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The molecular structure of chloropropanone oxime [ClCH2C(CH3)=NOH] has been determined by gas electron diffraction (GED), microwave spectroscopy (MW) and quantum chemical calculations. Potential energy curves for the internal rotation of CH2Cl group in (E)- and (Z)-isomers as well as the optimized geometries and force constants for four conformations have been calculated by the quantum chemical calculations. Combined data analysis of the GED and MW data revealed the conformational mixture of 68(4) % (E)-anticlinal and 32 % (Z)-synclinal conformers. The principal values of geometrical parameters of the E-anticlinal conformer are: r g(ClH2C–C) = 1.499(2) A, r g(C–CH3) = 1.503(2) A, r g(C=N) = 1.276(4) A, r g(C–Cl) = 1.805(3) A, r g(N–O) = 1.398(4) A, ∠αC–C=N = 113.2(16)°, ∠αC–C–Cl = 111.1°(5), ∠αH3C–C=N = 127.0°(13), ϕ(NCCCl) = 121.1°(21). Numbers in parentheses are three times standard deviations of the data fit.

The gas-phase structure of ( E )-benzaldehyde oxime (C 6 H 5 CH 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 C C 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.

The microwave spectrum of chloropropanone oxime was observed in the frequency range from 26.5 to 40.0 GHz. The rotational constants (A-level) (MHz) were determined as A=6501.04(15), B=1464.98(1), and C=1326.80(1) for 35ClCH2C(CH3)NOH(35Cl species) and A=6519.5(15), B=1428.07(1), and C=1298.00(1) for 37ClCH2C(CH3)NOH(37Cl species) in the ground vibrational state. The values of Δ I (=I c −I b −I a ) obtained for the 35Cl and 37Cl species were found to be −41.811(7) and −42.06(2) u A2, respectively. The observed rotational constants, ΔI, and rs-coordinates of the chlorine atom were in good agreement with those of anticlinal form in E-isomer (E-ac), having the dihedral angle (φ) of ClC 1 C 2 N =116.8° , as shown in Fig. 2 . One vibrationally excited state was observed and assigned to the C1–C2 torsional mode (80(20) cm−1).

The gas-phase structure of dichloroacetaldehyde oxime (Cl 2 CH–CH NOH, DCAO), was determined by gas-phase electron diffraction (GED) combined with microwave (MW) spectroscopic data. The nozzle temperature in the GED experiment was about 53°C. Structural constraints in the GED data analysis were obtained by the ab initio MO calculation of DCAO at the MP2/6-31G(d, p) level of theory. Vibrational amplitudes, shrinkage corrections for the data analysis of GED and vibrational corrections of the experimental rotational constants were calculated from the harmonic force constants given by normal coordinate analysis. The ( E )-isomer with the dihedral angle of φ (ClCCN)=119.7(2)° was the dominant conformer. The MW spectroscopic investigation and the optimized structure in the ab initio calculations were consistent with the present result. The population of the dominant conformer was 80(1)%. The results of the data analysis indicated that there were two other conformers involved, whose conformations and populations were: ( E )-isomer with one chlorine atom on the plane of the molecular skeleton (10(1)%) and ( Z )-isomer with φ of about 105° (10(1)%). The principal bond distances and angles ( r g /A and ∠ α /deg) of the dominant conformer, ( E )-isomer, were: r (C–C)=1.497(8); r (C N)=1.281(4); r (C–Cl)=1.784(2); r (N–O)=1.415(4); ∠CCN=117.0(8); ∠CCCl=109.4(3); ∠CNO=111.1(5); and ∠NOH=97.2(50). The values in parentheses were three times the standard deviations.

The molecular structure and conformation of gaseous l -form of α-alanine have been reinvestigated using electron diffraction data and rotational constants. It was reconfirmed that the molecules take a neutral form in the gas phase. The molecular parameters of two species were determined. In the vibrational ground state, the main species has the conformation with intramolecular hydrogen bonding of the NH 2 ⋯O C with the dihedral angle NCC O of −16.6(4)°, and the minor species has the conformation with intramolecular hydrogen bonding of the H 2 N⋯HO with the dihedral angle NCC–O of −16.9(4)°. Both species of gaseous l -alanine would take these minus dihedral angles in order to reduce the repulsion between the other atomic groups.

