Toru Egawa

Molecular structure and conformation of methyl acrylate. A gas electron diffraction study augmented by ab initio calculation and rotational constants

Abstract The molecular structure and conformational properties of methyl acrylate, CH 2 CHCOOCH 3 , were studied by a joint analysis of gas electron diffraction data and rotational constants. The structures optimized by HF/4-31G∗ ab initio calculations taken from the literature were utilized as structural constraints in the data analysis. Mean amplitudes of vibration and shrinkage corrections were calculated on the basis of the vibrational spectra recorded for this analysis. At room temperature the molecule exists in a conformational equilibrium of two forms, s-cis and s-trans, in a ratio of 67(11):33. The following r z structural parameters were found for the s-cis conformer: r( C = C ) = 1.332(7) A ; r( C  C ) = 1.480(6) A ; r( C = O ) = 1.207(2) A ; r( C (= O ) O ) = 1.345(3) A ; r( O  C Me ) − r( C (= O ) O ) = 0.089 A (assumed); r( C  H ) = 1.079(5) A (averaged value); ∠=CC = 120.3(8)°; ∠CC=O = 126.1(5)°; ∠CCO = 110.3(3)°; ∠COC = 116.4(5)°. Parenthesized values are error estimates (3σ) referring to the last significant digit.

Structural and conformational analysis of diethyl ether by molecular orbital constrained electron diffraction combined with microwave spectroscopic data

Abstract The molecular structure and conformation of diethyl ether, C(3)H 3 C(2)H 2 O(1)C(4)H 2 C(5)H 3 , at 27°C was studied by a joint analysis of gas electron diffraction and microwave spectroscopic data. Vibrational mean amplitudes and shrinkage corrections were calculated on the basis of the vibrational spectra measured in the vapor and liquid phases. Ab initio geometry optimization at the HF/4-21G level was performed on four possible conformers and the results were used as structural constraints. Diffraction and vibrational spectroscopic data are consistent with the presence of two conformers, trans-trans (TT, dihedral angles φ 1 (C 4 O 1 C 2 C 3 ) = φ 2 (C 2 O 1 C 4 C 5 ) = 180°) and trans-gauche (TG), in the vapor phase. The compositions of the TT and TG conformers were determined to be 69(8) and 31%, respectively, by the joint analysis. The structural parameters of the TT form determined are r g (OC) = 1.419(1) A, r g (CC) = 1.514(2) A, 〈 r g (CH)〉 = 1.114(2) A, ∠ α COC = 113.5(4)°, ∠ α OCC = 108.6(1)°, ∠ α OCH = 110.4(9)°, and 〈∠ α CCH〉 = 110.5(7)°, where values in parentheses are error estimates (3σ) and those in angle brackets denote average values. The structural differences between the TT and TG conformers were taken from the 4-21G calculations except for the dihedral angles of the TG form, which were determined to be φ 1 = 76(10)° and φ 2 = 161(15)°.

Electron diffraction study of thermal decomposition products of trimethylamine: molecular structure of CH3NCH2

Abstract Structural studies of thermal decomposition products of trimethylamine have been performed by gas electron diffraction aided by mass spectrometry. Trimethylamine vapor is heated in a quartz tube shortly before the nozzle tip which is kept at room temperature. When the temperature inside the quartz tube is 515°C, N(CH 3 ) 3 simply decomposes into CH 4 and short-lived CH 3 NCH 2 . However, more complicated reactions, which include CH 3 NCH 2 → CH 4 + HCN, take place at the reaction temperature of 535°C. The zero-point average structure of N -methylmethyleneimine (CH 3 NCH 2 ) has been determined by a joint analysis of electron diffraction data and rotational constants, and then compared with ab initio calculations. Principal structural parameters are as follows: r z ( N  C ) = 1.279(6) A , r z ( N  C ) = 1.458(8) A and θ z (CNC) = 116.62(12)°. The molecular structure of trimethylamine has been determined much more precisely than that given in the literature.

