Molecular structure of (E)-benzaldehyde oxime from gas-phase electron diffraction, quantum-chemical calculations and microwave spectroscopy

Journal of Molecular Structure 978 (2010) 195–200

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Molecular structure of (E)-benzaldehyde oxime from gas-phase electron diffraction, quantum-chemical calculations and microwave spectroscopy Nobuhiko Kuze a,*, Takeshi Sakaizumi a, Osamu Ohashi a, Yutaka Yokouchi b, Kinya Iijima b a b

Department of Chemistry, Faculty of Science and Technology, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan Department of Chemistry, Faculty of Science, Shizuoka University, Oya, Shizuoka 422-8529, Japan

a r t i c l e

i n f o

Article history: Received 1 December 2009 Received in revised form 15 February 2010 Accepted 15 February 2010 Available online 19 February 2010 Keywords: Molecular conformation Gas-phase electron diffraction Benzaldehyde oxime Ab initio calculation Rotational spectroscopy

a b s t r a c t The gas-phase structure of (E)-benzaldehyde oxime (C6H5ACH@NOH), has been determined by gas-phase electron diffraction (GED), microwave spectroscopy (MW) and quantum-chemical calculations. Two sets of the data analyses were performed. One was GED + MW data analysis with a small-amplitude vibrational model. A planar conformation for this molecule was adopted in the analysis. Another was GED data analysis of a large-amplitude motion of the CAC torsion. The potential minimum was located on the planar conformation of this molecule. Above two sets of the data analyses were led to the one consistent result that showed good agreement between the experimental and calculated molecular intensities. Ó 2010 Elsevier B.V. All rights reserved.

1. Introduction Benzaldehyde oxime (C6H5ACH@NOH) is the prototype of the aromatic oximes, it has two geometrical isomers. The C(@N)AH and NAO bonds of benzaldehyde oxime are in the eclipsed and anti orientations for the (E)- and (Z)-isomers, respectively (see Fig. 1). Infrared spectra in low-temperature Ar and N2 matrices [1], and IR and Raman spectra in the gas phase, solution and solid phase [2] of this molecule are reported. They were assigned by the comparison with the calculated spectra. The (E)-isomer is highly predominant in the matrixes after deposition [1]. The molecular structure of (E)-benzaldehyde oxime in the solid phase was different from that in the gas phase. The CCCN dihedral angle, /, between the planes of the phenyl and the oxime groups in the solid phase was reported to be about 20° by X-ray diffraction (XRD) [3]. In contrast, the molecular conformation of this molecule in the gas phase was planar. Several years ago, we reported the microwave (MW) spectra in the ground vibrational states of (E)benzaldehyde oxime, C6H5ACH@NOH and its deuterated species, C6H5ACH@NOD [4]. The experimental values of the DI ( = Ic  Ia  Ib) in the normal (0.295 (6) uÅ2) and deuterated (0.28 (5) uÅ2) species and the rs coordinate of the hydrogen atom of the OH group suggested that the molecular conformation of this molecule was planar one in the gas phase. The values of

* Corresponding author. Tel.: +81 0332383458; fax: +81 0332383361. E-mail address: [email protected] (N. Kuze). 0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2010.02.042

other dihedral angles, CCNO and CNOH, were almost 180° and 180°, respectively. Since six rotational constants obtained in the MW study were insufficient in determining all structural parameters independently, the scaling of the whole ab initio geometry was performed to reproduce of the observed rotational constants [4]. One of the few experimental techniques for determining the molecular structure in the gas phase is gas-phase electron diffraction (GED). This technique is widely used to investigate the structures of benzene derivatives. However, there were no GED data for aromatic oximes in the gas phase. This paper reports the molecular structure of (E)-benzaldehyde oxime in the gas phase determined by GED and MW data with the aid of the quantum-chemical calculations in order to derive the precise structural and dynamical information by the experiment. 2. Experimental (E)-Benzaldehyde oxime with 98% purity obtained from Aldrich Chemical Company Inc. was purified by vacuum sublimation. Electron diffraction patterns were recorded on Kodak projector slide plates in the apparatus equipped with an r3-sector and the high temperature nozzle at Shizuoka University [5]. Nozzle-to-plate distances of 143.25 mm (short) and 293.71 mm (long) were used. The experimental conditions were summarized in Table 1. The wavelengths of the incident electrons were estimated by measuring the accelerating voltage of 39.99 kV. The optical densities of the

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(E)–isomer

11

12

C3

C4 13

1.0

C2

C5

long

sM(s)

0.5

Obs.

