Low-N lines of the A6sigma+-X6sigma+ (1,0) band of CrH

The (1,0) band of the A6sigma+-X6sigma+ electronic transition of CrH has been observed by laser-induced fluorescence following the reaction of laser-ablated Cr atoms with methanol under supersonic free-jet cooled conditions. Rotational assignments of the levels with N < or = 3 have been made by combination differences and dispersed fluorescence experiments on selected lines. These assignments complement those made from previously-recorded Fourier transform emission spectra, in which higher-N lines were assigned. The low-N rotational levels are extensively perturbed, presumably by levels of the a4sigma+, upsilon = 1 and B6pi, upsilon = 0 states.     

Electronic contributions to the sigma(p) parameter of the Hammett equation

A statistical procedure to obtain the intrinsic electronic contributions to the Hammett substituent constant sigma(p) is reported. The method is based on the comparison between the experimental sigma(p) values and the electronic electrophilicity index omega evaluated for a series of 42 functional groups commonly present in organic compounds.     

Spectroscopic study of the E(4)1sigma+ state in NaLi

Polarization labelling spectroscopy is applied to study the excited E1sigma+ state of NaLi in the energy range 26,500-28,000 cm(-1) above the bottom of the ground state. The potential curve of the E state is constructed using the Inverted Perturbation Approach method. The values of Te, omega(e) and Re are found to be 26,474.82(4), 180.3(2) cm(-1) and 3.343(1) A, respectively.     

Reactive oligomers. II. Polymerization of glycol bis(allyl phthalate)s and glycol bis(allyl succinate)s

Seven glycol bis(allyl phthalate)s (GBAP) and four glycol bis(allyl succinate)s (GBASu) as reactive oligomers were prepared and their polymerization behaviors were investigated in detail in terms of cyclopolymerization and gelation as compared with diallyl dicarboxylates. Thus, the rates of polymerization of GBAPs were reduced compared to diallyl phthalate, being attributed to the steric effect on the intermolecular propagation of the uncyclized radical, whereas those of GBASus were enhanced as a consequence of intermolecular association by dipole–dipole interaction in polar GBASu monomers. Cyclization was enhanced in the following order: diallyl aliphatic dicarboxylates series < GBASu series < GBAP series. Gelation was discussed according to Gordon's theory; the actual gel-point conversions increased with an increase in the molecular weight of monomers, although the discrepancy between actual and theoretical gel-point conversion inversely tended to be decreased. The decreased delay in gelation with an increase of the molecular weight of monomers is ascribed to the reduction of excluded volume effects on crosslinking.     

Heterocyclic Poly(Bismaleimide)s. II. Synthesis and Characterization of New Poly(Ether-Bismaleimide)s Containing Parabanic Rings

Abstract

New poly(ether-bismaleimide)s containing parabanic rings were obtained by the nucleophilic substitution reactions of 1,3-bis(4-dichloromaleimido-phenyl)parabanic acid (4) with various bisphenols. The structures of the resulting polymers were confirmed by IR and elemental analysis. The polymers are soluble in aprotic dipolar solvents and showed lower thermal stability than other polymers without parabanic rings.     

Molecular interpretation for the solvation of poly(acrylamide)s. I. Solvent-dependent changes in the C=O stretching band region of poly(N,N-dialkylacrylamide)s

The solvation of poly(N,N-dimethylacrylamide) (PNdMA) and poly(N,N-diethylacrylamide) (PNdEA) in various protic and aprotic solvents has been studied by using infrared (IR) spectroscopy. Because PNdMA and PNdEA have the same polar functional group, their IR spectra show quite similar solvent effects. Unexpectedly, the solvent-dependent changes of the C=O stretching vibration (nu(C=O)) bands of the two polymers cannot be explained only by dielectric constants of the solvents. Then, infrared spectra of N,N-dimethylacetamide (NdMA) and N,N-diethylacetamide (NdEA), monomer models for PNdMA and PNdEA, respectively, in the same solvents as the polymer solutions have also been examined. Interestingly, the solvent-dependent spectra in the nu(C=O) band region of NdMA and NdEA are correlated with those of PNdMA and PNdEA, respectively, except for slight deviations, which may be ascribed to molecular mobility and/or exclusive volume. These correlations permit one to regard the solvation of the polymers as that of the corresponding monomers. As a result, we have proposed the assignments of nu(C=O) bands for the PNdMA and PNdEA solutions regarding the interactions between solvents and NdMA and NdEA as hydrogen bondings. In the IR spectra of PNdMA and PNdEA in the protic solvents, two C=O bands are mainly observed; one appears at a similar frequency to that of a C=O band observed for the monomer solution, and the other is characteristic of the polymer systems. The former band is likely to reflect the solvation behavior of PNdMA and PNdEA. The results clearly show that the solvation of a polymer can be interpreted at the molecular level using infrared spectroscopy sensitive to solvent effects.     

