Daniele Casarini - Academia.edu (original) (raw)

Papers by Daniele Casarini

Research paper thumbnail of Variable-temperature high-resolution carbon-13 studies of molecular motion in solid bisphenol-F diglycidyl ether

Magnetic Resonance in Chemistry, 1992

Variable-temperature cross-polarization magic-angle spinning solid-state "C NMR spectra of bísphe... more Variable-temperature cross-polarization magic-angle spinning solid-state "C NMR spectra of bísphenol-F digiycidyl ether were obtained in the temperature range 25-67 O C. Dynamic phenomena are observed, and the experimental data are in accord with an inbomogeneous distributioo of correlation times, perhaps related to a second-order phase change. Single-pulse excitation expenments uoder comparable conditions conñrmed the presente of motional inhomogeoeity, characterized by a fraction of mobile molecuies within the sample. Diñereotial scanniog calorimetric measurements revealed a phase transition at ca. 50 "C.

Research paper thumbnail of Carbon-13 NMR studies of solid bisphenol-A alkanoates

Journal of Molecular Structure, 1995

Magic-angle spinning 13C spectra are reported for six bisphenol-A alkanoates, usually with cross-... more Magic-angle spinning 13C spectra are reported for six bisphenol-A alkanoates, usually with cross-polarisation. These reveal effects arising from crystallographic non-equivalence, molecular motion (phenylene ring-flipping) and non-crystalline forms. The data are complemented by DSC and solution-state NMR measurements. Apparently inhomogeneous ring-flipping for some of the compounds is discussed.

Research paper thumbnail of Stereochemical Stability and Absolute Configuration of Atropisomeric Alkylthioporphyrazines by Dynamic NMR and HPLC Studies and Computational Analysis of HPLC-ECD Recorded Spectra

European Journal of Organic Chemistry, 2018

hen As You Like It's Duke Senior asks the Lord if Jaques, found weeping over a wounded deer in th... more hen As You Like It's Duke Senior asks the Lord if Jaques, found weeping over a wounded deer in the forest, "moralize[d] the spectacle," the Lord quips: "O, yes, into a thousand similes" (2.1.43-5). 1 In an ecocritical study on the use of simile in this play, Robert Watson asks, "which has done more insidious violence to pristine nature as a collectivity during its long siege by humanity: shooting it with a single arrow, or shattering it into a thousand similes?" 2 Watson forces us to consider whether the dangers of killing the deer, which Duke Senior and his companions are about to do, are any more violent than Jaques's poetic lament over the wounded deer. While Watson goes on to argue that the Late Renaissance nostalgia for nature was rooted in a profound epistemological anxiety that the phenomenal world could never be truly accessed, I find his argument useful as a framework for understanding the making of poetic persona at the expense of the environment in Aemilia Lanyer's "The Description of Cooke-ham" and Ben Jonson's "To Penshurst." 3 In sum, Lanyer's poetic farewell to Cooke-ham is no less aggressive or destructive than Jonson's poetic hunt for power in Penshurst. 4 My reading of "Cooke-ham" is indebted to much of the feminist critical focus on Lanyer's work, which examines the ways in which she challenges patriarchy in general and the male-dominated English patronage system in particular throughout Salve Deus Rex Judaeorum, and especially in "Cooke-ham." 5 These scholars almost unfailingly set "Cooke-ham" beside "To Penshurst" as the leading examples, respectively, of a feminine and a masculine approach to the country house poem. While a number of critics have even combined gender theory and ecocriticism to interpret these poems, they have only treated each individually. None, however, have examined "Cooke-ham" and "To Penshurst" together under an ecocritical lens as a way of investigating the creation of each poet's voice. In doing so, I move beyond the poems' clear differences-the one masculine, active, and invasive, and the other feminine, seemingly passive, and non-invasive-to suggest that Lanyer's destruction of the symbiosis between the landscape and W

Research paper thumbnail of Carbon-13 NMR studies of solid bisphenol-A alkanoates

Journal of Molecular Structure, 1995

Magic-angle spinning 13C spectra are reported for six bisphenol-A alkanoates, usually with cross-... more Magic-angle spinning 13C spectra are reported for six bisphenol-A alkanoates, usually with cross-polarisation. These reveal effects arising from crystallographic non-equivalence, molecular motion (phenylene ring-flipping) and non-crystalline forms. The data are complemented by DSC and solution-state NMR measurements. Apparently inhomogeneous ring-flipping for some of the compounds is discussed.