The molecular structure of gaseous 3-amino-1-propanol has been determined from electron diffraction and microwave spectroscopic data. Its conformation is gauche-gauche, forming an intramolecular hydrogen bond. The geometrical parameters of the skeleton are r g ( C  C ) = 1.537(2) A , r g ( C  O ) = 1.425(3) A , r g ( C  N ) = 1.469(3) A , ∢ CCC = 113.2(3)° , ∢ CCO = 111.9(4)° , ∢ CCN = 112.0(4)° , o(CCCO) = 72.1(8)°, and o(CCCN) = − 57(2)°. The unsymmetrical deviations of the dihedral angles o(CCCO) and o(CCCN) from the normal gauche angle would be caused by the steric effect.

The molecular structure of gaseous acetoxime has been determined from a least-squares analysis of electron diffraction data. The skeleton of the gaseous molecule is planar and there are asymmetrical distortions on the CC distances and the CCN angles. The conformations of the two methyl groups are also different. The geometrical molecular parameters obtained are r g ( C 1  C 2 ) = 1.490(3) A , r g ( C 2  C 3 ) = 1.521(5) A , r g ( C 2  N ) = 1.289(1) A , r g ( NO ) = 1.423(2) A , ∠C1C2N = 116.4(2)°, ∠C1C2N = 123.4(3)° and ∠C2NO = 111.2(2)°.

Molecular structure and conformational stability of E and Z geometrical isomers of propionaldehyde oxime (C(1)H3C(2)H2C(3)HNOH) have been studied by using the ab initio and DFT methods. The molecular geometries were optimized by employing the atomic basis sets 6-31G* at the HF-SCF and MP2 levels of theory in the ab initio method. The basis sets 6-31G and 6-31G* are used in the BLYP method of DFT to optimize the molecule. The optimized structural parameters of the above methods are discussed in the light of the electron diffraction results of the molecule. The variations in CN bond length, C1C2C3 and C2C3N angles of the sp and ac conformers of E isomer and of the ap conformer of Z isomer have been discussed in terms of nonbonding interactions of CH3 and NOH groups. The rotational potential energy surfaces of E and Z isomers were obtained for the C2−C3 rotational angle of propionaldehyde oxime at HF/6-31G*, MP2/6-31G*, and BLYP/6-31G* levels of theory. The global minimum occurs at φ(CCCN) = 120° and φ = 0° ...

The microwave spectra of ( Z )- 35 ClCH 2 CH=NOH, ( Z )- 37 ClCH 2 CH=NOH, ( Z )- 35 ClCH 2 CH=NOD, and ( Z )- 37 ClCH 2 CH=NOD have been observed in the frequency range from 16.5 to 40.0 GHz. The rotational and centrifugal distortion constants of four isotopic species and the nuclear quadrupole coupling constants of the 35 Cl species were determined. The values of planar moment ( P cc = ( I a + I b − I c )/2) obtained for four isotopic species were found to be 1.761(14), 1.800(18), 1.777(19), and 1.770(18) u A 2 in the ground vibrational state. The unchanged values of P cc show that the chlorine and hydroxyl hydrogen atoms lie in or are very close to the ab inertial plane of the molecule. The conformation of the Z -form was determined to be Calcd I (φ 1 = 180°, φ 2 = 180°), as shown in Fig. 1, from the comparison of the observed and calculated rotational constants and coordinates of the chlorine and hydroxyl hydrogen atoms. The determined conformation is consistent with that reported by an electron diffraction study (K. Iijima, T. Hanamori, T. Sakaizumi, and O. Ohashi, J. Mol. Struct. 299, 149–153 (1993).). One excited vibrational state is assigned to the C–C torsional mode, and it is anharmonic. This fact is also consistent with the result of a large amplitude motion about the C–C single bond reported by a gas-phase electron diffraction study. Assuming the skeleton of the heavy atoms is a planar molecule, the seven structural parameters of the Z -form (anti-form) were fitted to the eight rotational constants ( B and C ) of four isotopic species. The obtained structural parameters ( r 0 ) are almost the same as those obtained by electron diffraction study ( r α ) within the errors.

