Crystal structures of chloro-, bromo-, and nitro-substituted chromium(III) acetylacetonates

The molecular and crystal structures of chlorine-, bromine-, and nitro-substituted chromium(III) acetylacetonate are determined. Connecting the substituent to the central atom does not change bond lengths and valence angles in metal chelate rings. Studied chromium complexes are characterized by greater intermolecular interactions compared with analogous metal acetylacetonates. In some cases, intermolecular interactions increase the bend of chelate rings along the O?O line. Substituents do not interact with chromium ions of neighboring molecules because metal is blocked by three ligands.     

Mass spectra of chloro-, aminochloro- and ethylaminochloro-s-triazines

The mass spectra of cyanuric chloride and all of the possible amino-and ethylaminochloro-s-triazines have been investigated. The simpler compounds provide evidence for the structures of low mass fragment ions found in the spectra of the more complex derivatives. Fragmentation patterns are presented which account for most of the major ions. These pathways involve either the initial loss of a chlorine atom (important for the simple aminochlorotriazines) or ring cleavage with expulsion of cyanogen chloride (important for cyanuric chloride). The ethyl derivatives undergo cleavage of the side chain prior to either ring cleavage or chlorine expulsion.     

Vibrational spectra of bromo- and chloro-fluorotriphosphazenes

Infrared and Raman spectra have been obtained for the nongeminally substituted mixed halides N₃P₃Br_nF_6-n, and N₃P₃Cl_nF_6-n using the pure cis or trans isomers for n = 2 and 3, but isomer mixtures when n = 4. The spectra are compared with those for the corresponding geminally substituted compounds and by comparison with data for the homogeneously substituted hexahalides the bands between 1300 cm⁻¹ and 150 cm⁻¹ are tentatively assigned.     

A photoelectron study (HeI,HeII) of the tautomeric equilibrium of chloro- and bromo-1,2,4-triazoles

Photoelectron spectroscopy HeI,HeII and quantum mechanical calculations (STO-3G) were used to analyze the electronic structure of tautomers of 1,2,4-triazole and its halogenated derivatives.The photoelectron spectra of the title compounds compared to those of fixed structure models demonstrated that 3-chloro and 5-bromo-1,2,4-(1H)-triazole exist in the vapor phase.     

Microwave spectra of isotopic pyrazoles and molecular structure of pyrazole

Microwave spectra of the complete set of monosubstituted isotopic pyrazoles have been investigated and the complete r_s structure of pyrazole determined. The deuterated and ¹⁵N species of pyrazole were prepared, while the ¹³C species were examined in natural abundance. The spectrum of the parent compound was remeasured yielding rotational and centrifugal distortion constants.The mutual position of the hydrogen atoms and the direction of the dipole moment in the pyrazole principal axis system has been unambiguously established.The ¹⁴N quadrupole hyperfine structure was resolved and the quadrupole coupling constants derived by Blackman et al. [8] were confirmed.An estimated r_z structure is compared to crystal structures derived by X-ray and neutron diffraction showing the N-H bond in the crystal to be prolonged. But, otherwise no significant differences seem to develop when bringing the molecule from its isolated state into the crystal with its strong hydrogen bonds.     

Stereochemical course of the enzymic amination of chloro- and bromo- fumaric acid by 3-methylaspartate ammonia-lyase

Enzymic amination of chloro- and bromo- fumaric acid using 3-methylaspartate ammonia-lyase in the presence of ammonia leads to the formation of 3-chloro- and 3-bromo-aspartic acid respectively; the absolute configuration of each product is (R) at C-2 and (S) at C-3.     