On the mechanism of the dimethyldioxirane oxidation of sigma(H) adducts (Meisenheimer complexes) generated from nitroarenes and carbanions

The mechanism of the novel dimethyldioxirane (DMD) oxidation of sigma(H) adducts (Meisenheimer complexes) generated from nitroarenes and carbanions was elucidated. The proposed mechanism, which is akin to that of the oxidative Nef reaction, is supported by the isolation of the cyclohexadienone intermediate and the lack of a primary kinetic isotopic effect. Protic solvents (H(2)O, MeOH) enhance the reactivity of DMD through intermolecular hydrogen bonding.     

Core localization and sigma* delocalization in the O 1s core-excited sulfur dioxide molecule

Electron-ion-ion coincidence measurements of sulfur dioxide at discrete resonances near the O 1s ionization edge are reported. The spectra are analyzed using a model based upon molecular symmetry and on the geometry of the molecule. We find clear evidence for molecular alignment that can be ascribed to symmetry properties of the ground and core-excited states. Configuration interaction (CI) calculations indicate geometry changes in accord with the measured spectra. For the SO(2) molecule, however, we find that the localized core hole does not produce measurable evidence for valence localization, since the transition dipole moment is not parallel to a breaking sigma* O-S bond, in contrast to the case of ozone. The dissociation behavior based upon the CI calculations using symmetry-broken orbitals while fixing a localized core-hole site is found to be nearly equivalent to that using symmetry-adapted orbitals. This implies that the core-localization effect is not strong enough to localize the sigma* valence orbital.     

Gelation Dynamics and Mechanism(s) in Stereoregular Poly(Methyl Methacrylate)s

Chain conformation and gel structure of syndiotactic PMMA thermoreversible gels have been investigated using small angle neutron scattering (SANS). A double helix model for the chain conformation is proposed alongside a gel network model where the fibrils are formed by the proposed double helix and the junctions by the aggregation of 3 double helices. Preliminary results, also obtained by SANS, for stereocomplex gels prepared in bromobenzene are presented.     

Synthesis of hydrogen-terminated aliphatic bis(ethynyl ketone)s and aliphatic poly(enamine-ketone)s and poly(enonesulfide)s

Hydrogen-terminated aliphatic bis(ethynyl ketone)s (H-ABEKs): 1,9-decadiyne-3,8-dione ( 3a ) and 1,13-tetradecadiyne-3,12-dione ( 3b ) were prepared by the Friedel-Crafts reaction of bis(trimethylsilyl) acetylene (BTMSA) with adipoyl chloride and sebacoyl chloride, followed by desilylation with an aqueous buffer solution. Aliphatic poly(enamine-ketone)s (APEKs) and aliphatic poly(enonesulfide)s (APESs) were prepared in nearly quantitative yield by the nucleophilic addition polymerization of 3a,b with various diamines and dithiols in N,N-dimethylformamide (DMF) and m-cresol at room temperature during 14-22 h. Aromatic diamines and dithiols gave polymers that were soluble only in m-cresol. Primary diamines gave exclusively APEKs with the cis (Z) configuration. Dithiols gave APESs which contained more cis (Z) than trans (E) configurations. The inherent viscosities (η_inh) of the APEKs ranged from 0.05 to 0.73 dL/g. The APESs gave η_inh ranging from 0.36 to 2.21 dL/g.     

New poly (amide-imide) syntheses. IX. Preparation and properties of poly(amide-imide)s derived from 2,7-bis (4-aminophenoxy) naphthalene and various bis (trimellitimide)s

Eleven bis(phenoxy) naphthalene-containing poly(amide-imide)s IIIa–k were synthesized by the direct polycondensation of 2,7-bis (4-aminophenoxy) naphthalene (DAPON) with various aromatic bis (trimellitimide)s IIa–k in N-methyl-2-pyrrolidone (NMP) using triphenyl phosphite and pyridine as condensing agents. Poly (amide-imide)s IIIa–k having inherent viscosities of 0.70–1.12 dL/g were obtained in quantitative yields. The polymers containing p-phenylene or bis(phenoxy) benzene units exhibited crystalline x-ray diffraction patterns. Most of the polymers were readily soluble in various solvents such as NMP, N, N-dimethylacetamide, dimethyl sulfoxide, m-cresol, o-chlorophenol, and pyridine, and gave transparent, and flexible films cast from DMAc solutions. Cast films showed obvious yield points in the stress-strain curves and had strength at break up to 87 MPa, elongation to break up to 11%, and initial modulus up to 2.10 GPa. These poly(amide-imide)s had glass transition temperatures in the range of 255–321°C, and the 10% weight loss temperatures were recorded in the range of 529–586°C in nitrogen. The properties of poly(amideimide)s IIIa–k were compared with those of the corresponding isomeric poly (amide-imide)s III′ prepared from 2,7-bis(4-trimellitimidophenoxy) naphthalene and aromatic diamines. © 1994 John Wiley & Sons, Inc.     

