Selenoketene substitution structure

Microwave studies (26.5–40 GHz) of further isotopic species of selenoketene formed by pyrolysis of 1,2,3-selenodiazole (¹²CH₂¹²C^76,77,82Se, ¹²CH₂¹³C⁸⁰Se and ¹³CH₂¹²C⁸⁰Se) and by pyrolysis of 5-deuterio-1,2,3-selenodiazole (¹²CHD¹²C^78,80Se) are reported. In conjunction with earlier results for ¹²CH¹²C^78,80Se an r_s structure has been derived with distances SeC (1.706 Å), CC (1.303 Å), CH (1.0908 A) and a HCH bond angle of 119.7°. The geometry of the CH₂C moiety of selenoketene is closer to allene, CH₂CCH₂, than to ketene, CH₂CO.     

Selenirene as an intermediate in the pyrolysis of 1,2,3-selenadiazole. Microwave spectra of 13C labelled selenoketene

Microwave Spectra of ¹³CH₂¹²C^80,78Se and ¹²CH₂¹³C^80,78Se (selenoketene) are recorded. B 5-¹³C-1,2,3-selenadiazole all four species are formed. The ¹³C scrambling may take place via a three-membered ring, selenirene, but as expected its microwave spectrum was not observed.     

3,3′‐Seleno­bis­(propionic acid)

In contrast to Se[CH₂C(O)OH]₂versus S[CH₂C(O)OH]₂, the title compound, Se[CH₂CH₂C(O)OH]₂ or C₆H₁₀O₄Se, is structurally quite similar to its sulfur analogue. The mol­ecule has twofold symmetry. The C—Se—C bond angle is 96.48 (8)° and the Se—C bond lengths are 1.9610 (14) Å. The shortest Se?O intermolecular distance is 3.5410 (11) Å. The O?O distances in the carboxyl­ic acid dimers are 2.684 (2) Å. The temperature dependence of the IR spectrum suggests tautomerism in the solid state.     

Structure, 31P and 13C chemical shift anisotrophy of (CH3)3P, (CH3)3PO, (CH3)3PS and (CH3)3PSe as determined by liquid crystal NMR spectroscopy

The ¹³P and ¹³C spectra of the triply ¹³C labelled molecules (CH₃)₃P, (CH₃)₃PO, (CH₃)₃PS and (CH₃)₃PSe oriented in a nematic phase are reported. The CPC bond angles have been measured. The ¹³P chemical shift tensor shows a large anisotropy except in the case of (CH₃)₃P. The abnormal large value observed for the PSe bond length suggests a large anisotropy of the ¹J(PSe) spin coupling.     

Cinetique et mecanisme de la reaction de prototropie des composes propargyliques alleniques et propynyliques portant un heteroatome (colonne vb et vib)

A detailed kinetic study of the prototropic rearrangement of the system RMCH₂CCH?RMCHCCH₂?RMCCCH₃ where M = NR, O, Se is presented. using deuterated substrates the nature of the reactive intermediates and, in the case of M = S, the activation energy-reaction profile are established.     

Automatic assignment of 13C NMR signals based on the Karplus-Pople equation

A modified version of the method of automatic assignment of ¹³C NMR spectra, based on the Karplus-Pople equation is applied to six substituted benzenes. The results are the same as in the case of simple ¹³C chemical shift/charge density linear relationship previously used: -XR substituted aryls (XO, RH, CH₃, CH₂CH₂OH) yield good correlation and correct automatic assignment, while -CH₂CH₂Y substituents (YH, OH, NH₂) yield poor correlation and incorrect assignment.     

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.     

Platinumolefin bond strength in Pt(PPh3)2(CH2CH2) and Pt(PPh3)2 {C(CN)2C(CN)2}

The enthalpy of the reaction: Pt(PPh₃)₂ (CH₂CH₂)(cryst.) + C(CN)₂C(CN)₂ (g) → Pt(PPh₃)₂ {C(CN)₂C(CN)₂}(cryst.) + CH₂ CH₂ (g) has been determined as ΔH₂₉₈=?155.8±8.0 kJ·mol^?1, from solution calorimetry. The interpretation, that the platinumethylene bond is much weaker than the platinumtetracyanoethylene bond, is contrary to conclusions drawn recently from electron emission spectroscopic studies, but in agreement with available structural data.     

