@article {4327,
	title = {An investigation of the yang photocyclization reaction in the solid state: Asymmetric induction studies and crystal structure-reactivity relationships},
	journal = {Journal of the American Chemical Society},
	volume = {120},
	number = {49},
	year = {1998},
	note = {ISI Document Delivery No.: 149MWTimes Cited: 101Cited Reference Count: 61},
	month = {Dec},
	pages = {12755-12769},
	type = {Article},
	abstract = {The Norrish/Yang type II photochemistry of 16 ketones having the basic cis-4-tert-butyl-1-benzoylcyclohexane or 2-benzoyladamantane structure has been investigated in the solid state and solution. In both media, ketones bearing methyl substituents alpha to the benzoyl group undergo stereoselective Yang photocyclization to afford endo-arylcyclobutanols. Quantum yield and quenching studies in solution show that the reactions are efficient triplet-mediated processes. Asymmetric induction studies were carried out by providing the reactants with carboxylic acid substituents to which "ionic chiral auxiliaries" were attached through salt formation with optically active amines. Irradiation of the salts (17 in total) in solution gave racemic cyclobutanols, but in the crystalline state, moderate to near-quantitative enantiomeric excesses were obtained. Single crystal X-ray diffraction studies were successfully performed on 10 neutral ketones and four salts. This allowed the reactive gamma-hydrogen atoms to be identified and the distance and angular parameters associated with their abstraction to be tabulated. For the 14 compounds whose crystal structures were determined, the average value of d, the C=O ... H abstraction distance, was 2.61 +/- 0.07 Angstrom, and the values of omega (the gamma-hydrogen out-of-plane angle), Delta (the C=O ... H, angle) and a (the C-H-gamma... O angle) were 53 +/- 11, 84 +/- 7, and 115 +/- 2 degrees, respectively. In a similar manner, the geometric parameters associated with the ring closure reactions of the intermediate 1,4-hydroxy biradicals were estimated from the crystallographic data. This indicates that the biradicals are 66.5 +/- 9.8 and 32.7 +/- 3.2 degrees out of alignment for cleavage, but that they are well oriented for cyclization, with radical separations (D) of 3.08 +/- 0.09 Angstrom. For one of the salts in the adamantane series, the solid-state photoreaction was shown to be topotactic; that is, a single crystal of the reactant salt was transformed quantitatively into a single crystal of the corresponding cyclobutanol salt. Since the absolute configuration of the ionic chiral auxiliary in this case was known, this permitted the absolute steric course of the reaction to be mapped by X-ray crystallography and the abstracted gamma-hydrogen to be identified unequivocally. In addition, the crystal structure of a partially reacted crystal containing 60\% product and 40\% reactant was successfully determined. This showed that the two compounds in the mixed crystal have nearly identical shapes and orientations, thus accounting for the single crystal nature of the process. Finally, it was found that ketones lacking methyl substituents alpha to the benzoyl group an either photochemically unreactive or undergo Norrish type II cleavage. Possible reasons for this difference in behavior are presented and discussed.},
	keywords = {BIRADICALS, CHEMISTRY, CONFORMATIONAL MEMORY, HYDROGEN-ATOM TRANSFERS, II PHOTOPROCESSES, KETONES, ORGANIC-PHOTOCHEMISTRY, PHENYL, POLYMERIZATION, SINGLE-CRYSTAL, TRANSITION STRUCTURES, TRIPLET},
	isbn = {0002-7863},
	url = {<Go to ISI>://000077610100007},
	author = {Leibovitch, M. and Olovsson, G. and Scheffer, J. R. and Trotter, J.}
}
@article {4327,
	title = {An investigation of the yang photocyclization reaction in the solid state: Asymmetric induction studies and crystal structure-reactivity relationships},
	journal = {Journal of the American Chemical Society},
	volume = {120},
	number = {49},
	year = {1998},
	note = {ISI Document Delivery No.: 149MWTimes Cited: 101Cited Reference Count: 61},
	month = {Dec},
	pages = {12755-12769},
	type = {Article},