Microwave spectra of isotopic glycolaldehydes,substitution structure,intramolecular hydrogen bond and dipole moment

The microwave spectra of ¹³CH₂OH-CHO, CH₂OH-¹³CHO, and CH₂OH-CH¹⁸O are reported and have been used in combination with previously published data on other monosubstituted glycolaldehydes to determine the substitution structure of the molecule as r(CO) = 1.209 Å, r(C-O) = 1.437 Å, r(C-C) = 1.499 Å, r(O-H) = 1.051 Å, r(C-H_ald) = 1.102 Å, r(C-H_alc) = 1.093 Å, r(O β H) = 2.007 Å, r(O β O) = 2.697 Å, ∠(C-CO) = 122°44', ∠(C-C-H_ald) = 115°16', ∠(C-C-O) = 111°28', ∠(C-O-H) = 101°34', ∠(C-C-H_alc) = 109°13', ∠(H-C-H) = 107°34', ∠(O-H β O) = 120°33', ∠(H β OC) = 83°41', and ∠(O-H, C0) = 24°14'. The intramolecular hydrogen bond and the other structural parameters are discussed and compared to related molecules. The dipole moment is redetermined to be μ_a = 0.262 ±0.002 D, μ_b = 2.33 ± 0.01 D, and μ_tot = 2.34 ± 0.01 D. Relative intensity measurements yielded 195 ± 30 cm^?1 for the C-C torsional fundamental and 260±40 cm^?1 for the lowest in-plane skeletal bending mode. Computations performed by the CNDO/2 method correctly predict the observed cis hydrogen-bonded conformer to be the energetically favoured one and in addition yield some indication of the existence of at least two other non-hydrogen-bonded forms of higher energy.     

Molecular structure and vibrational spectra of trimethylarsenite

The molecular structure and vibrational spectra of trimethylarsenite were studied by gas phase electron diffractometry and IR and Raman spectroscopv. The configuration of the O-methyl groups with respect to the lone electron pair of the arsenic atom is established to be close to gosh-gosh-trans. The main geometrical parameters are: bond lengths (r_a, Å) As-O 1.780, C-0 1.451, and C-H 1.101; bond angles (deg) As-O-C 115.0, O-As-0 99.5, and O-C-H 115.3. The experimental IR and Raman spectra were obtained for pure liquid and CCl₄ solution. The frequencies and forms of normal vibrations were calculated.     

Rotational spectra of rare isotopic species of bromofluoromethane: determination of the equilibrium structure from ab initio calculations and microwave spectroscopy

Guided by theoretical predictions, the rotational spectra of the mono- and bideuterated species of bromofluoromethane, CDH(79)BrF, CDH(81)BrF, CD(2) (79)BrF, and CD(2) (81)BrF, have been recorded for the first time. Assignment of a few hundred rotational transitions led to the accurate determination of the ground-state rotational constants, all of the quartic and most of the sextic centrifugal distortion constants, as well as the full bromine quadrupole-coupling tensor for both (79)Br and (81)Br, in good agreement with corresponding theoretical predictions based on high-level coupled-cluster calculations. The rotational spectra of the (13)C containing species (13)CH(2) (79)BrF and (13)CH(2) (81)BrF have been observed in natural abundance and have been assigned, thus allowing the determination of the rotational and centrifugal distortion constants as well as the bromine quadrupole-coupling tensor. Furthermore, empirical equilibrium structures have been obtained within a least-squares fit procedure using the available experimental ground-state rotational constants for various isotopic species. Vibrational effects have been accounted for in the analysis using vibration-rotation interaction constants derived from anharmonic force fields computed at the second-order Moller-Plesset perturbation theory as well as coupled-cluster (CC) levels. The empirical equilibrium geometries obtained in this way agree well with the corresponding theoretical predictions obtained from CC calculations [at the CCSD(T) level] after extrapolation to the complete basis set limit and inclusion of core-valence correlation corrections and relativistic effects.     