0.0

10

C1

C6 14

φ

C7 15

Calc.

short

-0.5

0.5 0.0

-1.0

-0.5

N8 O9

0.0

16

Obs.-Calc. 5

10

15

20

25

30

0.0

35

s / A-1

(Z)–isomer

Fig. 2. Experimental (circles) and theoretical (solid curves) molecular scattering intensities of (E)-benzaldehyde oxime. The theoretical curve was calculated from the best fitting parameters for GED + MW data analysis.

Fig. 1. Molecular conformations of benzaldehyde oxime with atom numbering. The C2C1C7N8 dihedral angle / is defined to be zero when the molecular conformation is planar.

Vð/Þ ¼

Table 1 Experimental conditions.

Camera distance (mm) Accelerating voltage (kV) Beam current (mA) Background pressure (Pa) Nozzle temperature (K) Exposure time (s) Range of the intensity data (Å1)

mizations of this molecule were carried out by varying the dihedral angle, /, which is the torsional angle between the plane of the phenyl group and that of the oxime moiety, in steps of 5° from / = 0° to 90° at the MP2/6-31G(d,p) and B3LYP/6-31G(d,p) levels. Then the fully optimizations were performed, the optimized structure was almost planar one. In addition, the harmonic vibrational frequencies were calculated for the optimized structure to obtain the force constants at the B3LYP/6-31G(d,p) level. The potential energy function for the internal rotation around the C1AC7 bond can be obtained by fitting the energies to the six-term truncated Fourier expansion for the potential function, V(/) [13,14].

Short

Long

143.25 39.99 0.55 7.6  103 357–366 150 s = 3.125–17.000

293.71 39.99 0.77 1.1  103 357–366 73 s = 6.50–34.25

photographic plates were measured by using a microphotometer [5] for three plates which were selected from among those exposed at each camera distance. They were averaged and the densities were converted into intensities. Numerical data of total experimental intensities and backgrounds are available as Supplementary information. Elastic and inelastic atomic scattering factors were taken from Refs. [6] and [7]. The molecular scattering intensities were obtained at intervals of 0.125 and 0.25 Å1 for long and short camera distances, respectively. The experimental molecular scattering intensities are shown in Fig. 2 along with the ones calculated in the final data analysis. The numerical data of the intensities (IT) and background (IB) were deposited as Supplementary materials (Table S1). 3. Theoretical calculations Quantum mechanical calculations on (E)-benzaldehyde oxime were performed at the MP2/6-31G(d,p) [8,9] and density functional (DFT) hybrid B3LYP/6-31G(d,p) [10,11] levels of theory, using the Gaussian 98 program package [12]. The structural opti-

6 X 1 V i ð1  cos i/Þ: 2 i¼1

The potential coefficients (in kJ mol1), V1–V6, have been obtained: V1 = 0.001, V2 = 19.113, V3 = 0.007, V4 = 3.582, V5 = 0.007, and V6 = 0.032, for MP2/6-31G(d,p) level; V1 = 0.005, V2 = 26.392, V3 = 0.005, V4 = 2.824, V5 = 0.005, and V6 = 0.222, for B3LYP/6-31G(d,p) level. 4. Normal coordinate analysis The force constants of (E)-benzaldehyde oxime in the Cartesiancoordinate system, obtained by the DFT calculations were converted into those in the local-symmetry coordinates. Then the converted force constants were scaled so as to reproduce the observed vibrational frequencies [15]. The definition of the local-symmetry coordinates with the scale factors, the scaled force constants and the observed and calculated vibrational frequencies with potential energy distributions are listed in Tables S2–S4 in Supplementary information. 5. Structural analysis In the structure refinement, the following assumptions and constraints were made to reduce the number of adjustable parameters referring to the results of the ab initio calculation (1) the phenyl and the oxime groups were planar; (2) the differences of the corresponding bond distances and angles were equal to those given by the MP2/6-31G(d,p) calculations (see Table S5); (3) the differences between the valence angles of the phenyl ring, C6C1C2, C1C2C3 and C1C6C5, had to be constrained to the values obtained by MP2/6-31G(d,p) calculation, other three angles were calculated

