共查询到20条相似文献,搜索用时 12 毫秒
1.
The molecular structure and conformation of 2,3-dichloro-1-propene have been determined by gas-phase electron diffraction at nozzle temperatures of 24, 90 and 273°C. The molecules exist as a mixture of two conformers with the chlorine atoms anti (torsion angle ∠φ = 0°) or gauche (∠φ = 109°) to each other and with the anti form the more stable. The composition (mole fraction) of the vapor with uncertainties estimated at 2σ was found to be 0.55 (0.08), 0.49 (0.08) and 0.41 (0.10) at 24, 90 and 273°, respectively. These values correspond to an energy difference with estimated standard deviation ΔE° = E°g-E°a = 0.7 ± 0.3 kcal mol?1 and an entropy difference ΔS° = S°g-S°a = 0.6 ± 0.9 cal mol?1 K?1. Some of the diffraction results, together with spectroscopic observations, permit the evaluation of an approximate torsional potential function of the form 2V = V1 (1 - cos φ) + V2 (1 - cos 2φ) + V3 (1 - cos 3φ); the results are V1 = 4.4 ± 0.5, V2 = ?2.9 ± 0.5 and V3 = 4.8 ± 0.2, all in kcal mol?1. The results at 24°C for the distance (ra) and angle (∠α) parameters, with estimated uncertainties of 2σ, are: r(Csp2-H) = 1.098(0.020)Å, r(Csp3-H) = 1.103(0.020)Å, r(CC) = 1.334(0.009)Å, r(C-C) = 1.504(0.013)Å, r(Csp2-Cl) = 1.752(0.021)Å, r(Csp3-Cl) = 1.776(0.020)Å, ∠C-CC = 127.6(1.1)°, ∠Csp3-Csp2-Cl = 110.2(1.0), ∠Csp2-Csp3-Cl = 113.1(1.2)°, ∠H-Csp3-H = 109.5° (assumed), ∠CC-H = 120.0° (assumed) and ∠φ = 108.9(3.4)°. 相似文献
2.
Quang Shen 《Journal of Molecular Structure》1983,102(3-4):325-332
Dichlorotetramethyldisiloxane is studied by gas-phase electron diffraction at room temperature. The least-squares values of the bond distances (rg) and bond angles () are: r(C---H)=1.084(5) Å, r(Si---O) = 1.624(2) Å, r(Si---C) = 1.852(2) Å, r(Si---Cl) = 2.067(2) Å, SiOSi = 154.0° (1.5), ClSiO = 110.2° (0.8), ClSiC = 109.6°(0.7), HCSi = 111.7°(1.5), OSiC = 110.0°(0.8), τ1 (zero corresponds to the Si---Cl bond trans to the Si---O---Si linkage) = 78°(6) and τ2 = 141°(19). A two-conformer model cannot be ruled out. 相似文献
3.
S. H. Schei 《Journal of Molecular Structure》1983,102(3-4):305-313
A gas phase electron diffraction study of 3-bromo-2-methyl-1-propene shows that there is predominantly a gauche conformer present. Data recorded at 20 and 180°C show 4(8) and 5(4)% respectively of a second confomer with a planar heavy atom skeleton. The gauche structural results in terms of ra distances and angles at 20°C were found to be: r(C---C) = 1.331(9) Å, r(C---CH2Br) = 1.484(6) Å, r(C---CH3) — r(C---CH2Br) = 0.017 Å, (assumed), r(C---Br) = 1.965(6) Å, C=C---CH2Br = 121.5(0.7)°, C=C---CH2Br — C=C---CH3 = 0.7° (constraint from molecular mechanics calculation), C---C---Br = 112.2(0.5)°, torsional ANGLE = 112.5(2.2)°. Uncertainties are given as 2σ, where σ includes uncertainties due to correlation among observations, electron wavelength and other parameters used in the data reduction. The results obtained from the 180°C data agree very well with those given above. The molecular mechanics calculations yield information consistent with the experimental results. 相似文献
4.
The molecular structure of vinyldimethylchlorosilane has been determined by gas phase electron diffraction at room temperature. The least squares values of the bond lengths (rg) and bond angles (∠α) are : r(CH) = 1.086(6) Å, r(CC) = 1.347(5) Å, r(SiC=) = 1.838(6) Å, r(SiC) = 1.876(3) Å, r(SiCl) = 2.078(2) Å, ∠CCSi = 127.8° (1.2) and ∠=CSiCl = 107° (1). Models with pure syn form and a mixture of syn and gauche gave equally good agreement with the diffraction data. 相似文献
5.