The molecular structures of two rotational isomers (anticlinal and synperiplanar forms) of gaseous (E)-propionaldehyde oxime have been determined from electron diffraction and microwave spectroscopic data. The anticlinal form is more stable by 0.15 ± 0.10 kcal mol−1 than the synperiplanar form. The molecular parameters of the anticlinal form are rg(C1–C2) = 1.552(3) A, rg(C2–C3) = 1.493(2) A, rg(C3=N) = 1.284(2) A, rg(N–O) = 1.429(2) A, ∠C1C2C3 = 111.5(1)°, ∠C2C3N = 119.0(3)°, and ∠C3NO = 109.4(2)°. The ∠C2C3N, ∠C1C2C3, and rg(C3–N) values of the synperiplanar form (122.6(6)°, 112.6(6)°, and 1.291(3) A, respectively) are not equal to those of the anticlinal form.

The molecular structure of gaseous trichloromethylbenzene has been determined from electron diffraction data. An internal rotation of the CCl3 group around the CC bond was treated as a precession motion. The rotational barrier height of the CCl3 group is 1.3(6) kJ mol−1, and the minimum of the barrier is at the position such that one of the CCl bonds lies on the phenyl plane. The tilt angle of the C3v symmetry axis is 4.6(14)° at the potential minimum position and 3.0(8)° at the potential maximum position. The molecular parameters and uncertainties are r g ( CC ) ring = 1.399(1) A , r g ( CH ) = 1.096(6) A , r g ( CC ) = 1.531(5) A , r g ( CCl ) = 1.784(2) A and r g ( Cl⋯Cl ) = 2.885(2) A , where the rg(CC)ring is the average value in the ring.

The molecular structure of gaseous ( E )-chloroacetaldehyde oxime has been determined from electron diffraction data. The geometrical molecular parameters obtained, with estimated limits of error, are r g ( CCl ) = 1.799 ± 0.002 A , r g ( CC ) = 1.516 ± 0.007 A , r g ( CN ) = 1.287 ± 0.003 A , r g ( NO ) = 1.418 ± 0.005 A , ∠CCCl = 109.6 ± 0.4°, ∠CCN = 116.4 116.4 ± 0.7°, ∠CNO = 110.7 ± 0.5° and the torsional angle ф( NCCCl ) = 123.2 ± 1.4° . A least-squares analysis of the data have given the fraction of the E -isomer in the gas phase to be 66 ± 2% at 43°C.

On an oxidative dimerization in dichloromethane containing diisopropylamine, methyl 1-ethoxycarbonyl2,5,6,11-tetrahydro-3-oxo-3H-indolizino[8,7-b]indole-5-carboxylate gave a trichotomine derivative bearing ethoxycarbonyl groups on C1 and C1′. In the presence of triethylamine, the initially formed trichotomine derivative changed to a blue compound, which had the skeleton of the trichotomine derivative and a =CH–CH= group. The X-ray crystallographic analysis of the trichotomine derivative showed the torsion around the central C–C double bond, and the dihedral angle of the adjacent two five-membered rings was 30.0°. This torsion is due to the steric interactions between the ethoxycarbonyl groups and the amido carbonyl groups, and might explain the difference of the λmax between the trichotomine derivative (690 nm) and the blue compound (633 nm).

The molecular structure of gaseous (Z)-chloroacetaldehyde oxime has been determined by gas-phase electron diffraction and molecular structure optimization has been carried out by molecular orbital calculations. The molecular skeleton is planar and the potential barrier height to internal rotation around the C C bond ( V 1 ) was estimated to be 2.7 kcal mol −1 . The geometrical parameters obtained are: r g ( Cl)=1.789±0.001A, r g (C C)=1.513±0.003A, r g (C N)=1.284±0.001A, r g (N O)=1.416±0.001A, ∠CCCl=109.7±0.2°, ∠CCN=124.9±0.3°, ∠CNO=110.6±0.2°.

The molecular structure of gaseous ( Z )-(propionaldehyde oxime) has been determined by the joint analysis of electron diffraction data and rotational constants. The molecular structure optimization has also been performed by molecular orbital calculations. The molecular skeleton is planar, but the internal rotation around the C-C(N) bond is a large amplitude motion with a potential barrier height of V 1 = 1.5 kcal mol −1 . The geometrical molecular parameters obtained are: r g (C m C) = 1.549 ± 0.003 A, r g (CC) = 1.497 ± 0.002 A, r g (C N) = 1.295 ± 0.001 A, r g (NO) = 1.430 ± 0.002 A, ∠ CCC = 109.4 ± 0.4°, ∠ CCN = 127.5 ± 0.3° and ∠ CNO = 109.3 ± 0.3°.

