studies of monosaccharides and monosaccharide nitrates. Using direct calculation of the derivatives …2m ~ =2Qi † and taking into account the data on the normal vibrations forms makes it possible to control the choice of an appropriate set of empirical force constants when analysing normal vibrations. Thus, on the one hand, the calculated intensities show if the calculated model corresponds to the real molecule of the investigated compound. On the other hand, the calculated intensities give additional information on the vibrating molecule, since they are more dependent on the great number of molecular parameters than the frequencies. In the intensities the features of the electronic structure are reflected most pronouncedly. They are more sensitive to intermolecular interactions. The aim of the present work is to provide an interpretation of the IR spectra of 2,3-di-O-nitro-methylb-d-glucopyranoside (2,3-diNMG) and 2,3,6-tri-Onitro-methyl-b-d-glucopyranoside (2,3,6-triNMG) on the basis of complete theoretical study of normal vibrations frequencies and absolute intensities.

2. Calculation procedure 2.1. Programs for calculating frequencies and intensities in IR spectra of complex molecules The original highly automated complex of programs [18,19] for calculating the vibrational spectra of polyatomic molecules (containing up to 120 atoms), both isolated and taking into account their molecular environment is used. These programs

provide a coupled analysis of the IR spectrum, which combines a classical method of calculation of normal vibrations with a quantum-chemical CNDO/2 evaluation of intensities. Analysis of normal vibrations is performed in the valence-force field approximation using Wilson’s GF matrix method. Calculations of absolute intensities in the IR spectra can be made in two approximations: (1) a quasi-isolated molecule (QIM); and (2) a molecule with its molecular environment (for example, a molecule in a cluster). As the QIM approximation, an isolated molecule is considered. The average influence of the intermolecular interactions is taken into account only in the molecule’s force field without regard to the influence on the electronic structure in calculating the intensities of vibrations. As the second approximation, the influence of the molecules surrounding the molecule under study on the electronic structure is taken into account. For example, this approximation permitted us to make the simulation of spectroscopic effects of the formation of H-bonds in the a-d-glucose crystal [26] as well as the adsorption of benzene on the surface of softened zeolites [22]. Finally, the software program technique created makes it possible to interpret the IR spectra, to forecast the effect of intermolecular interactions upon the intensities (in particular, to study and model the effects of formation of hydrogen bonds, adsorption complexes, etc.) of various organic compounds (proteins, carbohydrates, etc.). 2.2. Calculation algorithm The algorithm for the CNDO/2 calculation of intensities is based on a matrix expression convenient for programming. The following is an expression for the derivative of the molecule dipole moment with respect to the normal coordinate [18]: !



2P

2q 0

2m ~ ⫺1



2Q ˆ 4:8 Z ⫺ 4:8 jRj 2r ⫺ 7:337 z 2r i

~~

Lp

 EB i where 兩Z 0 兩 is a matrix containing the values of charges Z 0 A localized at the atomic nuclei

M.V. Korolevich, R.G. Zhbankov / Journal of Molecular Structure 556 (2000) 157–172

(Z 0A

ˆ ZA ⫺ PAA ; ZAis the charge of the atom A skeleton, PAAis the electron charge density on the atom A); 兩R兩 is a matrix of cartesian components of radius vectors of atomic nuclei in the equilibrium state; z is an orbital exponent of an atom; 兩2q=2r兩 and 兩2P=2r兩 are, respectively, matrices of derivatives of the electron charge densities on atoms and of the non-diagonal elements of the density matrix P2s…A†;2pk …A† …k ˆ x; y; z† with respect to the cartesian atomic displacements; and E is a diagonal matrix of dimensionless inverse atomic masses; and the matrices B and L are those agreed upon in the theory of normal vibrations. ~~ p 储i is determined The column 储2~r=2Qi 储 ˆ EB储L when solving the direct mechanical problem on vibrations of a molecule. The elements of the matrices 兩2q=2r兩 and 兩2P=2r兩 are calculated by the CNDO/2 technique by numerical differentiation. The absolute vibration intensities are calculated by the formula ˆ Acalc i

pNa 3c



2m ~ 2Qi

2 0

where Na is the Avogadro constant, c is the velocity of light, and i is the number of the vibration. These values correspond to the experimental integrated intensities of the absorption bands in the IR spectrum ˆ Aexp i

  1 Z J ln 0 2ni J Cl ni

where C is the substance concentration, and l is the absorbing layer thickness. The spectral curve of absorbance Dcalc …n† is the sum of gaussian-shape bands obtained from the theoretically calculated absolute intensities and specified half-widths. The latter are evaluated on the basis of the experimental spectrum 2 G i … n† ˆ

3

6 ln 2…n ⫺ n † 6 0i exp6⫺  2 4 1:06pi pi 2 Acalc i

2

7 7 7 5

where n0i is the frequency at a maximum, pi is a halfwidth, and the index i stands for the ith normal

159

vibration. Dcalc …n† ˆ

X

Gi …n†:

i

3. Results and discussion The IR spectra of nitrosubstituted glucopyranosides are characterized by the presence of intense absorption bands in the ranges 1700–1600, 1290–1260, 900–800 and 750–650 cm ⫺1, caused by the vibrations of the nitro-groups. These bands do not overlap the bands corresponding to the glucoside skeleton vibrations and have a considerably higher intensity. A structure of complex nitro-group absorption bands is specific for every compound investigated. This particularly holds true for the band of the characteristic asymmetric stretching vibrations of the nitro-groups n as(ONO2) in the region of 1700–1600 cm ⫺1. Experimental IR spectroscopic investigations of a number of selectively substituted monosaccharide nitrates performed did not reveal regularities of formation of absorption bands in the regions of vibrations of the nitro-groups. Complete theoretical investigation of the IR spectrum of tetra-nitrate-methyl-b-d-glucopyranoside (TNMG) was made by us in [24,29]. The experimental and calculated IR absorption spectra of TNMG are presented in Fig. 1. Not only qualitative, but also quantitative agreement with experiment has been achieved, both in frequencies and intensities. It allowed one to perform a detailed interpretation of the observable IR spectrum of TNMG as well as to discover the absorption spectra sensitivity to the spot of the nitrate group localization and also to estimate the role of the intra- and intermolecular effects on the formation of the spectra of nitrates of monosaccharides. As found in [29,30], the TNMG molecule force field obtained possesses the transferability and the possibility of performing, on its basis, a priori calculations of normal vibration frequencies of selectively substituted nitrates of glucopyranosides. Earlier [29], using the TNMG force field model we made the calculation of only frequencies of normal vibrations of the 2,3-diNMG molecule. The force field chosen was not refined through comparison of

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Fig. 1. Experimental (a) and calculated (b) IR absorption spectra of tetranitrate-methyl-b-d-glucopyranoside.

the calculated frequencies with the experimental ones using a least squares technique. The results obtained reproduce qualitatively the observed changes in the spectra when passing from TNMG to 2,3-diNMG. On the basis of such a proposed normal coordinate analysis of molecules of 2,3-, 2,6- and 3,6- diNMGs and 2,3,6-triNMG, a study has been made of the influ-

ence of the nitro-group location and degree of hydroxylgroup substitution on the complex structure of analytically important nitro-group vibration bands in the IR spectra of samples of monosaccharide nitrates. In the present paper, to supplement our investigations and improve the assignment proposed, we report coupled calculations of normal vibration frequencies