A gas phase electron diffraction investigation of 1-chloro-1-(trichlorovinyl)cyclopropane at 65° showed the existence of one conformer having a perpendicular arrangement of the cyclopropyl- and the trichlorovinylgroup, with torsional angle τ = 91(3)° relative to τ = 180° for the antiperiplanar conformer (CCl-CClanti arrangement). Both the experimental data and a molecular mechanics calculation indicate the lower barrier toward the antiperiplanar form,less than 40 kJ · mol-1. The second barrier was by molecular mechanics calculated to 60 kJ · mol-1. 相似文献
6.
Quang Shen Craig A. Kapfer Philip Boudjouk Richard L. Hilderbrandt 《Journal of organometallic chemistry》1979,169(2):147-154
The structure of 1-methyl-1-silaadamantane (MSA) has been determined by gas phase electron diffraction. There appears to be somewhat less ring strain at the silicon bridgehead of MSA than in the previously studied 1-methyl-1-silabicyclo[2.2.1]heptane (MSBH). The average SiC bond length [1.879(3) Å is comparable to those found in acyclic organosilicon systems. Also, the average CC bond length (1.547(2) Å) is only slightly longer than that observed for adamantane (1.540(2) Å). Valence angles at the silicon bridgehead experience only a moderate perturbation away from their unstrained tetrahedral values. On this basis it is expected that MSA should be somewhat less reactive than MSBH under SN2 conditions according to the reaction mechanism suggested by L.H. Sommer. 相似文献
7.
Frans C. Mijlhoff Gerrit H. Renes Kunio Kohata Kazuko Oyanagi Kozo Kuchitsu 《Journal of Molecular Structure》1977,39(2):241-252
The structure of 1,1-difluoroethylene was determined, from gas phase electron diffraction data obtained independently in Leiden and Tokyo and the rotational constants of F2CCH2, F2CCHD and F2CCD2 derived from the microwave study by Chauffoureaux. The two electron diffraction data agreed without significant discrepancy. From a joint least squares analysis of the diffraction and microwave data, the following rg bond distances and rz bond angles were derived: CC = 1.340 ± 0.006 Å, C-F = 1.315 ± 0.003 Å, C-H = 1.091 ± 0.010 Å, ∠C-C-F = 124.7 ± 0.3°, ∠C-C-H = 119.0 ± 0.4°, where the uncertainties represent estimated limits of error. 相似文献
8.
Chloroacetyl chloride is studied by gas-phase electron diffraction at nozzle-tip tempera- tures of 18, 110 and 215°C. The molecules exist as a mixture of anti and gauche confor- mers with the anti form the more stable. The composition (mole fraction) of the vapor with uncertainties estimated at 2σ is found to be 0.770 (0.070), 0.673 (0.086) and 0.572 (0.086) at 18, 110 and 215°C, respectively. These values correspond to an energy difference with estimated standard deviation ΔEo = Eog -Eoa = 1.3 ± 0.4 kcal mol?1 and an entropy difference ΔSo = Sog -Soa = 0.7 ± 1.1 cal mol?1 K?1. Certain of the diffraction results permit the evaluation of an approximate torsional potential function of the form 2V = V1(1 - cos φ) + V2(1 - cos 2φ) + V3(1 - cos 3φ); the results are V1 = 1.19 ± 0.33, V2 = 0.56 ± 0.20 and V3 = 0.94 ± 0.12, all in kcal mol?1. The results for the distance (ra), angle (∠α) and r.m.s. amplitude parameters obtained at the three temperatures are entirely consistent. At 18°C the more important parameters are, with estimated uncertainties of 2σ, r(C-H) = 1.062(0.030) Å, r(CO) = 1.182(0.004) Å, r(C-C) = 1.521(0.009) Å. r(CO-Cl) = 1.772(0.016) Å, r(CH2-Cl) = 1.782(0.018) Å, ∠C-C-0 = 126.9(0.9)°, ∠CH2-CO-C1 = 110.0(0.7)°,∠CO-CH2-C1 = 112.9(1–7)°, ∠H-C-H = 109.5° (assumed), ∠φ (gauche torsion angle relative to 0° for the anti form) = 116.4(7.7)°, δ (r.m.s. amplitude of torsional vibration in the anti conformer) == 17.5(4.2)°. 相似文献
9.