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ra  rz ¼

3 hDx2 i0 þ hDy2 i0 hDz2 iT aðhDz2 iT  hDz2 i0 Þ þ  þ dr T 2 2r r

Where hDx2i + hDy2i and hDz2i were perpendicular and parallel mean amplitudes, respectively; dr denoted the centrifugal distortion term; the subscripts T and 0 indicated T = 323 and 0 K, respectively. The Morse anharmonicity constant, a, was assumed to be 2 Å1 [17] for bonded atom pairs and while it was neglected for non-bonded atom pairs. The rotational constants, B0, for the normal and deuterated species [8] were converted to the rotational constants for the zero-point average structure, Bz, by the harmonic vibrational corrections [17], using the scaled force constants determined by normal coordinate analysis. The uncertainty of Bz were estimated as r(obs.) = (r21 þ r22 )1/2, where r1 was the standard error of the observed rotational constant and r2 was taken to be 10% of the vibrational correction which represented the uncertainty accompanying the force constants. Table 2 lists the rotational constants and vibrational corrections. Since the calculated rotational constants, B0a , derived by the analysis of GED data were consistent with Bz, the relative weights of the rotational constants were estimated for the joint analysis of GED and MW data. As the planarity of the molecule constrains the rotational constants of each species, only B and C rotational constants are available. The relative weights of the rotational constants B and C were taken to be 1.0  107 and 1.0  108, for the normal species and 1.0  105 and 1.0  105 for the deuterated species, respectively. Vibrational corrections were recalculated for the deuterated species using the atomic mass of deuterium and the same harmonic force field. They were used in the joint analysis. Thus all values of the ra parameters were not changed upon deuteration but the ra values

Table 2 Rotational constants and DI of (E)-benzaldehyde oximea. B0 (MW)b Normal A B C DI

Bz (MW)c

species (C6H5ACH@NOH) 5183.13 (29) 5192.2 (27) 895.367 (3) 895.439 (22) 763.819 (3) 763.811 (4) 0.295 0.073

d-Species (C6H5ACH@NOD) A 5158.4 (23) 5168.0 (37) B 869.44 (2) 869.52 (3) C 744.34 (2) 744.34 (2) DI 0.279 0.039

B0a (GED)d

Bz (GED + MW)e

5148 (13) 898 (11) 765 (11) 0.000

5193.7 (49) 895.52 (14) 763.82 (5) 0.000

5120 (13) 872 (11) 745 (11) 0.000

5167.2 (49) 869.49 (28) 744.25 (17) 0.000

a Rotational constants in MHz and DI in uÅ2. Errors in parentheses represent 2.5 times the standard deviation. b Observed rotational constants in the ground vibrational state [8]. c Observed rotational constants with harmonic vibrational corrections (see text). d Rotational constants calculated from the geometry obtained by the analysis of GED data. e Best-fit rotational constants obtained from the joint analysis.

of the deuterated species were different from those in the nondeuterated species. Next, the GED data analysis of the large-amplitude motion model (GED(LAM)) was taken into account by assuming the potential function for the internal rotation around the C1AC7 bond as follows:

Vð/Þ ¼ ð1=2ÞV 2 ð1  cos 2/Þ þ ð1=2ÞV 4 ð1  cos 4/Þ: The six potential energy coefficients calculated from the quantum-chemical calculations suggested that the values of V1, V3, V5 and V6 were very small or almost zero. Therefore we simply set the potential function as above. The pseudo-conformers with the dihedral angle, /, ranging from 0° to 90° in steps of 5° were used in the data analysis. The population of each pseudo-conformer was assumed proportional to the Boltzmann factor. The bond distances and angles were varied as a function of /, the structural constraints among these parameters were made (see Table S5). Vibrational amplitudes and shrinkage corrections for each pseudo-conformer were recalculated from the force constants by neglecting the contributions of the C1AC7 torsion. The vibrational frequency of this torsion was 86 cm1. Since the potential parameters, V2 and V4, were not refined simultaneously in the GED data analysis, only the V2 term was refined, fixing the value of V4 to be zero.