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161

Table 1 ˚ ), of the 2,3-di-O-nitro-methyl-b-d-glucopyranoside (2,3-diNMG) and 2,3,6-tri-O-nitro-methyl-b-dThe cartesian coordinates of atoms (in A glucopyranoside (2,3,6-triNMG) molecules 2,3-diNMG

2,3,6-triNMG

Atom number

x

y

z

Atom number

x

y

z

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

6.1221 6.8740 8.3406 8.9840 8.1065 8.6662 3.9455 4.8850 6.3004 8.9995 10.2149 6.8167 7.9515 6.0279 6.7994 8.3927 9.2039 8.0561 9.7375 8.4426 3.0310 3.9051 4.3727 5.3578 4.7005 5.3640 9.6429 9.6863 10.0599 11.0928 7.8941

5.0565 4.6553 4.3452 5.3938 5.7134 6.8966 5.6916 5.5053 3.4340 4.3751 4.7954 6.1214 6.9115 4.2669 5.5142 3.3473 6.3260 4.9346 6.8110 7.7775 6.0378 4.7917 6.4332 3.6080 2.6180 4.6376 3.1742 2.2862 3.2599 5.3834 7.7910

⫺0.9203 ⫺2.1833 ⫺1.9259 ⫺1.0507 0.1742 0.9379 ⫺0.2468 ⫺1.3279 ⫺2.7136 ⫺3.2164 ⫺0.5613 ⫺0.2955 2.1776 ⫺0.1749 ⫺2.8502 ⫺1.4906 ⫺1.5710 0.9352 1.1196 0.3362 ⫺0.7285 0.3704 0.4313 ⫺3.7502 ⫺3.9195 ⫺4.3574 ⫺3.6275 ⫺2.8412 ⫺4.7481 ⫺0.6568 2.6011

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

6.1221 6.8740 8.3406 8.9840 8.1065 8.6662 3.9455 4.8850 6.3004 8.9995 10.2149 6.8167 7.9515 6.0279 6.7994 8.3927 9.2039 8.0561 9.7375 8.4426 3.0310 3.9051 4.3727 5.3578 4.7005 5.3640 9.6429 9.6863 10.0599 11.0928 7.8693 7.4414 8.2181

5.0565 4.6553 4.3452 5.3938 5.7134 6.8966 5.6916 5.5053 3.4340 4.3751 4.7954 6.1214 6.9115 4.2669 5.5142 3.3473 6.3260 4.9346 6.8110 7.7775 6.0378 4.7917 6.4332 3.6080 2.6180 4.6376 3.1742 2.2862 3.2599 5.3834 8.1709 8.1097 9.1392

⫺0.9203 ⫺2.1833 ⫺1.9259 ⫺1.0507 0.1742 0.9379 ⫺0.2468 ⫺1.3279 ⫺2.7136 ⫺3.2164 ⫺0.5613 ⫺0.2955 2.1776 ⫺0.1749 ⫺2.8502 ⫺1.4906 ⫺1.5710 0.9352 1.1196 0.3362 ⫺0.7285 0.3704 0.4313 ⫺3.7502 ⫺3.9195 ⫺4.3574 ⫺3.6275 ⫺2.8412 ⫺4.7481 ⫺0.6568 2.7841 3.9110 2.1755

from the point of view of the valence-force field scheme and of absolute IR band intensities by the CNDO/2 method for the 2,3-diNMG and 2,3,6triNMG molecules. A fairly good agreement with the experiment is obtained, which allows one to perform a detailed interpretation of the observable IR spectra of the compound investigated. We also present some results of the absolute intensities calculation for the 2,6- and 3,6-diNMG molecules. Here we qualitatively compared the calculated absolute intensities with the corresponding experimental intensities in the analysis of the normal vibra-

tions, because in the literature there are no data on the experimental integral intensities of the band components and their half-widths. This is explained by the fact that the spectra of these compounds consist of a great number of closely spaced overlapping absorption bands. The experimental study of intensities in the spectra of saccharides represents a complex independent problem. To improve the resolution of the spectra of native cellulose, a-d-glucose and b-d-glucose the methods of the second derivative [31–33] and deconvolution [34–37] have been used. However,

162 M.V. Korolevich, R.G. Zhbankov / Journal of Molecular Structure 556 (2000) 157–172 Fig. 2. Schematic structure and numbering of atoms of the (a) 2,3-di-O-nitro-methyl-b-d-glucopyranosides and (b) 2,3,6-tri-O-nitro-methyl-b-d-glucopyranoside molecules.

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163

Fig. 3. Definition of the internal coordinates of nitro-groups in nitrates of glucopyranoside. Each torsional coordinate t involves all the atoms attached to the torsional axis. Out-of-plane coordinate gi ˆ gkl⫺m⫺n ; where index k corresponds to the bond r 1; l, m and n to the atoms Oi, Ni and Oi2 forming the plane.

this makes it possible to determine only the maxima of the components of the absorption bands in the spectra of the compound investigated. Because of this, of particular importance is the theoretical calculation of the intensities of the absorption bands in the spectra of saccharides and their derivatives.

conformation of CO–NO2 differs considerably from planar. Table 1 gives the cartesian coordinates of atoms of the 2,3-diNMG and 2,3,6-triNMG molecules, which we used in the calculations of the frequencies of normal vibrations and in the CNDO/2 calculations of the absolute intensities of IR bands. 3.2. Force field model

3.1. Structure model The calculation of the IR spectra of the 2,3-diNMG and 2,3,6-triNMG molecules has been made using the QIM model. The choice of this model was based on the conclusion of [26]. Within the cluster approximation the influence of the intermolecular hydrogen bonds upon the electronic structure and intensities of the absorption bands of crystalline monosaccharides was studied in [26]. It was shown that to interpret the spectral range between 3000 and 600 cm ⫺1 one may resort to the QIM approximation in calculating the IR spectra of monosaccharides. The numbering of atoms of the 2,3-diNMG and 2,3,6-triNMG molecules is shown in Fig. 2. The data for the molecular geometry were taken from [38] on the X-ray structural analysis of TNMG rystals. The glucopyranose ring is in the chair conformation C1[38]. The authors of [38] elucidated that the nitrate groups of the molecules are practically planar, and the

For the initial approximation of the force field of the 2,3-diNMG and 2,3,6-triNMG molecules we took the corresponding force constants obtained for the TNMG molecule [29] and for the b-d-glucose molecule (for hydroxyl groups) [28]. The good agreement obtained for both molecules between the position and intensities of the bands in the calculated and experimental spectra is evidence for the adequacy of the determined force fields to the real molecules. In the present work, to improve the correspondence with the experimental spectra the correction of the chosen TNMG force field was performed by way of solving the inverse spectral problem with regard to the influence of the force field on the absolute intensities for the 2,3-diNMG and 2,3,6triNMG molecules. The calculation of spectra of the 2,6-diNMG and 3,6-diNMG molecules has been made using the additive force field model, which differs from the TNMG

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M.V. Korolevich, R.G. Zhbankov / Journal of Molecular Structure 556 (2000) 157–172

force field in that the corresponding values of the diagonal force constants of the NvO and N–O bonds are the same in all the nitro-groups, irrespective of their place of localization. This initial force field approximation chosen for the 2,6-diNMG and 3,6diNMG molecules was not refined. Thus, the calculation performed for these molecules has a predicted character. The system of internal coordinates for the nitrogroup is shown in Fig. 3. The nitro-group force field used in the present and previous calculations of the vibrations of glucopyranoside nitrates is characterized by the following types of force constants: stretch: S, R, r 1, r 2; bend:a , b 1, b 2; stretch–stretch: S R, R r 1, R r 2, r 1 r 2, S r 1, S r 2; stretch–bend: R a , S a , R b 1, r 1 b 1, R b 2, r 2 b 2, r 1 b 2, r 2 b 1, r 1 a , r 2 a , S b 1, S b 2; 5. bend–bend: b 1 b 2, a b 1, a b 2; 6. torsion: t S, t R; 7. out-of-plane: g i.