Research paper thumbnail of Structural and Electrical Characterization of Processable Bis-Silylated Thiophene Oligomers

Chemistry of Materials, 1998

ABSTRACT A new class of processable, chemically stable, and easily synthesized and purified α,ω-b... more ABSTRACT A new class of processable, chemically stable, and easily synthesized and purified α,ω-bis(dimethyl-tert-butylsilyl) oligothiophenes is described. Information on the solid-state properties was obtained by single crystal X-ray diffraction and CPMAS NMR spectroscopy. Molecular packing was characterized by a sandwich-type organization, with the molecular planes between adjacent layers along the stacking direction being exactly parallel. Vacuum-evaporated thin films of the tetramer, pentamer, and hexamer displayed field effect transistor activity, with charge mobilities increasing with the substrate deposition temperatures in the range 28−80 °C. The best FET performance was achieved with the pentamer which was characterized by an on/off ratio > 103, reproducibility, and a device stability in air of months.

Research paper thumbnail of Conformational studies by dynamic NMR. 66. Ring inversion in a cyclic disilane: 1,1,4,4-tetramethyl-1,4-disilacyclohexane

Tetrahedron, 1998

ABSTRACT The barrier to ring inversion of the title compound (ΔG≠ = 6.0 kcal mol−1) has been foun... more ABSTRACT The barrier to ring inversion of the title compound (ΔG≠ = 6.0 kcal mol−1) has been found to be much lower than that (ΔG≠ = 11.1 kcal mol−1) of the corresponding cyclohexane derivative (1,1,4,4-tetramethylcyclohexane).

Research paper thumbnail of The effect of exocyclic conjugation on the inversion of a saturated six-membered ring. A dynamic NMR study of N-substituted morpholines

Tetrahedron, 1991

The effect of exocychc conjuganon on the mverston of a saturated six-membered nng 1~ shown m a

Research paper thumbnail of Conformational Studies by Dynamic NMR. Part 46. The Effect of Exocyclic Conjugation on the Inversion of a Saturated Six-Membered Ring. A Dynamic NMR Study of N-Substituted Morpholines

Cheminform, 1991

ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Research paper thumbnail of Conformational studies by dynamic NMR. 100. Enantiomerization process of stereolabile atropisomers in pyridine-substituted adamantane derivatives

The Journal of organic chemistry, Jan 20, 2004

The barriers for interconverting the conformational enantiomers (stereolabile atropisomers) of py... more The barriers for interconverting the conformational enantiomers (stereolabile atropisomers) of pyridine-substituted adamantane derivatives have been determined by dynamic 13C NMR spectroscopy. The trend of these values parallels that anticipated by MM calculations. In at least one case, the computed structure was found to agree with that obtained by single-crystal X-ray diffraction. In addition, it has been possible to achieve a physical separation of a pair of these stereolabile atropisomers at -60 degrees C by means of the enantioselective cryogenic HPLC technique.

Research paper thumbnail of Conformational studies by dynamic NMR. 97. Structure, conformation, stereodynamics and enantioseparation of aryl substituted norbornanes

The Journal of organic chemistry, Jan 23, 2004

The structure of a 1,7,7-triaryl norbornane (compound 3) has been determined by X-ray diffraction... more The structure of a 1,7,7-triaryl norbornane (compound 3) has been determined by X-ray diffraction and was found essentially equal to that predicted by molecular mechanics calculations. Restricted rotation of the aryl groups also has been observed by dynamic NMR spectroscopy in this compound and in a number of analogously substituted norbornanes. The aryl-norbornane bond rotation barriers were measured by line shape analysis of the (13)C NMR spectra obtained at temperatures lower than -100 degrees C and were found to cover the range 6.0 to 7.9 kcal mol(-1). An exception was the rotation involving the o-anisyl group in compound 5, which occurs near ambient temperature since the corresponding barrier is much higher (14.4 kcal mol(-1)). In one case (compound 4) configurational enantiomers could be separated by chiral HPLC and the corresponding CD spectra recorded.

Research paper thumbnail of ChemInform Abstract: Recent Advances in Stereodynamics and Conformational Analysis by Dynamic NMR and Theoretical Calculations

Research paper thumbnail of Recent trends in conformational analysis

Wiley Interdisciplinary Reviews: Computational Molecular Science, 2011

... interconvert. Figure 6. NOE experiments (600 MHz at −80°C in CD 2 Cl 2 ) carried out by excit... more ... interconvert. Figure 6. NOE experiments (600 MHz at −80°C in CD 2 Cl 2 ) carried out by excitation of the CH multiplet of the ortho-isopropyl group of the minor (ap) and major (sc) atropisomer (traces b and c, respectively). The ...