f(r)

under the conditions of the ring planarity and closure; (4) the values of CCH angles were fixed at the theoretical values; (5) the value of CNOH dihedral angle was 180°. Thus adjustable structural parameters were as follows: r(CAC) (phenyl group), r(C1AC7), r(C@N), r(NAO), r(CAH), r(OAH), C6C1C2, \C2C1C7, \CAC@N, \C@NAO, and \NAOAH. Structural parameters and indices of resolution were determined by least-squares calculations on molecular scattering intensities, sM(s). Vibrational amplitudes, l, and shrinkage corrections, K0 = ra  ra, were calculated from the force constants obtained by normal coordinate analysis. The anharmonicity constants, j, of bonded atom pairs were estimated by the conventional method [16], while those of non-bonded atom pairs were assumed to be zero. The mean amplitudes of the non-bonded atom pairs were divided into four groups and were refined in the least-squares analysis. The groups were selected according to the ra distances such as (1) ra = 2.6– 2.85 Å (the third peak of the RD curve); (2) ra = 2.85–4.0 Å (the fourth peak); (3) ra = 4.0–4.5 Å (the fifth peak) and (4) ra > 4.5 Å (the sixth peak). In the early stage of the GED data analysis, non-planar conformation with the dihedral angle, /, of 23 (7)° was obtained under the small-amplitude vibrational model. This result was not consistent with that of MW study [4], where the molecule was planar. The non-planar structure from the GED was due to the effect of the vibrational correction. Therefore we performed two sets of the data analyses of the two molecular models. One was the single-conformation model based on the small-amplitude vibrations. The molecular conformation was planar one. We combined the GED data and the MW data, i.e., rotational constants in the analysis. Another model was the molecule took a large-amplitude vibrational motion as a function of /. Only the GED data were used in the analysis. In the refinement GED + MW data, the shrinkage corrections, ra  rz, were calculated by the following relation [17]:

Obs.-Calc. 0

1

2

3

4

5

6

7

8

r/A Fig. 3. Radial distribution curve of (E)-benzaldehyde oxime for the GED + MW data analysis. Distance distributions for the final analysis are indicated by vertical bars (see Table 3).

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6. Discussion The final RD curve by the GED + MW analysis is shown in Fig. 3, where the distance distributions are indicated by vertical bars. The calculated molecular intensities and the RD curve from the GED(LAM) analysis were essentially equal to those in the

GED + MW analysis. The agreement between observed and calculated RD curves shows that validity of the planar conformation as the equilibrium structure. The calculated and refined mean amplitudes with the corresponding ra distances and the grouping are listed in Table 3. All refined amplitudes are derived from the GED + MW analysis. The refined amplitudes in the groups (2)–(4)

Table 3 Mean amplitudes, interatomic distances and shrinkage correctionsa.

a b c d

Atom pairb

lobs.

O9AH16 C2AH10 C4AH12 C5AH13 C3AH11 C6AH14 C7AH15 C7AN8 C5AC6 C2AC3 C4AC5 C3AC4 N8AO9 C1AC2 C1AC6 C1AC7 N8AH16 N8AH15 C6AH13 C2AH11 C1AH10 C4AH11 C5AH14 C4AH13 C1AH14 C3AH12 C5AH12 C3AH10 C1AH15 C7AO9 H14AH15 C1AN8 O9AH15 C3AC5 C1AC3 C4AC6 C2AC6 C1AC5 C2AC4 C6AC7 H13AH14 H11AH12 H10AH11 H12AH13 C2AC7 N8AH10 C7AH14 C6AH15 C7AH10 C3AC6 C2AC5 C1AC4 C2AN8 C7AH16 H15AH16 C5AH11 C3AH13 C1AH11 C6AH10 C2AH14