1. 2. 3. 4.

The force field of the TNMG molecule consists of the force fields of the glucoside skeleton and of the nitro-groups localized at the 2nd, 3rd, 4th and 6th carbon atoms. Of all the force constants characterizing the nitro-groups, only the diagonal constants of the NvO bonds, being in trans-position (r 2), localized at the C(2) and C(6) atoms, as well as the force constant of the N–O bond (R), localized at the C(6) atom, differ from each other. 3.3. Analysis of results The calculated frequencies, PED of normal vibrations, the deviations of the calculated values of the vibration frequencies from the experimental ones and the absolute IR intensities corresponding to the final force fields of the 2,3-diNMG and 2,3,6-triNMG molecules are presented in Tables 2 and 3, respectively. In Fig. 4 the experimental IR spectrum [39] of 2,3-diNMG is shown. Table 4 gives the proposed calculation results for the 2,6- and 3,6-diNMG molecules in the 1280–1200 cm ⫺1 range obtained with the use of unrefined additive force field model. The vibrational spectra of the considered compounds may be divided into several frequency

ranges in which vibrations of various forms are observed. Let us dwell on the interpretation of the spectral range between 3600 and 800 cm ⫺1. 3.3.1. 3600–3100 cm ⫺1 range The very wide intense band in this range is due to the OH stretching vibrations, which are highly characteristic. 3.3.2. 3050–2800 cm ⫺1 range In this range lie highly characteristic frequencies of stretching vibrations of the CH bonds of the methyl CH3 group, methylene CH2OH group and the lateral CH groups of the glucoside skeleton. 3.3.3. 1700–1600 cm ⫺1 range The presence of a very strong absorption band in this range is characteristic for selectively substituted glucopyranoside nitrates. Every compound investigated has a specific structure for this band. Thus, in the experimental spectrum of TNMG, a broad (about 50 cm ⫺1) splitting of the band is observed. This broad and very intense band has three maxima. In 2,3-diNMG this band has an obvious doublet structure with a splitting of about 15 cm ⫺1. In the spectrum of 2,3,6-tri-O-nitro-4-O-methyl-b-methyld-glucopyranoside (4-O-methyl 2,3,6-triNMG), the structure of this band is not resolved. Our calculation, in agreement with experiment, shows that the intensity of the absorption band in the 1700–1600 cm ⫺1 range characteristic for the ONO2 groups is one order of magnitude higher than ones that are not associated with the vibrations of nitro-groups. There is a good agreement between the calculated and experimental vibration frequencies and absorption band intensities for the investigated substituted methyl-b-d-glucopyranoside nitrates in the 1700–1600 cm ⫺1 range. Analysis of the results allows the following interpretation of the structure of the absorption band in the region of 1700–1600 cm ⫺1. It is caused by the asymmetric stretching vibrations of the NvO bonds n as(ONO2), to whose PED deformations of the ONO2 group angles make their contribution. In the TNMG spectrum, this broad and very intense band has three maxima at 1685, 1662 and 1632 cm ⫺1 (Fig. 1), each corresponding to the vibration of a particular NvO bond. Two of these vibrations are

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165

Table 2 The observed frequencies [39] n (cm ⫺1) in the IR spectrum, the calculated frequencies n i (cm ⫺1), the PED (%) of the normal vibrations, the absolute intensities Aicalc (10 16 cm 2 mol ⫺1s ⫺1) of the absorption bands in the IR spectrum of 2,3-di-O-nitro-methyl-b-d-glucopyranoside and the deviations Dn ˆ nexp ⫺ ncalc . H pl denotes an H atom of the methyl group practically lying in the C(1) –O(1) –C(7) plane and being in the trans position with respect to the C(7)(O)–C(1) bond (the angle between C(1) –O(1) –C(7) and O(1) –C(7) –H pl planes being 179.71⬚). H npl denotes the other two H atoms of the CH3 group, disposed on either side of the C(1) –O(1) –C(7) plane. The following designations are used for internal coordinates: …O–N†i to Oi –Ni ; (NvO)i to Ni vOik …k ˆ 1; 2†; same for (O–Nv)i; and (CON)i to CiOiNi, where i represents the atom numbering according to Fig. 2. Torsional coordinates are designated by t : t…O–N†i to t…Oi –Ni †; t (CO)i to t…Ci –Oi ). Out-of-plane coordinates are designated by g : g i to g (ONO2)i. Abbreviations: vs, very strong; s, strong; w, weak; vw, very weak; sh, shoulder

n [39]

i

nI

3410– 3280

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

3355 3355 3019 3003 2953 2947 2942 2930 2916 2908 2894 2853 1660 1646 1502 1473 1462 1457 1430 1424 1407 1398 1366 1351 1331 1322 1305 1300 1283 1278 1278 1273 1251 1219 1194 1159 1143 1141 1119 1115 1091 1079 1074 1051 1047 1009