Research paper thumbnail of Naphthoyl ?-radicals: elucidation of their conformational behaviour by electron spin resonance

Journal of the Chemical Society, Perkin Transactions 2, 1986

ABSTRACT

Research paper thumbnail of Enantioselective Synthesis and Absolute Stereochemistry of Both the Enantiomers of trans-Magnolione, a Fragrance Structurally Related to trans-Methyl Jasmonate

ChemInform, 2004

Both enantiomers of the trans stereoisomer of magnolione 4 have been prepared by asymmetric Micha... more Both enantiomers of the trans stereoisomer of magnolione 4 have been prepared by asymmetric Michael addition of ethyl acetoacetate to 2-pentylcyclopentenone, followed by hydrolysis/decarboxylation. The Michael reaction occurs under solid/liquid phase transfer catalysis in the presence of N-methylanthracenylquininium (or quinidinium) chloride. Enantiomeric excesses up to 76% are obtained. The trans structure of the compounds has been fully established by a careful NMR analysis, while the absolute configuration has been assigned as (2S,3S) for (þ)-4 by the analysis of the CD spectrum. q

Research paper thumbnail of Conformational studies by dynamic nuclear magnetic resonance Part XI. The detection of restricted rotation in 2-NN-dimethylaminothiazoles

Tetrahedron Letters, 1977

Research paper thumbnail of Conformational studies by dynamic NMR. Part 56. Enantiotopomerization and conformational analysis of hindered aryl alkyl ketones investigated by dynamic and solid state NMR

Tetrahedron, 1996

ABSTRACT

Research paper thumbnail of Conformational profile, energy barriers and optical properties of quinquethiophene-S,S-dioxides

Tetrahedron, 2002

Theoretical calculations, dynamic NMR experiments and absorption and photoluminescence data in so... more Theoretical calculations, dynamic NMR experiments and absorption and photoluminescence data in solution are reported for a series of quinquethiophene S,S-dioxides substituted with alkyl groups of variable size and steric hindrance. Ab initio B3LYP/6-31G p and force field MM3 theoretical calculations show that the energy barriers for rotation around the inter-ring C -C bonds amount to a few kcal/mol even in the presence of very bulky substituents such as the cyclohexyl group. Dynamic NMR data were in agreement with the results of theoretical calculations. It was found that changing the steric hindrance of the substituents leaves the emission and photoluminesce properties unaltered. However, the photoluminesce intensities and wavelengths of all compounds were found to be very sensitive to solvent variations. q

Research paper thumbnail of Conformational studies by dynamic NMR. 47. Conformation, stereodynamics, and chiral separation of the rotational enantiomers of hindered naphthyl ketones

Journal of the American Chemical Society, 1992

ABSTRACT

Research paper thumbnail of Conformational studies by dynamic NMR. 35. Structure, conformation, and stereodynamics of hindered naphthylamines

Journal of the American Chemical Society, 1988

Research paper thumbnail of Stereolabile and Configurationally Stable Atropisomers of Hindered Aryl Carbinols

The Journal of Organic Chemistry, 2005

Carbinols of the Ar-C(OH)R(2) type, Ar being o-isopropylphenyl, exist as stereolabile syn-clinal ... more Carbinols of the Ar-C(OH)R(2) type, Ar being o-isopropylphenyl, exist as stereolabile syn-clinal (sc) and anti-periplanar (ap) atropisomers when R = Me, Et, i-Pr. In the latter compound, the major atropisomer also comprises two enantiomeric forms that interchange with a barrier of 6.4 kcal mol(-1). X-ray diffraction, NOE experiments, and ab initio calculations indicate that the sc-atropisomer is the more stable form when R = Me, i-Pr, t-Bu but is the less stable one when R = Et. NMR spectra at variable temperature allowed the determination of the barriers for the interconversion of the sc- into the ap-atropisomers (DeltaG++ = 7.6, 8.8, and 13.5 kcal mol(-1) for Me, Et, i-Pr, respectively). When R is a tert-butyl group, the two atropisomers are configurationally stable: the ap-atropisomer is obtained as the kinetic controlled compound, which can be transformed into the thermodynamically more stable sc-atropisomer with a free energy of activation of 29.3 kcal mol(-1). Both atropisomers exhibit restricted rotation of the tert-butyl moiety, the corresponding DeltaG++ values being 9.4 and 8.8 kcal mol(-1) for the sc- and ap-atropisomer, respectively.