Shen Q Brown JW Malona JA Cochran JC Richardson AD 《The journal of physical chemistry. A》2006,110(23):7491-7495
The molecular structure of chloronitromethane was studied in the gas phase at a nozzle-tip temperature of 373 K. The experimental data were interpreted using a dynamic model where the molecules are undergoing torsional motion governed by a potential function: V = V2/2x(1 - cos 2tau) + V4/2x(1 - cos 4tau) with V2 = 0.81(30) and V4 = 0.12(40) kcal/mol (tau is the dihedral angle between the C-Cl and N-O bond). The conformer with a zero degree dihedral angle is the most stable conformer. Comparison with results from HF/MP2/B3LYP 6-311G(d,p) calculations were made. The important geometrical parameter values (for the eclipsed form) obtained from least-squares refinements are the following: r(C-H) = 1.061(18)A, r(C-N) = 1.509 (5)A, r(N-O) = 1.223(1)A, r(C-Cl) = 1.742(2)A, angleClCN = 115.2(7) degrees, angleO4NC = 118.9(10) degrees, angleO5NC = 114.9(16) degrees, and angleClCH 115(4) degrees. 相似文献
10.
《Journal of Molecular Structure》2006,780(1-3):151-157
The molecular structure of caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) was determined by means of gas electron diffraction. The nozzle temperature was 185 °C. The results of MP2 and B3LYP calculations with the 6-31G7 basis set were used as supporting information. These calculations predicted that caffeine has only one conformer and some of the methyl groups perform low frequency internal rotation. The electron diffraction data were analyzed on this basis. The determined structural parameters (rg and ∠α) of caffeine are as follows: <r(NC)ring> = 1.382(3) Å; r(CC) = 1.382(←) Å; r(CC) = 1.446(18) Å; r(CN) = 1.297(11) Å; <r(NCmethyl)> = 1.459(13) Å; <r(CO)> = 1.206(5) Å; <r(CH)> = 1.085(11) Å; ∠N1C2N3 = 116.5(11)°; ∠N3C4C5 = 121. 5(13)°; ∠C4C5C6 = 122.9(10)°; ∠C4C5N7 = 104.7(14)°; ∠N9–C4=C5 = 111.6(10)°; <∠NCHmethyl> = 108.5(28)°. Angle brackets denote average values; parenthesized values are the estimated limits of error (3σ) referring to the last significant digit; left arrow in parentheses means that this parameter is bound to the preceding one. 相似文献
11.
Bromoacetyl chloride and bromoacetyl bromide are studied by gas phase electron diffraction at nozzle-tip temperatures of 70°C and 77°C, respectively. Both compounds exist as mixtures of anti and gauche conformers. The mole fraction anti, with uncertainties estimated at 2σ, was found to be 0.474(0.080) for bromoacetyl chloride and 0.615(0.069) for bromoacetyl bromide. The results for the distance (ra)and angle (∠α) parameters, with parenthesized uncertainties of 2σ including estimated uncertainty in the electron wave length and correlation effects are as follows: (1) bromoacetyl chloride, r(C-H) = 1.086(0.062) Å, r(CO) = 1.188(0.009) Å, r(C-C) = 1.519(0.018) Å, r(C-Cl) = 1.789(0.011) Å, r(C-Br) = 1.935(0.012) Å, ∠C-CO = 127.6(1.3)°, ∠C-C-Cl = 111.3(1.1)°, ∠C-C-Br = 111.0(1.5)°, ∠H-C-H = 109.5°(assumed), /o (gauche torsion angle relative to 0° for the anti form) = 110.0°(assumed); (2) bromoacetyl bromide, r(C-H) =1.110(0.088) Å, r(C=O) = 1.175(0.013) Å, r(C-C) = 1.513(0.020) Å, r(CO-Br) = 1.987(0.020) Å, r(CH2-Br) = 1.915(0.020) Å, ∠C-CO = 129.4(1.7)°, ∠CH2-CO-Br = 110.7(1.5)°, ∠CO-CH2-Br = 111.7(1.8)°, ∠H-C-H = 109.5°(assumed), ∠ø (gauche torsion angle relative to 0° for the anti form) = 105.0°(assumed). The structural results are discussed in connection with the structures of related molecules. 相似文献
12.
The molecular structure of Cis- and trans-bicyclo[4.2.0]octane in the gas phase was studied. Molecular mechanics calculations applying Boyd's force Held were used for constraining differences between structural parameters during least squares analysis and for calculating vibrational amplitudes. The cyclohexane ring was found to have a distorted chair conformation, the ring in the cis isomer being flattened along the junction and more twisted in the other part. For the trans compound the reverse is true. The following structural parameters were obtained (ra-structure):cis: r(C-C)av. = 1.535 Å. Cyclohexane ring: average bond angle 112.9°; average torsional angle 48°. Cyclobutane ring: average bond angle 88.9°; puckering 157°. The dihedral angle between the bisecting planes of the C(2)-C(1)-C(6)-C(5) and C(8)-C(1)-C(6)-C(7) torsional angles, is 119° - the “connection angle” of the two rings.trans: r(C-C)av.= 1.532 Å. Cyclohexane ring: average bond angle 110.4° ; average torsional angle 57°. Cyclobutane ring: average bond angle 87.3°; puckering 145°. The “connection angle” is 180° (C2 symmetry).Comparison is made with structures of related compounds. 相似文献
13.
