Systematische Untersuchungen zum Polymorphismus organischer Substanzen

The zero-field splitting parameters D of the symmetrically disubstituted and unsymmetrically monosubstituted 1,3-diaryl-1,3-cyclopentanediyl triplet diradicals 1, 2 (X = p-MeO, p-Me, p-Cl, p-NH(2), p-CO(2)Me, p-CN, p-NO(2)), and 5 were determined in 2-methyltetrahydrofuran glass at 77 K. The linear plot (m = 0.558, r(2) = 0.993) of the experimental D values for the symmetrically disubstituted derivatives versus the corresponding monosubstituted ones reveals that the electronic substituent effects are additive and implies (except for the magnetic dipolar interaction) that each benzyl-type radical site acts independently in the localized diradicals. This additivity permits us to view these triplet diradicals as a composite of the two separate monoradical components and allows us to assess valuable electronic properties of benzyl-type monoradicals from the D parameter of the triplet diradical species. A theoretical analysis shows that the D parameter is a measure of the spin density rho at the benzylic positions and the inter-radical distance d in localized diradicals. A good correlation exists between the D parameter of these triplet diradicals (constant inter-radical distance d) and the EPR hyperfine coupling constants of the corresponding benzyl-type monoradicals, which establishes that the observed electronic substituent effects reflect changes in the spin densities at the radical sites. The novel DeltaD scale allows us to quantify spectroscopically the para substituent effect on the spin delocalization at the benzylic position.

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“…1-(4 ‘ -Methylphenyl)-3-phenyl-1,3-propanedione (6d, X = p -Me): 52%, colorless needles, mp 83 °C (ethanol, lit. , mp 84 °C).…”

Section: Methodsmentioning

confidence: 99%

The D Parameter (EPR Zero-Field Splitting) of Localized 1,3-Cyclopentanediyl Triplet Diradicals as a Measure of Electronic Substituent Effects on the Spin Densities in Para-Substituted Benzyl-Type Radicals

et al. 1996

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“…187 This compound was studied in detail by Weygand in 1929 who reported finding no less than 13 different forms. 188 Once the stable room temperature form has been obtained, it is extremely difficult to obtain any of the other forms. The compound is prepared by a simple condensation reaction between an aldehyde and a ketone.…”

Section: Polymorphs (Crystal Forms) and Patentsmentioning

confidence: 99%

“…As an example of this dilemma from the scientific point of view is our experience with p ′-methylchalcone . This compound was studied in detail by Weygand in 1929 who reported finding no less than 13 different forms . Once the stable room temperature form has been obtained, it is extremely difficult to obtain any of the other forms.…”

Section: Polymorphs (Crystal Forms) and Patentsmentioning

confidence: 99%

Polymorphism − A Perspective

Bernstein

2011

Crystal Growth & Design

344

297

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“…mp 57-58 °C). 42 2-Hydroxy-2-phenylpropionanilide (12). A solution of «-(2-thienyltelluro)acetanilide (0.35 g, 1.02 mmol) and benzaldehyde (0.11 g, 1.09 mmol) in dry THF (3 mL) was added dropwise during 5 min to a solution of lithium 2-thienyltellurolate [prepared according to procedure A from thiophene (0.25 g, 3.0 mmol), butyllithium (1.5 mL, 1.6 M, 2.4 mmol), and elemental tellurium (0.30 g, 2.35 mmol) in dry THF (10 mL)].…”

Section: Methodsmentioning

confidence: 99%

Organotellurium chemistry. 7. Reductive removal of electronegative .alpha.-substituents of ketones and acids by a tellurolate reagent

Engman¹,

Cava²

1982

J. Org. Chem.

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Lithium and sodium 2-thiophenetellurolates have been used for the reductive dehalogenation of a variety of -halo ketones and acids. Acetoxy, mesyloxy, and phenylthio groups were also successfully removed from the a position of an acetophenone. The reductions could in many cases be carried out by using sodium borohydride as the reducing agent in the presence of only a catalytic amount of the organotellurium reagent. Evidence is presented in support of a two-step mechanism involving the formation of -aryltelluro carbonyl derivatives and enolate anions in succession.Methods for the selective removal of certain functional groups adjacent to a carbonyl have recently received considerable attention. In particular, a number of procedures have been developed to bring about the reductive dehalogenation of -halo ketones. Zinc in acetic acid,1 11phos-phines2-5 and various inorganic phosphorus compounds,6 sodium borohydride,7 iodide ion,8-11 thiols12 and selenols,13 titanium trichloride,14 vanadium(II) chloride,15 N¿f-dimethylaniline,16 organotin hydrides,17 sodium dithionite,18 and various metal carbonyls19-21 are some of the reagents that have been used.The recent report of the use of sodium hydrogen telluride for the denomination of uic-dibromides22 and the early observation by Bergson23 that sodium telluride and sodium ditelluride reduced chloroacetic acid to acetic acid suggested that anionic organotellurium reagents might be capable of effecting the reductive dehalogenation of «-halo carbonyl compounds. We now describe the reductions of some «-substituted ketones and carboxylic acids using lithium and sodium 2-thiophenetellurolate (1). Results and DiscussionLithium arenetellurolates are readily available by the insertion of elemental tellurium into the carbon-metal bond of various organolithium compounds. This reaction is especially effective when the aromatic moiety is heter-

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Systematische Untersuchungen zum Polymorphismus organischer Substanzen

Cited by 31 publications

References 7 publications

The D Parameter (EPR Zero-Field Splitting) of Localized 1,3-Cyclopentanediyl Triplet Diradicals as a Measure of Electronic Substituent Effects on the Spin Densities in Para-Substituted Benzyl-Type Radicals

The D Parameter (EPR Zero-Field Splitting) of Localized 1,3-Cyclopentanediyl Triplet Diradicals as a Measure of Electronic Substituent Effects on the Spin Densities in Para-Substituted Benzyl-Type Radicals

Polymorphism − A Perspective

Organotellurium chemistry. 7. Reductive removal of electronegative .alpha.-substituents of ketones and acids by a tellurolate reagent

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