Formation,microwave spectrum and preliminary structure of selenoketene

Hitherto unknown selenoketene, CH₂CSe, has been produced by pyrolysis of 1,2,3-selenodiazole and identified by observation of microwave absorption from CH₂C&.dbnd;⁸⁰Se and CH₂C⁷⁸Se. The CC and CSe bond lengths of selenoketene agree with bond lengths in ketene, CH₂CO, and in carbonyl sulphide, OCS.     

The molecular structure of fumaric acid and the deformation of carboxyl group geometry on crystallization

The molecular structure of fumaric acid was studied by means of gas electron diffraction at 260° C. The molecular parameters and their standard deviations obtained for a C_2h model are (r_a distances in Å, angles in degrees): CO: 1.202(0.002), C-O: 1.341(0.006), C-C: 1.486(0.004), CC: 1.356(0.016). C-C-O: 112.1(1.0), C-CO: 124.4(1.1), C-CC: 121.8(1.2). From the available data on carboxylic acids the weighted average deformation of the structure of a carboxylic group on crystallization was determined; a significant expansion of the O-H bond (0.040 Å ), the CO bond (0.010 Å ) and the C-C-O bond angle (1.5° ) and a shrinkage of the C-O bond (0.041 Å ), the C_α-C bond (0.012 Å ) and the C-CO bond angle (2.0° ) was found. The energy for these deformations was estimated to be 1.8 kcal mol^?1.     

Organophosphorus chemistry: Part IV. Vibrational spectroscopic study of the PO,PS and PSe bonds in triarylphosphorous chalcogenides

The infrared and Raman spectra of the series (4-XC₆H₄)_3-n(C₆H₅)_nPY, (3-XC₆H₄)_3-n (C₆H₅)_nPY (X = Cl or F, n = 0,1,2) and (4-FC₆H₄)_3-n (3-FC₆H₄)_nPY (n = 1,2) (Y = O, S and Se) compounds have been studied and assignments for the v(P=O), v(P=S) and v(P=Se) stretching frequencies are proposed. The results indicate that the frequency shifts caused by the substituents bonded to phosphorus are more important in the PS and PSe bond than in the PO bond. Mechanisms for the changes in PY bond order as a result of changing the aromatic substituent are discussed.     

Solvent effects on the infrared spectra of thionyl and seleninyl chlorides

Infrared spectra of thionyl and seleninyl chlorides are reported and discussed. Complete assignment for both molecules is given on the basis of C_s symmetry. Solvent effects on XO bond (X = S, Se) have been studied in comparison with CO bond for carbonyl compounds and by means of the Kirkwood, Bauer and Magat relationship. Acceptor properties of oxychlorides for pyridinic adducts are shown.     

Raman and infrared spectroscopic investigation of alkyl derivatives of arsenic acid: Part VI. On the AsO-bond - calculation of force constants and vibrational energy distribution in compounds of the type RAsO3X2 And R2A

Normal coordinate analyses and force constant calculations were carried out using frequencies of infrared and Raman-spectra of the molecules and ions RAsO₃^2?, RAs(O)(OR)₂, RAs(O)(OH)₂, RAs(OH)O₂^?, RzAsO₂^?, R₂As(O)OH, and [R'₂As(OH)₂]⁺ (R = CH₃, R' = C₂H₅). Comparing bond orders of the AsO bond with those in corresponding phosphorus, selenium and sulphur compounds, we found influences of the electron deficiency effect and of bond polarity.     

Gehinderte Ligandenbewegungen in Übergangsmetallkomplexen : VII. Rotation der olefinliganden L = malein- und furmarsäuredimethylester in komplexen des typs C5H5Mn(CO)2L und C5H5Cr(CO)(NO)L