Molecular structure and confirmation of ethyl acetate as studied by gas electron diffraction

Abstract The molecular structure and conformation of ethyl acetate, , have been determined by gas electron diffraction. The result of ab initio calculations reported by Manning was used as an aid to the analysis. The torsional vibrations of C 3 (acetoxy) methyl and ethyl groups were treated as large amplitude motions and the potential function was obtained for the ethyl torsion. The O 2 C 1 O 4 C 5 dihedral angle was fixed at O° and the C 6 methyl group was assumed to take the staggered conformation against the C 5 C 6 bond. Two stable conformers, trans and gauche, are found to have the dihedral angles C 1 O 4 C 5 C 6 , of 180° and 79°, respectively. The abundance of the trans conformer is derived to be 38 ± 7%. The structural parameters of the trans conformer are determined as follows (the numbers in parentheses represent estimated limits of error): r g (C 3 H 7 = 1.105(3)A, r g (C 1 O 2 ) = 1.203(2)A, r g (C 1 C 3 = 1.508(2) A, r g (C 1 O 4 ) = 1.345(3) A r g (O 4 C 5 ) = 1.448(3) A, r g (C 5 C 6 ) = 1.515(2) A, ∠ α O 2 C 1 C 3 = 124.1(10)°, ∠ α O 2 C 1 O 4 =124.0(3)°, ∠ α C 1 O 4 C 5 = 115.7(5)°, ∠O 4 C 5 C 6 =108.2(11)°, ∠ α C 1 C 3 H = 107.7(13)° and ∠ α C 5 C 6 H = 108.1(13)°.

Structural study and conformational analysis of t-butyl ethyl ether by gas electron diffraction, ab initio calculations and vibrational spectroscopy

Abstract The molecular structure and conformational properties of t -butyl ethyl ether were studied by gas electron diffraction. Structural constraints of the data analysis were obtained from HF/4-21G ab initio geometry optimizations, and mean amplitudes of vibration and shrinkage corrections were calculated from vibrational spectra recorded for this analysis. At room temperature the compound exists in a conformational equilibrium of two forms, trans and skew, in a ratio of 70: 30 ± 24%. Subject to the constraints of the analysis, the following structural parameters were found for the trans conformer; r g (OC) t -Bu = 1.436(3) A; r g (OC) t -Bu − r g (OC) Et = 0.014A (assumed); r g (CC) t -Bu = 1.532(2)A (averaged value); r g (CC) t -Bu − r g (CC) Et = 0.008A (assumed); r g (CH) = 1.121(3)A; ∠ α COC = 119.9(12)°; ∠ α CCC t −Bu = 111.1(5)°; ∠ α OCC Et = 109.3(15)°; the tilt angle of the t -butyl group τ α = 4.5(8)°. Parenthesized values are error estimates (3σ) referring to the last significant digit. The effects of steric repulsion on the structural parameters are discussed.

Reactions of N, N-dichloroalkylamines with solid base as studied by FTIR combined with DFT calculations

Abstract Products of vacuum gas–solid reactions of N, N-dichloroalkylamines with KOH have been identified by FTIR spectroscopy and DFT calculations. It has been found that the reactions consist of elimination of two Cl atoms accompanied with migration of an H atom, a ring carbon or a methyl group from the α-carbon to the N atom and unstable imines with a C N double bond are formed.

Structural study of methyl isonicotinate by gas phase electron diffraction combined with ab initio calculations

Abstract The molecular structure of methyl isonicotinate was studied by gas phase electron diffraction combined with ab initio calculations. The molecular skeleton was assumed to be planar. The determined values of principal structure parameters ( r g and ∠ α ) are as follows: r( NC ) = 1.343(5) A , r( C…C ) ring = 1.401(3) A , r( C γ  C ) = 1.499(9) A , r( C  O ) = 1.205(5) A , r( C ( O ) O ) = 1.331(8) A , r( OC Me ) = 1.430(8) A , 〈r( CH )〉 = 1.103(10) A , ∠CNC = 117.6(9)°, ∠C β C γ C β = 118.7(9)°, ∠C β ,trans C γ C(O) = 118.6(12), ∠C γ CO = 121.4(12)°, ∠C γ CO = 114.2(10)°, ∠COC = 115.4(15)°, where angled brackets denote average values and C γ,trans denotes the carbon atom which is trans to the carbonyl oxygen atom. Values in parentheses are the estimated limits of error (3σ) referring to the last significant digit. The structure of the ring in methyl isonicotinate agrees with that of pyridine within experimental error. In contrast, the structure parameters of the COOCH 3 group are significantly different from those of methyl acrylate and methyl acetate. These differences have been discussed in terms of hyperconjugation and steric effects.

