Effect of configuration and conformation on the spin multiplicity in xylylene type biradicals
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Xylylene
Multiplicity (mathematics)
We judge the energetic sequence of spin states in substituted methylenes by ab initio multiconfigurational computations and, where feasible, density functional modeling techniques. The best of these calculations reproduce well-established singlet−triplet gaps in X−C−Y species, in which X can be phenyl and Y can be H, methyl, or chloro. Similar computations on p-phenylene-coupled Y−methylenes and meta-coupled Y−methylenes support the suggestion by Zuev and Sheridan that bis(chloromethylene)-p-phenylene has a singlet diradical ground state. However, despite the density functional computations' support for those authors' suggestion that bis(chloromethylene)-m-phenylene has a singlet ground state, we find that our best MCSCF calculations place the quintet ground state suggested by the simplest theory almost equal in energy to that singlet.
Diradical
Methylene
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Abstract Spiro ‐di‐ o ‐xylylene polymerizes via a free‐radical mechanism to give high molecular weight poly( o ‐xylylene). It reacts with olefinic molecules, such as styrene, acrylonitrile, methyl methacrylate, vinylidine fluoride, and butadiene to give copolymers containing di‐ o ‐xylylene units in its backbone. Solutions of spiro ‐di‐ o ‐xylylene can be titrated with iodine, and di‐ o ‐xylylene‐di‐iodide is produced stoichiometrically. Telomers of di‐ o ‐xylylene are obtained when the spiro compound is allowed to react in the presence of chain transfer agents such as HSR and CBr 4 .
Xylylene
Chloroprene
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Organic molecules with a strong preference for triplet ground states, in which the triplet state is below the lowest singlet state by ≥10 kcal/mol, are typically short-lived and mostly detected as reactive intermediates. We now report a triplet ground state derivative of aza-m-xylylene diradical with a large singlet−triplet energy gap (ΔEST) of ∼10 kcal/mol, which is comparable to ΔEST for the well-known reactive intermediate m-xylylene diradical. The aminyl diradical persists in solution at room temperature on the time scale of minutes.
Diradical
Xylylene
Derivative (finance)
Singlet fission
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The TG(DTG) and DTA of poly(p-xylylene) and poly(α,α,α′,α′-tetrafluoro-p-xylylene) are reported. The degradation was performed from ambient temperature to 900°C in both air and nitrogen. Both polymer degrade faster in air than under nitrogen but the fluorinated polymer eventually decomposed at higher temperature in air than in nitrogen atmosphere. The activation energies of the degradation processes is given.
Xylylene
Degradation
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ポリマーマトリックスにジメチルアンモニウム,ピペリジニウムおよびモルホリニウムを保有するポリカチオン(Mx)の7,7,8,8-テトラシアノキノジメタソアニオンラジカル塩(CQ塩)を合成し,N置換基の電導性におよぼす影響を比抵抗ρおよび電導の活性化エネルギー Eaから検討した。XX-CQ, PX-CQおよびMX-CQのρは, simple saltではそれぞれ1.4x10 10,1.8x10 10,6.5x10 3 Ω,cm, complex saltでは4.6x10 2,4.8x10 3,2.0x10 2Ω,cmであった。 dopeによりXX-CQはPX-CQに比較してρおよびEaの低下がいちじるしいが,これはピペリジン基がCQのpackingに大きく影響するためと考えられる。MX-CQのsimple saltではいちじるしくρが低く, dopingによるρの低下もきわめて小さい。これはモルホリン環の酸素原子が電導にいちじるしく寄与しており,dopeにさいしてはモルホリソ環が配列の障害となってρの低下を妨げるものと推定した。
Xylylene
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We describe synthesis and characterization of a derivative of aza-m-xylylene, diradical 2, that is persistent in solution at room temperature with the half-life measured in minutes (∼80-250 s) and in which the triplet ground state is below the lowest singlet state by >10 kcal mol(-1). The triplet ground states and ΔEST of 2 in glassy solvent matrix are determined by a new approach based on statistical analyses of their EPR spectra. Characterization and analysis of the analogous diradical 1 are carried out for comparison. Statistical analyses of their EPR spectra reliably provide improved lower bounds for ΔEST (from >0.4 to >0.6 kcal mol(-1)) and are compatible with a wide range of relative contents of diradical vs monoradical, including samples in which the diradical and monoradical are minor and major components, respectively. This demonstrates a new powerful method for the determination of the triplet ground states and ΔEST applicable to moderately pure diradicals in matrices.
Diradical
Xylylene
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Xylylene
Diradical
Coupling constant
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Abstract The singlet–triplet energy difference in para ‐, meta ‐, and ortho ‐xylylenes is studied as the interaction of two radical centers through the benzene ring. An SCF perturbative procedure adapted to open‐shell systems leads to two benzyl‐like nonbonding molecular orbitals ( NBMOS ) and to benzene‐like occupied and vacant MOS whatever the xylylene isomer. The superposition of these NBMOS in para ‐, meta ‐, and ortho ‐positions and their interaction with the benzene‐like MOS lead, at the configuration interaction level, to the following results: The exchange energy (which favors the triplet state) and the charge transfer energy (which favors the singlet state) are important only in the meta ‐xylylene; the dynamic (or double) spin polarization favors the triplet in meta and the singlet in para and ortho ‐isomers; the super‐exchange energy (which favors the singlet) is important only in para ‐ and ortho ‐isomers. The above results are independent of the chosen geometry.
Xylylene
Interaction energy
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Xylylene
Atmospheric temperature range
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Abstract The air oxidation of poly‐ p ‐xylylene films was studied at temperatures between 125 and 200°C. The oxidation kinetics were obtained from neutron activation (NA) oxygen analyses and infrared (IR) Spectroscopy. A correlation between the NA oxygen analyses and mechanical properties indicated that the amount of oxygen incorporated into these polymers before a significant degradation mechanical properties is about 1000 ppm for poly(dichloro‐ p ‐xylylene) and 5000 ppm for poly(monochloro‐ p ‐xylylene) or poly‐ p ‐xylylene. The activation energy for the oxidation of these polymers was about 30 kcal/mole. Long‐term‐use (100,000 hr) temperatures were also estimated for each of the poly‐ p ‐xylylenes studied. The 100,000‐hr maximum continuous‐use temperature is 112°C for poly(dichloro‐ p ‐xylylene), 72°C for poly(monochloro‐ p ‐xylylene), and 57°C for poly‐ p ‐xylylene.
Xylylene
Thermal Stability
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