The microwave and infrared spectra and structure of hydrothiophosphoryl difluoride

The microwave spectra of ³²SPHF₂, ³⁴SPHF₂ and ³²SPDF₂ have been analyzed. The structural parameters obtained from this analysis are: d(S-P) = 1.867±0.005Å, d(P-F) = 1.551 ±0.005Å, (P-H) = 1.392±0.005Å, ∠SPF = 117.4 ± 0.2 °, ∠SPH = 119.2±0.2 °, ∠FPF = 98.6±0.2 °. Centrifugal distortion coefficients were obtained for ³²SPHF₂. The spectra of two vibrational excited states of ³²SPHF₂ were observed. The two sets of rotational constants (A) 8336.72, 3726.70, 2807.56 MHz and (B) 8344.88, 3727.73, 2798.75 MHz were associated with the vibrational states with measured infrared frequencies 419 cm^?1 and 344 cm^?1 respectively. An analysis of the infrared spectrum is included. Dipole moment measurements yielded μ = 1.87±0.03 D for ³²SPHF₂ and μ = 1.86±0.03 D for ³²SPDF₂     

The reductions of chloro-, bromo- and iodopentacyanocobaltate(III) anions by titanium(III) in aqueous acidic solution

Summary The reduction of chloro-, bromo- and iodopentacyanocobaltate(III) anions by aquatitanium(III) has been studied in aqueous solution with ionic strength, I = 1.0 mol dm^-3 (LiCl, KBr or KI) at T = 25 °C. The dependence of the observed second-order rate constant, k _obs, on [H⁺] has been investigated over the acid range 0.005–0.100 mol dm ^–3 and is of the general limiting form: k _obs k ₀ + k[H ⁺] ^–1, where k ₀ is appreciable in all cases and k is a composite rate constant. Using values of K _a (associated with the Ti^III hydrolytic equilibrium constant), obtained from the kinetic data for the Ti^III/Co^III redox reactions, and comparison of the rate constants obtained with those for the corresponding V^II reductions of the same Co^III complexes, it is concluded that the Ti^III reductions of these halopentacyanocobaltate(III) complexes proceed via an outer-sphere mechanism.Author to whom all correspondence should be directed, who is presently on leave of absence from Obafemi Awolowo University.     

Distinct mechanisms for the oxidative addition of chloro-, bromo-, and iodoarenes to a bisphosphine palladium(0) complex with hindered ligands

We report an example of a bisphosphine palladium(0) complex with hindered ligands that undergoes oxidative addition of chloro-, bromo-, and iodoarenes in high yield. Addition of PhX (X = I, Br, Cl) to [Pd(Q-phos-tol)2] produced [Pd(Q-phos-tol)(Ph)(I)], [Pd(Q-phos-tol)(Ph)(Br)], and [Pd(Q-phos-tol)(Ph)(Cl)]2. To study the mechanisms of the oxidative addition of the three haloarenes to [Pd(Q-phos-tol)2], we determined the order of the reaction on the concentration of ligand and haloarene. The different haloarenes reacted through different mechanistic pathways. Addition of iodobenzene occurred by irreversible associative displacement of a phosphine. Addition of bromobenzene occurred by rate-limiting dissociation of phosphine. Addition of chlorobenzene occurred by reversible dissociation of phosphine, followed by rate-limiting oxidative addition. The mechanism of exchange of ligands from the Pd(0)L2 was also studied. The rate constant value for dissociation of ligand calculated from ligand exchange experiments is in agreement with the value calculated through experiments on oxidative addition.     

Molecular structure and vibrational spectra of 4-, 5-, 6-chloroindole

The molecular geometry, IR intensities, harmonic and anharmonic vibrational frequencies of 4-, 5-, 6-chloroindole in the ground state were calculated by DFT/B3LYP level of theory using the 6-31G (d, p) basis set. To give complete and reasonable vibrational assignments, the normal coordinate analysis has been performed for 4-chloroindole, 5-chloroindole and 6-chloroindole. The effect of position of chloro atom on the molecular properties (electron density, dipole moments and energies) of the indole aromatic system is examined on the basis of calculation data for 4-, 5- and 6-chloroindoles.     