The restricted rotation of the olefin ligands L = dimethyl maleate and dimethyl fumarate in complexes of the type C₅H₅Mn(CO)₂L and C₅H₅Cr(CO)-(NO)L, respectively, has been investigated on the basis of their temperature-dependent ¹H NMR spectra. The olefinic ligand is arranged preferably in a position where the CC double bond is parallel to the plane of the cyclopentadienyl ring. The possible stereoisomers are discussed using this model. The ¹H NMR spectra of C₅H₅Cr(CO)(NO)(trans-CH₃OOCCHCHCOOCH₃) provide direct evidence that the configuration (R or S) at the metal is stable up to 120°C, and that the restricted motion of the olefin is exclusively rotation around the metal—olefin bond. The activation barriers of the olefin rotation are found to be appreciably lower in the C₅H₅Mn(CO)₂L complexes (ΔG^≠(T_C) 11–12 kcal mol^?1) than in the isoelectric C₅H₅Cr(CO)(NO)L compounds (ΔG^≠(T_C) 15–20 kcal mol^?1).     

gem-Difluoroallyllithium: Preparation by the transmetalation procedure and some reactions

3,3-Difluoroallyltrimethyltin has been prepared by the reaction of β-trimethylstannylethylidenetriphenylphosphorane with chlorodifluoromethane. This tin compound reacts with n-butyllithium in tetrahydrofuran at -95°C to generate gem-difluoroallyllithium. The latter, however, is not stable in solution at that temperature. If generated in situ in the presence of a triorganochlorosilane, products of the type R₃SiCF₂CHCH₂ are obtained in good yield. Addition to the CO bond of 3-pentanone to give (C₂H₅)₂C(OH)CF₂CHCH₂ was achieved by the method of alternate, incremental additions.     

1-Alkoxy-2-azaallenyl-komplexe von chrom und wolfram

The successive reaction of (CO)₆M with Na[NCR₂¹] and [Et₃O]BF₄ yields (CO)₅M[C(NCR₂¹)OEt] (II: M = Cr; III: M = W; CR₂¹ = C(C₆H₄Br-p)₂ (a), CPh₂ (b), C(C₆H₄OMe-p)₂ (c), C(C₆H₄)₂O (d), CBu₂^tt (e)). Hexacarbonyltungsten, (CO)₆W, reacts with Na[NCPh₂] and MeOSO₂F to give (CO)₅W[C(NCPh₂) OMe] (IV). X-Ray analysis of IIe shows that: (1) the CNC fragment is almost linear (171.7°); (2) the two NC bond lengths are equal within experimental error; and (3) the O,C,Cr,N plane is perpendicular to the C(Me₃),C,N,C(Me₃) plane (90.0°). Therefore compounds II–IV are best described as 1-alkoxy-2-azaallenyl complexes.     

Estimates for systematic empirical corrections of consistent 4–21G ab initio geometries and their correlations to total energy group increments

The structural parameters of the completely relaxed 4–21G ab initio geometries of more than 30 basic organic compounds are compared to experimental results. Some ranges for systematic empirical corrections, which relate 4–21G bond distances to experimental parameters, are associated with total energy increments. In general, for the currently feasible comparisons, the following corrections can be given which relate calculated distances to experimental r_g parameters and calculated angles to r_s-structures For CC single bond distances, deviations between calculated and observed parameters (r_g) are in the ranges of ?0.006(2) to ?0.010(2) Å for normal or unstrained hydrocarbons; ?0.011(3) to ?0.016(3) Å for cyclobutane type compounds; and +0.001(5) to +0.004(4) Å for CH₃ conjugated with CO. For CO single bonds the ranges are ?0.006(9) to +0.002(3) Å for CO conjugated with CO; and ?0.019(3) to ?0.027(9) Å for aliphatic and ether compounds. A very large and exceptional discrepancy exists for the highly strained ethylene oxide, r_s — r_e = ?0.049(5) Å and in CH₃OCH₃ and C₂H₅OCH₃ the r_s — r_e differences are ?0.029(5), ?0.040(10) and ?0.025(10) Å. Some of these discrepancies may also be due to deficiencies of the microwave substitution method caused by atomic coordinates close to inertial planes. For CN bonds, two types of NCH₃ corrections are from +0.005(6) to ?0.006(6) and from ?0.009(2) to ?0.014(6) Å; and the range for NCO is +0.012(3) to +0.028(4) Å. For isolated CC double bonds the range is + 0.025(2) to +0.028(2) Å. For conjugated CC double bonds the correction is less positive (+0.014(1) Å for benzene). For CO double bonds the corrections are ?0.004(3) to +0.003(3) Å. For bond angles of type HCH, CCH, CCC, CCO, CCO, OCO, NCO and CCC the corrections are of the order of magnitude about 1–2° (or better). Angles centered at heteroatoms are less accurate than that, when hydrogen atoms are involved. Differences in HOC and NHC angles were found in a range of ?2.3(5)° to ?6.2(4)°.     

