Multiphoton infrared absorption from a focused, pulsed CO(2) laser was used to initiate gas-phase thermal reactions of cis- and trans-3-penten-2-yl acetate. By varying the helium buffer gas pressure, it was possible to deduce the product distribution from the initial unimolecular reactions, separate from secondary reactions in a thermal cascade. Thus, trans-3-penten-2-yl acetate gives 54 +/- 5% of beta-elimination to give trans-1,3-pentadiene, 40 +/- 3% of [3,3]-sigmatropic rearrangement to give cis-3-penten-2-yl acetate and 6 +/- 4% of cis-1,3-pentadiene. Similar irradiation of cis-3-penten-2-yl acetate gives 45 +/- 1% of beta-elimination to give cis-1,3-pentadiene, 32 +/- 2% of [3,3]-sigmatropic rearrangement to give trans-3-penten-2-yl acetate and 23 +/- 2% of trans-1,3-pentadiene. The latter process is an eight-centered delta-elimination, which is argued to be a pseudopericyclic reaction. Although beta-eliminations have been suggested to be pericyclic, B3LYP/6-31G(d,p), MP2 and MP4 calculations suggest that both beta- and delta-eliminations, as well as [3,3]-sigmatropic rearrangements of esters are primarily pseudopericyclic in character, as judged by both geometrical, energetic and transition state aromaticity (NICS) criteria. Small distortions from the ideal pseudopericyclic geometries are argued to reflect small pericyclic contributions. It is further argued that when both pericyclic and pseudopericyclic orbital topologies are allowed and geometrically feasible, the calculated transition state may be the result of proportional mixing of the two states; this offers an explanation of the range of pseudopericyclic and pericyclic characters found in related reactions.
A novel inorganic sol-gel method for preparation of high-quality zirconia fibers was proposed, with starting from the reaction between ZrOCl 2 Á 8H 2 O (ZOC) and H 2 O 2 . The spinning solution with good spinnability was obtained by controlling the mole ratio of H 2 O 2 /ZOC to 4 for reaction, and the mole ratio of Cl/Zr remained close to 1 in the reacted solution. The double chain structure of the inorganic polyzirconium molecule in the spinning solution was determined by elemental analysis and FT-IR. The precursor fibers were obtained by using a novel 30,000 rpm centrifugal spinning apparatus. Being heat-treated to 1300 C under steam atmosphere, the precursor fibers transformed to zirconia fibers which had relatively high strength and good flexibility, with length of more than 10 cm and diameters of 5-10 mm.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.