Vibrational spectrum and force field of trimethyl- methoxysilane

The IR and Raman spectra of (CH₃)₃SiOCH₃, (CH₃)₃SiOCD₃, (CD₃)₃SiOCH₃ and (CD₃)₃ SiOCD₃ are presented together with results of normal coordinate calculations. Numerical values of certain force constants and effects of mechanical coupling between Si-O-C bridge vibrations and some of internal vibrations of (CH₃)₃Si and OCH₃ groups are briefly discussed.     

Molecular mechanics calculations for conformational energies and torional force constants in fluoro propenes and butenes

Experimental data on conformational energies of the molecules FH₂CHCCH₂, FH₂CFCCH₂, FH₂C(CH₃)C&.dbnd;CH₂ trans-FH₂CHCC(CH₃)H have been used to establish parameter values for the nonbonding atom ⋯ atom interaction F ⋯ C(sp²) within the Morse potential formulation. Torsional potentials have been calculated for the four molecules mentioned above and in addition for cis- and trans-FH₂CHCCHF, (FH₂C)₂CCH₂, cis-FH₂CHCCHCH₂F, CH₃FCHHCCH₂ and FH₂CCH₂HCCH₂. Calculated results have been compared with experimental values. Torsional force constants for the molecules have been obtained. A comparison between fluoro, chloro and bromo compounds is presented.     

Schwingungsverhalten des syn- und anti-acetaldoxims: 1. Mitt. Schwingungsspektren

The infrared spectra of CH₃CHNOH, CH₃CHNOD, CH₃CDNOD and CD₃CDNOD have been recorded and studied. On the basis of the symmetry properties the normal vibrations were assigned by comparison.     

Infrarot-und Raman-Spektren von unvollständig und vollständig deuterierten Tetramethyl-Verbindungen (CH3) n M(CD3)4-n der ElementeM=Si,Ge, Sn und Pb

The infrared andRaman spectra of theM(CH₃)₄ andM(CD₃)₄ species,M=Si, Ge, Sn and Pb, have been reinvestigated. The spectra of the mixed tetramethyl compounds (CH₃)₃ MCD₃,M=Si, Ge, Sn and Pb, and of (CH₃)₂Si(CD₃)₂ and CH₃Si(CD₃)₃ have been recorded in the gaseous (i.r.) and liquid states (Raman). The proposed assignment is supported by a normal coordinate analysis.

     

Schwingungsverhalten des syn- und anti-acetaldoxims: 2. Mitt. normalkoordinatenbehandlung

Normal coordinate calculations on CH₃CHNOH, CH₃CHNOD, CH₃CDNOD and CD₃CDNOD have been carried out applying the general harmonic valence force field. The calculated frequencies of the normal vibrations considered agree satisfactorily with the corresponding values obtained from the spectra. The potential energy distributions have also been calculated; they were used to interpret the behaviour of characteristic vibrations.     

Synthesis and X-ray structure of two isomeric aminocarbene complexes of tungsten containing a free carbon-carbon double bond

The reaction of allylamine with (CO)₅WC(OCH₂CH₃)CH₃ gives two isomeric aminocarbene complexes (CO)₅WC(NHCH₂CHCH₂)CH₃ 2E and 2Z. Refluxing of a solution of this mixture in benzene gives the complexes (CO)₄WC(η²NHCH₂CHCH₂)CH₂ (3) and 2E, which have been separated. 2E was fully characterized by X-ray diffraction. Crystals of 2E are monoclinic, space group P2₁/n with Z = 4, a 7.188(3), b 14.312(2), c 12.530(2) Å and β 91.06(3)°.The same mixture when treated with lithium diisopropylamide (LDA) followed by allyl bromide gives a mixture of (CO)₅WC(N(CH₂CHCH₂)₂)CH₃ (4) and 2Z. These complexes were separated, and 2Z fully characterized by X-ray diffraction. Crystals of 2Z are monoclinic, space group P2₁/c, with Z = 4, a 6.593(5), b 14.584(3), c 13.323(1) Å and β 95.13(4)°.     