Research paper thumbnail of Variable-temperature high-resolution carbon-13 studies of molecular motion in solid bisphenol-F diglycidyl ether

Magnetic Resonance in Chemistry, 1992

Variable-temperature cross-polarization magic-angle spinning solid-state "C NMR spectra of bísphe... more Variable-temperature cross-polarization magic-angle spinning solid-state "C NMR spectra of bísphenol-F digiycidyl ether were obtained in the temperature range 25-67 O C. Dynamic phenomena are observed, and the experimental data are in accord with an inbomogeneous distributioo of correlation times, perhaps related to a second-order phase change. Single-pulse excitation expenments uoder comparable conditions conñrmed the presente of motional inhomogeoeity, characterized by a fraction of mobile molecuies within the sample. Diñereotial scanniog calorimetric measurements revealed a phase transition at ca. 50 "C.

Research paper thumbnail of Carbon-13 NMR studies of solid bisphenol-A alkanoates

Journal of Molecular Structure, 1995

Magic-angle spinning 13C spectra are reported for six bisphenol-A alkanoates, usually with cross-... more Magic-angle spinning 13C spectra are reported for six bisphenol-A alkanoates, usually with cross-polarisation. These reveal effects arising from crystallographic non-equivalence, molecular motion (phenylene ring-flipping) and non-crystalline forms. The data are complemented by DSC and solution-state NMR measurements. Apparently inhomogeneous ring-flipping for some of the compounds is discussed.

Research paper thumbnail of Stereochemical Stability and Absolute Configuration of Atropisomeric Alkylthioporphyrazines by Dynamic NMR and HPLC Studies and Computational Analysis of HPLC-ECD Recorded Spectra

European Journal of Organic Chemistry, 2018

hen As You Like It's Duke Senior asks the Lord if Jaques, found weeping over a wounded deer in th... more hen As You Like It's Duke Senior asks the Lord if Jaques, found weeping over a wounded deer in the forest, "moralize[d] the spectacle," the Lord quips: "O, yes, into a thousand similes" (2.1.43-5). 1 In an ecocritical study on the use of simile in this play, Robert Watson asks, "which has done more insidious violence to pristine nature as a collectivity during its long siege by humanity: shooting it with a single arrow, or shattering it into a thousand similes?" 2 Watson forces us to consider whether the dangers of killing the deer, which Duke Senior and his companions are about to do, are any more violent than Jaques's poetic lament over the wounded deer. While Watson goes on to argue that the Late Renaissance nostalgia for nature was rooted in a profound epistemological anxiety that the phenomenal world could never be truly accessed, I find his argument useful as a framework for understanding the making of poetic persona at the expense of the environment in Aemilia Lanyer's "The Description of Cooke-ham" and Ben Jonson's "To Penshurst." 3 In sum, Lanyer's poetic farewell to Cooke-ham is no less aggressive or destructive than Jonson's poetic hunt for power in Penshurst. 4 My reading of "Cooke-ham" is indebted to much of the feminist critical focus on Lanyer's work, which examines the ways in which she challenges patriarchy in general and the male-dominated English patronage system in particular throughout Salve Deus Rex Judaeorum, and especially in "Cooke-ham." 5 These scholars almost unfailingly set "Cooke-ham" beside "To Penshurst" as the leading examples, respectively, of a feminine and a masculine approach to the country house poem. While a number of critics have even combined gender theory and ecocriticism to interpret these poems, they have only treated each individually. None, however, have examined "Cooke-ham" and "To Penshurst" together under an ecocritical lens as a way of investigating the creation of each poet's voice. In doing so, I move beyond the poems' clear differences-the one masculine, active, and invasive, and the other feminine, seemingly passive, and non-invasive-to suggest that Lanyer's destruction of the symbiosis between the landscape and W

Research paper thumbnail of Carbon-13 NMR studies of solid bisphenol-A alkanoates

Journal of Molecular Structure, 1995

Magic-angle spinning 13C spectra are reported for six bisphenol-A alkanoates, usually with cross-... more Magic-angle spinning 13C spectra are reported for six bisphenol-A alkanoates, usually with cross-polarisation. These reveal effects arising from crystallographic non-equivalence, molecular motion (phenylene ring-flipping) and non-crystalline forms. The data are complemented by DSC and solution-state NMR measurements. Apparently inhomogeneous ring-flipping for some of the compounds is discussed.