3020 2965 2952

2919 2890 2850 1658 vs 1643 vs 1466 1445

1410 w 1387 1365

1310 1283 vs 1270 vs 1238 1220 1197 1155

1125 1105 sh 1087 vs 1072 vs 1048 vs 998 vs

Dn i

1 12 5

3 ⫺4 ⫺3 ⫺2 ⫺3 ⫺7 ⫺12

3 ⫺11 ⫺1

5

⫺13 1 3 ⫺4

6 ⫺10 8 ⫺2 1 ⫺11

PEDi

Aicalc

99 (OH)4 99 (OH)6 73 C7H pl, 25 C7H npl 94 C6H 32 C3H, 25 C2H, 19 C4H, 9 C1H, 6 C5H 98 C7H npl 27 C5H, 23 C4H, 22 C1H, 21 C2H 33 C5H, 31 C3H, 29 C1H 27 C4H, 26 C1H, 24 C2H, 18 C5H 32 C3H, 25 C2H, 25 C4H, 8 C1H, 5 C5H 93 C6H 73 C7H npl, 25 C7H pl 101 (NvO)3, 24 (O–Nv)3, 7 (CON)3 101 (NvO)2, 24 (O–Nv)2, 24 (O–N ˆ O)2, 6 (CON)2 51 H plC7H npl, 22 O1C7H npl, 8 O1C7H pl 61 O6C6H, 29 HC6H, 6 C6OH 35 H plC7H npl, 23 H nplC7H npl, 18 O1C7H pl, 5 O1C7H npl 40 C4C5H, 15 C6C5H, 8 O5C5H, 7 C4C3H 55 O1C7H npl, 15 H nplC7H npl, 12 H plC7H npl, 5 O1C1H 16 C3C4H, 15 C5C4H, 11 C2C3H, 10 C4C3H 41 O1C1H, 29 O5C1H, 6 C3C2H 14 C1C2H, 13 C2C3H, 10 C4C3H, 9 O1C1H, 8 C3C2H, 7 C4C5H, 5 O5C1H, 5C6C5H 18 C1C2H, 15 C5C4H, 8 O2C2H, 8 O5C1H, 6 C3C4H, 6 C3C2H 12 C5C6H, 8 C1C2H, 9 C3C4H, 8 O4C4H, 7 O5C1H, 6 O3C3H, 6 O5C5H, 5 C4C3H 36 C6OH, 9 C2C1H, 9 O3C3H, 9 O5C5H, 7 HC6H, 5 C6C5H 31 O4C4H, 25 O2C2H, 11 C5C4H, 7 C2C1H, 6 C3C2H 26 O6C6H, 12 C6OH, 8 O3C3H, 7 O2C2H, 6 C2C1H, 6 C3C2H, 6 C5C6H 28 O2C2H, 21 O4C4H, 18 O3C3H, 6 C3C2H, 5 O4C3H, 5 O5C5H 27 O3C3H, 17 C2C1, 15 C2C3H, 10 O4C4H, 7 O1C1H 27 O6C6H, 18 C6C5H, 18 O5C5H, 8C5C6H 62 (NvO)2, 8 (O–Nv)2, 5 (O–N)2 68 (NvO)3, 9 (O–Nv)3, 5 (O–N)3 30 O6C6H, 26 C6OH, 21 O5C5H, 13 C6C5H, 14 C5C6 50 C1O1, 10 C1O5, 9 H nplC7H npl, 5 O1C7H pl, 5 O1C7H npl, 5 H plC7H npl 11 C4OH, 8 C2C3, 8 C3C4, 6 C5C6H, 5 C5O5 24 C5C6H, 22 C5O5, 19 C4C5, 10 C4OH, 9 C4O4, 5 C6C5O5 15 C5O5, 12 C4O4, 11 C2O2, 7 C5C6H, 6 C2C3 49 O1C7H npl, 30 H plC7H npl 45 C2O2, 17 C2C3, 14 C1C2, 8 C1C2C3, 7 C3C4, 6 C4OH, 5 C2C1O1 59 C3O3, 8 C2C3, 7 C3C4 35 C1O5, 18 C1C2, 10 C6O6, 9 C2C3, 9 C5C6H 27 O1C7H pl, 20 C1C2, 16 H nplC7H npl, 14 C2C3, 8 C1O1, 7 O1C7H npl 30 C6O6, 27 C4C5, 25 C5C6, 16 C3C4, 6 C5C4H, 5 C4C5O5 30 C4O4, 14 C4C5, 14 C2O2, 10 C3C4, 10 C6O6, 5 C1O5, 5 C4OH 29 C4O4, 16 C6O6, 13 C4C5, 8 C1O5, 8 C4OH, 7 C1C2, 5 C3O3, 5 C5C4O4, 5 C4C5O5 28 C4OH, 25 C7O1, 10 C3C4, 7 C4C5, 7 O4C4H, 6 C1C2, 6 C2C3, 6 C4O4

173.30 9.72 10.78 88.27 10.90 11.57 4.26 38.77 1.14 38.67 189.50 5.29 352.10 356.60 8.08 106.50 4.04 183.80 11.37 17.18 12.38 34.87 20.13 58.97 23.80 52.70 11.12 6.87 201.80 238.40 110.80 73.49 1.03 85.15 2.64 264.70 0.18 3.08 42.80 54.73 12.23 33.54 47.23 40.53 9.17 25.51

166

M.V. Korolevich, R.G. Zhbankov / Journal of Molecular Structure 556 (2000) 157–172

Table 2 (continued)

n [39] 962 930 w 892 s 850 vs 840 vs 752 737 711 696 s 666 626 600 565 520 486 vw 455 405

i 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87

nI 985 980 930 908 851 844 791 736 724 705 684 672 618 595 541 513 489 462 439 414 359 333 323 296 279 261 237 215 198 162 157 122 110 98 78 66 64 58 53 44 39

Dn i ⫺18 0 ⫺16 ⫺1 ⫺4 16 13 6 12 ⫺6 8 5 24 7 ⫺3 ⫺7 ⫺9

Aicalc

PEDi 17 C1C2, 16 C3C4, 11 C7O1, 10 C4OH, 8 C6O6, 5 O4C4H 46 C7O1, 10 C2C3, 5 C5C6, 5 C6C6, 5 C5C6H 30 C5C6, 16 C1O5, 13 C5C6H, 9 C6O6, 8 C5O5, 7 C1O1, 7 O5C1O1, 5 O5C5H, 5 HC6H 33 C5C6H, 27 C5O5, 26 C5C6, 7 C1O5C5, 5 O5C1O1 25 (O–NvO)2, 22 (O–N)2, 13 (O–NvO)3, 12(O–N)3 35 (O–NvO)3, 21 (O–N)3, 13 (O–NvO)2, 9 (O–N)2 20 (O–NvO)2, 17 (CON)2, 10 (CON)3, 8 (O–NvO)3, 5 g 2 24 g 2, 21 g 3, 8 (CON)3, 6 (O–NvO)3, 6 (O–N)3 59 g 3, 24 g 2 19 g 2, 11 (O–N)2, 10 g 3, 6 (O–N)3, 6 (O–NvO)2, 5 (CON)2 21 (O–NvO)2, 10 g 2, 7 (O–N)2, 7 C2C1O5, 7 C3C2O2 44 (O–NvO)3, 11 (O–NvO)2, 7 C4C3O3, 6 C5C6O6 13 O5C1O1, 7 (O–N)2, 6 C4C5, 6 C4C5O5 9 C6C5O5, 8 C2C3O3, 8 C5C4O4, 7 C2C1O1, 7 C5C6O6, 6 O5C1O1, 6 C3C4O4, 5 C1C2O2, 5 C4C5C6 20 (O–N)3, 8 C4C5O5, 5 C1O5C5, 5 C5C6O6 24 (O–NvO)2 9 C1O5C5, 8t (CO)6, 6 C6C5O5, 5 (O–N)2, 5 C4C3O3, 5 C4C5C6 15 C5C6O6, 6 C2C1O5, 6 C6C5H, 5 (O–NvO)3 69 t (CO)6 34 (O–NvO)3 17 (O–NvO)2, 7 C1C2O2, 6 C1O5C5, 5 C3O3, 5 C1C2H 8 C3C4C5, 7 C4C5O5, 5 C1O5C5, 5 C1O1, 5 C2C1O5 15 C3C4O4, 10 (O–NvO)3, 8 C6C5O5, 6 C1C2O2, 5 O5C1O1, 5 C5C6O6 61 t (CO)4, 11 C5C4O4 13 C1C2O2, 11 C2C1O1, 11 O5C1O1, 8 C5C6O6, 5 (CON)2, 5 C4C5O5, 5 t (CO)1 21 C2C3O3, 12 C4C3O3, 10 (O–NvO)2, 9 C1C2O2, 8 t (CO)3, 6 t (O–N)3 7 C5C6O6, 6 C2C1O1, 6 C3C2O2, 5 C3C4, 5 C4C5, 5 C2C1O5, 5 C4C3O3, 5 (O–NvO)3 23 t (CO)4, 15 C3C4O4, 13 C5C4O4, 7 C5C6O6 10 (O–N)2, 10 C3C2O2, 10 C4C3O3, 10 C5C4O4, 7 C1C2C3, 7 C4C5C6, 6 (O–N)3 27 C6C5O5, 9 (CON)3, 8 C4C5C6, 6 C1O5C5, 5 (O–N)3 11 C2C3, 10 (CON)3, 9 C3C4O4, 8 (CON)2, 8 C6C5O5, 5 (O–N)2 13 C1O5C5, 13 C4C5C6, 11 C2C1O5, 10 C1O1C7, 10 t (CO)7, 6 t (C1C2), 6 t (C5C6), 5 t (CO)1 16 t (CO)1, 9 (CON)2, 7 (CON)3, 5 C1C2C3, 5 C1O1C7, 5 t (O–N)2, 5 t (C4C5) 20 t (CO)7, 15 t (C5C6), 10 t (CO)1, 6 C1O1C7, 5 O5C1O1 59 t (CO)7, 17 t (C5C6), 8 t (CO)1 27 t (CO)1, 21 t (C5C6), 5 C6C5O5 14 t (O–N)3, 13 t (CO)2, 11t (CO)3, 10 t (O–N)2, 10 C1O1C7, 8 C4C5C6, 7 C4C3O3 56 C1O1C7, 14 C2C1O1, 10 t (O–N)2, 8 t (CO)1, 5 O5C1O1 33 t (O–N)3, 20 t (O–N)2, 8 C2C3O3, 8 t (C3C4), 6 t (C5C6) 23 t (O–N)2, 12 C1O1C7, 9 t (C3C4), 8 C4C3O3, 7 C3C4C5, 6 t (C5C6), 5 t (C4C5) 26 t (O–N)3, 23 t (CO)2, 19 t (CO)3, 15 t (O–N)2 37 t (CO)3, 29 t (CO)2, 8 C3C2O2, 8 C2C3O3 21 t (C2C3), 18 t (C1C2), 9 C1C2C3, 9 C1O1C7, 8 t (CO)2