Allylbutyltin halides (CH2CHCH2)SnBu3−nCln (n = 0, 1, 2, 3). Preparation,carbon-13 NMR characterization and allylstannylation ability towards ketones and aldehydes

Mixed allylbutyltin halides (CH₂CHCH₂)SnBu_3-nCl_n (n = 0–3) have been prepared, and characterized by carbon-13 NMR spectroscopy. Their ability to bring about allylstannylation of ketones and aldehydes, to form organostannoxy compounds, Bu_3-nSnCl_nOC(R′)(R″)CH₂CHCH₂, has been shown to increase on increasing the value of n, that is on increasing the acceptor ability of the tin centre.     

Direct spectroscopic study of silaolefins,Ar-matrix stabilization and IR spectrum of 1,1-dimethyl-1-silaethylene-d3

The IR spectrum of 1-methyl, 1-trideuteromethyl-1-silaethylene, CH₃(CD₃)-SiCH₂, formed in the gas phase by vacuum pyrolysis of the corresponding morosilacyclobutane has been recorded in an argon matrix at 10 K. The attribution of the spectral bands to the unstable species was carried out using the dependence of the spectra on temperature and pressure in the pyrolysis zone or on the matrix temperature. A possible assignment of some bands to the ν(SiC) and ρ(CH₂) vibrations is discussed.     

Some novel oxime ethers. The synthesis of 1,1-difluoro-2-alkoxymethanimines

The syntheses of four novel 1,1-difluoro-2-alkoxymethanimines, RONCF₂, are reported. The oxime ethers are prepared in excellent yield by dehydrofluorination of the amines, RON(H)CF₃ (RCF₃, (CF₃)₂CF, CH₃, (CH₃)₃C) with KF. These oxime ethers are thermally stable at 24°C and are characterized by IR, NMR, and physical properties. The two perfluoro compounds undergo dimerization to give CF₃N(OR)CFNOR in the presence of CsF at room temperature.     

The molecular structures of cis-3-hexene and trans-3-hexene in the gas phase by electron diffraction and molecular mechanical calculations

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 r_α⁰-structural parameters are: cis-3-hexene: C-H = 1.073 Å, CC = 1.330 Å, C(sp²)-C(sp³) = 1.505 Å, ∠CCH(in CH₂) = 111.1°, ∠CCC = 111.4°, ∠(CC-C) = 129.1° trans-3-hexene: C-H = 1.078 Å, CC = 1.342 Å, C(sp²)-C(sp³) = 1.506 Å, ∠CCH(in CH₂) = 109.3°, ∠CCC = 112.8, ∠CC—C = 124.1°The agreement between calculated and experimental geometries and vibrational amplitudes is good.     

Microwave spectrum,structure and dipole moment of trimethylamine-borane

The ground state rotational spectra often isotopic species of trimethylamineborane, (CH₃)₃N¹⁰BH₃, (CH₃)₃N¹¹BH₃, (CH₃)₃N¹⁰BD₃, (CH₃)₃N¹¹BD₃, (CH₃)₃N¹¹BD₂H, (CD₃)₃N¹⁰BH₃, (CD₃)₃N¹¹BH₃, (CD₃)₃N¹⁰BD₃, (CD₃)₃N¹¹BD₃ and (¹³CH₃)(¹²CH₃)₂N¹¹BH₃, have been measured and the effective moments of inertia obtained. The utilization of Kraitchman's equations leads to an r_s value of the B-H distance of 1.211±0.003 Å and a NBH angle of 105.32±0.16°. By a least squares fit of the rotational constants the following structural parameters were obtained: r(NC) = 1.495 Å, r(BN) = 1.609 Å, and ∠BNC = 110.9°. The value of the dipole moment was found to be 4.59±0.13 D. A lower limit to the barrier to internal rotation of the BH₃ group was determined to be 3.4 kcal/mole.     