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.     

Insertion d'une phosphine acétylénique dans un complexe μ-alkylidénique du tungstène suivie de la rupture d'une liaison CP

The diphosphinoalkyne Ph₂PCCPPh₂ (2) reacts with the μ-alkylidene complex (CO)₉W₂[CHCHC(CH₃)₂] (1) to give, upon insertion of the alkyne into one of the CW bonds of the bridging carbene followed by rupture of a CP bond, a phosphido complex (CO)₈W₂[C(PPh₂)CCHCHC(CH₃)₂] PPh₂ (3). An unexpected long-range ¹H³¹P coupling, through five bonds, is observed in complex 3.     

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)°.     

Synthesis and x-ray structures of some homonuclear μ-alkylidenetungsten complexes

The complexes W₂{μ-CHCHC(CH₃)₂](CO)₁₀} and W₂{μ-CHCHC(CH₃)(CH₂)₃CH₃][(CO)₁₀} have been synthesized, and an X-ray diffraction study has revealed the presence of five CO groups on each metal center. The analogy between W₂{μ-CHCHC(CH₃)₂][(CO)₉]} anda complex of W(CO)₄ and a tungstabutadiene (CO)₅WCHCHC(CCH₃)₂ prompted the synthesis of the first heteroatom-substitued μ-alkylidene complexes of tungsten, starting from conjugated Fischer-typ carbene complexes (CO)₅WC(OR)CHCHR. The X-ray structure of the complex W₂{μ-C(OEt)CHCH(CH₃)][(CO)₉]} has also been determined. In the case of the simplest conjugated compelx (CO)₅WC(OR)CHCH₂, an interesting rearrangement initiated by addition of W(CO)₅ to the terminal CC double bond giving a dinuclear complex W(CO)₅[η²-CH₂CHC(OMe)W(CO)₅] in which the two metal centers are not directly linked, has been observed.     

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.     

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.     

Carbon-13-nuclear magnetic resonance spectra of 5-coordinate tris-olefin complexes of rhodium(I)

Studies of the ¹³C N.M.R. spectra of the series RhX[P(Ch₂CH₂CHCH₂)₃] and RhX[P(CH₂CH₂CH₂CHCH₂)₃] where x  Cl or Br have revealed that (a) the J(¹⁰³Rh-¹³C) (olefin) for the complexes studied is only $\text{1}\text{2}$ ? $\text{1}\text{3}$ that found for square-planar complexes, and (b) the fluxional character in the olefinic carbons observed for the compounds RhX[P(CH₂CH₂CHCH₂)₃] is related to the partial rotation of the olefin about the rhodium-olefin bond.     

Studies on vinyl isocyanides

The vinyl Isocyanides 2,4,6-(CH₃)₃C₆H₂CHCHNC and (CH₃)₃CCHCHNC and the new 1,3-dienyl isocyanide CH₃CHCH(CH₃)-CHCHNC have been prepared from the corresponding aldehydes and methyl isocyanide using a method first developed by Schöllkopf, Stafforst, and Jentsch. ⁵ The new vinyl isocyanides (CH₃)₂CCHNC and CH₃CHC(CH₃)NC have been prepared by the Cu₂O-catalyzed isomerization of the corresponding allyl isocyanides The liquid vinyl isocyanides may be characterized by the formation of solid cis-(RNC)₂Mo(CO)₄ derivatives through reaction with norbornadienetetracarbonylmolybdenum in hexane solution at ambient temperature. Examination of these molybdenum carbonyl complexes by proton and carbon-13 NMR spectroscopy Indicates that the isocyanide carbon atom but not the carbon-carbon double bond of the vinyl 1socyanide ligands is bonded to the molybdenum atom. The proton-decoupled carbon-13 NMR spectra of the vinyl isocyanides, but not their molybdenum carbonyl complexes, indicate coupling of the isocyanide nitrogen to both the isocyanide carbon (¹J(C-N)6 Hz. ) and the vinyl carbon bearing the isocyanide group (¹J(C-N)11-13 Hz. ) leading to 1:1:1 triplets for these resonances. These vinyl carbonyl resonances are used to estimate the cis-trans isomer ratios in vinyl isocyanides of the type RCHCHNC. Such studies suggest that the formation of vinyl isocyanides by the copper(I) catalyzed isomerization of the corresponding allylic isocyanides is more nearly stereospecific than the formation of vinyl isocyanides by the elimination reaction of the Schollkopf/Stafforst/Jentsch synthetic method.     