The rg structure of cyclopentene oxide has been determined by the simultaneous least squares analysis of electron diffraction and microwave spectroscopic data. The investigation has reaffirmed previous studies indicating that the molecule prefers a boat conformation. The methylene and epoxide flap angles obtained are 152.3±2.1° and 104.7±1.0° respectively. Other structural parameters determined are: rg (C-H avg.) = 1.120±0.004 Å; rg (C-C avg.) = 1.538±0.002 Å; rg (C-O) = 1.443±0.003 Å, and rg (C-C) = 1.482±0.004 Å for the carbon-carbon bond in the three membered epoxide ring. These results compare favorably with the reported structures of ethylene oxide and cyclohexene oxide. A tentative rationalization of the unusual boat conformation is also offered. 相似文献
14.
We have investigated the molecular structure and conformation of diethylmethylamine, C(4)H3C(2)H2N(1)[CH3]C(3)H2C(5)H3, by gas electron diffraction and vibrational spectroscopy with the aid of theoretical calculations. Diffraction data are consistent with a conformational mixture of 35(14)% tt + 27(14)% g+t + 20(17)% g−t + 18(23)% g+g+ where the numbers in parentheses denote three times the standard errors (3σ). Normal-coordinate analysis based on B3LYP/6-311+G** calculations supports the existence of the four conformers. The dihedral angle 1(C4C2N1C3) (= −2(C5C3N1C2)) of the tt conformer was 170(4)° whereas the 1 and 2 values of the other conformers were fixed at the B3LYP/6-311++G(2df,p) values: 72.4° and −163.3° for the g+t, −66.0° and −158.2° for the g−t, and 60.3° and 63.5° for the g+g+. Average values of the structural parameters (rg/Å and α/°) with 3σ are: r(N–C) = 1.462(2), r(C–C) = 1.523(3), r(C–H) = 1.113(2), CNC = 111.6(5), NCC = 114.5(5), NCH/CCHMe = 110.6(5). 相似文献
15.
The structure of 1,3-dichloropropyne has been studied by gas electron diffraction. The resulting parameters ra have been converted into rαo distances. A geometrical structure has been fitted to these internuclear distances. Thus the following parameters (rαo) have been determined: r(C1-Cl1) = 1.629 (10) A, r(C1C2) = 1.201 (13) Å, r(C3-Cl2) = 1.791 (6) A, ∠(C2-C3-Cl2) = 111.1° (1.0°), ∠(H-C3-H) = 98.8° (3.1°), ∠(C2-C3-H) = 108.7° (3.2°). ∠(Cl1-C1C2) = 176.6° (1.1°), ∠(C1C2-C3) = 182.7° (1.4°). Inconsistencies have been detected between our results and the rotational constants reported by Günther and Zeil. Discussion of the problem including rotational constants of the first excited vibrational state leads to the conclusion that the observed discrepancies are due to temperature effects. 相似文献
16.
Quang Shen 《Journal of Molecular Structure》1985,130(3-4):275-282
The molecular structure of gaseous epichlorohydrin has been investigated using electron diffraction data obtained at 67°C. The conformational composition at this temperature is such that the molecules exist predominantly in a gauche-2 conformer (where the C---Cl bond is 160° away from the C---O) bond). Refinements showed that 33% (σ = 4) of the molecule exist in the gauche-1 form. The important distances (rg) and angle () with the associated uncertainties are r(C---H) = 1.095(5) Å, r(C---O) = 1.442(3) Å, r(C---C) = 1.475(8) Å, r(C---CM) = 1.523(7) Å, r(C---Cl) = 1.788(2) Å, CCO = 114° (1), CCCM = 119°(1), ClCC = 108.9° (7), and Tau(ClCCO) = −150°(10) (gauche-2) and Tau(ClCCO) = 78° (10) (gauche-1). 相似文献
17.
