A 1H NMR Investigation of Rotational Isomerism and Hydrogen Bonding in 1,2-Diarylethanols.

Abraham, Raymond J.; Bakke, Jan M.; Nybergh, Anna; Vallén, Staffan; Enzell, Curt R.

doi:10.3891/acta.chem.scand.35b-0367

Cited by 7 publications

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“…The stability of the endo structure 1b had been attributed to intramolecular OH···π-density hydrogen bonding , We propose an explanation of the relative stabilities of 1a − c that considers the conformation dependences of the effects of electron−electron repulsion between the O lone pairs and the benzene π-cloud, the charge−charge attraction between the hydroxyl H atom and the benzene π-density, and the dipole−dipole interaction associated with the CH 2 −C ipso and −OH bonds. Note that the charge−charge attraction between the hydroxyl H atom and the benzene π-density would be very much different from the OH···π-density hydrogen bonding invoked by others.…”

Section: Resultsmentioning

confidence: 95%

Conformational Preferences and Pathways for Enantiomerization and Diastereomerization of Benzyl Alcohol. Data Mining and ab Initio Quantum-Mechanical Study

and

Nichols

2000

J. Org. Chem.

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The potential energy surface of benzyl alcohol has been explored at the RHF/6-31G* and MP2-(full)/6-31G* levels of ab initio theory. The exo and endo minimum structures and all of the transition-state structures for their enantiomerization and diastereomerization were located. The thermochemical functions were computed, and relative enthalpies and free enthalpies were determined. The computed relative free enthalpy is in excellent agreement with known NMR data. Benzyl alcohol is a highly flexible molecule, which allows for essentially unhindered enantiomerization and diastereomerization of the minima; all pertinent relative energies and free enthalpies are less than 3 kcal/mol, and the entire conformational space about the CC and CO bonds is easily accessible. An examination of the crystallographic record shows a much greater variety of conformations to occur in the solid state as a result of the optimization of intermolecular interactions in the crystals. Data mining shows that the conformations about the CC and CO bonds of all of the CC-staggered and CO-gauche structures are correlated, and consequently, the conformational preferences about the C-O bond greatly deviate from the expected 3-fold barrier. The theoretical study shows the correlation to be instrinsic and offers an explanation. Natural population analysis provides a rational for the relative stabilities of the benzyl alcohol conformations on the basis of the conformation dependence of the effects of electron-electron repulsion between the O-lone pairs and the benzene π-cloud, the charge-charge attraction between the hydroxyl H-atom and the benzene π-density, and the dipole-dipole interaction associated with the CH 2 -C ipso and OH bonds. Our analysis emphasizes the importance of the dipole alignment of the CH 2 -C ipso and OH bond dipole moments.

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Section: Resultsmentioning

confidence: 95%

Conformational Preferences and Pathways for Enantiomerization and Diastereomerization of Benzyl Alcohol. Data Mining and ab Initio Quantum-Mechanical Study

and

Nichols

2000

J. Org. Chem.

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ChemInform Abstract: A PROTON NMR INVESTIGATION OF ROTATIONAL ISOMERISM AND HYDROGEN BONDING IN 1,2‐DIARYLETHANOLS

Abraham¹,

Bakke²

1982

Chemischer Informationsdienst

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Combretastatin Analogs via Hydration of Stilbene Derivatives

Mannila

Talvitie

1993

Liebigs Ann. Chem.

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Hydration of the double bond of some stilbene congeners of Picea abies bark by TiC14 . NaBH4 reagent is described. Five racemic 1,2-diphenylethanol derivatives (9-13), structurally related to (R)-(-)-combretastatin [(R)-11, have been obtained and characterized mainly by 13C-and 'H-NMR as well as mass spectrometry. The antileukemic activity of each compound has preliminarily been tested by the mouse leukemia L1210 system. Compound 10 has been synthesized by Friedel-Crafts acylation.Combretastatins and their synthetic analogs, having a few structural features resembling those of colchicine, also display similar modes of action. Several naturally occurring combretastatins and their derivatives have been isolated or synthesized. (R)-( -)-Cornbretastatin, an antineoplastic and antimitotic agent originally isolated from Combreturn caffrum, consists structurally of two substituted benzene rings linked together by a saturated, hydroxysubstituted two-carbon bridge"]. Such a structure can easily be prepared from stilbene by a direct hydration of the skeleton double bond.In connection with our studies of the bark constituents of Piceu ubies we have made some progress in the improvement of the biological activity by modifying the structures of the isolated stilbene derivatives by methylation of the aromatic hydroxy groups and hydrogenation of the stilbene double b~n d [~,~] .One highly active, one active and several somewhat active compounds have been obtained from these reactions when provided by mouse leukemia model L1210 treatmentr3x4]. In the present paper we report on the results obtained by modifying the structures by hydration of the stilbene double bond in order to prepare racemic compounds structur-The NaBH4 . TiC14 reagent has been selected from several direct double bond hydration methods mainly because in the selected method the use of strong acids or alkalis is not needed, and the possible dehydration of the expected reaction product is avoidedr5]. However, some limitations to this method are observed. Unsubstituted (E)-stilbene (2) as a model compound can easily be hydrated to (?)-1,2-diphenylethanol (3). (E)-3,3',4,5'-tetramethoxystilbene (4) and (E)-3,4',5-trimethoxystilbene (5) react in a very similar way to afford a mixture of the isomers 9 and 10 from 4 as well as of 11 and 12 from 5, respectively, in a ratio of 3:2. A strong regioselectivity is observed in the hydration reaction of 3,4,5'-trimethoxystilben-3'-01 (6), as (?)-1-(3-hydroxy-5-methoxypheny1)-2-(3,4-dimethoxypheny1)ethanol (13) is the only product that can be isolated and characterized. The application of the NaBH4 . TiC14 method has proven to be unsuccessful when the stilbene bears several aromatic hydroxy substituents or contains a glucosidic bond, for example natural (E)-3-methoxystilbene-3',4,5'-tri01[~1 and its 3'-0-p-D-glucopyranosiderz1. The separation of the compounds 9 and 10 with a standard adsorption chromatographic equipment gives almost pure 9, but only enriched 10. A small amount of 10, needed for recording a IH-NMR spectrum and ...

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A 1H NMR Investigation of Rotational Isomerism and Hydrogen Bonding in 1,2-Diarylethanols.

Cited by 7 publications

References 0 publications

Conformational Preferences and Pathways for Enantiomerization and Diastereomerization of Benzyl Alcohol. Data Mining and ab Initio Quantum-Mechanical Study

Conformational Preferences and Pathways for Enantiomerization and Diastereomerization of Benzyl Alcohol. Data Mining and ab Initio Quantum-Mechanical Study

ChemInform Abstract: A PROTON NMR INVESTIGATION OF ROTATIONAL ISOMERISM AND HYDROGEN BONDING IN 1,2‐DIARYLETHANOLS

Combretastatin Analogs via Hydration of Stilbene Derivatives

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