Synthesis and proposed conformations of l-prolyl-l-leucyl-β-alanine alkylamides

The synthesis of H-Pro-Leu-β-Ala-NH₂, H-Pro-Leu-β-Ala-NHCH₃ and H-Pro-Leu-β-Ala-N(CH₃)₂ is described. On the basis of IR and ¹H NMR spectral data, a 7-membered ring including the NH of β-alanine with the CO of proline should be assigned for the H-Pro-Leu-β-Ala-N(CH₃)₂. Consequently, the plausible conformations for H-Pro-Leu-β-Ala-NH₂ and H-Pro-Leu-β-Ala-NHCH₃ derive from the formation of an 11-membered ring, between the trans amide proton and the CO of Pro, or from the formation of an 8-membered ring, between this carboxamide proton and the CO of Leu, plus the aforementioned 7-membered ring.     

Cleavage of iron2-alkenyl and iron2-alkynyl bonds by mercury(II) chloride

Reactions of HgCl₂ with η⁵-C₅H₅Fe(CO)₂R (R  CH₂CHCH₂ and CH₂C(CH₃)CH₂) in THF at 25°C rapidly afford $\text{1}\text{1}$ adducts of the two reactants. These adducts were converted to the corresponding PF₆^? salts, [η⁵-C₅H₅Fe(CO)₂(η²-CH₂C(R)CH₂HgCl)]⁺ PF₆^? (R  H and CH₃), for characterization. Slower reactions with cleavage of the ironcarbon σ bond and elimination of the R group from η⁵-C₅H₅Fe(CO)₂R occur for R  CH₂CHC(CH₃)₂, CH₂CHCHC₆H₅, and CH₂CCC₆H₅. Both elimination and $\text{1}\text{1}$ adduct formation are observed when R  CH₂CHCHCH₃. The kinetics of the cleavage reactions are presented and possible mechanisms for both cleavage and $\text{1}\text{1}$ adduct formation are discussed.     

Dialkylmetallhydroxamate-monomere metallorganische fünfringmoleküle des galliums,indiums und thalliums

The reaction of HON(CH₃)C(O)CH₃ with the trialkyl derivatives of gallium, indium and thallium yields dialkylmetal hydroxamates. The IR-, Raman and ¹H NMR-spectra of these monomeric products with five-membered ringskeletons are discussed. ab]Die Trialkyle des Galliums, Indiums und Thalliums reagieren mit HON(CH₃)C(O)CH₃ unter Bildung von Dialkylmetallhydroxamaten. Die IR-, Raman- und ¹H- NMR-Spektren dieser monomeren Fünfringmoleküle werden diskutiert.     

A re-investigation of the molecular structure of trifluoroacetic acid by means of gas phase electron diffraction

Analysis of the electron diffraction patterns of trifluoroacetic acid at 140°C indicates the existence of one conformation with the CF₃-group rotated 17.3± 0.9° from a position with a fluorine atom eclipsed with respect to the CO bond. The data does not exclude the possibility of free internal rotation but it seems improbable.The important bond lengths, r_g(1), and bond angles with their standard deviations in parentheses, are: C-F: 1.325 (0.003), C-C: 1.546 (0.005), CO: 1.192 (0.003), C-O: 1.353 (0.014) Å, C-C-F: 109.5 (0.3), C-CO: 126.8 (0.8), C-C-O: 111.1 (0.9)°.