The molecular structure of α-alanine has been studied using gas-phase electron diffraction data collected on the Balzers KDG2 instrument at UMIST. Only one conformer exists in the vapour of α-alanine and it is a neutral species. The principal structure,parameters of the molecule were observed to be: r g (C-N)=1.471(7) A, r g (C-C)=1.544(10) A, r g (C=O)=1.192(2) A, r g (C-O)=1.347(3) A, r g (C- m )=1.509(16) A, ∠NCC=110.1(8)°, ∠CC=O=125.6(7)°, ∠CC=0110.3(7)°, ∠CCC m 111.6(11)°, ∠NCC m =111.0(16)° and =l7(2)°,where is the dihedral angle between the NCC plane and the CC=O plane. The distortion is in the direction of reducing the repulsion between the methyl group and the carboxyl group.

The potential energy barrier of internal rotation of the trifluoromethyl group is somewhat higher than that of the methyl group: the barrier height is 6.0 kcal mol-’ in (CF3)20 [l], 5.8 kcal mol-l in ClSCF, [2] and 5.2 kcal mol-’ in CF,SCF, [ 21. However, there are some compounds with comparatively low barrier heights such as 1.67 kcal mol-l in CFsCOF [3] and 1.19 kcal mol-l in CF, COCHzBr [ 41. Andreassen et al. [ 51 have determined the molecular structure of gaseous hexafluoroacetylacetone from electron diffraction data on the assumption of C, symmetry. They treated the internal rotation of the CF, groups as a rigid rotor and obtained the OCCF dihedral angle of 47’) although they mentioned that this is an “average structure” value. The present study was undertaken to investigate the rotational barrier height of CF, groups in hexafluoroacetylacetone by gas-phase electron diffraction. The molecular symmetry was checked again because acetylacetone has been revealed not to be symmetric [ 6,7]. Long and short camera-distance photographs were taken at room temperature by the use of an r3-sector. The exposure times were 50 and 95 s for the long and short camera-distance photographs, respectively, with an electron beam current of 0.6 ,uA. The wavelength of the electron beam was estimated from the measured accelerating voltage of 40 kV [ 81. The procedures of data reduction and molecular-structure analysis were the same as those used previously for acetylacetone [ 71. The vibrational mean amplitudes and the shrinkage corrections used in the analysis were calculated from the force field [91. Assuming an unsymmetric ring skeleton the analysis did not achieve convergence, as in the previous study [5]. The molecular skeleton was then assumed to be symmetric. The analysis assuming the rigid rotor to the CF, groups

The molecular structure of gaseous ( Z )-(propionaldehyde oxime) has been determined by the joint analysis of electron diffraction data and rotational constants. The molecular structure optimization has also been performed by molecular orbital calculations. The molecular skeleton is planar, but the internal rotation around the C-C(N) bond is a large amplitude motion with a potential barrier height of V 1 = 1.5 kcal mol −1 . The geometrical molecular parameters obtained are: r g (C m C) = 1.549 ± 0.003 A, r g (CC) = 1.497 ± 0.002 A, r g (C N) = 1.295 ± 0.001 A, r g (NO) = 1.430 ± 0.002 A, ∠ CCC = 109.4 ± 0.4°, ∠ CCN = 127.5 ± 0.3° and ∠ CNO = 109.3 ± 0.3°.

On an oxidative dimerization in dichloromethane containing diisopropylamine, methyl 1-ethoxycarbonyl2,5,6,11-tetrahydro-3-oxo-3H-indolizino[8,7-b]indole-5-carboxylate gave a trichotomine derivative bearing ethoxycarbonyl groups on C1 and C1′. In the presence of triethylamine, the initially formed trichotomine derivative changed to a blue compound, which had the skeleton of the trichotomine derivative and a =CH–CH= group. The X-ray crystallographic analysis of the trichotomine derivative showed the torsion around the central C–C double bond, and the dihedral angle of the adjacent two five-membered rings was 30.0°. This torsion is due to the steric interactions between the ethoxycarbonyl groups and the amido carbonyl groups, and might explain the difference of the λmax between the trichotomine derivative (690 nm) and the blue compound (633 nm).

