Carbon-13 NMR Spectra of Some Group VIIB Transition Metal Thiocarbonyl and Selenocarbonyl Complexes

Recently, we reported the discovery of the first examples of transition metal selenocarbonyl complexes, (n⁵-C₅H₅) Mn (CO)₂ (CSe) and (n⁶-C₆H₅CO₂CH₂(CO)₂ (CSe).¹ These complexes are particularly interesting because, unlike CO and CS, the diatomic CSe molecule has so far eluded isolation even at very low temperatures,² and so these complexes represent the stabilization of a chemically unstable species through coordination to a metal (cf. metal carbene complexes). We have also synthesized several thiocarbonyl complexes of the same type,^3,4 as well as the analogous rhenium selenocarbonyl complexes.⁴ While many detailed studies of the ¹³C nmr spectra of transition metal carbonyls have appeared in the literature over the past few years, there have been no such studies for the closely related thiocarbonyls and selenocarbonyls, although a few isolated data have been reported recently for metal thiocarbonyls.^5,6 In this communication, we report the ¹³C nmr spectra of the isoelectronic series of complexes, (n⁵-C₅H₄R) M(COI)₂ (CX) (M = Mn, R = H, CH₃; M = Re, R = H; X = O,S, Se).     

Characterization of the Charge Transfer Complex from Furan and Maleic Anhydride and the Alternating Copolymer

A previously unreported copolymer between furan and maleic anhydride was readily obtained by free radical initiation of benzene solutions of the comonomers. The product copolymers exhibit remarkably uniform composition regardless of monomer feed ratios. A donor-acceptor complex was suspected to account for the 1:1 alternating sequence of the monomers in the product. The complex was easily detected and partially characterized, although its exact role in the mechanism is uncertain.     

Novel Copolymers of Styrene and Alkyl and Alkoxy Ring‐Trisubstituted Methyl 2‐Cyano‐3‐phenyl‐2‐propenoates

Electrophilic trisubstituted ethylene monomers, akyl and alkoxy ring‐trisubstituted methyl 2‐cyano‐3‐phenyl‐2‐propenoates, RC₆H₂CH[dbnd]C(CN)CO₂CH_3, (where R is 2,3‐dimethyl‐4‐methoxy, 2,5‐dimethyl‐4‐methoxy‐, 2,3,4‐trimethoxy‐, 2,4,5‐trimethoxy, 2,4,6‐trimethoxy, and 2,4‐dimethoxy‐3‐methyl), were synthesized by the piperidine catalyzed Knoevenagel condensation of ring‐substituted benzaldehydes and methyl cyanoacetate, and characterized by CHN elemental analysis, IR, ¹H‐ and ¹³C‐NMR. Novel copolymers of the ethylenes and styrene were prepared at equimolar monomer feed composition by solution copolymerization in the presence of a radical initiator (AIBN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, ¹H and ¹³C NMR, GPC, DSC, and TGA. High T_g of the copolymers in comparison with that of polystyrene indicates a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. The gravimetric analysis indicated that the copolymers decompose in the 283–306°C range.     

Studies in Cyclocopolymerization. X. Cyclocopolymerization of Tetrahydronaphthoquinone and Dimethyl Tetrahydronaphthoquinone with Divinyl Ether

Abstract

Tetrahydronaphthoquinone (THNQ) and dimethyl tetrahydronaphthoquinone (DMTHNQ) were found by UV spectroscopy to form donor-acceptor complexes with divinyl ether (DVE), the latter being the electron donor. Since the participation of such complexed species has been considered in the cyclocopolymerization of a 1,4-diene with a monoolefin such as DVE-maleic anhydride (MA) and DVE-fumaronitrile (FN) systems, radical copolymerization of THNQ and DMTHNQ with DVE was studied. It was found that these copolymers have constant 1:1 composition regardless of the feed composition. The terpolymerization of DVE-THNQ-DMTHNQ confirmed the 1:1 donor-acceptor composition in the polymer. The integration of the NMR spectrum was used in determining the copolymer composition. The spectroscopic data suggest a cyclized repeating unit in which the copolymer main chain consists of only DVE units. There is a marked difference between these copolymers and the typical cyclo-copolymers, such as DVE-MA and DVE-FN, in which the copolymer main chains consist of DVE and the comonomer alternately, with the overall composition being 1:2. These results are interpreted in terms of the steric effect by the bulky acceptor monomers and the electronic interaction between the comonomers. The competition between an acceptor monomer and the charge-transfer (CT) complex toward the cyclized DVE radical in the propagation step appears to favor the CT complex.     