Sulfur-containing carbene-metal compounds: General route from carbon disulfide manganese complexes; X-ray structure of 1,3-dithiol-2-ylidenemanganese(I) derivative

Chiral carbene-manganese(I) complexes have been synthesized by the cyclo-addition of dimethyl acetylenedicarboxylate to the coordinated CS₂ ligand in Mn(η²-CS₂)(CO)(L)C₅H₄R (L = P(OMe)₃; PMe₂Ph; PMe₃). Irrespective of the nature of the ligand L, these 1,3-dithiol-2-ylidenemanganese(I) complexes are stable towards isomerisation into heterometallocycles and exhibit low frequency carbonyl absorption bands in the infrared consistent with a strong electron releasing effect of the carbene ligand. The structure of Mn(CS₂C₂(CO₂Me)₂)(CO)(P(OMe)₃)(C₅H₅) has been determined by X-ray analysis of a suitable crystal. The molecule shows a carbene carbonmanganese bond C(7)Mn of length 1.876 Å and a planar carbene which does not adopt the 1,3-dithiolium aromatic-ring geometry but contains a carboncarbon double bond, C(8)C(9), of length of 1.341 Å. The CO₂Me groups are out of the plane of the carbene ligand and two positions with equal occupancy are found for each oxygen atom O(3) and O(5) belonging to the CO groups.     

Reactions of pentafluorosulfanyliminodihalosulfanes,SF5NSX2, with nucleophiles. Preparation and characterization of pentafluorosulfanylsulfinylamine,SF5NSO.

Reactions of SF₅NSF₂ with sodium alkoxides and aryloxides have produced both the mono- and disubstituted derivatives SF₅NS(F)OR and SF₅NS(OR)₂, where RCH₃, CH₂CHCH₂, C₆H₅, p-C₆H₄NO₂, p-C₆H₄Br, p-C₆H₄CN. The reaction of SF₅NSCl₂ with AgNCO produced SF₅NS(NCO)₂. This diisocyanate can also be prepared from the reaction of SF₅NSCl₂ with KOCN in liquid SO₂. The proposed intermediate, SF₅NSO, in the hydrolysis of SF₅NSF₂ was prepared from the low temperature reaction of SF₅NSCl₂ and Ag₂O in C₆H₅NO₂. The new pentafluorosulfanyl derivatives were characterized by IR, ¹H and ¹⁹F NMR, mass spectrometry and where possible ¹³C NMR and elemental analysis.     

The molecular structure of gaseous tetrachloro-p-benzoquinone and tetrachloro-o-benzoquinone by electron diffraction

The structures of tetrachloro-p-benzoquinone and tetrachloro-o-benzoquinone (p- and o-chloranil) have been investigated by gas electron diffraction. The ring distances are slightly larger and the carbonyl bonds slightly smaller than in the corresponding unsubstituted quinones. The molecules are planar to within experimental error, but small deviations from planarity such as those found for the para compound in the crystal are completely compatible with the data. Values for the geometrical parameters (r_a distances and bond angles) and for some of the more important amplitudes (l) with parenthesized uncertainties of 2σ including estimated systematic error and correlation effects are as follows. Tetrachloro-p-benzoquinone: D_2h symmetry (assumed); r(CO) = 1.216 Å(4), r(CC) = 1.353 Å(6), r(C-C) = 1.492 Å(3), r(C-Cl) = 1.701 Å(3), ∠C-C-C = 117.1° (7), ∠CC-C1 = 122.7° (2), l(CO)= 0.037 Å(5), l(CC) = l(C-C) - 0.008 Å(assumed) = 0.049 Å(7), and l(C-Cl) = 0.054 Å(3). Tetrachloro-o-benzoquinone: C_2v symmetry (assumed); r(CO) = 1.205 Å(5), r(CC) = 1.354 Å(9), r(C_cl-C_cl) = 1.478 Å(28), r(Co-C_cl) = 1.483 Å(24), r(C_o-C_o) = 1.526 Å(2), r(C-Cl)= 1.705 Å(3), <C_o-CO = 121.0° (22), ∠C-C-C = 117.2° (9), ∠C_co, ClC-Cl = 118.9° (22), ∠C_ccl, ClC-Cl = 122.2°(12), l(CO) = 0.039 Å(5), and l(C_cl-C_cl) = l(C_o-C_cl) = l( Co-Co) = l(CC) + 0.060 Å(equalities assumed) = 0.055 Å(9). Vibrational'shortenings (shrinkages) of a few of the long non-bond distances have also been measured.     