The potential energy barrier of internal rotation of the trifluoromethyl group is somewhat higher than that of the methyl group: the barrier height is 6.0 kcal mol-’ in (CF3)20 [l], 5.8 kcal mol-l in ClSCF, [2] and 5.2 kcal mol-’ in CF,SCF, [ 21. However, there are some compounds with comparatively low barrier heights such as 1.67 kcal mol-l in CFsCOF [3] and 1.19 kcal mol-l in CF, COCHzBr [ 41. Andreassen et al. [ 51 have determined the molecular structure of gaseous hexafluoroacetylacetone from electron diffraction data on the assumption of C, symmetry. They treated the internal rotation of the CF, groups as a rigid rotor and obtained the OCCF dihedral angle of 47’) although they mentioned that this is an “average structure” value. The present study was undertaken to investigate the rotational barrier height of CF, groups in hexafluoroacetylacetone by gas-phase electron diffraction. The molecular symmetry was checked again because acetylacetone has been revealed not to be symmetric [ 6,7]. Long and short camera-distance photographs were taken at room temperature by the use of an r3-sector. The exposure times were 50 and 95 s for the long and short camera-distance photographs, respectively, with an electron beam current of 0.6 ,uA. The wavelength of the electron beam was estimated from the measured accelerating voltage of 40 kV [ 81. The procedures of data reduction and molecular-structure analysis were the same as those used previously for acetylacetone [ 71. The vibrational mean amplitudes and the shrinkage corrections used in the analysis were calculated from the force field [91. Assuming an unsymmetric ring skeleton the analysis did not achieve convergence, as in the previous study [5]. The molecular skeleton was then assumed to be symmetric. The analysis assuming the rigid rotor to the CF, groups

The molecular structure of α-alanine has been studied using gas-phase electron diffraction data collected on the Balzers KDG2 instrument at UMIST. Only one conformer exists in the vapour of α-alanine and it is a neutral species. The principal structure,parameters of the molecule were observed to be: r g (C-N)=1.471(7) A, r g (C-C)=1.544(10) A, r g (C=O)=1.192(2) A, r g (C-O)=1.347(3) A, r g (C- m )=1.509(16) A, ∠NCC=110.1(8)°, ∠CC=O=125.6(7)°, ∠CC=0110.3(7)°, ∠CCC m 111.6(11)°, ∠NCC m =111.0(16)° and =l7(2)°,where is the dihedral angle between the NCC plane and the CC=O plane. The distortion is in the direction of reducing the repulsion between the methyl group and the carboxyl group.

The molecular structure of the main conformer of gaseous glycine has been determined by the joint analysis of electron diffraction data and rotational constants, in conjunction with the results of an ab initio calculation. The glycine molecule has an unionized form in the gas phase. The molecular skeleton is planar and the amine and hydroxyl groups are in the anti-position with respect to each other. The molecular parameters obtained are: r g (NC)=1.469(6) A, r g (CC) = 1.532(4) A, r g (CO)=1.207(1) A, r g (CO)=1.357(2) A, ∠NCC=113.0(3)°, ∠CCO=125.0(3)° and ∠CCO=111.5(2)°.

Ab initio calculations have indicated intramolecular hydrogen bonding in glycolic acid and the existence of rotamers in the gas phase [ 1,2]. The most stable rotamer predicted by these calculations has a planar skeleton with a five-membered ring formed by a hydrogen bond between the hydroxyl group and the carbonyl oxygen. In the secondary rotamer, a hydrogen bond is formed between the two hydroxyl groups. The calculated energy difference between them is 1.8 [l] or 2.7 [2] kcal mol-’ . Accordingly, both rotamers would be observed in the gas phase if the energy difference is as small as those shown in the calculations. Microwave spectroscopy studies, however, have reported only the most stable rotamer [3,4]. The less abundant species with a small dipole moment might be overlooked in this method, but gas phase electron diffraction allows the observation of all the species existing in a gas sample, which has been proved in the analysis of glycine [5]. Thus, we undertook the analysis of gaseous glycolic acid by gas phase electron diffraction in order to elucidate the composition of the gas and the potential energy barrier between the rotamers. Commercial glycolic acid (hydroxyacetic acid)