New poly(amide-imide)s syntheses. XVII. Preparation and properties of poly(amide-imide)s derived from 3,3-Bis[4-(4-aminophenoxy)phenyl]phthalimidine and various bis(trimellitimide)s

A series of novel bis(phenoxy)phthalimidine-containing poly(amide-imide)s III were synthesized by the direct polycondensation of 3,3-bis[4-(4-aminophenoxy)phenyl]phthalimidine (BAPP) with various aromatic bis(trimellitimide)s in N-methyl-2-pyrrolidone (NMP) using triphenyl phosphite and pyridine as condensing agents. Poly(amide-imide)s III , having inherent viscosities up to 1.36 dL/g, were obtained in quantitative yields. All resulting polymers showed an amorphous nature and were readily soluble in polar solvents such as NMP and N,N-dimethylacetamide. All the soluble poly(amide-imide)s afforded transparent, flexible, and tough films. The glass transition temperatures of these polymers were in the range of 267–322°C and the 10% weight loss temperatures were above 490°C in nitrogen. Some properties of poly(amide-imide)s III were compared with those of the corresponding isomeric poly(amide-imide)s III′ prepared from 3,3-[4-(4-trimellitimidophenoxy)phenyl]-phthalimidine and various aromatic diamines. © 1996 John Wiley & Sons, Inc.     

New poly(amide-lmide)s syntheses. XV. Preparation and properties of poly(amide-imide)s derived from 9, 9-bis[4-(4-aminophenoxy) phenyl]fluorene and various bis(trimellitimide)s

Fifteen bis(phenoxy) fluorene-containing poly(amide-imide)s III were synthesized by the direct polycondensation of 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene (BAPPF) with var-ious aromatic bis(trimellitimide)s II in N-methyl-2-pyrrolidone (NMP) using triphenyl phosphite and pyridine as condensing agents. Poly(amide-imide)s III having inherent vis-cosities up to 1.45 dL/g were obtained in quantitative yields. Most of the resulting polymers showed an amorphous nature and were readily soluble in polar solvents such as NMP and N,N-dimethylacetamide. All the soluble poly(amide-imide)s afforded transparent, flexible, and tough films. The glass transition temperatures of these polymers were in the range of 263–315°C and the 10% weight loss temperatures were above 510°C in nitrogen. Some properties of poly(amide-imide)s III were compared with those of the corresponding isomeric poly(amide-imide)s III ′ prepared from 9,9-[4-(4-trimellitimidophenoxy)phenyl]fluorene and various aromatic diamines. © 1995 John Wiley & Sons, Inc.     

Distinguishing the early and late transition states and exploring the validity of sigma --> sigma*#, sigma# --> sigma*, and sigma --> pi*(C=O) concepts in diastereoselection from NBO analysis

Natural bond orbital (NBO) analysis of several early TSs does not support the sigma --> sigma*# hypothesis. The sigma --> pi*(C=O) interaction controls the carbonyl pyramidalization that, in turn, controls the pi-selectivity of a nucleophilic addition. In contrast, late TSs are devoid of sigma --> pi*(C=O) interactions, and they benefit from sigma --> sigma*# interactions that control pi-selectivity. The evidence in favor of Anh-Felkin's sigma# --> sigma* hypothesis is weak. The electron-withdrawing sigma(C-F) in the 2-fluoropropanal-LiCN TS did not align anti to the incipient bond even though there was complete conformational freedom. The initial guess for the TS in which sigma(C-F) was held anti to sigma# optimized to what had lost the said geometrical relationship. Furthermore, in the TS for axial addition of LiCN to 2-ax-F-cyclohexanone, the net sigma --> sigma*# interaction was considerably larger than the net sigma# --> sigma* interaction. The relative TS energies require that the equatorial addition of LiCN to 2-ax-F-cyclohexanone be favored over the axial addition in good compliance with the available experimental results.