Molecular structure and OH-stretch spectra of liquid water surface

Molecular dynamics simulations are used to investigate typical coordination shells of molecules in the liquid water surface, for two potential energy surfaces. The major undercoordinated species found in the surface include three-coordinated H2O with either a dangling-H or a dangling-O atom and two-coordinated H2O with one hydrogen bond via H, and another via O. Vibrational signatures of the different coordinations are calculated. The 3400 cm(-1) band in the surface sum frequency generation (SFG) spectrum is assigned to four-coordinated molecules within the surface layer. The low-frequency wing of the OH-stretch band, near 3200 cm(-1) in the SFG spectrum, is proposed to be due to collective excitations of a relatively small number of intermolecularly coupled O-H bond vibrations.     

Electronic structure of methoxy-, bromo-, and nitrobenzene grafted onto Si(111)

The properties of Si(111) surfaces grafted with benzene derivatives were investigated using ultraviolet photoemission spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). The investigated materials were nitro-, bromo-, and methoxybenzene layers (-C(6)H(4)-X, with X = NO(2), Br, O-CH(3)) deposited from diazonium salt solutions in a potentiostatic electrochemical process. The UPS spectra of the valence band region are governed by the molecular orbital density of states of the adsorbates, which is modified from the isolated state in the gas phase due to molecule-molecule and molecule-substrate interaction. Depending on the adsorbate, clearly different emission features are observed. The analysis of XPS intensities clearly proves multilayer formation for bromo- and nitrobenzene in agreement with the amount of charge transferred during the grafting process. Methoxybenzene forms only a sub-monolayer coverage. The detailed analysis of binding energy shifts of the XPS emissions for determining the band bending and the secondary electron onset in UPS spectra for determining the work function allow one to discriminate between surface dipole layers--changing the electron affinity--and band bending, affecting only the work function. Thus, complete energy band diagrams of the grafted Si(111) surfaces can be constructed. It was found that silicon surface engineering can be accomplished by the electrochemical grafting process using nitrobenzene and bromobenzene: silicon-derived interface gap states are chemically passivated, and the adsorbate-related surface dipole effects an increase of the electron affinity.     

Molecular structure and vibrational spectra of phenolphthalein and its dianion

Infrared (IR) and Raman spectra of phenolphthalein (PP) and its dianion form (sodium and potassium salts) were studied both in the solid state and in aqueous solution. Band assignments were carried out on the basis of the isotope shifts of the ring deuterated and 13C-substituted derivatives. Spectral analyses reveal that the PP dianion exists as mixtures of the benzenoid form (colorless) and the quinonoid form (colored) in the solid state and in aqueous solution, while the neutral PP solely takes the gamma-lactone form. This work provides the first vibrational spectroscopic evidence for the coexistence of the two species in the PP dianions.     

Molecular structure, vibrational spectra and NBO analysis of phenylisothiocyanate by density functional method

The molecular geometry, vibrational frequencies and NBO analysis of phenylisothiocyanate (PITC) in the ground state have been calculated by using density functional theory calculation (B3LYP) with 6-311++G(d,p) basis set. The optimized geometrical parameters obtained by DFT calculations are in good agreement with experimental values. Comparison of the observed fundamental vibrational frequencies of the PITC and calculated result by density functional theory (B3LYP) indicates B3LYP is superior for molecular vibrational problems. The entropy of the title compound was also performed at HF/B3LYP/6-311++G(d,p) levels of theory. Natural bond orbital (NBO) analysis of title molecule is also carried out. A detailed interpretation of the IR and Raman spectra of PITC is reported on the basis of the calculated potential energy distribution (PED). The theoretical spectrogram for IR spectrum of the title molecule has been constructed.     

Prediction of vibrational spectra from microwave spectra

Explicit and simple relations are derived for the Kivelson-Wilson parameters which can directly generate the vibrational spectrum of XY₂ bent type molecules. These relations are also shown to generate the above parameters for the different isotopes of a parent molecule. These predictions are verified in the case of some molecules of the above symmetry for which experimental microwave studies have been made.