The microwave spectrum of (E)-benzaldehyde oxime, C(6)H(5)-CHdbond;NOH and C(6)H(5)-CHdbond;NOD, has been observed in the frequency range from 26.5 to 40.0 GHz. The spectrum of the ground vibrational state was assigned and fitted to the Watson's A-reduced Hamiltonian to obtain these rotational and centrifugal distortion constants: A = 5183.13(29) MHz, B = 895.367(3) MHz, C = 763.819(3) MHz, Delta(J) = 0.019(3) kHz, and Delta(JK) = 0.204(7) kHz for the normal species, and A = 5158.4(23) MHz, B = 869.44(2) MHz, C = 744.34(2) MHz, Delta(J) = 0.023(2) kHz, and Delta(JK) = 0.193(7) kHz for the deuterated species. The values of the DeltaI (=I(c) - I(a) - I(b)) obtained for the normal and deuterated species were -0.295(6) and -0.28(5) a.m.u. Å(2), respectively. The molecular conformation of this molecule was a planar one in which the values of the dihedral angles, CCNO and CNOH, were almost 180 degrees and 180 degrees, respectively. Copyright 1999 Academic Press.

A gas-phase electron diffraction study of dimethyl(2,4-pentanedionato)gold(III) indicates a square-planar structure with ra(Au–O)= 2.085(7), ra(Au–C)= 2.054(5)A, angle OAuO 90.9(6)°, and CAuC 92.7(24)°, as well as the normal parameters of an acetylacetone ligand.

The molecular structure of trimethylamine–boron triiodide (CH3)3N·BI3 has been determined from gas electron-diffraction data. The molecular parameter values and their uncertainties are rg(B–I)=2.245±0.004 A, rg(N–B)=1.663±0.013 A, rg(C–N)=1.497±0.005 A, rg(C–H)=1.103±0.010 A, ∠IBI=108.6±0.4°, and ∠CNC=106.0±0.8°. The potential barrier around the N–B bond has also been estimated to be about 3.5 kcal mol−1 (1 cal=4.184J).

The molecular structure of trimethylphosphine-boron triiodide (CH3)3P·BI3 has been determined by means of gas-electron diffraction. The molecular parameters and their uncertainties were rg(B–I)=2.233±0.003 A, rg(P–B)=1.947±0.011 A, rg(C–P)=1.809±0.003 A, rg(C–H)=1.094±0.008 A, ∠IBI=111.6±0.3°, and ∠CPC=106.0±0.5°. The gaseous molecule was rigid with respect to the rotational vibration around the P–B bond.

The molecular structure of trimethylphosphine–boron tribromide (CH3)3P·BBr3 has been determined from gas electron-diffraction and vibrational-spectroscopic data. The molecular parameters and their uncertainties were rg(B–Br)=2.010±0.009 A, rg(P–B)=1.946±0.029 A, rg(C–P)=1.804±0.004 A, rg(C–H)=1.098±0.010 A, ∠BrBBr=111.7±0.7°, and ∠CPC=108.0±0.7°. The potential barrier around the P–B bond was also estimated to be about 10 kcal mol−1 (1 cal=4.184 J).

The molecular structure of the enol form of gaseous acetylacetone has been determined from electron diffraction data. The molecular skeleton is planar but it is not symmetric. The bond distances in the ring are r g (CO) = 1.243 ± 0.002 A, r g (CO) = 1.319 ± 0.003 A, r g (CC) = 1.382 ± 0.007, r g (CC) = 1.430 ± 0.008 A, r g (OH) = 1.049 ± 0.015 A and r g (O⋯O) = 2.512 ± 0.008 A. The hydrogen atom of the internal hydrogen bond lies 0.45 ± 0.08 A out of the molecular plane with the OHO angle of 137 ± 7°.

The molecular structure of trimethylamine–borane (CH3)3N·BH3 has been determined from gas electron-diffraction data with spectroscopic data. The molecular parameter values and their uncertainties are rg(B–H)=1.261±0.006 A, rg(N–B)=1.656±0.002 A, rg(C–N)=1.485±0.001 A, rg(C–H)=1.108±0.002 A, ∠HBH=112.8±0.4°, and ∠CNC=109.2±0.2°. The potential barrier around the N–B bond has been estimated to be larger than 5 kcal mol−1 (1 cal=4.183 J). The isotope effects on the B–D bond distance and the DBD angle have also been estimated to be −0.006 A and 0.4°, respectively, in rα0 parameters.

