Rolf B. Johannesen

UEAITR: A NEW COMPUTER PROGRAM FOR ANALYSIS OF NMR SPECTRA: ANALYSIS OF THE PROTON SPECTRUM OF TRIISOPROPYLPHOSPHINE.

Abstract A new computer program for the analysis of NMR spectra is reported. It adds iterative evaluation of input parameters to an earlier program (UEANMR II) which makes use of magnetic equivalence factoring to reduce the size of certain matrices. The present program, by iterating on line frequencies rather than energy levels, and by using magnetic equivalence factoring, offers advantages of speed and convenience over previously described computer programs for NMR analysis. The analysis of the proton spectrum of triisopropylphosphine is described as an example and the trend of 2 J H - P with increased alkyl substitution is found to be opposite to that of the trend of 2 J H - X for all other hetero-atoms, X , reported in the literature.

Predicting toxicity using computed molecular topologies: The example of triorganotin compounds

Abstract The LC50 values of eight triorganotin compounds for crab zoeae, Rhithropanopeus harrisii correlate with substituent constants reflecting partitioning effects. Computed molar surface areas predict toxicity as well as any parameter used suggesting that partitioning into lipids controls the toxicity.

CONTROLLED ATMOSPHERE CHAMBER

An inert atmosphere chamber for the transfer of reactive materials is described. It has the advantages of being inexpensive, easily cleaned, and can be evacuated.

Jahn–Teller Distortion: Magnetic Studies of Vanadium Tetrachloride

Paramagnetic resonance of polycrystalline VCl4 diluted with TiCl4 has been observed near 9,24, and 36 GHz below 9°K. Both g values and hyperfine A tensors are axially symmetric and temperature independent with the same principal axes: g‖ = 1.920, g⊥ = 1.899, | A‖ | = 72 G, | A⊥ | = 120 G. The average g value obtained from susceptibility data is in agreement with the resonance value. The paramagnetic relaxation time T1 varies with temperature as shown by the relation T1 = 2 × 10− 9exp(25/T) sec, indicating the presence of a potential barrier approximately 18 cm− 1 in height. The results indicate a static Jahn–Teller distortion, but with large zero‐point vibrations. This situation is in between Ballhausen–de Heers ligand field and Ball‐hausen–Liehrs crystal‐field calculations.

Magnetic Nonequivalence in the High‐Resolution NMR Spectra of Diborane

Proton and boron‐11 nuclear magnetic resonance spectra of 11B‐enriched neat diborane have been measured over the temperature range from −7° to −60°C. The terminal‐proton resonance and the 11B spectrum exhibit partially resolved fine structure which arises from the magnetic nonequivalence of the terminal protons and of the boron nuclei due to long‐range spin coupling. Spectra were calculated which agree quite well with the observed spectra and result in a reasonably accurate determination of the magnitudes and most of the relative signs of the various coupling constants. These values are: JBB = ∓5 Hz, JBHb = +46.2 Hz, JBHt = +133 Hz, J′BHt = +4 Hz, | JHtHb | = 7.2 Hz, JHtHb (trans or cis) = ±14 Hz, JHtHt (cis or trans) = ±6 Hz, | JHtHtgem | < 3 Hz, δ(Ht − Hb) = −4.50 ppm.

An algorithm for automatic correction of quadrature phase detector outputs

Abstract A computer algorithm is described which automatically corrects phase and amplitude errors when quadrature phase detectors are used in Fourier transform NMR. A procedure for averaging unlocked scans in the time domain is discussed.

