92548-78-2Relevant articles and documents
Structure-Kinetics Correlations in Isostructural Crystals of α-(ortho-Tolyl)-acetophenones: Pinning Down Electronic Effects Using Laser-Flash Photolysis in the Solid State
Ayitou, Anoklase J.-L.,Flynn, Kristen,Jockusch, Steffen,Khan, Saeed I.,Garcia-Garibay, Miguel A.
supporting information, p. 2644 - 2648 (2016/03/12)
Aqueous suspensions of nanocrystals in the 200-500 nm size range of isostructural α-(ortho-tolyl)-acetophenone (1a) and α-(ortho-tolyl)-para-methylacetophenone (1b) displayed good absorption characteristics for flash photolysis experiments in a flow system, with transient spectra and decay kinetics with a quality that is similar to that recorded in solution. In contrast to solution measurements, reactions in the solid state were characterized by a rate limiting hydrogen transfer reaction from the triplet excited state and a very short-lived biradical intermediate, which does not accumulate. Notably, the rate for δ-hydrogen atom transfer of 1a (2.7 × 107 s-1) in the crystalline phase is 18-fold larger than that of 1b (1.5 × 106 s-1). With nearly identical molecular and crystal structures, this decrease in the rate of δ-hydrogen abstraction can be assigned unambiguously to an electronic effect by the para-methyl group in 1b, which increases the contribution of the 3π,π? configuration relative to the reactive 3n,π? configuration in the lowest triplet excited state. These results highlight the potential of relating single crystal X-ray structural data with absolute kinetics from laser flash photolysis.
Addition and Cyclization Reactions in the Thermal Conversion of Hydrocarbons with Enyne Structure, I. Detailed Analysis of the Reaction Products of Ethynylbenzene
Hofmann, Joerg,Zimmermann, Gerhard,Guthier, Klaus,Hebgen, Peter,Homann, Klaus-Heinrich
, p. 631 - 636 (2007/10/02)
The pyrolysis of ethynylbenzene (C8H6, 1) was studied in a flow system between 700 and 1100 deg C (reaction time about 0.3 s) by using a mixture of 5 mol-percent of 1 in nitrogen and also in hydrogen at 700 deg C.The products were analyzed gas chromatogra
Diverse photochemistry of sterically congested α-arylacetophenones: ground-state conformational control of reactivity
Wagner, Peter J.,Zhou, Boli,Hasegawa, Tadashi,Ward, Donald L.
, p. 9640 - 9654 (2007/10/02)
The effects of α and ortho substituents on the photoreactivity of various α-(o-tolyl)- and α-mesitylacetophenones have been measured. In general, both types of substitution lower the efficiency of cyclization to 2-indanol derivatives in solution. 1,3-Rearrangement of an α-mesityl group to group to form enol ethers and α-cleavage to radicals compete to various degrees, in some cases becoming dominant. Quenching studies in solution show that all three reactions occur from the same n,π* triplet state; α-substitution lowers rate constants for δ-hydrogen abstraction and increases those for α-cleavage and 1,3-rearrangement. X-ray crystal analysis and MMX calculations both show that any additional substitution at the α-carbon of α-aryl (phenyl, tolyl, or mesityl) ketones favors conformers in which the α-aryl group have rotated 120° away from eclipsing the carbonyl. In agreement with this, α-phenyl and α-(o-tolyl) ketones undergo γ-hydrogen abstraction (Norrish type II reaction) with rate constants almost as large as those of the nonarylated ketones. NMR line-broadening studies show that, in most of the α-mesityl ketones, the rate constants for rotation around the mesityl-α-carbon bond (104-106 s-1) are much slower than triplet decay. The same is true for rotations around the carbonyl-α-carbon bond in the α-arylisobutyrophenones. Considered of the spectroscopic evidence, triplet lifetimes, and calculated rotational barriers indicates that ground-state conformational preferences determine which excited-state reactions can occur in most of these ketones. Many of the ketones that cyclize in low yield in solution do so in much higher yield when irradiated as solids, presumably because α-cleavage to radicals becomes mostly revertible. The solid-state reactivity demonstrates that hydrogen abstraction can occur from what are supposedly nonideal geometries; in particular, large values (60-70°) for the dihedral angle and rate constants for hydrogen abstraction in solution plane of the carbonyl π system. The relationship between this angle and rate constants for hydrogen abstraction in solution is discussed. Rate constants for α-cleavage reveal the separate influences of steric congestion and conjugation of the developing benzyl radicals. The 1,3-aryl migration to oxygen appears to arise from initial CT complexation of the α-aryl to the carbonyl; subsequent bonding of oxygen to the benzene ring apparently relieves steric congestion. The 50:50 initial mixture of Z and E enol ethers suggests that the rearrangement is adiabatic, generating enol ether in its twisted triplet state. A large enhancement of indanol yields by alcoholic solvents is suggested to involve protonation of the same CT complex.