The molecular structure of tris(dipivaloylmethanato)erbium has been determined by gas-phase electron diffraction. The experimental data are consistent with a monomeric trigonal prismatic structure. The structural parameters are as follows: ra(ErO) = 2.218 ± 0.005, ra(CO) = 1.274 ± 0.004, ra(CCring) = 1.405 ± 0.006, ra(CCtext) = 1.513 ± 0.014, ra(CCmeth) = 1.550 ± 0.006 A, and ∠OErO = 75.0 ± 0.5°. The folding of the ligand about the OO axis is 22.2 ± 1.5°, and the t-butyl groups rotate freely.

The molecular structures of six Ln(dpm) 3 (Ln = Sm, Eu, Gd, Tb, Dy and Ho; dpm = (CH 3 ) 3 CCOCHCOC(CH 3 ) 3 ) have been determined by gas-phase eletron diffraction. The experimental data are consistent with a trigonal prismatic structure with the slightly pitched OLnO planes. The observed LnO distances show the predicted lanthanide contraction: r a (SmO) = 2.278(7) A to r a (HoO) = 2.226(8) A. The OLnO and the pitch angles also depend on the atomic number. The structural parameters of the dpm ligand are as follows (average values with stranded deviations): r a (CO) = 1.279(8) A, r a (CC r ) = 1.411(12) A, r a (CC t ) = 1.523(19) A, r a (C t C m = 1.548(9) A, r a (O…O) = 2.716(23)A, ∠OCC r = 124.5(6)°, ∠CC r C′ = 122.2(5)° and ∠C r CC t = 117.6(9)°.

The molecular structure of trimethylphosphine–borane has been determined from gas electron diffraction and spectroscopic data. The molecular parameters and their uncertainties are rg(B–H)=1.225±0.011 A, rg(P–B)=1.899±0.006 A, rg(C–P)=1.815±0.003 A, rg(C–H)=1.103±0.002 A, ∠HBH=108.6±0.6°, and ∠CPC=104.6±0.3°. The P–B distance of this complex is about 0.04 A shorter than those of trimethylphosphine–boron trihalides.

The molecular structure of gaseous copper(I) trifluoroacetate was determined by electron diffraction. The molecule is dimeric and its skeleton is essentially planar. The molecular parameters and the uncertainties are r g (CuCu) = 2.566 ± 0.018 A, r g (CuO) = 1.874 ± 0.002 A, r g (CO) = 1.253 ± 0.004 A r g (CC) = 1.542 ± 0.005 A, r g (CF) = 1.333 ± 0.003 A and ∠OCuO′ = 170.3 ± 0.6°. The rotational barrier height of the CF 3 group is 5.9 ± 2.5 kJ mol −1 , and the minimum of the barrier is at the position such that one of the CF bonds lies on the plane perpendicular to the ring.

The molecular structures of trimethylamine-boron trichloride (CH3)3N·BCl3 and trimethylamine-boron tribromide (CH3)3N·BBr3 were determined from gas electron diffraction and vibrational-spectroscopic data. The molecular parameters and their uncertainties for (CH3)3N·BCl3 were rg(B–Cl)=1.836±0.002 A, rg(N–B)=1.652±0.009 A, rg(C–N)=1.497±0.003 A, rg(C–H)=1.107±0.005 A, ∠ClBCl=110.9±0.2°, ∠CNC=108.1±0.3°, while those for (CH3)3N·BBr3 were rg(B–Br)=2.001±0.003 A, rg(N–B)=1.663±0.013 A, rg(C–N)=1.500±0.005 A, rg(C–H)=1.095±0.007 A, ∠BrBBr=110.3±0.3°, ∠CNC=107.8±0.5°. The potential barriers around the N–B bonds in (CH3)3N·BCl3 and (CH3)3N·BBr3 were also estimated to be higher than 18 kcal mol−1 and about 12 kcal mol−1 respectively.