The gas-phase molecular structure of methyl formate,determined by electron diffraction

The structure of methyl formate in the gas phase has been reinvestigated by electron diffraction. The results confirm that the molecular skeleton is cis-planar, with bond lengths and angles in close agreement with those found by microwave techniques. Principal parameters (r_a) are: r(CO) 120.2(2) pm, r(C-O) 134.0(2), and 143.5(3) pm; ∠ (OC-O) 125.4(5)°, and ∠ (C-O-C) 115.9(5)°.     

Elucidating Interactions between DMSO and Chelate‐Based Ionic Liquids

The C?D bond stretching vibrations of deuterated dimethyl sulfoxide ([D₆]DMSO) and the C₂?H bond stretching vibrations of 1,1,1,5,5,5‐hexafluoropentane‐2,4‐dione (hfac) ligand in anion are chosen as probes to elucidate the solvent–solute interaction between chelate‐based ionic liquids (ILs) and DMSO by vibrational spectroscopic studies. The indirect effect from the interaction of the adjacent S=O functional group of DMSO with the cation [C₁₀mim]⁺ and anion [Mn(hfac)₃]^? of the ILs leads to the blue‐shift of the C?D stretching vibrations of DMSO. The C₂?H bond stretching vibrations in hfac ligand is closely related to the ionic hydrogen bond strength between the cation and anion of chelate‐based ILs. EPR studies reveal that the crystal field of the central metal is kept when the chelate‐based ILs are in different microstructure environment in the solution.     

Geometries and vibrational frequencies for silanone,silanoic acid and silicic acid

The geometries of silanone, H₂SiO, silanoic acid, (HO)HSiO, and silicic acid, (HO)₂SiO, have been calculated using gradient techniques with 3-21G and DZ + P basis sets. The SiO bond length is found not to be strongly dependent on the substitution of OH for H. Vibrational frequencies have been calculated by numerical differentiation of the gradient at the 3–21G level. Good agreement with experiment is found after uniform scaling. For the three compounds considered, the frequency for the SiO stretch is found to increase as OH is substituted for H, confirming the experimental result.     

Molecular structure of acetyldimethylphosphine,MeC(O)PMe2: I. Gas phase electron diffraction study

An electron diffraction study of the MeC(O)PMe₂ molecule has been carried out which shows that the bond configuration at phosphorus in this compound is flattened from that observed in methylphosphines and dimethylcyanophosphine. This finding, as well as some lowering of barriers to inversion at phosphorus in acylphosphines, may be attributed to a contribution from conjugation of the amide type.Two models with different angles of rotation of the acetyl group about the PC_Ac bond, ψ, are consistent with the experimental data, those with ψ of 5.7 ± 6.6° (model I) and 78.8± 12.0° (model II) (ψ is measured relative to the C_s conformation with the C_MePC_Me bisector being cis with respect to the CO bond). Other parameters of the two models agree within uncertainties represented by three times standard deviation values 3σ (distances, r_a, in nm; angles in degrees): model I model II PC (average) 0.1863(2) 0.1862(2) CC 0.1536(9) 0.1540(9) CO 0.1219(4) 0.1218(3) CH 0.1094(6) 0.1094(6) C_MePC_Me 105.7 (0.9) 105.1 (3.3) C_MePC_Me 99.3 (2.0) 102.2 (7.5) PCO 123.0 (0.6) 121.9 (0.6) PCC 115.3 (0.9) 112.7 (0.9) The greater errors for phosphorus valence angles and the angle of rotation, ψ, in the case of model II are due to high correlation between these para A possible difference between the PC_Me and PC_Ac bond lengths has been estimated to be. ± 0.001nm(model I) or ± 0.003 nm(model II). Neither of the models can be preferred on the basis of the electron diffraction data; the results'obtained are also compatible with' the suggestion of large amplitude torsion motions.     

