92548-78-2Relevant academic research and scientific papers
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.
Molecular conformations of jet-cooled 2-methylindan and 2-phenylindan
Hamza, Abdulhamid
experimental part, p. 939 - 945 (2011/11/01)
The molecular conformations of jet-cooled 2-methylindan (2MI) and 2-phenylindan (2PI) have been studied using resonant-enhanced two-photon ionization spectroscopy in combination with ab initio calculations. Both axial (2MIax) and equatorial (2MIeq) conformers of 2MI have been observed. A 2MIeq/2MIax conformer ratio of 2.3 was estimated at 298 K, leading to the energy difference, of 0.49 kcal/mol. Ab initio calculations predicted three stable conformers of 2PI: Two equatorial conformers (2PIeq0 and 2PIeq90), and one axial conformer (2PIax). Only the axial conformer of 2PI (2PIax) was experimentally observed. The indan ring of 2PIax is slightly more planar than the indan rings of the two equatorial conformers of 2PI because of the intramolecular Csp2-H/π interactions in 2PIax. The equatorial conformers of 2PI relax to the more stable axial conformer because of the high pre-expansion temperature (383 K), and relatively low barrier (1.68 kcal/mol) to axial-equatorial interconversion. The barrier (2.33 kcal/mol) to axial-equatorial interconversion in 2MI is high enough to prevent conformational relaxation at the pre-expansion temperature of 298 K. Intramolecular C-H/π interactions are found to be more important in determining the conformational preference of 2PI than 2MI; this can be attributed to the higher acidity of the Csp2-H bond than that of Csp3-H bond.
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
Photocyclization of -(o-Tolyl)acetophenones: Triplet and 1,5-biradical reactivity
Wagner, Peter J.,Meador, Michael A.,Zhou, Boli,Park, Bong-Ser
, p. 9630 - 9639 (2007/10/02)
Several ring-substituted α-(o-tolyl)acetophenones undergo photocyclization to 2-indanol derivatives in high quantum efficiency in solution and in high chemical yield as solids. The mechanism for reaction involves triplet state δ-hydrogen atom abstraction that generates 1,5-biradicals. Quenching studies indicate that the n.π* excited triplets of these ketones react, with rate constants >108 s-1. Variations in triplet reactivity are ascribed to conformational equilibria that populate reactive and unreactive geometries to different extents. The α-aryl ring eclipses the carbonyl in the lowest energy geometry, from which the most favorable geometry for reaction can be reached by small bond rotations. α-(2,4,6-Triisopropylpheny)acetophenone forms the relatively long lived enol as well as indanol in solvent-dependent ratios; deuterium labeling indicates that the 1,5-biradical disproportionates to form enol. This does not happen with α-mesitylacetophenone, so its 54% cyclization quantum efficiency is ascribed to an internal triplet quenching that competes with hydrogen abstraction. This internal quenching is presumed to be of the charge-transfer type and does not appear to lead directly to 1,5-biradicals. 1-Methyl-2-phenyl-2-indanol is formed from α-(o-ethylpheny)acetophenone with a Z/E ratio of 20:1 in benzene and 2:1 in methanol. The 1,5-biradical intermediates were characterized by flash spectroscopy; they have lifetimes between 15 and 45 ns, with those derived from α-(o-isopropylphenyl) ketones being twice as long-lived as those derived from α-(o-methylphenyl) ketones, and show only a small solvent dependence. Biradical lifetimes and the diastereoselectivity of cyclization are interpreted in terms of biradical intersystem crossing occurring preferentially along the reaction coordinate for cyclization, such that the two processes effectively occur concurrently. The applicability of this concept to other biradicals is discussed.
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.
EFFICIENT SOLID STATE PHOTOCYCLIZATION OF STERICALLY CONGESTED α-o-TOLYL KETONES DESPITE "POOR" GEOMETRIES FOR HYDROGEN ABSTRACTION
Wagner, Peter J.,Zhou, Boli
, p. 5389 - 5392 (2007/10/02)
Several α-mesityl and α-(o-tolyl)acetophenones undergo photocyclization to 2-indanols almost quantitatively when irradiated as crystals, even those that undergo significant competing α-cleavage or 1,3-aryl shift in solution.The requisite triplet δ-hydrogen abstraction apparently can occur at what appears to be a "bad" geometry.One ketone, α-(o-tolyl)propiophenone, partially rearranges to the β-isomer, which arises from disproportionation of the radicals formed by initial α-cleavage.
Prospects for solar synthesis. II. Study of the photocyclization of α-(o-tolyl)acetophenone in solution and in crosslinked ethylene-vinyl acetate beads
Guillet, J. E.,MacInnis, W. K.,Redpath, A. E.
, p. 1333 - 1336 (2007/10/02)
Studies of the photocyclization of α-(o-tolyl)acetophenone dissolved in crosslinked ethylene-vinyl acetate beads show that quantum yields close to unity can be achieved, even in the solid polymer matrix.In preliminary experiments using solar radiation it
Acidities of Indene and Phenyl-, Diphenyl-, and Triphenylindenes
Bordwell, F.G.,Drucker, George E.
, p. 3325 - 3328 (2007/10/02)
Equilibrium acidities in Me2SO for indene and 2-phenyl-, 3-phenyl-, 1,3-diphenyl-, 2,3-diphenyl-, and 1,2,3-triphenylindenes are reported.The pKa values for indene and 1,3-diphenylindene agree reasonably well with literature values once the lat
