Theoretical study of substituent effects on the acidity of the methyl group: Structure of anions CH2X−

Geometries have been optimized using molecular-orbital calculations (a) with a 4-31G Gaussian basis set for carbanions CH₂X^? where X = H, CH₃, NH₂, OH, F, C?CH, CH?CH₂, CHO, COCH₃, CN, and NO₂; and (b) with an STO -3G basis set for methyl acetate and acetyl deprotonated methyl acetate. All the carbanions containing unsaturated substituents are planar, with a considerable shortening of the C? X bond. Carbanions containing saturated substituents are pyramidal with the out-of-plane angle α increasing with the electronegativity of the substituent. Double-zeta basis set calculations give proton affinities over the range 449 (for CH₃CH₂^?) to 355 kcal/mol (for CH₂NO₂^?), with all unsaturated anions having smaller affinities than saturated anions. The correlation of proton affinities with 1s binding energies, and with charges on both the carbon of the anion and on the acidic proton of the neutral molecule are examined.     

A theoretical study of α-substituted cyclopropyl and isopropyl radicals

The structures of α-X-cyclopropyl and α-X-isopropyl radicals (X = H, CH₃, NH₂, OH, F, CN, and NC) are reported at the RHF 3-21G level of theory. The isopropyl radicals are pyramidal with out-of-plane angles varying from 12° (X = CN) to 39° (X = NH₂), and barriers to inversion ranging from 0.4 kcal/mol (X = H) to 4.0 kcal/mol (X = NH₂). The cyclopropyl radicals have larger out-of-plane angles, from 39.9° (X = CN) to 49.4° (X = NH₂), and their barriers to inversion, which increase with the inclusion of polarization functions, vary from 5.5 kcal/mol (X = H) to 16.7 kcal/mol (X = F). In both types of radicals the amino group is the most stabilizing substituent, while the α-fluoro has little effect. The β-fluoro group is weakly destabilizing in the cyclopropyl radical. The strain energies of the cyclopropyl radicals (36–43 kcal/mol) are compared with those of similarly substituted anions, cations, and cyclopropanes.     

A theoretical study of α-substituted isopropyl and cyclopropyl anions

Ab initio molecular orbital theory has been used to probe the effect of the substituent X on the structures, strain energies, stabilization energies, inversion barriers, and proton affinities of carbanions CH₃CX CH and cis-C₃H₄X^?, where X = H, F, CN, and NC. All geometries have been optimized with a 3-21G basis set, and the parent anions (X = H) were also optimized with the same basis set with a diffuse function added (i.e. the 3-21 + G basis set). The anions, with the exception of the α-cyanoisopropyl anion, are pyramidal. The out-of-plane angle, α, for the pyramidal anions decreases in the order F > H ≈ NC > CN, and the barriers to inversion follow the same order with the cyclopropyl anions consistently having higher barriers than the isopropyl anions. The substituents strongly stabilize the anions with the stabilization energy following the order CN > NC > F. The cyano group slightly reduces the strain energy of cyclopropane, but the isocyano and fluoro substituents are weakly and strongly destabilizing, respectively. The pyramidal cyclopropyl anions are less strained than the cyclopropanes except when the substituent is a cyano group where the strain energies are reversed but are very similar. The planar anions all have higher strain energies than the cyclopropanes.     

FTIR study of adsorption and surface reactions of N(CH3)3 on TiO2

Fourier transform infrared spectroscopy has been employed to investigate the N(CH3)3 adsorption, thermal stability, and photochemical reactions on powdered TiO2. N(CH3)3 molecules are adsorbed on TiO2 without dissociation at 35 degrees C and are completely desorbed from the surface at 300 degrees C in a vacuum. The CH3 rocking frequencies of N(CH3)3 on TiO2 are affected via the interaction between N(CH3)3 and TiO2 surface OH groups. In the presence of O2, adsorbed N(CH3)3 decomposes thermally at 230 degrees C and photochemically under UV irradiation. In the latter case with comparative (16)O2 and (18)O2 studies, CO2(g), NCO(a), HCOO(a), and surface species containing C=N or NH(x) functional groups are identified to be the photoreaction products or intermediates. In the presence of (18)O2, the main formate species formed is HC(16)O(18)O(a). As H2O is added to the photoreaction system, a larger percentage of adsorbed N(CH3)3 is consumed. However, in the presence of (18)O2 and H2O, the amount of HC(16)O(18)O(a) becomes relatively small, compared to HC(16)O(16)O(a). A mechanism is invoked to explain these results. Furthermore, based on the comparison of isotopic oxygens in the formate products obtained from CH3O(a) photooxidation in (16)O2 and (18)O2, it is concluded that the N(CH3)3 photooxidation does not generate CH3O(a) in which the oxygen belongs to TiO2.     

Synthesis and characterization of new low bandgap polyfluorene copolymers for bulk heterojunction solar cells

Two new low bandgap alternating polyfluorene copolymers based on dioctylfluorene and donor‐acceptor‐donor monomers have been synthesized via a Suzuki polymerization reaction. The resulting copolymers have low optical bandgaps at 1.99–1.98 eV. The bulk heterojunction polymer solar cells were fabricated with the conjugated polymers as the electron donor and 6.6‐phenyl C₆₁‐butyric acid methyl ester as the electron acceptor. The power conversion efficiencies of the solar cells based on copolymers 1 and 2 are 0.37 and 0.42%, respectively, under the illumination of AM 1.5, 100 mW/cm². The results indicate that the two copolymers are promising conjugated polymers for polymer solar cells. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5336–5343, 2009     

Robust control for Takagi–Sugeno fuzzy systems with time-varying state and input delays

The paper investigates the robust control for uncertain Takagi–Sugeno (T–S) fuzzy systems with time-varying state and input delays. Delay-dependent stabilization criterion is proposed to guarantee the asymptotic stabilization of fuzzy systems with parametric uncertainties. The result of [Lee HJ, Park JB, Joo YH. Robust control for uncertain Takagi–Sugeno fuzzy systems with time-varying input delay. ASME J Dyn Syst Meas Control 2005;127:302–6] is extended to uncertain fuzzy systems with time-varying state and input delays. Simulations show that significant improvement over the previous results can be obtained.