Characterization of organometallic copolymers and copolymerization by size-exclusion chromatography coupled with trace metal- and mass-sensitive detectors

Abstract An important class of controlled-release, biocidal triorganotin-containing copolymers (OMPs) is produced by the free radical initiated reaction of a triorganotin methacrylate (typically tributyltin methacrylate, TBTM) with methyl methacrylate. In earlier studies, we have demonstrated that size-exclusion chromatography (SEC) on μStyragel, coupled with an in-line graphite furnace atomic absorption detector (GFAA) quantifies at least two well-resolved tin-bearing molecular weight fractions observed in many different commercial OMP formulations: a polymer fraction, and, probably, unreacted TBTM. When tetrahydrofuran is used as the eluent, a third component, believed to be an ionic tin-containing compound, is adsorbed and slowly eluted. We now verify that a dilute solution of acetic acid in the tetrahydrofuran efficiently desorbs this species. If a one percent solution of acetic acid in tetrahydrofuran is introduced into the mobile phase as a discrete, injected volume several minutes after the injection of the polymer formulation, there appears in the SEC—GFAA chromatogram: the polymer peak, the monomer peak, several minutes of tailing, and, finally a spike, with little additional tailing. However, when a one percent solution of acetic acid in tetrahydrofuran is used as the eluent, the high polymer peak is substantially reduced in size owing to acid hydrolysis of polymeric esters to which the tributyltin is chemically bonded; the low-molecular-weight peak is substantially increased. Thus, delayed injection of acetic acid serves the purpose of avoiding acid hydrolysis of the polymer. In the work described, only trace amounts of acetic acid (0.5 μl to 5.0 μl) were introduced by injection into the tetrahydrofuran mobile phase, whereas prolonged exposure to dilute solutions of acetic acid in tetrahydrofuran — e.g. , introduced by a gradient method— could be expected to shorten column life. Partial decomposition of esters was found in partially reacted OMPs after one year of storage at −780°C.

NMR Studies of Inorganic Fluorides. III. Si3F8

A high‐resolution NMR study of octafluorotrisilane, Si3F8, is reported. The chemical shifts of 19F and 29Si, relative to SiF4 as a reference, are given. Coupling constants, including in every case the relative sign, are given for isotopic species containing not more than one 29Si atom. The results are compared with the corresponding values for SiF4 and Si2F6.

Holistic molecular conformation and total surface area calculations as predictors for solution properties and chromatographic parameters

Abstract Group VA triphenyl derivatives, (C 6 H 5 ) 3 M, were separated using a reversedphase bonded C 18 column with a methanol—water (70:30, v/v) mobile phase. The SAREA program was used to calculate holistic total surface area (TSA) values for the compounds in various conformations. A significant linear correlation was obtained between the natural logarithms of the capacity factor and the TSA values for only one particular set of conformers implying preferred solute-column chemistry based on preferred CM bond rotations. The advantages of using a holistic approach for the calculation of TSA values are that it distinguishes the local carbon and metal geometries and weights their contribution to the overall TSA predictor which is not possible using a fragment approach. This is particularly significant for organometallic systems due to the ability of the central metal or metalloid atom to expand its coordination number. This effectively would increase the range of geometries which is not the case for organic molecules.

Nuclear magnetic resonance studies of inorganic fluorides VI. Magnetic nonequivalence in Bis(perfluorovinyl)mercury

Fluorine magnetic resonance and 19F{199Hg} resonance spectra of bis(perfluorovinyl)mercury and methyl(perfluorovinyl)mercury have been observed. Proton resonance and 1H{199Hg} spectra of methyl(perfluorovinyl)mercury and dimethylmercury have also been observed. The magnitudes and signs of all possible F-F, F-Hg, and H-Hg coupling constants in these three compounds have been determined. The spectrum of bis(perfluorovinyl)mercury calculated from the determined parameters is in excellent agreement with observation and the presence of long-range F-F coupling constants in this molecule, none of which are zero, verifies an earlier suggestion as to the reason for the complexity of the spectrum. The fluorine chemical shifts and F-F coupling constants within a perfluorovinyl group are within the previously reported range for these paramters. The mercury chemical shifts determined by INDOR spectroscopy are as follows: dimethylmercury 0 (reference), methyl(perfluorovinyl)mercury + 482 ± 3 ppm, bis(perfluorovinyl)mercury + 957 ± 3 ppm.