The molecular structures of pyridine complexes with boron trifluoride, boron trichloride and boron tribromide have been determined from gas electron-diffraction data. The molecular parameters of the boron trifluoride complex are r g (NB) = 1.669(7) A, r g (BF) = 1.366(2) A, ∠FBF = 113.3(4)°, r g (CN) = 1.345(6) A and r g (CC) = 1.382(4) A. The corresponding values for the boron trichloride complex are 1.706(12) A, 1.830(3) A, 112.5(3)°, 1.360(10) A and 1.390(6) A, and those of boron tribromide complex are 1.694(17) A, 1.986(3) A, 111.9(3)°, 1.362(12) A and 1.392(8) A. On complex formation the structure change of the acceptor molecules is much larger than that of the donor molecule and increases with the increase of atomic number of the halogen atoms.

The molecular structure of trimethylamine-boron trifluoride (CH3)3N·BF3 was determined from gas electron-diffraction data with vibrational and rotational spectroscopic data. The geometric parameters of the molecule were found to be very close to those inferred from the preliminary analysis of the diffraction data alone. The structural parameters and uncertainties were rg(N–B)=1.674(4) A, rg(B–F)=1.374(2) A, rg(C–N)=1.485(2) A, rg(C–H)=1.100(3) A, rg(F…F)=2.288(2) A, and rg(C…C)=2.420(4) A. The potential barrier about the N–B axis was estimated to be 4.3±0.3 kcal/mol in the gas phase; this value is much larger than that from NMR spectra.

The molecular structure of trimethylphosphine-boron trichloride (CH3)3P·BCl3 has been determined from gas electron-diffraction data. The structure parameters and uncertainties are rg(P–B)=1.941(16) A, rg(B–Cl)=1.851(7) A, rg(C–P)=1.800(4) A, rg(C–H)=1.099(5) A, rg(Cl…Cl)=3.022(5) A, and rg(C…C)=2.936(10) A. The potential barrier about the P–B axis is 3.8±0.7 kcal mol−1 in the gas phase. The data show that the molecular structure in the gas phase is nearly equal to that in the solid phase.

The molecular structure of gaseous xanthone has been determined from electron diffraction data. The molecule is planar and has C 2v symmetry. The molecular parameters obtained from the least-squares analysis are r g (CC) = 1.402±0.002 A, r g (CH) = 1.088±0.009 A, r g (CO) = 1.367±0.008 A, r g (CC c ) = 1.492±0.005 A, r g (C c O) = 1.239±0.007 A, ∠ COC = 119.7±1.1° and ∠ CC c C=115.7±0.8°. The benzene ring in the molecule was assumed to be a regular hexagon in the analysis, but the symmetry of the ring appeared to be lower.

The molecular structure of thioxanthone has been determined from gas electron-diffraction data. The molecular parameter values and their uncertainties are rg(C–C)=1.401±0.001 A, rg(C–H)=1.099±0.007 A, rg(C–S)=1.751±0.002 A, rg(C–Cc)=1.498±0.004 A, rg(Cc–O)=1.232±0.006 A, ∠CSC=103.4±0.3°, ∠CCcC=119.4±0.6°, and θ(dihedral angle)=169.0±1.6°, where the angle parameters are rα parameters. The dihedral angle of thioxanthone is much larger than those of related molecules.

The molecular structure of copper nitrate has been reinvestigated by gaseous electron diffraction. The experimental data were found to be consistent with a square-planar arrangement of the oxygen atoms of two bidentate nitrate groups. The bond distances and angles were determined as follows: CuO = 1.946 ± 0.003 A, NO(coordinated) = 1.298 ± 0.003 A, NO(terminal) = 1.205 ± 0.005 A, OCuO = 67.8 ± 0.2°. The sample of copper nitrate was also found to be considerably decomposed by heating at 150°C.

三ハロゲン化ホウ素を受容体とするトリメチルアミン,トリメチルボスフィン,ピリジン,ジメチルエーテルなどn-v型電荷移動錯体の構造について気体電子回折法により決定した結果を,X線やマイクロ波分光などほかの方法からの結果と比較し,これまで行なわれた多くの研究による混乱したデータに統一を与えた。さらにこれらの電子線回折法によって得た自由分子の精密な構造決定のデータの検討によって,受容体のハロゲンや供与体の種類によって錯体の構造はいちじるしく変化し,それらが系統的であることを見いだし,変化の大きさから受容体および供与体の強度につぎのような順序を与えた。BF3＜BC13＜BBr3＜BI3Me20＜C5H5N＜Me3N＜Me3P