0.070 0.077 0.077 0.077 0.077 0.077 0.078 0.041 0.046 0.046 0.046 0.046 0.050 0.046 0.047 0.049 0.101 0.097 0.100 0.100 0.100 0.100 0.099 0.100 0.100 0.100 0.100 0.100 0.103 0.060 0.207 0.063 0.144 0.056 0.056 0.056 0.057 0.056 0.056 0.067 0.161 0.162 0.162 0.162 0.066 0.184 0.140 0.145 0.140 0.064 0.064 0.063 0.107 0.093 0.152 0.096 0.095 0.096 0.096 0.096

lcalc.c

ra

ra  rz

0.138 (4) 0.143 0.138 0.061 0.061 0.061 0.114 (9) 0.100 0.159 0.102 0.102 0.102 0.102 0.103

0.967 1.083 1.084 1.084 1.084 1.085 1.090 1.296 1.398 1.398 1.399 1.402 1.402 1.403 1.406 1.470 1.867 2.080 2.144 2.145 2.146 2.147 2.151 2.151 2.152 2.154 2.156 2.158 2.210 2.220 2.370 2.386 2.387 2.414 2.420 2.423 2.424 2.431 2.434 2.450 2.466 2.469 2.478 2.484 2.529 2.586 2.627 2.652 2.753 2.785 2.801 2.811 2.877 2.978 3.304 3.388 3.392 3.393 3.395 3.398

0.033 0.012 0.013 0.012 0.012 0.012 0.016 0.006 0.003 0.002 0.002 0.002 0.005 0.001 0.002 0.002 0.012 0.016 0.006 0.006 0.005 0.005 0.006 0.005 0.005 0.007 0.006 0.006 0.008 0.003 0.000 0.002 0.004 0.001 0.001 0.002 0.001 0.002 0.002 0.001 0.004 0.003 0.003 0.003 0.001 0.003 0.000 0.003 0.000 0.000 0.001 0.002 0.000 0.013 0.016 0.004 0.004 0.004 0.004 0.004

nd

Atom pairb

lobs.

lcalc.c

ra

ra  rz

nd

1 1 1 1 1 1 2 2 2 2 2 2 2 2

C4AH14 C6AH12 C1AH13 C2AH12 C4AH10 C2AH15 C1AO9 C6AN8 C5AC7 C3AC7 H10AH15 C6AH11 C3AH14 C5AH10 C2AH13 C1AH12 N8AH14 O9AH10 C5AH15 H10AH16 C1AH16 C2AO9 C3AN8 C4AC7 H11AH13 H10AH14 H12AH14 H10AH12 C7AH13 C3AH15 C2AH16 C6AO9 C7AH11 O9AH14 H13AH15 C5AN8 C4AH15 N8AH11 H11AH14 H10AH13 C4AN8 C7AH12 C6AH16 H14AH16 H11AH15 C3AO9 N8AH13 H12AH15 C5AO9 C3AH16 N8AH12 O9AH11 C4AO9 H11AH16 C5AH16 O9AH13 C4AH16 O9AH12 H13AH16 H12AH16

0.096 0.095 0.096 0.096 0.096 0.100 0.065 0.066 0.067 0.066 0.154 0.096 0.096 0.095 0.096 0.095 0.140 0.196 0.146 0.248 0.109 0.106 0.109 0.069 0.130 0.131 0.130 0.131 0.112 0.110 0.168 0.088 0.110 0.176 0.186 0.072 0.131 0.158 0.119 0.119 0.092 0.099 0.107 0.178 0.133 0.104 0.107 0.152 0.080 0.174 0.119 0.162 0.083 0.233 0.111 0.128 0.140 0.111 0.138 0.164