Raman intensities of ethylene and deuterated derivatives in the gas phase

Experimental gas phase Raman scattering differential cross sections and depolarization ratios of ethylenes C₂H₄, C₂H₃D, C₂H₂D₂-a, C₂HD₃ and C₂D₄ are reported. An interpretation of these data is accomplished using the bond polarizability model. Within constraints imposed to the first order parameters, the CH bond polarizability derivatives here obtained compare quite well with the values reported for the same bond in other hydrocarbons. The CC bond electrooptical properties are found to be between those of the CC in ethane and CC in acetylene.     

On the effect of molecular structure on the superposition of normal modes of vibration

The normal modes of vibration in cartesian coordinates were calculated for ethylene, C₂H₄, and an ethylene complex, C₂H₄-Tl³⁺-H₂O, which is presumably formed during the catalytic oxidation of C₂H₄. For the CC bond of C₂H₄ as the critical coordinate of this reaction the distortions were then calculated which are caused by superimposing the normal modes. These calculations indicate that the maximum distortion of the CC bond which is attainable by superimposing normal modes in their ground state is larger in some conformations of the complex than in the free molecule. This indicates the general possibility that, depending on proper symmetry, complex formation may increase the reactivity of a compound because, compared to the free molecule, the superposition of a greater number of 3N-6 normal modes can produce greater momentary distortions of internal coordinates. The effect could be of considerable importance for the reactivity of very large systems, like, e.g., enzyme-substrate complexes.     

The geometry of small rings—V : Geometric variations and hybridization in three-membered heretocycles C2X (X=N,O, Si,P, S) and CXY (X,Y=N,O)

Structural data relating to 369 organic derivatives of C₂X(X=N, O, Si, P, S) and CXY(X, Y=N, O) heterocycles have been retrieved from the Cambridge Crystallogrphic Database and analysed in conjuction with pertinent gas-phase results. Heterocycle geometries are compared with each other, and with those for the ‘parent’ carbocycles cyclopropane and cyclopropene. For saturated C₂X rings the previously observed (gas phase) decrease in CC bond length (d_cc) and bent-back angle (γ) with increasing heteroatom electronegativity (χ_x) are confirmed as linear relationships using mean solid state geometry for X=C, N, O, S. The CX bonds shows an effective increase in length with increasing χ_x, in line with their facile cleavage in ring opening reactions. A model for hybridization changes at C in saturated C₂X rings is derived empirically and is in broad agreement with theoretical studies. There is no evidence for geometric variations in the heterocyclic rings induced by π-acceptor substituents, but π-donor substituent effects are directly comparable to those occurring in cyclopropane and cyclopropene. Geometric variations in unsaturated heterocycles are analogous to those in cyclopropene derivatives; CC double bond lengths in available C₂X systems appear to indicate a π_x dependence. Heteroatom-heteroatom bonds in CYX systems are weak, with N weaker than NN, in agreement with thermochemical reasoning.     

Komplexchemie reaktiver organischer verbindungen : XXXVII. Metallinduzierter abbau eines σ,π-koordinierten ketens in ein π-allyl/σ-aryl/π-olefin-system

Photolysis of diphenylketene in the presence of pentacarbonyliron yields the π-allyl/σ-acyl type compound [η³:η¹-(C₆H₅)₂CCO)Fe(CO)₃ (III) the molecular structure of which has been established by means of X-ray diffraction techniques. Metal-centered carboncarbon bond breaking and bond making in III is evident from ¹³CO labelling and crossover experiments. The dinuclear compound IV, structurally characterized by the π-allyl/σ-aryl/π-olefin hydrocarbon ligand CH(C₆H₄)C₆H₅, is formed upon irreversible decarbonylation of the ketene precursor III.