Ata Shirazi

Unexpected affects of Me3Si-X on reactions of higher order cyanocuprates

Abstract The assumed compatibility of Me3SiCl with higher order cyanocuprates has been studied by both chemical and spectroscopic (1H, 7Li, 29Si NMR) means. Both types of experiments confirm that Me3Si-X significantly alters the composition of both homo (R2Cu(CN)Li2) and mixed (RR′Cu(CN)Li2) reagents.

Comparison of Conformations of Diesters of Stabilized Phosphonium Ylides in Solution and in the Crystal

Computed bond lengths and angles of methyl ethyl and dimethyl triphenyl phosphonium ylidic diesters, 1b, c , respectively, are similar to those in the crystal, as for the diethyl ester, 1a , where both acyl oxygens are anti to phosphorus. The 1 H and 13 C NMR spectra of the methyl ethyl diester, 1b , where one acyl oxygen is syn and the other anti to phosphorus, are as expected in terms of the conformation in the crystal, but the dimethyl ester, 1c , in the crystal is an equimolar mixture of conformers. For a given ylidic diester the different conformers have similar energies from B3LYP//6-31G(d) computations, interconversions of conformers should not be slow at ambient temperatures and 1 H and 13 C NMR signals in solution are sharp. Estimation of Natural Atomic Charges indicates significant cationoid character on phosphorus and the acyl carbons, and anionoid character on the ylidic carbon and the ester oxygens depending on orientations towards phosphorus.

Phosphorus nuclear magnetic resonance of diverse phosvitin species

1. High resolution 31P nuclear magnetic resonance (NMR) spectra, with and without proton decoupling, of the principal egg phosphoproteins--phosvitins--of a bird (Gallus gallus), an amphibian (Xenopus laevis) and a fish (Salmo gairdneri) were obtained. 2. The spectra were evaluated with special reference to available amino acid sequences and the major NMR resonance in all three spectra was assigned to phosphoserine clusters. 3. The resolution of numerous additional phosphorus resonances provides the basis for further investigation of the particular molecular environments of phosvitin-bound phosphoryl groups and their involvement in the diverse binding modes for metal complex formation by phosvitins.

A Common Conformation of Stabilized Triphenyl Phosphonium Ylidic Diesters with Bulky Alkoxy Groups

The phosphonium ylidic diesters, methyl and ethyl isopropyl and, methyl and ethyl t-butyl triphenylphosphoranylidene malonates, 1a,b and 2a,b , respectively, have the syn-anti conformation in solution, as in the crystal, and the bulkier alkoxy group is oriented towards phosphorus. The 1 H NMR spectra show that in 1a,b , the isopropyl group is oriented towards the face of a phenyl group, consistent with π shielding in the 1 H signals, and examination of the 1 H coupled 13 C NMR spectra allows assignment of the acyl carbon signals. Computed bond lengths and angles for isolated molecules are similar to those in the crystal, and the geometry and the NMR spectra indicate extensive ylidic resonance. Estimated partial atomic charges on the ester oxygens are more negative when they are oriented towards, rather than away from, phosphorus.

Cyano Triphenyl Phosphonium Ylides Stabilized by Ester or Keto Groups: Computed Conformations and Crystal Structures

The mixed stabilized triphenyl phosphonium ylides Ph3P = C(CN)CO-R and Ph3P = C(CN)COOR, R = CH3, C2H5, CH(CH3)2, 1a,c and 2a,b, respectively, have sharp 1H and 13C NMR signals, except for 2b in some conditions. Ab initio geometrical optimizations indicate that in the preferred conformer the acyl oxygen is syn- to phosphorus, with barriers to rotation about the ylidic bond of 15–18 kcal. mol−1, and differences between the syn- and anti-conformers of ca. 4 and 11 kcal. mol−1 for the keto and ester derivatives, respectively. These energetic differences are not very sensitive to changes in the alkyl group, R, or the level of computation. The computed geometries indicate that the ylidic moieties are approximately planar with extensive electronic delocalization, as in crystalline 1a and 2a. The 13C NMR signals of the ylidic carbons are shifted strongly up field, consistent with their anionoid character.

Propensity toward formation of higher aggregates in anionic and cationic iron tetraphenylporphyrin μ-oxo dimers: evidence from 1H and 13C NMR spectroscopy

The μ-oxo dimeric form of anionic iron(III) tetra(p-sulfonatophenyl) porphyrin, FeTSPP, and iron(III) tetra(p- carboxyphenyl) porphyrin, FeTCPP, as well as cationic iron(III) tetra(4-N-methylpyridyl) porphyrin, FeTMPYP, and iron(III) tetra(4-N,N,N-trimethylanilyl) porphyrin, FeTMAP, were investigated by 1H and 13C NMR methods in aqueous solution. Concentration dependence, chemical shifts, splitting patterns and line-broadening properties of phenyl/pyridyl and porphyrin β-pyrrolic resonances suggest the aggregation tendencies of these porphyrin dimers increase in the order TMPYP <TMAP<TSPP<TCPP. The diffused nature of positive charge in the N- methylpyridyl group of TMPYP makes this dimer least susceptible to aggregation. On the other hand, the steric/ spatial dimensions of the localized charged groups in the meso-phenyl substituted TMAP, TSPP and TCPP porphyrins are most likely to affect their aggregation tendencies. The resolved splittings of ortho-phenyl protons observed at 50 mM concentration in the anionic systems suggest a tighter stacking of dimer/higher aggregates and slower formation/dissociation processes on the NMR time scale, than those found in the cationic analogs.