Tetrakis(phenylethynyl)tin(IV)

The asymmetric unit of the crystal structure of the title compound, [Sn(C8H5)4], consists of one fourth of a discrete tin complex and one half of another which both possess nearly ideal tetrahedral symmetry; the site symmetries of the two Sn atoms are \overline4 and 2. The bond angles at all acetylide C atoms are almost linear. The Sn—C distances [2.076 (6) and 2.065 (6)–2.069 (6) Å in the two complexes) are short when compared to the sum of the covalent radii of C and Sn (2.177 Å), but consistent with another tetrakis(alkynyl)tin complex. The acetylenic bond distances [1.196 (7) and 1.183 (7)–1.207 (7) Å] are consistent with a triple C[triple-bond]C bond. Therefore, despite the short Sn—C distances, the ligands are mainly σ-bonded to the metal. In the solid state, these complexes form a three-dimensional network via agostic C—H interactions as a phenyl proton in the ortho position interacts with the acetylenic carbon in the α position to the tin center.

β-Enolization in α-phenyl-α,α′,α′-trimethylcycloalkanones

Ring expansion through β-proton abstraction from α-methyl groups has been observed for the α-phenyl-α,α′,α′,-tri-methyl derivatives of cyclopentanone and cyclohexanone upon treatment with t-BuO−/t-BuOH/185 °C. This contrasts with the lack of rearrangement found for the α,α,α′,α′-tetramethyl derivatives but is analogous to the behavior of some α-phenyl acyclic ketones. However, this process is reversible in the cyclic systems, but irreversible in the acyclic cases. For all of these α-phenyl substituted ketones, rearrangement is in competition with Haller–Bauer type cleavage. In the cyclic systems, a minor process was observed whereby some of the ring-expanded product is reduced to the corresponding secondary alcohol but there was no evidence of rearrangement through γ-enolate formation involving phenyl proton abstraction, which is a minor process in the α-phenyl acyclic systems.

Determination of Sequence Distribution in Styrene-Butadiene Copolymer I. 1H-NMR Study of Styrene Oligomers

The 1 H-NMR spectra of styrene oligomers were measured as a model of styrene sequences in SBR. The ortho-phenyl proton, methine proton, and methylene proton signals shift to a higher magnetic field as the degree of polymerization increased. The methine proton signal split into two peaks, reflecting the tacticity. The methylene proton flanked by methylene and methine protons had a higher chemical shift value than the methylene proton flanked by two methine protons. It is demonstrated that the average sequence length of the styrene units in SBR can be determined by the relative intensity ratio of the two methylene proton signals. It is also found that the fraction of styrene sequences longer than 6 units can be estimated from the relative intensity of ortho-phenyl proton signals resonated higher than 6.7 ppm.

Nuclear Magnetic Resonance Spectroscopic Method for Determination of Penicillamine in Capsules

A rapid and specific nuclear magnetic resonance (NMR) spectroscopic method for the determination of penicillamine in capsules is presented. The sample is directly dissolved in D2O and its spectrum recorded on a 90 MHz instrument. The 2 singlets appearing at 1.58–1.64 ppm, due to the nonequivalent gem-dimethyl groups, were integrated and compared with the integral obtained for the phenyl proton signals of sodium saccharin, which is the internal standard. The results obtained by the proposed method closely agreed with those found by the method of USP XX.

Studies on the PMR Spectra of Oxetanes. VI 2-(3-Chlorophenyl)oxetane and 2-(2-Chlorophenyl)oxetane at 60 and 100 MHz

The 100 MHz spectra of the phenyl protons in 2-(3-chlorophenyl) oxetane and 2-(2-chlorophenyl) oxetane have been analysed. The 60 MHz PMR chemical shifts and proton-proton coupling constants have been studied in the temperature range from -20 C to +80 °C. The chemical shifts were sensitive to temperature, while the coupling constants were not, except the long range 5Jm coupling constant between the methine proton and the meta positioned phenyl proton in 2-(2-chlorophenyl) oxetane.

An Investigation of Substituent Effects on Coupling Constants to Vinyl Protons in Styrene Derivatives

Experimental long-range phenyl proton–vinyl proton coupling constants in 4-substituted styrenes are substituent independent. This is also predicted by INDO–finite perturbation theory calculations of these coupling constants. Comparison with calculated and experimental long-range coupling constants for 4-substituted benzaldehydes suggests that the previously reported substituent dependence for the latter coupling constants arises from substituent-induced changes in molecular geometry.Geminal vinyl coupling constants in 4-substituted styrenes, α-methylstyrenes, and α-t-butylstyrenes are substituent dependent with substituent effects increasing as phenyl and vinyl groups are twisted out of planarity. These trends are reproduced by INDO–FPT calculations. It is concluded that the substituent effects are primarily transmitted through space.Both experimental and calculated vinyl 13C–1H coupling constants show strong stereospecific substituent effects. From the pattern of results (particularly the greater field dependence for JC(β)H(9) than JC β)H(8)) it is concluded that these coupling constants.also reflect through-space substituent effects. This is supported by calculations on model compounds with no intervening phenyl group.