	abstract = {The Norrish/Yang type II photochemistry of 16 ketones having the basic cis-4-tert-butyl-1-benzoylcyclohexane or 2-benzoyladamantane structure has been investigated in the solid state and solution. In both media, ketones bearing methyl substituents alpha to the benzoyl group undergo stereoselective Yang photocyclization to afford endo-arylcyclobutanols. Quantum yield and quenching studies in solution show that the reactions are efficient triplet-mediated processes. Asymmetric induction studies were carried out by providing the reactants with carboxylic acid substituents to which "ionic chiral auxiliaries" were attached through salt formation with optically active amines. Irradiation of the salts (17 in total) in solution gave racemic cyclobutanols, but in the crystalline state, moderate to near-quantitative enantiomeric excesses were obtained. Single crystal X-ray diffraction studies were successfully performed on 10 neutral ketones and four salts. This allowed the reactive gamma-hydrogen atoms to be identified and the distance and angular parameters associated with their abstraction to be tabulated. For the 14 compounds whose crystal structures were determined, the average value of d, the C=O ... H abstraction distance, was 2.61 +/- 0.07 Angstrom, and the values of omega (the gamma-hydrogen out-of-plane angle), Delta (the C=O ... H, angle) and a (the C-H-gamma... O angle) were 53 +/- 11, 84 +/- 7, and 115 +/- 2 degrees, respectively. In a similar manner, the geometric parameters associated with the ring closure reactions of the intermediate 1,4-hydroxy biradicals were estimated from the crystallographic data. This indicates that the biradicals are 66.5 +/- 9.8 and 32.7 +/- 3.2 degrees out of alignment for cleavage, but that they are well oriented for cyclization, with radical separations (D) of 3.08 +/- 0.09 Angstrom. For one of the salts in the adamantane series, the solid-state photoreaction was shown to be topotactic; that is, a single crystal of the reactant salt was transformed quantitatively into a single crystal of the corresponding cyclobutanol salt. Since the absolute configuration of the ionic chiral auxiliary in this case was known, this permitted the absolute steric course of the reaction to be mapped by X-ray crystallography and the abstracted gamma-hydrogen to be identified unequivocally. In addition, the crystal structure of a partially reacted crystal containing 60\% product and 40\% reactant was successfully determined. This showed that the two compounds in the mixed crystal have nearly identical shapes and orientations, thus accounting for the single crystal nature of the process. Finally, it was found that ketones lacking methyl substituents alpha to the benzoyl group an either photochemically unreactive or undergo Norrish type II cleavage. Possible reasons for this difference in behavior are presented and discussed.},
	keywords = {BIRADICALS, CHEMISTRY, CONFORMATIONAL MEMORY, HYDROGEN-ATOM TRANSFERS, II PHOTOPROCESSES, KETONES, ORGANIC-PHOTOCHEMISTRY, PHENYL, POLYMERIZATION, SINGLE-CRYSTAL, TRANSITION STRUCTURES, TRIPLET},
	isbn = {0002-7863},
	url = {<Go to ISI>://000077610100007},
	author = {Leibovitch, M. and Olovsson, G. and Scheffer, J. R. and Trotter, J.}
}
@article {3687,
	title = {Geometric requirements for hydrogen abstractability and 1,4-biradical reactivity in the Norrish/Yang type II reaction: Studies based on the solid state photochemistry and X-ray crystallography of medium-sized ring and macrocyclic diketones},
	journal = {Journal of the American Chemical Society},
	volume = {118},
	number = {26},
	year = {1996},
	note = {ISI Document Delivery No.: UV292Times Cited: 41Cited Reference Count: 76},
	month = {Jul},
	pages = {6167-6184},
	type = {Article},
	abstract = {The Norrish/yang type II photochemistry of ten even-numbered cyclic diketones ranging in ring size from 10-membered to 26-membered has been studied in the crystalline state as well as in solution, In the solid state, the diketones undergo stereoselective cyclobutanol formation in which the cis or trans ring fusion stereochemistry of the photoproducts is governed by the conformation of the diketone present in the crystal as determined by X-ray crystallography. The reactive gamma-hydrogen atoms are identified and the distance and angular parameters associated with their abstraction are derived from the crystallographic data. For the most part, the abstractions occur through boatlike rather than chairlike six-atom geometries, and the average value of d, the C=O ... H abstraction distance, for 16 reactive gamma-hydrogens was found to be 2.74 +/- 0.04 Angstrom; the average values of the angular parameters omega (the gamma-hydrogen out-of-plane angle), Delta (the C=O ... H-gamma angle), and theta (the C-H gamma ... O angle) are 53 +/- 5 degrees, 83 +/- 4 degrees, and 115 +/- 2 degrees, respectively. In a similar manner, the geometric parameters associated with the ring closure