The Fundamental Basis for Cyclopolymerization. VII. A Cyclopolymerization Study of Certain Allylcycloalkenes

The cyclopolymerization characteristics of 3-allylcyclopentene, 3 allylcyclopentene, 3-allylcyclohexene, and 4-allylohexene were studied and the extent of their cyclopolymerization by cationic initiation were compared with previously reported solvolysis results involving the same intermediate carbonium ion. The results of this study were also compared with previously reported results on 4-vinylcyclohexene and 1, 4-dimethylenecyclohexane. The allylcycloalkenes were also polymerized by metal alkyl coordination catalysts and the extent of cyclization in each case was determined. The polymers derived from these monomers invariably contained polymeric fractions (27 to 99%) which were soluble in non-polar organic solvents. Calculations based on NMR spectral data indicated the cationic polymers were 68 to 95% cyclized. The extent of cyclization was found to parallel the interolefinic separation in the monomer. Coordination polymerization yielded somewhat lower ratios of cyclizations (54 to 80%) in all cases except for 4-allylcyclohexene. 4-Allylcyclohexene gave only 5 to 54% cyclization, 4-Vinylcyclohexene, 3-allylcyclopentene, and 3-allylcyclohexene produced soluble copolymers with maleic anhydride. Elemental analysis indicated the composition of these copolymers to be 2:1 molar in maleic anhydride and diene units. A cyclic copolymerization mechanism suggested the formation of a multicyclic repeating unit. The other monomers gave crosslinked polymers since maleic anhydride could not be incorporated into a six-membered ring.     

Matching extension in the powers of n-connected graphs

Let G be a graph on p vertices. Then for a positive integer n₁ G is said to be n-extendible if (i) n < p/2, (ii) G has a set of n independent edges, and (iii) every such set is contained in a perfect matching of G. In this paper we will show that if p is even and G is n-connected, then G^k is -extendible for every integer k ≥ 2 such that . © 1996 John Wiley & Sons, Inc.     

Entry distribution, fission barrier, and formation mechanism of 254102No

The entry distribution in angular momentum and excitation energy for the formation of 254No has been measured after the 208Pb(48Ca,2n) reaction at 215 and 219 MeV. This nucleus is populated up to spin 22Planck's over 2pi and excitation energy greater, similar6 MeV above the yrast line, with the half-maximum points of the energy distributions at approximately 5 MeV for spins between 12Planck's over 2pi and 22Planck's over 2pi. This suggests that the fission barrier is greater, similar5 MeV and that the shell-correction energy persists to high spin.     

1-Soliton solution and conservation laws for nonlinear wave equation in semiconductors

This paper obtains the 1-soliton solution of a nonlinear wave equation that arises in the study of semiconductors. The conserved quantities are also calculated from this equation. Furthermore, additional non-trivial conserved quantities are computed using the invariance and multiplier approach based on the well known result that the Euler-Lagrange operator annihilates the total divergence.     

Invariance Analysis and Variational Conservation Laws for the Wave Equation on Some Manifolds

In this paper we discuss symmetries of a nonlinear wave equation that arises as a consequence of some Riemannian metrics of signature −2. The objective of this study is to show how geometry can be responsible in giving rise to a nonlinear inhomogeneous wave equation rather than assuming nonlinearities in the wave equation from physical considerations. We find Lie point symmetries of the corresponding wave equations and give their solutions in two cases. Some interesting physical conclusions relating to conservation laws such as energy, linear and angular momenta are also determined.