Structural and conformational analysis of N-chloro-N-ethylethanamine by gas electron diffraction, ab initio calculations and vibrational spectroscopy

Abstract The structural and conformational properties of N -chloro- N -ethylethanamine, C(3)H 3 C(2)H 2 N(1)ClC(4)H 2 C(5)H 3 , were studied by gas electron diffraction (GED). Vibrational amplitudes and shrinkage corrections were calculated on the basis of a normal coordinate analysis of the vibrational spectra measured in the vapor and liquid phases. The geometries of six possible conformers were optimized by ab initio HF/4-21G * /3-3-21G * calculations and the results were used in the data analysis as structural constraints. At 25°C, two conformers were observed. On the basis of the GED data analysis it is possible to identify the trans-trans conformer (TT, dihedral angles φ 1 (C 4 N 1 C 2 C 3 )= −φ 2 (C 2 N 1 C 4 C 5 ) = 175(1)°) as the most stable one, but the nature of the minor component is uncertain, since various mixtures of TT with one of three different gauche forms, TG, TG′ or GG′, fit the experimental data reasonably well. The best fitting model is a mixture of TT and TG (dihedral angles φ 1 = 80(6)° and φ 2 = −175(1)°), with a relative abundance of 68(8) and 32%, respectively. The vibrational spectra are consistent with the existence of two conformers in the vapor and liquid phases. The structural parameters of TT determined by this analysis (with error limits of 3σ and average values in brackets) are r g (NC) = 1.471(2) A, r g (NCl) = 1.765(2) A, r g (CC) = 1.530(3) A, 〈 r g (CH)〉 = 1.118(3) A, ∠ α NCC = 112.6(4)°, 〈 ∠ α NCH> = 109.6(18)°, ∠ α CNC = 11066(8)°, ∠ α CNCl = 108.3(2)°, α CCH > = 109.4(11)° and φ 1 = (−φ 2 ) = 175(1)°. The structural differences between the TT and TG conformers were taken from the calculated ones.

Gas-phase structure and conformation of diethyl ketone studied by molecular orbital constrained electron diffraction

Abstract The molecular structure and conformation of diethyl ketone (3-pentanone), C(3)H 3 C(2)H 2 C(1)OC(4)H 2 C(5)H 3 , at 27°C were studied by gas electron diffraction (GED). Vibrational mean amplitudes and shrinkage corrections were calculated on the basis of the vibrational spectra measured in the vapor and liquid phases. Structural constraints were obtained from RHF/6-31G∗ ab initio calculations. Diffraction data were reproduced best by a mixture of two conformers, trans-trans (TT, dihedral angles ф 1 (C 4 C 1 C 2 C 3 ) = ф 2 (C 2 C 1 C 4 C 5 ) = 180°) and trans-gauche (TG). The structural parameters of the TT form determined by GED, with error estimates (3σ) in parentheses, are: r g (CO) = 1.217(2)A, r g (C 1 −C) = 1.519(1)A, r g (C 2 −C 3 ) = 1.524(1)A, 〈 r g (C−H〉 = 1.103(3)A, ∠ α CC(O)C = 116.0(6)°, ∠ α C(O)CC = 114.2(6)°, ∠ α C(O)CH = 108.2(7)°, and 〈∠ α C 2 C 3 H〉 = 111.4(7)°, where 〈 〉 denotes average value. The difference between r (C 1 −C) and r (C 2 −C 3 ) was assumed. Similarly ∠C(O)CH and ∠C 2 C 3 H were refined in groups. The structural differences between the TT and TG conformers were taken from the 6–31G∗ calculations except for the dihedral angles. The dihedral angles of the TG form were determined to be ф 1 = 61(7)° and ф 2 = 151(14)° . The relative abundances of the TT and TG conformers are 50(10) and 50%, respectively.

Molecular structure of N-chloroazetidine studied by gas electron diffraction combined with microwave spectroscopy

Abstract The geometric structure of N -chloroazetidine has been determined by gas electron diffraction (GED) and microwave (MW) spectroscopy. Rotational transitions of the vibrational ground state and excited states of the ν 16 (ring puckering) mode were measured by MW spectroscopy. In order to calculate mean amplitudes and shrinkage corrections, a normal coordinate analysis has been performed on the vibrational spectra recorded in the vapour and liquid phases. All the observed MW transitions and vibrational spectra were assigned to a single conformer. The data analysis of GED also shows that only the equatorial conformer exists at room temperature. The structural parameters ( r z values) determined by a joint analysis of GED and MW data are r (NC) = 1.485(3) A, r (CC) = 1.551(3) A, r (NCl) = 1.741(2) A, r (CH) = 1.0984 A, ∠CNC = 90.4(4)°, ∠CNCl = 115.0(2)° and φ = 32.4(17)°, where φ is the dihedral angle of the ring.