localized on carbon atoms C(6) and C(2), and provide, respectively, the low-frequency 1632 cm ⫺1 calc ⫺1 (n ˆ 1635 cm ) and the mean 1662 cm ⫺1 (n calc ˆ 1662 cm ⫺1) maxima of the band n as(ONO2). The other two vibrations are of the mixed type and practically coincide in frequency. They are related to the vibrations of the neighboring nitro-groups at C(3)

35.14 5.01 1.23 32.98 24.18 56.64 19.74 3.13 30.74 17.32 4.33 0.55 3.01 5.03 8.80 48.54 1.98 20.49 5.40 6.16 19.96 90.02 3.04 8.37 0.97 11.02 0.51 3.38 19.95 18.69 4.97 10.57 9.51 21.39 2.10 0.13 0.29 4.34 0.38 18.88 1.66

and C(4) and correspond to the high-frequency peak at 1685 cm ⫺1. In the spectrum of 2,3-diNMG, this band has a vivid doublet structure with maxima at 1658 and 1643 cm ⫺1. As shown by calculation, this band is due to two asymmetric stretching vibrations n as(ONO2). One of these is localized on atom C(3)

M.V. Korolevich, R.G. Zhbankov / Journal of Molecular Structure 556 (2000) 157–172

167

Table 3 The observed frequencies n (cm ⫺1) in the IR spectrum of 2,3,6-tri-O-nitro-4-O-methyl-b-methyl-d-glucopyranoside, the calculated frequencies n i (cm ⫺1), the PED (%) of the normal vibrations, the absolute intensities Aicalc (10 16 cm 2 mol ⫺1 s ⫺1) of the absorption bands in the IR spectrum of 2,3,6-tri-O-nitro-methyl-b-d-glucopyranoside and the deviations Dn ˆ nexp ⫺ ncalc . Designations as in Table 2. Numbering of the atoms is given in Fig. 2

n

i

ni

3445–3270

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

3355 3019 3003 2953 2947 2942 2930 2916 2908 2895 2853 1667 1662 1642 1502 1464 1462 1457 1430 1425 1407 1399 1366 1352 1324 1313 1304 1291 1284 1281 1274 1267 1265 1220 1195 1161 1143 1141 1122 1120 1099 1083 1079 1063 1051 1023 1009 986 962 918

3006 2977 2953 2928

2890 2854 1664 1641 1467 1455 1432

1394 1380 1360 1333

1279

1226 1193 1168 1149 1119

1081 1072 1041 1013 1002 976 960 917

Dn i

3 24 6 ⫺2 ⫺5 1 ⫺3 ⫺1 3 ⫺2 2

⫺5 14 8 9

6 ⫺2 7 6 ⫺3 ⫺2 ⫺7 ⫺10 ⫺10 ⫺7 ⫺10 ⫺2 ⫺1

PEDi

Aicalc

99 (OH)4 73 C7H pl, 25 C7H npl 93 C6H 32 C3H, 25 C2H, 19 C4H, 9 C1H, 6 C5H 98 C7H npl 27 C5H, 23 C4H, 22 C1H, 21 C2H 33 C5H, 31 C3H, 29 C1H 27 C4H, 26 C1H, 24 C2H, 17 C5H 32 C3H, 25 C2H, 25 C4H, 8 C1H, 5 C5H 93 C6H 73 C7H npl, 25 C7H pl 99 (NvO)3, 22 (O–NvO)3, 6 (CON)3 99 (NvO)3, 23 (O–NvO)2, 6 (CON)2 100 (NvO)6, 25 (O–NvO)6, 7 (CON)6 51 H plC7H npl, 22 O1C7H npl, 8 O1C7H pl 55 O6C6H, 30 HC6H 35 H plC7H npl, 23 H nplC7H npl, 18 O1C7H pl, 5 O1C7H npl 35 C4C5H, 13 C6C5H, 8 O5C5H, 7 C4C3H, 6 O6C6H 53 O1C7H npl, 14 H nplC7H npl, 12 H plC7H npl, 5 O1C1H 15 C3C4H, 14 C5C4H, 11 C2C3H, 11 C4C3H 39 O1C1H, 28 O5C1H, 7 C3C2H 13 C1C2H, 12 O1C1H, 12 C2C3H, 8 O5C1H, 8 C4C3H, 7C3C2H, 7 C4C5H, 5C6C5H 17 C1C2H, 16 C5C4H, 9 O2C2H, 8 O5C1H, 7 C3C4H, 5 C3C2H 9 C1C2H, 9 C3C4H, 7 O5C1H, 7 O3C3H, 7 O4C4H, 6 C4C3H, 6 C5C6H, 5 C2C1H, 6 O6C6H 29 O4C4H, 17 O2C2H, 14 C2H1, 7 C3C3H, 7 C5C4H, 6 O1C1H, 6 C4C3H 17 C5C6H, 17 O2C2H, 9 C3C2H, 9 O3C3H, 7 O5C5H, 7 O6C6H, 6 C6C5H, 5 C2C1H, 5 HC6H 19 O3C3H, 16 O2C2H, 14 O5C5H, 12 O4C4H, 6 C4C3H, 6 C6C5H 15 O5C5H, 13 (NvO)6, 12 O4C4H, 9 O6C6H, 7 O2C2H, 6 C6C5H, 5 C2C1H, 5 C3C4H 22 O3C3H, 15 C2C3H, 14 O4C4H, 13 C2C1H, 7 O1C1H, 6 O2C2H, 5 C3C2H 67 O6C6H, 9 C6C5H 69 (NvO)2, 13 (O–NvO)2, 7 (O–N)2 34 (NvO)3, 26 (NvO)6, 7 (O–NvO)3, 5 C6C5H, 5 O5C5H 31 (NvO)3, 27 (NvO)6, 9 O5C5H, 7 C6C5H, 6 (O–NvO)3 51 C1O1, 9 C1O5, 9 H nplC7H npl, 5 O1C7H pl, 5 O1C7H npl, 5 H plC7H npl 11 C4OH, 8 C2C3, 8 C3C4, 7 C5C6H, 6 O5C5H, 5 C5O5 28 C5C6H, 21 C5O5, 18 C4C5, 8 C4OH, 7 C4O4, 6 C6C5O5 14 O1C7H npl, 10 C4O4, 9 C5O5, 8 C2O2, 5 C2C3, 5 C5C6H, 5 H plC7H npl 37 O1C7H npl, 23 H plC7H npl, 5 C4O4 38 C3O3, 11 C3C4, 11 C5C6, 9 C6O6, 7 C2O2 42 C2O2, 22 C2C3, 13 C1C2, 8 C4OH, 5 C3O3, 5 C2C1O1 29 C6O6, 20 C3O3, 13 C1O5, 10 C5C6, 8 C1C2, 6 C2C3, 5 C5C6H 22 C6O6, 20 C1O5, 12 C4C5, 9 C1C2, 9 C3C4, 7 C5C6, 5 O1C7H pl 25 O1C7H pl, 23 C1C2, 15 C2C3, 15 H nplC7H npl, 9 C1O1, 7 O1C7H npl 29 C4C5, 18 C3C4, 17 C5C6, 7 C4O4, 6 C2O2, 6 C5O5, 6 C5C6H, 5 C5C4H 39 C4O4, 11 C4C5, 6 C1C2, 6 C4OH, 5 C1O5, 5 C2O2, 5 C5C4O4, 5 C4C5O5 24 C5C6, 14 C4O4, 9 C4OH, 9 (CON)6, 8 C1C2, 8 C3O3, 6 C4C5, 6 HC6H, 5 C5C6O6, 5 O5C5H 30 C7O1, 25 C4OH, 14 C3C4, 6 O4C4H 20 C7O1, 14 C1C2, 14 C3C4, 12 C4OH, 64 O4C4H 26 C7O1, 13 C2C3, 11 C1O1, 10 C5C6, 9 C1O5, 5 C3C2H 37 C5O5, 33 C5C6H, 12 C1O5, 11 O5C1O1, 7 C1O5C5