Reactivity of hypervalent species of silicon: cleavage of the allyl-silicon bond

The reactivities of the silicon-allyl bonds in two kinds of pentacoordinated silicon species CH₂CHCH₂Si(o-O₂C₆H₄)₂ ⁻NMe₄⁺ (1) and CH₂CHCH₂- Si(OCH₂CH₂)₃N (2) has been compared. In the allyl transfer to carbonyl compounds under nucleophilic conditions (NaOMe, KF or Bu₄NF) and electrophilic conditions (TiCl₄, AlCl₃, BF₃) these two species show quite different behaviour. Complex 1 is activated by nucleophiles, while for 2 transfer occurs under electrophilic conditions. These results indicate that the reactivity of these species is a function of their overall charge and geometry.     

Electronic effect of η5-cyclopentadienyl and η3-allyl ligands on the nature of the metal—olefin bond: Reversal of the relative olefin affinity of palladium(II) and platinum(II) ions

The barrier to olefin rotation in [Pt(η³-CH₂CMeCH₂)(olefin)(PPh₃)]PF₆ (3) (olefin = CH₂CH₂, E-MeCHCHMe) has been found to be extremely low compared to those in the other known, 4-coordinate olefin complexes of Pt^II. This can be ascribed to the smaller steric congestion around the olefin in 3. The corresponding barrier in [Pt(η⁵-C₅H₅)(CH₂CH₂)(PPh₃]ClO₄ (2), possessing likewise small steric congestion, was substantially higher than that in 3 (olefin = CH₂CH₂). The ¹³C and ³¹P NMR measurements have revealed much larger J(Pt-C(olefin)) in 2 than that in 3 (olefin = CH₂CH₂), while J(Pt-P) are comparable in these two. Stability constant data suggested that Pd^II ion in the Pd(η⁵-C₅H₅)(PPh₃)⁺ moiety is a better π-donor to olefins than Pt^II ion in the Pt(η³-CH₂CMeCH₂)(PPh₃)⁺ moiety, a reversal of the normal trend in the relative olefin affinity of these metal ions. The above spectral and stability features have been related to the electronic effect of the Cp ligand in enhancing the π back-bond interaction in one particular orientation of the CC bond.     

Reactions of perfluoronitriles. II. Interactions with phenylphosphine

Treatment of perfluoro-n-octanonitrile with phenylphosphine gave tetraphenyltetraphosphine and a spectrum of reduction and interaction products. Fifteen compounds were identified. The imine, (R_fC₇F₁₅) R_fCHNH, and the amine, R_fCH₂NH₂, were the primary reduction products. Secondary phosphorus-free products, some formed following ammonia evolution, were the following: R_fCHNCH₂R_f, R_fCH₂CH(NH₂)R_f, R_fC(NH)NCR_f(NH₂), R_fCH₂NHCR_f(NH), (R_fCN)₃, R_fCHNCR_fNCR_f(NH), R_fCH₂NCR_fNHCH₂R_f, and R_fCH₂NCR_fNHCR_f(NH). Only three phosphorus-containing materials were definitely identified: R_fCH(NH₂)P(C₆H₅)H, R_fCH[P(C₆H₅)H]NCHR_f, and R_fC(NH)P(C₆H₅)CR_f(NH). Depending on reaction conditions, specific phosphorus-containing compounds could be preferentially produced. All the structure assignments are based solely on mass spectral breakdown patterns, since pure compounds were not isolated.     

Etude vibrationnelle du composé partiellement deutérié pur Br(CO)4CrCCHD2 et détermination du champ de force des complexes carbyniques de la famille Br(CO)4CrCR (RCH3, CH2D,CHD2 et CD3)

Raman and infrared spectroscopic studies of Br(CO)₄CrCCHD₂ allowed a precise assignment of the vibrational frequencies and we confirmed the assignment of the vibrational frequencies of the Br(CO)₄CrCR (RCH₃, CH₂D, CHD₂ and CD₃) series. The force field of the Br(CO)₄CrCR series was determined by a Normal Coordinates Analysis.     