reactions of the intermediate 1,4-hydroxy biradicals were estimated from the crystallographic data. This indicates that both the pre-cis and pre-trans biradicals are poorly aligned for cleavage but are well oriented for closure, with radical separations of 3.1-3.2 Angstrom. For four of the diketones, the solid state photoproduct ratios were found to be temperature dependent as a result of enantiotropic phase transitions. For two of the diketones, the high-temperature, metastable phases were characterized by solid state C-13 and H-2 NMR spectroscopy. Crystals of 1,14-cyclohexacosanedione were found to be dimorphic, and the conformation adopted by the macrocycle is very different in the two dimorphs. As a result, irradiation of one of the dimorphs leads to cis-cyclobutanol and photolysis of the other gives trans, a particularly clear demonstration of the effect of conformational polymorphism on solid state chemical reactivity. Overall, the solid state results indicate that the product distribution is determined by the relative rates of forward rather than reverse hydrogen atom transfer and that the biradicals react in a least-motion, conformation-specific manner. In solution, on the other hand, the photoreaction is ring size-dependent, resembling the solid state results for the 12- and 14-membered-ring diketones, and consisting mainly of type II elimination accompanied by reduced amounts of nonstereoselective cyclobutanol formation for the 16-26-membered-ring compounds. It is suggested that this ring size dependence stems from the relative conformational freedom of the intermediate 1,4-biradicals in the fluid medium-motions that are slow compared to closure for the 12- and 14-membered rings, but that permit alignment for biradical cleavage and alternative modes of closure in the {\textquoteright}{\textquoteright}floppier{\textquoteright}{\textquoteright} 16-membered and larger rings. The one exception to the above generalizations is 1,6-cyclodecanedione, which was found to be photochemically inert both in the solid state and solution despite having a crystal conformation favorable for type II photochemistry. Possible reasons for this behavior are presented and discussed.},
	keywords = {ATOM TRANSFERS, C-H...O, CONFORMATION, CYCLOALKANONES, CYCLODODECANONE, CYCLOHEXADECANE, MOLECULAR MECHANICS METHODOLOGY, PHENYL KETONES, PHOTOPROCESSES, TRANSITION STRUCTURES},
	isbn = {0002-7863},
	url = {<Go to ISI>://A1996UV29200012},
	author = {Gudmundsdottir, A. D. and Lewis, T. J. and Randall, L. H. and Scheffer, J. R. and Rettig, S. J. and Trotter, J. and Wu, C. H.}
}
@article {3687,
	title = {Geometric requirements for hydrogen abstractability and 1,4-biradical reactivity in the Norrish/Yang type II reaction: Studies based on the solid state photochemistry and X-ray crystallography of medium-sized ring and macrocyclic diketones},
	journal = {Journal of the American Chemical Society},
	volume = {118},
	number = {26},
	year = {1996},
	note = {ISI Document Delivery No.: UV292Times Cited: 41Cited Reference Count: 76},
	month = {Jul},
	pages = {6167-6184},
	type = {Article},
	abstract = {The Norrish/yang type II photochemistry of ten even-numbered cyclic diketones ranging in ring size from 10-membered to 26-membered has been studied in the crystalline state as well as in solution, In the solid state, the diketones undergo stereoselective cyclobutanol formation in which the cis or trans ring fusion stereochemistry of the photoproducts is governed by the conformation of the diketone present in the crystal as determined by X-ray crystallography. The reactive gamma-hydrogen atoms are identified and the distance and angular parameters associated with their abstraction are derived from the crystallographic data. For the most part, the abstractions occur through boatlike rather than chairlike six-atom geometries, and the average value of d, the C=O ... H abstraction distance, for 16 reactive gamma-hydrogens was found to be 2.74 +/- 0.04 Angstrom; the average values of the angular parameters omega (the gamma-hydrogen out-of-plane angle), Delta (the C=O ... H-gamma angle), and theta (the C-H gamma ... O angle) are 53 +/- 5 degrees, 83 +/- 4 degrees, and 115 +/- 2 degrees, respectively. In a similar manner, the geometric parameters associated with the ring closure reactions of the intermediate 1,4-hydroxy biradicals were estimated from the crystallographic data. This indicates that both the pre-cis and pre-trans biradicals are poorly aligned for cleavage but are well oriented for closure, with