219.30 8.75 70.74 9.92 5.63 9.39 44.42 0.17 36.93 218.70 7.92 320.60 375.50 304.30 11.04 49.09 4.26 354.10 19.65 35.34 18.62 34.65 13.23 38.06 26.37 62.95 22.45 72.00 350.50 168.80 79.06 148.50 81.98 91.88 5.90 398.80 7.35 1.86 58.02 32.36 53.52 79.25 31.21 10.66 40.75 56.02 41.58 39.06 0.31 19.23

168

M.V. Korolevich, R.G. Zhbankov / Journal of Molecular Structure 556 (2000) 157–172

Table 3 (continued)

n

i

895 872 843

51 52 53 54 55 56 57 58 59 60 61 62 63 64

880 870 843 794 770 742 727 718 692 682 662 627 613 570

65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93

541 501 475 438 418 365 332 317 309 293 262 239 223 197 181 160 157 123 116 106 83 67 61 54 53 46 44 39 31

749 728 695 639 622 591 544 511

ni

Dn i 15 2 0

7 1 3 ⫺23

21 3 10

Aicalc

PEDi 22 (O–N)2, 20 (O–N)3, 14 (O–NvO)2, 13 (O–NvO)3 21 (O–N)3, 17 (O–N)2, 21 (O–NvO)3, 16 (O–NvO)2 40 (O–N)6, 36 (O–NvO)6, 5 (NvO)6 18 (O–NvO)2, 15 (CON)2, 11 (CON)3, 11 (O–NvO)3, 5g 2 19 (O–NvO)6, 16 (CON)6, 5 C5C6H 22 g 2, 11 g 3, 10 (O–NvO)3, 11 (CON)3, 5 (O–N)3 38 g 3, 31 g 2, 6 (O–N)2 41 g 3, 7 (O–N)2, 6 g 2 46 g 6, 13 (O–NvO)2, 12 g 2 38 g 6, 25 (O–NvO)2, 6 g 2 45 (O–NvO)3, 5 (O–NvO)6, 5 C4C3O3 24 (O–NvO)6, 7 (O–N)2, 5 C4C5, 5 C5C6O6 16 (O–NvO)6, 13 O5C1O1, 9 C5C4O4, 6 C4C5C6 10 C2C1O1, 9 C3C4O4, 7 C1C2O2, 7 O5C1O1, 7 (O–NvO)6, 6 (O–N)6, 6 C6C5O5, 5 C3C2O2,5 C2C3O3 14 C1O5C5, 13 C4C5O5, 7 (O–N)3, 7 C2C1O5, 6 (O–N)6, 6 (O–NvO)2 33 (O–NvO)6, 6 (O–NvO)3, 6 (O–N)3, 6 C6O6, 5 C4C3O3, 5 C6C5H 29 (O–NvO)2, 10 (O–N)6, 5 C2O2 36 (O–NvO)3, 9 C1C2O2, 7 C5C4O4, 6 C3O3, 6 (O–NvO)2, 5 C1C2H 10 C3C4C5, 8 C4C5O5, 6 C1O5C5 16 C3C4O4, 10 (O–NvO)3, 7 C1C2O2, 6 O5C1O1 61 t (CO)4, 9 C5C4O4 16 C2C1O1, 7 C1C2O2, 7 (CON)2, 6 O5C1O1, 5 (O–NvO)2 23 (O–NvO)6, 14 C6C5O5, 13 (CON)6, 8 C2C3O3, 6 C4C5C6, 5 t (C5C6) 17 C2C3O3, 12 C1C2O2, 8 C3C2O2, 6 t (CO)3, 5 C4C3O3, 5 (O–NvO)2 25 t (CO)3, 21 C5C4O4, 10 (O–NvO)3,8 C4C3O3, 6 C3C4O4, 5 (CON)3, 10 C4C3O3, 8 (O–N)2, 8 (O–N)3, 8 C3C2O2, 7 C1C2C3, 5 C3C4O4 11 C4C5O5, 11 C5C6O6, 5 (CON)3 10 (CON)3, 9 C2C3, 6 C4C5O5, 6 t (CO)6 12 C1O5C5, 8 C5C6, 8 C2C1O5, 7 (CON)6, 6 C6C5O5, 5 (O–N)6 33 t (O–N)6, 14 t (C5C6), 11 t (CO)6, 9 C4C5C6, 5 C1O5C5 19 t (CO)1, 9 C1O1C7, 7 (CON)2, 6 C1C2C3, 6 (CON)3, 5 t (C4C5) 35 t (CO)7, 7 C5C6O6, 6 (CON)6, 5 t (C5C6) 10 t (CO)1, 8 C5C6O6, 8 t (CO)7, 7 C1O1C7, 5 O5C1O1, 5 t (CO)2 43 t (CO)7, 27 t (CO)1, 5 C3C2O2 17 C1O1C7, 16 t (O–N)3, 11 t (CO)2, 5 t (C3C4), 5 t (CO)1, 5 t (CO)3 41 C1O1C7, 23 t (O–N)2, 11 C2C1O1, 10 t (CO)1, 6 O5C1O1, 5 C3C3O2 42 t (O–N)3, 25 t (O–N)2, 13 C1O1C7, 6 C2C3O3 26 t (O–N)2, 17 t (CO)3, 15 t (CO)2, 13 t (O–N)3, 6 t (CO)6, 5 t (O–N)6 25 t (O–N)6, C1O1C7, 10 t (O–N)3, 6 C4C5C6, 6 t (C5C6), 5 C2C1O1 29 t (CO)6, 13 C4C5C6, 9 C6C5O5, 9 t (O–N)6,7 C5C6O6, 6 t (CO)3 39 t (CO)3, 29 t (CO)2, 8 C3C2O2, 8 C2C3O3 17 t (C5C6), 15 t (C2C3), 12 t (CO)2, 7 t (O–N)6, 5 t (C1C2), 5 t (C3C4) 23 t (C5C6), 12 t (C1C2), 10 t (C4C5), 7 t (CO)6, 6 C6C5O5

and gives a high-frequency maximum (n calc ˆ 1660 cm ⫺1). The second vibration is localized on C(2) and corresponds to the low-frequency component of the band (n calc ˆ 1646 cm ⫺1). In the 2,3,6-triNMG spectrum, the band has a complex unresolved shape with shoulders at 1664 and 1641 cm ⫺1. According to the calculations, the