Research paper thumbnail of Structural and Electrical Characterization of Processable Bis-Silylated Thiophene Oligomers

Chemistry of Materials, 1998

ABSTRACT A new class of processable, chemically stable, and easily synthesized and purified α,ω-b... more ABSTRACT A new class of processable, chemically stable, and easily synthesized and purified α,ω-bis(dimethyl-tert-butylsilyl) oligothiophenes is described. Information on the solid-state properties was obtained by single crystal X-ray diffraction and CPMAS NMR spectroscopy. Molecular packing was characterized by a sandwich-type organization, with the molecular planes between adjacent layers along the stacking direction being exactly parallel. Vacuum-evaporated thin films of the tetramer, pentamer, and hexamer displayed field effect transistor activity, with charge mobilities increasing with the substrate deposition temperatures in the range 28−80 °C. The best FET performance was achieved with the pentamer which was characterized by an on/off ratio > 103, reproducibility, and a device stability in air of months.

Research paper thumbnail of Conformational studies by dynamic NMR. 66. Ring inversion in a cyclic disilane: 1,1,4,4-tetramethyl-1,4-disilacyclohexane

Tetrahedron, 1998

ABSTRACT The barrier to ring inversion of the title compound (ΔG≠ = 6.0 kcal mol−1) has been foun... more ABSTRACT The barrier to ring inversion of the title compound (ΔG≠ = 6.0 kcal mol−1) has been found to be much lower than that (ΔG≠ = 11.1 kcal mol−1) of the corresponding cyclohexane derivative (1,1,4,4-tetramethylcyclohexane).

Research paper thumbnail of The effect of exocyclic conjugation on the inversion of a saturated six-membered ring. A dynamic NMR study of N-substituted morpholines

Tetrahedron, 1991

The effect of exocychc conjuganon on the mverston of a saturated six-membered nng 1~ shown m a

Research paper thumbnail of Conformational Studies by Dynamic NMR. Part 46. The Effect of Exocyclic Conjugation on the Inversion of a Saturated Six-Membered Ring. A Dynamic NMR Study of N-Substituted Morpholines

Cheminform, 1991

ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Research paper thumbnail of Conformational studies by dynamic NMR. 100. Enantiomerization process of stereolabile atropisomers in pyridine-substituted adamantane derivatives

The Journal of organic chemistry, Jan 20, 2004

The barriers for interconverting the conformational enantiomers (stereolabile atropisomers) of py... more The barriers for interconverting the conformational enantiomers (stereolabile atropisomers) of pyridine-substituted adamantane derivatives have been determined by dynamic 13C NMR spectroscopy. The trend of these values parallels that anticipated by MM calculations. In at least one case, the computed structure was found to agree with that obtained by single-crystal X-ray diffraction. In addition, it has been possible to achieve a physical separation of a pair of these stereolabile atropisomers at -60 degrees C by means of the enantioselective cryogenic HPLC technique.

Research paper thumbnail of Conformational studies by dynamic NMR. 97. Structure, conformation, stereodynamics and enantioseparation of aryl substituted norbornanes

The Journal of organic chemistry, Jan 23, 2004

The structure of a 1,7,7-triaryl norbornane (compound 3) has been determined by X-ray diffraction... more The structure of a 1,7,7-triaryl norbornane (compound 3) has been determined by X-ray diffraction and was found essentially equal to that predicted by molecular mechanics calculations. Restricted rotation of the aryl groups also has been observed by dynamic NMR spectroscopy in this compound and in a number of analogously substituted norbornanes. The aryl-norbornane bond rotation barriers were measured by line shape analysis of the (13)C NMR spectra obtained at temperatures lower than -100 degrees C and were found to cover the range 6.0 to 7.9 kcal mol(-1). An exception was the rotation involving the o-anisyl group in compound 5, which occurs near ambient temperature since the corresponding barrier is much higher (14.4 kcal mol(-1)). In one case (compound 4) configurational enantiomers could be separated by chiral HPLC and the corresponding CD spectra recorded.

Research paper thumbnail of ChemInform Abstract: Recent Advances in Stereodynamics and Conformational Analysis by Dynamic NMR and Theoretical Calculations

Research paper thumbnail of Recent trends in conformational analysis

Wiley Interdisciplinary Reviews: Computational Molecular Science, 2011

... interconvert. Figure 6. NOE experiments (600 MHz at −80°C in CD 2 Cl 2 ) carried out by excit... more ... interconvert. Figure 6. NOE experiments (600 MHz at −80°C in CD 2 Cl 2 ) carried out by excitation of the CH multiplet of the ortho-isopropyl group of the minor (ap) and major (sc) atropisomer (traces b and c, respectively). The ...