radical separations of 3.1-3.2 Angstrom. For four of the diketones, the solid state photoproduct ratios were found to be temperature dependent as a result of enantiotropic phase transitions. For two of the diketones, the high-temperature, metastable phases were characterized by solid state C-13 and H-2 NMR spectroscopy. Crystals of 1,14-cyclohexacosanedione were found to be dimorphic, and the conformation adopted by the macrocycle is very different in the two dimorphs. As a result, irradiation of one of the dimorphs leads to cis-cyclobutanol and photolysis of the other gives trans, a particularly clear demonstration of the effect of conformational polymorphism on solid state chemical reactivity. Overall, the solid state results indicate that the product distribution is determined by the relative rates of forward rather than reverse hydrogen atom transfer and that the biradicals react in a least-motion, conformation-specific manner. In solution, on the other hand, the photoreaction is ring size-dependent, resembling the solid state results for the 12- and 14-membered-ring diketones, and consisting mainly of type II elimination accompanied by reduced amounts of nonstereoselective cyclobutanol formation for the 16-26-membered-ring compounds. It is suggested that this ring size dependence stems from the relative conformational freedom of the intermediate 1,4-biradicals in the fluid medium-motions that are slow compared to closure for the 12- and 14-membered rings, but that permit alignment for biradical cleavage and alternative modes of closure in the {\textquoteright}{\textquoteright}floppier{\textquoteright}{\textquoteright} 16-membered and larger rings. The one exception to the above generalizations is 1,6-cyclodecanedione, which was found to be photochemically inert both in the solid state and solution despite having a crystal conformation favorable for type II photochemistry. Possible reasons for this behavior are presented and discussed.},
	keywords = {ATOM TRANSFERS, C-H...O, CONFORMATION, CYCLOALKANONES, CYCLODODECANONE, CYCLOHEXADECANE, MOLECULAR MECHANICS METHODOLOGY, PHENYL KETONES, PHOTOPROCESSES, TRANSITION STRUCTURES},
	isbn = {0002-7863},
	url = {<Go to ISI>://A1996UV29200012},
	author = {Gudmundsdottir, A. D. and Lewis, T. J. and Randall, L. H. and Scheffer, J. R. and Rettig, S. J. and Trotter, J. and Wu, C. H.}
}
@article {7308,
	title = {CRYSTALLOGRAPHIC DETERMINATION OF THE PREFERRED GEOMETRY FOR INTRAMOLECULAR HYDROGEN-ATOM ABSTRACTION IN 1,8-CYCLOHEXADECANEDIONE},
	journal = {Molecular Crystals and Liquid Crystals},
	volume = {219},
	year = {1992},
	note = {ISI Document Delivery No.: JD451Times Cited: 6Cited Reference Count: 2410TH INTERNATIONAL CONF ON THE CHEMISTRY OF THE ORGANIC SOLID STATE ( ICCOSS 10 )JUL 07-12, 1991VANCOUVER, CANADACHEM INST CANADA, NAT SCI \& ENGN RES COUNCIL CANADA, PETR RES FUND, UNIV BRIT COLUMBIA, BRUKER SPECTROSPIN CANADA, CHEMAGNETICS, DOTY SCI, GORDON \& BREACH SCI PUBL},
	pages = {17-28},
	type = {Proceedings Paper},
	keywords = {CRYSTAL STRUCTURE-REACTIVITY, HYDROGEN ABSTRACTION GEOMETRY, II REACTIONS, MACROCYCLIC DIKETONE, MOLECULAR MECHANICS METHODOLOGY, NORRISH TYPE-II REACTION, PHOTOCHEMISTRY, REACTIVITY, RELATIONSHIPS, SOLID STATE ORGANIC PHOTOCHEMISTRY, STATE, TRANSFERS, TRANSITION STRUCTURES},
	isbn = {0140-6566},
	url = {<Go to ISI>://A1992JD45100002},
	author = {Lewis, T. J. and Rettig, S. J. and Scheffer, J. R. and Trotter, J.}
}
@article {7308,
	title = {CRYSTALLOGRAPHIC DETERMINATION OF THE PREFERRED GEOMETRY FOR INTRAMOLECULAR HYDROGEN-ATOM ABSTRACTION IN 1,8-CYCLOHEXADECANEDIONE},
	journal = {Molecular Crystals and Liquid Crystals},
	volume = {219},
	year = {1992},
	note = {ISI Document Delivery No.: JD451Times Cited: 6Cited Reference Count: 2410TH INTERNATIONAL CONF ON THE CHEMISTRY OF THE ORGANIC SOLID STATE ( ICCOSS 10 )JUL 07-12, 1991VANCOUVER, CANADACHEM INST CANADA, NAT SCI \& ENGN RES COUNCIL CANADA, PETR RES FUND, UNIV BRIT COLUMBIA, BRUKER SPECTROSPIN CANADA, CHEMAGNETICS, DOTY SCI, GORDON \& BREACH SCI PUBL},
	pages = {17-28},
	type = {Proceedings Paper},
	keywords = {CRYSTAL STRUCTURE-REACTIVITY, HYDROGEN ABSTRACTION GEOMETRY, II REACTIONS, MACROCYCLIC DIKETONE, MOLECULAR MECHANICS METHODOLOGY, NORRISH TYPE-II REACTION, PHOTOCHEMISTRY, REACTIVITY, RELATIONSHIPS, SOLID STATE ORGANIC PHOTOCHEMISTRY, STATE, TRANSFERS, TRANSITION STRUCTURES},
	isbn = {0140-6566},
	url = {<Go to ISI>://A1992JD45100002},
	author = {Lewis, T. J. and Rettig, S. J. and Scheffer, J. R. and Trotter, J.}
}