0.102 0.102 0.102 0.102 0.102 0.107 0.072 0.073 0.073 0.073 0.161 0.102 0.102 0.102 0.102 0.102 0.147 0.203 0.148 (7) 0.249 0.111 0.108 0.110 0.071 0.132 0.132 0.132 0.132 0.122 (12) 0.120 0.178 0.098 0.120 0.187 0.196 0.082 0.141 0.169 0.129 0.129 0.102 0.109 0.118 0.188 0.143 0.115 0.118 0.162 0.090 0.184 0.130 0.173 0.093 0.243 0.121 0.138 0.151 0.121 0.148 0.174

3.398 3.400 3.402 3.405 3.411 3.482 3.606 3.627 3.745 3.791 3.819 3.860 3.861 3.875 3.876 3.886 3.913 3.954 4.045 4.134 4.238 4.266 4.269 4.277 4.279 4.280 4.289 4.296 4.591 4.624 4.653 4.659 4.664 4.674 4.700 4.809 4.861 4.933 4.935 4.949 5.074 5.351 5.411 5.528 5.574 5.653 5.738 5.914 5.958 6.045 6.129 6.328 6.383 6.594 6.647 6.798 6.924 7.449 7.543 7.970

0.005 0.006 0.005 0.006 0.006 0.006 0.002 0.001 0.001 0.001 0.005 0.003 0.003 0.004 0.004 0.006 0.000 0.003 0.003 0.000 0.008 0.000 0.000 0.001 0.005 0.005 0.006 0.008 0.003 0.004 0.004 0.000 0.003 0.002 0.003 0.001 0.003 0.001 0.005 0.006 0.000 0.004 0.005 0.003 0.005 0.000 0.002 0.005 0.000 0.002 0.003 0.000 0.001 0.000 0.004 0.001 0.003 0.002 0.004 0.004

2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4

All values are used in the GED + MW analysis (in Å). See Fig. 1 for the atom numberings. Numbers in parentheses are three times the standard deviation referring to the last significant digit. The group of mean amplitudes (see text).

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N. Kuze et al. / Journal of Molecular Structure 978 (2010) 195–200 Table 4 Molecular parametersa of (E)-benzaldehyde oxime from GED + MW, GED(LAM), quantum-chemical calculations (QC) and X-ray diffraction (XRD). GED + MWb rz Bond lengths (Å) C1AC2 C2AC3 C3AC4 C4AC5 C5AC6 C1AC6 C1AC7 C7AN8 N8AO9 C2AH10 C3AH11 C4AH12 C5AH13 C6AH14 C7AH15 O9AH16

1.401 1.396 1.400 1.397 1.395 1.405 1.468 1.290 1.397 1.071 1.072 1.071 1.072 1.074 1.074 0.934

(1)

Bond angles (°) C6AC1AC2 C1AC2AC3 C2AC3AC4 C3AC4AC5 C4AC5AC6 C5AC6AC1 C2AC1AC7 C6AC1AC7 C1AC7AN8 C7AN8AO9 C1AC2AH10 C2AC3AH11 C3AC4AH12 C4AC5AH13 C5AC6AH14 C1AC7AH15 N8AO9AH16

119.5 119.7 120.9 119.3 120.2 120.4 123.5 117.0 119.4 111.1 119.4 119.6 120.1 120.2 120.1 119.2 103.7

(1)

(6) (5) (6) (5)

(18)

(5) (6) (8)

(48)

Potential parameters (kJ mol1) V2 – V4 – Indices of resolution (k) k (long) 0.862 (3) k (short) 0.909 (6) R-factorf R 0.0322 a b c d e f

GED(LAM)b,c rg

ra

1.404 1.400 1.403 1.400 1.399 1.408 1.472 1.298 1.404 1.089 1.089 1.089 1.089 1.091 1.096 0.972

1.401 1.396 1.400 1.397 1.396 1.405 1.467 1.296 1.399 1.073 1.074 1.074 1.074 1.075 1.079 0.952

(1)

119.7 120.0 119.7 121.0 119.0 120.6 123.6 116.7 119.3 110.5 119.4 119.6 120.1 120.2 120.1 119.2 101.3

(2)

(6) (5) (6) (5)

(18)

(7) (8) (8)

(45)

74 (28) 0 (fixed)

