Infrared multiphoton photochemistry of vinylcyclopropane. Variation of yield and branching ratio with experimental parameters

Abstract

when the ligand atoms are arranged in a nearly collinear fashion, solution structural determinations such as those pertaining to the ligand fluxionality and kinetics, ligation of simple well-defined molecules to biological molecules in solution, etc. It is clear that such structural information involving the distant, normally nonbonding, shells can greatly facilitate either interpretation of the mode of binding of known ligands or identification of the unknown ligands. These applications will be subjects of future publications.Acknowledgment. I am indebted to Dr. P. A. Lee (Bell Laboratories) for his generous assistance and consultations throughout the course of this work. I am also grateful to Dr. J. Rowe (Bell Laboratories) and Dr. C. J. Powell (NBS) for helpful discussions on electron mean free path. Thanks also go to Dr. B. M. Kincaid, A. Simons, and B. Chambers for their assistance in programming and Drs. J. Miller and S. Lippard for samples of 2 and 3, respectively. The experimental EXAFS measurements were made at the Stanford Synchrotron Radiation Laboratory with the financial support of the National Science Foundation under Contract DMR 77-27489 in cooperation with the U.S. Department of Energy.Tables I-IV contain scattering amplitude and phase functions for carbon and oxygen and the least-squares refined fitting parameters for AB and ABC fits. Figures A and B contain best AB fits and parameter correlations for 1-3 (15 pages). Ordering information is given on any current masthead page. Abstract:The infrared photochemistry of vinylcyclcpropane has been comprehensively investigated. Irradiation of vinylcyclopropane at relatively low pressures with the partially focused output of a C 0 2 TEA laser leads to a mixture of the C5 products cyclopentene, cyclopentadiene, 1,4-pentadiene, and cis-and trans-1,3-pentadiene. The composition of the product mixture as well as the total product yields are a sensitive function of experimental parameters. The effects of bath gas pressure, laser power, laser intensity, laser frequency, and number of pulses have been systematically examined. A simple physical picture of the multiphoton activation and resulting decomposition is developed. RRKM theory is employed to calculate energy-dependent unimolecular reaction rates. The model is quite successful in rationalizing these data, providing good evidence for the qualitative validity of a rate equation description of infrared multiphoton dissociation.

Multiple Photon IR Laser Photophysics and Photochemistry. V

“…So, the products of IR MP molecular dissociation strongly depend on the conditions of their excitation. If at thermal initiation the channels of chemical reaction and the final products are fully determined by thermodynamics, at nonequilibrium IR MP initiation it is possible, as shown above (and other work, [26][27][28][29][30][31][32][33] to control the channels of chemical reactions and make the unusual channels studied under equilibrium conditions more competitive by changing the laser pulse parameters. In this respect the method of IR MP initiation (IR photolysis) is much more effective than the conventional pyrolysis of molecules.…”

Comparisons of Infrared Multiple Photon Reaction Yields of Some C3–C6 Hydrocarbons

“…The carbon number and product identification was checked by retention time data, and by direct injection of authentic samples of expected products based on prior reports on some of these molecules. [8][9][10][11][12][13][14] In some instances GC-MS analysis was performed to ascertain the product identity.…”

“…We have undertaken a comparative study in several molecules having not dissimilar vibrational frequency patterns as part of an investigation of the influence of vibrational state density, lower vibrational manifold level spacings and linear absorption band intensity on the MPD and MPE of small molecules. In this paper we present and compare low pressure (approximately collisionless during the laser pulse) multiple photon reaction yields at a number of CO2 laser lines in cyclopropane, propylene, methylcyclopropane, cyclopentene and 1-methylcyclopentene at constant experimental conditions (pressure and fluence) along with previous data on vinylcyclopropane 9 and cisand trans-2-butene. 1 MPE results will be the subject of a later report.…”

Infrared multiphoton isomerization and fragmentation reactions of organic molecules

“…is substantially lower than for the primary reaction (trans + cis isome.rization), the primary product would never be observed in a conventional thermal reaction. Control of laser fluence and buffer gas pressure allows optimization of the yield of thermally labile primary products (11,18).…”

“…This result can be predicted from the dependence of the calculated RRKM rate constants upon the average energy deposited in the reactant molecule by a single laser pulse. Thus it is possible to control the branching ratios for competing reactions by varying the laser fluence and buffer gas pressure (18,19).…”