22.57 58.27 53.85 19.61 10.25 6.52 37.21 3.15 6.13 12.35 2.76 0.26 12.34 15.55 14.18 14.24 10.17 5.97 2.26 5.98 100.50 4.80 144.50 0.17 4.27 9.03 4.75 2.72 37.30 28.65 9.12 0.26 1.67 0.10 12.40 0.60 0.53 5.82 1.54 10.60 32.24 0.39 2.70

low-frequency component of this band that gives a shoulder at 1641 cm ⫺1 is due to the vibration n as(ONO2) localized on C(6) (n calc ˆ 1642 cm ⫺1). The high-frequency shoulder at 1664 cm ⫺1 is due to a similar vibration localized on C(3) (n calc ˆ 1667 cm ⫺1). The vibration of the NvO bonds localized on C(2) has an intermediate frequency (n calc ˆ 1662

M.V. Korolevich, R.G. Zhbankov / Journal of Molecular Structure 556 (2000) 157–172 Table 4 The calculated frequencies n i cm ⫺1, the PED (%) of the normal vibrations and the absolute intensities Aicalc (10 16 cm 2 mol ⫺1 s ⫺1) of the absorption bands in the IR spectrum of 2,6-di-O-nitromethyl-b-d-glucopyranoside (2,6-diNMG) and 3,6-di-O-nitromethyl-b-d-glucopyranoside (3,6-diNMG) in the 1280– 1260 cm ⫺1 range

ni

Aicalc

PEDi

2,6-diNMG 1282 68 O6C6H, 8 C5C6H 1276 69 (NvO)2, 12 (O–NvO)2, 7 (O–N)2 1270 36 (NvO)6, 23 O5C5H, 18 C6C5H, 5 (O–NvO)6 1244 26 C3O3H, 11 O3C3H, 7 C2C3, 6 (NvO)2 1220 51 C1O1, 9 C1O5, 9 H nplCH npl, 6 H plCH npl, 5 O1C7H pl, 5 O1C7H npl 3,6-diNMG 1282 65 O6C6H, 8 C5C6H, 5 C2C1H 1272 37 (NvO)6, 18 O5C5H, 15 C6C5H, 6 (O–NvO)6, 5 (NvO)3 1267 55 (NvO)3, 105 (O–NvO)3, 6 (O–N)3, 5 O5C5H 1242 37 C3O3H, 9 C2C3, 9 O3C3H, 7 O2C2H, 6 (NvO)3 1220 51 C1O1, 9 H nplCH npl, 8 C1O5, 5 O1C7H pl, 5 H plCH npl, 5 O1C7H npl

82.58 63.71 124.80 108.60 114.80

50.55 118.30 84.40 44.22 82.47

cm ⫺1). It is evident that the corresponding intermediate component of the band overlaps with the high-frequency component. Thus, the dependence of the number and disposition of the components of the band in the 1700–1600 cm ⫺1 range on the location and degree of substitution of nitrate groups in 2,3-diNMG and 2,3,6-triNMG is similar to that in TNMG. 3.3.4. 1500–1200 cm ⫺1 range This range, as a whole, may be characterized as a range of complex deformation CCH, COH and OCH

169

vibrations, in which also fall frequencies of symmetric stretching vibrations of NvO bonds. It may be divided into the following three frequency ranges in which vibrations are homogeneous (with the prevailing contribution to its PED of internal coordinates of the same type): 1500–1280, 1280–1260 and 1260–1200 cm ⫺1. 3.3.5. 1500–1280 cm ⫺1 range The spectral curve observed in this range is formed by the overlap of a great number of closely spaced absorption bands. Their experimental assignment is very problematic. The calculation shows that the appearance of absorption bands in this spectral range is caused by the deformation vibrations of CH and CH2 groups, methyl group and hydroxyl COH groups. The internal deformation vibration of the methylene group and ones of the methyl group are isolated and have the largest frequencies. The other vibrations are complex deformation vibrations involving the participation of CCH, COH and OCH angles near different carbon atoms of the glucopyranoside ring. It does not concern the low-frequency vibration in the 1500–1280 cm ⫺1 range, which is localized on carbon atom C6. The PED of this vibration is influenced basically by the O6C6H and C6C5H angles deformations. Deformation of the O6C6H angle makes a dominant contribution to the PED. For brevity this vibration is denoted by n (OCH)6. Table 5 represents the calculated frequencies, PED and absolute intensities of n (OCH)6 vibration for the bd-glucose [28], TNMG [29], 2,3-, 2,6-, 3,6-diNMG and 2,3,6-triNMG molecules. The data in Table 5 make it possible to follow the effects of selective nitrosubstitution of the glucopyranoside ring hydroxyl groups. As can be seen, the

Fig. 4. Experimental [39] IR transmission spectrum of 2,3-di-O-nitro-methyl-b-d-glucopyranoside.

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Table 5 The calculated frequencies n (cm ⫺1), PED (%) and absolute intensities A calc(10 16 cm 2 mol ⫺1s ⫺1) of the normal vibration n (OCH)6 for b-d-glucose, 2,3,4,6-tetra-O-nitro-methyl-b-d-glucopyranoside (TNMG), 2,3,6-tri-O-nitro-methyl-b-d-glucopyranoside (2,3,6triNMG) and 2,3-, 2,6- and 3,6-di-O-nitro-methyl-b-d-glucopyranosides (2,3-, 2,6- and 3,6-diNMGs) Compound

n

PED

b-d-glucose

1260

TNMG 2,3,6-triNMG 2,3-diNMG

1281 1281 1278

2,6-diNMG 3,6-diNMG

1282 1282

17 O6C6H, 14 C5C6H, 13 C2O2H, 10 O3C3H, 12 C6O6H, 9 O2C2H, 8 CC3H, 6 C1O1H 59 O6C6H, 10 C5C6H, 5 C2C1H 67 O6C6H, 9 C6C5H 27 O6C6H, 18 C6C5H, 18 O5C5H, 8C5C6H 68 O6C6H, 8 C5C6H 65 O6C6H, 8 C5C6H, 5 C2C1H