QCd

XRDe

rg

MP2/6-31G(d,p) re

B3LYP/6-31G(d,p) re

1.404 1.400 1.403 1.401 1.399 1.408 1.471 1.299 1.406 1.090 1.091 1.091 1.091 1.092 1.098 0.985

1.3991 1.3943 1.3980 1.3952 1.3941 1.4025 1.4652 1.2906 1.4097 1.0819 1.0828 1.0825 1.0826 1.0840 1.0890 0.9661

1.3982 1.3947 1.3978 1.3954 1.3931 1.4045 1.4672 1.2816 1.4015 1.0845 1.0862 1.0860 1.0860 1.0869 1.0931 0.9669

1.401 1.386 1.388 1.383 1.388 1.392 1.466 1.277 1.400

119.54 119.80 120.59 119.69 119.93 120.45 121.92 118.54 120.73 109.94 119.36 119.57 120.12 120.18 120.09 119.24 101.82

119.24 120.01 120.53 119.70 119.88 120.64 122.14 118.62 121.64 110.87 119.23 119.57 120.12 120.24 120.00 118.23 102.43

118.97 120.02 120.40 119.87 120.04 120.65 122.01 119.01 121.10 111.60

19.113 3.582

26.392 2.824

104.5

0.860 (3) 0.907 (6) 0.0307

See Fig. 1 for the atom numberings. Errors in parentheses represent three times the standard deviation. This work. The CAC and CAH bond distances and CCC angles are dependent parameters (see text and Table S4). The values of CCH angles are fixed at the theoretical ones. The parameter values are averaged using the experimental potential function. This work. The optimized (planar) structures. Ref. [3]. The parameters for molecule A were listed. The mean value of CAH bond distance was 0.97 Å. P P R-factor: R = { iWi(DsM(s)i)2/ iWi(sM(s)iobs.)2}1/2, where DsM(s)i = sM(s)iobs.  sM(s)icalc. and Wi is a diagonal element of the weight matrix.

were slightly larger than those calculated from the normal coordinate analysis. The determined structural parameters in the GED + MW and GED(LAM) analyses are listed in Table 4. The parameter values for the latter analysis were averaged using the experimental potential function. The R factors are 0.0322 and 0.0307 for GED + MW and GED(LAM) analyses, respectively. The determined potential coefficient, V2, was determined to be 74 (28) kJ mol1 from the GED(LAM) analysis. We also performed the GED(LAM) analyses with fixed values of V2 and V4 using the MP2 and B3LYP results. They gave the R factors of 0.0309 and 0.0302 for MP2 and B3LYP potentials, respectively. The shape of the experimental potential curve is narrower than those calculated (see Fig. 4). Compared with the theoretical values, the experimental value of V2 is fairly high and its error is quite large. It shows that the effects of the large-amplitude motion for (E)-benzaldehyde

oxime is not fully elucidated from the GED data although the R factor of GED(LAM) analysis is the smallest among the results of these data analyses. We noted that all the values of bond distances and angles between GED + MW and GED(LAM) results were equal within their uncertainties. The structural parameters for the phenyl ring show the ring deformation. The C6AC1AC2 (angle a) and C3AC4AC5 angles were fitted as 119.5 (1)° and 119.3°, respectively, by the GED + MW analysis. This result is in agreement with the quantum chemical and XRD results. It seems that the effect of ring deformation in the gas phase is smaller than that in the solid phase by comparing the values of the ring parameters. The deformation of the carbon skeleton of the monosubstitute benzenes has been analyzed from the optimized structures by ab initio MO calculations by Campanelli et al. [18]. They presented some scattergrams between the

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Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.molstruc.2010.02.042. References

Fig. 4. The experimental and theoretical potential curves of (E)-benzaldehyde oxime as a function of the dihedral angle /.

angle a and other ring parameter. By applying our result for (E)benzaldehyde oxime to the scattergrams, the substituent effect of the oxime group on the phenyl ring is modest. It concluded that the deformation of the carbon skeleton of this molecule is very small in the gas phase. Acknowledgment We thank Prof. Mitsutoshi Tanimoto (Shizuoka University) for the GED data access to the computer at Shizuoka University and useful discussions.

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