The molecular structures of cis-3-hexene and of trans-3-hexene in the gas phase have been determined by electron diffraction combined with molecular mechanical calculations. For cis-3-hexene the data indicate the presence of the (+ac, +ac) and the (?ac, +ac) forms. In trans-3 -hexene three rotamers were observed, with an energy sequence E(+ac, +ac) ≈ E(?ac, +ac) < E(ac, sp). The refined rα0-structural parameters are: cis-3-hexene: C-H = 1.073 Å, CC = 1.330 Å, C(sp2)-C(sp3) = 1.505 Å, ∠CCH(in CH2) = 111.1°, ∠CCC = 111.4°, ∠(CC-C) = 129.1° trans-3-hexene: C-H = 1.078 Å, CC = 1.342 Å, C(sp2)-C(sp3) = 1.506 Å, ∠CCH(in CH2) = 109.3°, ∠CCC = 112.8, ∠CC—C = 124.1°The agreement between calculated and experimental geometries and vibrational amplitudes is good. 相似文献
18.
The structure and conformation of dichloroacetyl chloride have been determined by gas-phase electron diffraction at nozzle temperatures of 20 and 119°C. The molecules exist as a mixture of two conformers with the hydrogen and oxygen atoms syn and gauche to each other. The composition (mole fraction of syn form) of the vapor was found to be 0.72 ± 0.06 and 0.73 ± 0.12 at 20 and 119°C, respectively, corresponding to almost equal energy for the two forms. The results for the distance (rg), angle ∠α and r.m.s. amplitude (l) parameters obtained at the two temperatures are entirely consistent. At 20°C the more important parameters, with estimated uncertainties of 3σ are: r(C-H) = 1.062(0.049)Å, r(C0) = 1.189(0.003)Å, r(C-C) = 1.535(0.008)Å, r(CO-Cl) = 1.752 (0.009)Å, r(CHCl-Cl) = 1.771(0.004)Å, ∠C-CO = 123.3(1.3)°, ∠C-CO-Cl = 113.9 (5.9)°, ∠C-CHCl—Cl = 109.5(1.5)°, ∠C1-C-Cl = 111.7(0.5)°, ∠Cl-C-H = 108.0(1.5), φ1 (HCCO torsion angle in the syn conformer) = 0.0° (assumed), φ2 (HCCO torsion angle in the gauche conformer) = 138.2(5.1)°. 相似文献
19.
The molecular structure of p-dichlorobenzene in the vapour phase has been studied by electron diffraction. Least-squares refinement of a model with D2h symmetry has led to the accurate determination of the small deviations of the benzene ring from D6h symmetry caused by the chlorine substituents. The most appreciable effect is an increase from 120° to 121.6 ± 0.2° of the internal angle at the ipso carbon, associated with a shortening of the distance between the two ipso atoms. A less pronounced effect is a shortening of the C-C bonds that originate from the ipso carbons as compared to the central C-C bonds (rg = 139.0 ± 0.3 pm vs. 139.5 ± 0.4 pm). Other bond distances are rg (C-Cl) - 173.0 ± 0.4 pm and rg (C-H) = 109.4 ± 1.0 pm. The observed ring distortions are in agreement with those obtained by low-temperature X-ray crystallography on three different crystal phases of p-dichlorobenzene. They are also consistent with those obtained for chloro-benzene by gas-phase electron diffraction and by NMR spectroscopy in a nematic solvent. The rs structure of chlorobenzene obtained in a recent study by micro-wave spectroscopy is shown to need revision, as far as the ipso region of the ring is concerned. 相似文献
20.
The structure and conformations of trans- and of cis-bicyclo[4.3.0]nonane have been studied in the gas phase. Molecular mechanics calculations applying the force field of Ermer and Lifson were used to obtain geometrical constraints, vibrational amplitudes and perpendicular vibrational corrections. The vibrational parameters were corrected for the large amplitude motion of the five-membered ring. The refinement for the trans-isomer confirms completely the predictions of the force field calculations. Although a stable solution could not be obtained for the cis-compound there is no contradiction between experiment and model calculations. The cyclohexane ring in both isomers is found to have a distorted chair conformation. In the cis-isomer it is flattened along the junction and more twisted in the other part. For the trans-compound the reverse is true.The following structural parameters rg, rα-structure) are put forward, (a) trans-compound: C2-symmetry, r(C-C)av = 1.536 Å. Average bond angle and average torsion angle in the cyclohexane ring are 110.2° and 58.1°, respectively. The connection angle, defined as the angle between the planes bisecting C6-C1-C5-C9 and C2-C1-C5-C4, is 180°. (b) cis-compound: no symmetry, r(C-C)av = 1.536 Å. Average bond and torsion angles in the cyclohexane ring are 112.2° and 52.3°, respectively. The connection angle is 124.8°.A comparison is made with structures of related compounds. 相似文献