A calc 0.60

4.73 168.80 238.40 82.58 50.55

n (OCH)6 is subject to a strong influence from a substitution of hydroxyl groups. Full substitution leads to a 20 cm ⫺1 frequency shift and significant increasing of the intensity of the given vibration on passing from bd-glucose to 2,3,4,6-tetra-nitrate-methyl-b-d-glucopyranoside. Selective substitution of only two or three hydroxyl groups (compared to full substitution) is prominent in the band intensities. The intensity of n (OCH)6 vibration for di- and tri-NMGs (compared to TNMG) significantly increases, with its frequency remaining unaltered. 3.3.6. 1280–1260 cm ⫺1 range In the spectra of selectively substituted glucopyranoside nitrates in this narrow spectral interval only one very strong band is observed. In the TNMG spectrum, this band has a maximum at 1278 cm ⫺1. In the spectrum of 2,3-diNMG there are two maxima at 1283 and 1270 cm ⫺1 of this band. In the 2,3,6-triNMG spectrum, the band has a peak at 1279 cm ⫺1. As the calculation shows, in the 1280–1260 cm ⫺1 region symmetric stretching vibrations of the NvO bonds n s(ONO2) manifest themselves. To the band in this region in the TNMG spectrum there correspond four vibrations with calculated frequencies 1277, 1273, 1269 and 1265 cm ⫺1 [29]. Their total absolute intensity (corresponding to the absorption band intensity in the region under consideration) considerably exceeds the intensities of vibrations in the neighboring spectral intervals. The value of this intensity

and the ratio of intensities of vibrations in this region and the neighboring regions agree perfectly with experiment. In the case of not fully substituted glucopyranoside (diNMGs and 2,3,6-triNMG) the n (OCH)6 vibration is very strong. Its intensity is comparable well with the n s(ONO2) intensity. Because of this, the very strong characteristic band observed in 1280–1260 cm ⫺1 region is caused by the superposition of n (OCH)6 and n s(ONO2) vibrations, which coincide very closely both in frequencies and intensities. Such assignment given explains the availability of two maxima at 1283 and 1270 cm ⫺1 of the band under consideration in the 2,3-diNMG spectrum. 3.3.7. 1260–1200 cm ⫺1 range In the spectra of fully substituted and selectively substituted methyl-b-d-glucopyranoside nitrates the characteristic band with the maximum in the 1220– 1227 cm ⫺1 interval is observed. So, in the TNMG spectrum there is the band at 1227 cm ⫺1. In the spectrum of 4-O-methyl-2,3,6-triNMG there is the band at 1226 cm ⫺1. In the 2,3-diNMG spectrum, besides this band with maximum near 1220 cm ⫺1 the band near 1238 cm ⫺1 is observed. The calculation, in accordance with the experiment, yields the following interpretation of spectra in the 1260–1200 cm ⫺1 region. In this region fall frequencies of the characteristic vibration, both in frequency and form, with participation of the C1O1 bond and methylene group (see n 34 for 2,3-diNMG and 2,3,6triNMG) as well as the higher-frequency deformation vibration localized on atom C6, which involves the participation of OCH, COH and CCH angles (n 33 for 2,3-diNMG). The n 34 vibration corresponds to the band at 1220 cm ⫺1 in the 2,3-diNMG spectrum. This vibration is fairly characteristic in a frequency and highly characteristic in a form. The main contribution to the PED is made by the changes of the C1O1 bond (50%) and deformations of HCH and OCH angles of methyl group at C1 (24%). The contribution of the C1O5 bond is 10%. There are the same PEDs in the cases of 2,3,6triNMG, TNMG, and 2,6- and 3,6-diNMGs. The n 33 vibration is a deformation vibration involving the participation of the O6C6H, C6OH and O5C5H angles. This vibration occurs only for dinitrates of glucopyranoside.

M.V. Korolevich, R.G. Zhbankov / Journal of Molecular Structure 556 (2000) 157–172 ⫺1

3.3.8. 1200–950 cm range It is well known that all sugars are characterized by highly intense bands in this range. Here stretching C– O and C–C vibrations as well as the deformation vibrations of the methylene group can show up. The presence of an intense absorption band in the 1170–1120 cm ⫺1 interval is specific to the cyclic structure of monosaccharides [2]. In the case of 2,3-diNMG, 2,3,6-triNMG and TNMG that is the band near 1155, 1168 and 1166 cm ⫺1, respectively. As follows from the calculation, this band is due to the mixed vibration of the methylene group and glucoside ring bond C5O5 (see n 36 for 2,3-diNMG and 2,3,6-triNMG). In the range under consideration also fall frequencies of two deformation vibrations of the methyl group. One of them is a very weak vibration with calculated frequency n 38 ˆ 1143 cm ⫺1 in the case of 2,3-diNMG (n 38 ˆ 1141 cm ⫺1 for 2,3,6-triNMG). The other is an intense vibration with n 42 ˆ 1079 cm ⫺1 (n 43 ˆ 1079 cm ⫺1 for 2,3,6-triNMG), which corresponds to a very strong observed band near 1087 cm ⫺1 (1072 cm ⫺1 for 2,3,6-triNMG). 3.3.9. 950–800 cm ⫺1 range This range is convenient for analysing the structure of monosaccharides because of the absence of band overlapping and the sensitivity of the bands to configuration and conformation transformations of carbohydrates molecules [2–4]. In the IR spectrum of b-d-glucose in this region the higher frequency band corresponding to the band at 917 cm ⫺1 for the a-anomer barely changes its position, while the low-frequency one shifts by 60 cm ⫺1 towards higher frequency. So the spectrum represents an envelope of two closely spaced resolved bands with unequal peak intensities, one being the wide band at 913 cm ⫺1 and the other being the narrow band at 900 cm ⫺1. Our theoretical study [28] shows, that the band at 913 cm ⫺1 for b-d-glucose is mainly associated with the changes in the bonds of the molecular fragment C1 –O5 –C5 and the deformation of the CCH angles at C6. This vibration, which determines the configurationally sensitive band at 900 cm ⫺1, is a complex valence vibration of the atomic chain O5 –C5 –C6 – O6. These assignments had been obtained on the basis of the perfect coincidence of the calculated intensities in the frequency range being analysed.

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The substitution of the hydroxyl groups in the pyranose rings for the nitrate groups has a very pronounced effect on the spectral range under consideration. In this range fall frequencies of stretching vibrations of the N– O bonds. These vibrations occur in the 900–800 cm ⫺1 region and have a considerably higher intensity than the bands corresponding to the glucoside skeleton. In the TNMG spectrum the broad strong band near 839 cm ⫺1 with a high-frequency shoulder at 873 cm ⫺1 is observed in this region (denoted as n (N–O)). In the 2,3-diNMG spectrum there is a very strong band with small shoulders at the 850 and 840 cm ⫺1. In the spectrum of 2,3,6-triNMG there is a similar band near 843 cm ⫺1 with shoulders at 895 and 872 cm ⫺1. The structure of the n (N–O) band warrants a closer consideration. This band, together with the n as(ONO2) band, can be used for analytical purposes. Our calculation of normal vibration frequencies and absolute IR band intensities for TNMG showed that this band cannot be assigned to the uniform stretching vibrations. In this range, frequencies of those vibrations occur whose PEDs are influenced by the changes in the N–O bonds and the O–NvO deformation angles. To the n (N–O) band in TNMG there correspond four vibrations with frequencies 881, 877, 868 and 845 cm ⫺1, and three vibrations (880, 870 and 843 cm ⫺1) in 2,3,6-triNMG. Of these, the lowfrequency vibration is localized entirely on C(6) in both compounds. The others are mixed and related to the vibrations of the nitro-groups at C(2), C(3) and C(4) in TNMG and of the nitro-groups at C(2) and C(3) in 2,3,6-triNMG. In 2,3-diNMG the corresponding vibrations have frequencies 851 and 844 cm ⫺1. The nitro-groups at C(2) and C(3) participate in them concurrently. Thus, the nitrate group at C(6) is responsible for the low-frequency component. It should be noted that the intensities, predicted by calculations for 2,3-diNMG and 2,3,6-triNMG in this work, support the dependence of the vibrational frequency n (N–O) in these glucopyranoside nitrates on the location of nitro-groups in the pyranose ring established in [29,30].

4. Conclusion The combination of the normal vibration frequencies from the point of view of the valence-force field

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