Regioselective anion generation and alkylation at carbon α to nitrogen in (CO)5WC[N(CH3)2]C6H4-p-CH3

Treatment of (CO)₅WC[N(CH₃)₂]C₆H₄-p-CH₃ (1) with lithium diisopropylamide (LDA) in THF at −78°C followed by quenching with D₂O leads to incorporation of deuterium into the (E)-N-methyl group only. Reaction of the anion of 1 with benzyl bromide at −78°C followed by quenching with water gave the E-isomer of (CO)₅WC[N(CH₃)CH₂CH₂C₆H₅]C₆H₄-p-CH₃ (2E, 26%) and recovered 1. When a mixture of the anion of 1 and benzyl bromide was warmed from −78°C to ambient temperature, a mixture of the E-isomer of the dibenzylated product (CO)₅WC[N(CH₃)CH(CH₂C₆H₅)₂]C₆H₄-p-CH was obtained. Reaction of the anion of 1 with allyl bromide gave (CO)₅WC[N(CH₃)CH₂CH₂CHCH₂]C₆H₄-p-CH₃ (5, 38%) and with methyl iodide gave a mixture of (CO)₅WC[N(CH₃)CH₂CH₃]C₆H₄-p-CH₃ (6, 7%) and (CO)₅W C[N(CH₃)CH(CH₃)₂]C₆H₄-p-CH₃ (7, 16%).     

Spectra and structure of organophosphorus compounds—XXVIII. Vibrational and conformational analysis of dimethylmethoxyphosphine and some isotopically substituted derivatives

The i.r. spectra (3600-50 cm⁻¹) of the gaseous and solid states, and the Raman spectra (3600-10 cm⁻¹) of the gaseous, liquid and solid states of (CH₃)₂POCH₃, (CH₃)₂POCD₃, (CD₃)₂POCH₃ and (CD₃)₂POCD₃ have been recorded. Thirty-five of the 36 normal modes have been assigned and the asymmetric torsion has been observed as a broad weak feature centered at 106 cm⁻¹ in the far i.r. spectrum of gaseous (CH₃)₂POCH₃. A comparison of the vibrational spectra obtained for the fluid phases with those obtained for the amorphous and annealed solids indicates the existence of a second conformer present in a small amount in the gas phase but becoming more abundant in the liquid phase and the only remaining rotamer in the annealed solid. Asymmetric top i.r. band contour simulation provides evidence that the dominating species in the gas phase is one in which the methoxy methyl group is oriented approximately 60° (gauche) away from the lone pair of electrons on the phosphorus atom. The rotamer which remains in the spectra of the annealed solid has been assigned to a structure in which the lone pair on the phosphorus atom is oriented trans to the methoxy methyl group. These results are compared to similar data obtained for methoxy phosphoryl compounds and discussed in terms of both canonical molecular orbital and VSEPR thoery.     

On the transferability of conformation in FC(O)S-containing compounds: Conformation and properties of methylfluorocarbonyl disulphide FC(O)SSCH3

Methylfluorocarbonyl disulphide, FC(O)SSCH₃, was prepared for the first time by reaction of FC(O)SCl with CH₃SH at room temperature. Infrared data for the vapour and matrices (Ar, Ne and N₂) as well as Raman, UV, mass and ¹⁹F, ¹³C and ¹H NMR spectra have been obtained and interpreted.From these data, the most stable conformer was deduced to have the gauche conformation with respect to the FC(O) and CH₃ groups with the syn conformation between the CO and SS bonds having C₁ molecular symmetry. This conformer is in equilibrium with another, possibly the corresponding anti, referring to the CO and SS bonds.The main structure found for FC(O)S-containing compounds seems to be the syn conformation.     

Übergangsmetall—methylen-komplexe: LIX. Ein neues darstellungsverfahren für vinyliden-komplexe

The diazo olefins N₂CCR₂ (R/R = CH₃/CH₃ and (CH₂)₅, respectively), generated in situ from the corresponding cyclic N-nitrosourethanes 2a, 2b, are suitable precursors for the corresponding vinylidene ligands 6CCR₂. Thus, treatment of the RhRh complex [(η⁵-C₅Me₅)Rh(μ-CO)]₂ (1) with 2a, 2b in the presence of lithium ethoxide yields the otherwise inaccessible μ-vinylidene complexes (μ-CCR₂)[(η⁵-C₅Me₅)Rh(CO)]₂ (3a, 3b). This procedure extends the well-documented diazoalkane method for synthesis of μ-alkylidene complexes to the less stable diazoalkenes*