Elimination reactions of aryl esters of arylacetic acids 1 and 2 promoted by R2NH in MeCN have been investigated kinetically. The reactions are second-order and exhibit β = 0.44−0.84, |βlg| = 0.41−0.50, and ρH = 2.0−3.6. Brønsted β and |βlg| decrease with the electron-withdrawing ability of the β-aryl substituent. Hammett ρH values remain nearly the same, but the |βlg| value increases as the base strength becomes weaker. Both ρH and β decrease with the change of the leaving group from 4-nitrophenoxide to 2,4-dinitrophenoxide. The results are consistent with an E2 mechanism and a reaction coordinate with a large horizontal component corresponding to proton transfer. When the base−solvent system is changed from R2NH−MeCN to R2NH/R2NH2 +−70 mol % MeCN(aq), the Brønsted β, ρH, and |βlg| decrease. Finally, the ketene-forming elimination reactions from p-nitrophenyl p-nitrophenylacetate promoted by R2NH/R2NH2 + buffers in 70 mol % MeCN(aq) have been shown to proceed by concurrent E2 and E1cb mechanisms.

Polymerization reactions of α,α‘-bis(tetrahydrothiophenio)-p-xylene dichlorides with OH- in H2O have been studied kinetically. The reactions proceeded via the α-tetrahydrothiophenio-p-xylylene intermediates. Results of the H−D exchange experiments and kinetic studies reveal that the 1,6-elimination forming the intermediates proceeds reversibly via the ylide intermediate. The observed rate of disappearance of the intermediate was increased by the addition of OH-, tetrahydrothiophene, and S2O8 2- as well as by the photoirradiation with a tungsten lamp in the presence of Rose Bengal and was inhibited by TEMPO. However, the rate was found to be independent of ylide concentration. From these results, an elimination−free radical polymerization mechanism is proposed. The microscopic rate constants for each step of this mechanism were calculated from the change in the intermediate concentration with time. All of the rate data showed excellent correlations with the substituent constants in the Hammett plot.

The polymerization kinetics of 2,5-bis(tetrahydrothiopheniomethyl)thiophene dichloride were studied. The reaction proceeds via a 2,5-dihydrothiophene intermediate M. Results of kinetic and product studies revealed that the 1,6-elimination proceeded by an (E1cb)irr mechanism. The rate of the disappearance of M was not influenced by the addition of OH-, carbanions, and tetrahydrothiophene but was accelerated by S2O8 2- and inhibited by TEMPO. In addition, the reaction mixture exhibited an electron spin resonance signal with a g value of 2.003 G and induced the polymerization of acrylamide. These results indicated a free radical polymerization mechanism.

Two-photon absorption properties of 1,4-bis{4'-[N,N-bis(6''-trimethylammoniumhexyl)amino]styryl}benzene tetrabromide (C1) and its inclusion complexes (ICs) with cyclodextrins (CDs) have been studied. Upon complexation with CDs, the absorption spectra of C1 showed a slight red shift, whereas the emission spectra showed a blue shift with concomitant increase in the fluorescence quantum efficiency. A Stern-Volmer study using K(3)Fe(CN)(6) as a quencher revealed significant reduction in the photoinduced charge transfer quenching, in accord with the IC formation. Comparison of the spectroscopic results reveals that C1 forms increasingly more stable ICs in the order C1/beta-CD < C1/gamma-CD < C1/(3gamma:beta)-CD (gamma-CD/beta-CD 3:1, mole ratio). Moreover, the two-photon action cross section of C1 increased from 200 GM for C1 to 400 GM for C1/beta-CD, 460 GM for C1/gamma-CD, and 650 GM for C1/(3gamma:beta)-CD, respectively. Furthermore, the two-photon microscopy images of HeLa cells stained with C1 emitted strong two-photon excited fluorescence in the plasma membrane. These results provide a useful guideline for the development of efficient two-photon materials for bioimaging applications.

The polymerization in the title proceeds via an (E1cb)R elimination to form a quinodimethane intermediate followed by an anionic polymerization.Polymerization of a,a'-bis(tetrahydrothiopheni0)-p-xylene dichloride (SH) derivatives is of considerable interest because they are precursor polymers of poly(p-phenylenevinylene) (PPV), which has useful conducting and nonlinear optical properties.' The reaction is known to proceed via the quinodimethane intermediate (M) which is probably formed by 1,6-elimination. Both radical and anionic mechanisms have been proposed for the polymerization step (Scheme 1 ) . 2 4 However, the detailed mechanism of the elimination and polymerization processes is not clearly understood.In the present work, we have conducted a kinetic investigation of the reactions of SH with OH-, OD-, and HP04*-/ Po43-buffer in aqueous solution. The reaction was followed by monitoring the change of the absorbance at 320 nm, which was previously assigned to M by Lahti et aZ. ,3 with a UV-VIS spectrophotometer. In all cases, the absorbance first increased to a maximum value and then decreased with time, indicating that the intermediate accumulated before undergoing polymerization. Neither Wessling's mechanism nor the ionic mechanism could explain the spectral change on the basis of computer modelling.6 NMR spectroscopy showed that the benzylic C-H bonds are completely converted to C-D bonds in the presence of ODin D20 before an appreciable amount of polymer is formed. This