Research paper thumbnail of Naphthoyl ?-radicals: elucidation of their conformational behaviour by electron spin resonance

Journal of the Chemical Society, Perkin Transactions 2, 1986

ABSTRACT

Research paper thumbnail of Enantioselective Synthesis and Absolute Stereochemistry of Both the Enantiomers of trans-Magnolione, a Fragrance Structurally Related to trans-Methyl Jasmonate

ChemInform, 2004

Both enantiomers of the trans stereoisomer of magnolione 4 have been prepared by asymmetric Micha... more Both enantiomers of the trans stereoisomer of magnolione 4 have been prepared by asymmetric Michael addition of ethyl acetoacetate to 2-pentylcyclopentenone, followed by hydrolysis/decarboxylation. The Michael reaction occurs under solid/liquid phase transfer catalysis in the presence of N-methylanthracenylquininium (or quinidinium) chloride. Enantiomeric excesses up to 76% are obtained. The trans structure of the compounds has been fully established by a careful NMR analysis, while the absolute configuration has been assigned as (2S,3S) for (þ)-4 by the analysis of the CD spectrum. q

Research paper thumbnail of Conformational studies by dynamic nuclear magnetic resonance Part XI. The detection of restricted rotation in 2-NN-dimethylaminothiazoles

Tetrahedron Letters, 1977

Research paper thumbnail of Conformational studies by dynamic NMR. Part 56. Enantiotopomerization and conformational analysis of hindered aryl alkyl ketones investigated by dynamic and solid state NMR

Tetrahedron, 1996

ABSTRACT

Research paper thumbnail of Conformational profile, energy barriers and optical properties of quinquethiophene-S,S-dioxides

Tetrahedron, 2002

Theoretical calculations, dynamic NMR experiments and absorption and photoluminescence data in so... more Theoretical calculations, dynamic NMR experiments and absorption and photoluminescence data in solution are reported for a series of quinquethiophene S,S-dioxides substituted with alkyl groups of variable size and steric hindrance. Ab initio B3LYP/6-31G p and force field MM3 theoretical calculations show that the energy barriers for rotation around the inter-ring C -C bonds amount to a few kcal/mol even in the presence of very bulky substituents such as the cyclohexyl group. Dynamic NMR data were in agreement with the results of theoretical calculations. It was found that changing the steric hindrance of the substituents leaves the emission and photoluminesce properties unaltered. However, the photoluminesce intensities and wavelengths of all compounds were found to be very sensitive to solvent variations. q

Research paper thumbnail of Conformational studies by dynamic NMR. 47. Conformation, stereodynamics, and chiral separation of the rotational enantiomers of hindered naphthyl ketones

Journal of the American Chemical Society, 1992

ABSTRACT

Research paper thumbnail of Conformational studies by dynamic NMR. 35. Structure, conformation, and stereodynamics of hindered naphthylamines

Journal of the American Chemical Society, 1988

Research paper thumbnail of Stereolabile and Configurationally Stable Atropisomers of Hindered Aryl Carbinols

The Journal of Organic Chemistry, 2005

Carbinols of the Ar-C(OH)R(2) type, Ar being o-isopropylphenyl, exist as stereolabile syn-clinal ... more Carbinols of the Ar-C(OH)R(2) type, Ar being o-isopropylphenyl, exist as stereolabile syn-clinal (sc) and anti-periplanar (ap) atropisomers when R = Me, Et, i-Pr. In the latter compound, the major atropisomer also comprises two enantiomeric forms that interchange with a barrier of 6.4 kcal mol(-1). X-ray diffraction, NOE experiments, and ab initio calculations indicate that the sc-atropisomer is the more stable form when R = Me, i-Pr, t-Bu but is the less stable one when R = Et. NMR spectra at variable temperature allowed the determination of the barriers for the interconversion of the sc- into the ap-atropisomers (DeltaG++ = 7.6, 8.8, and 13.5 kcal mol(-1) for Me, Et, i-Pr, respectively). When R is a tert-butyl group, the two atropisomers are configurationally stable: the ap-atropisomer is obtained as the kinetic controlled compound, which can be transformed into the thermodynamically more stable sc-atropisomer with a free energy of activation of 29.3 kcal mol(-1). Both atropisomers exhibit restricted rotation of the tert-butyl moiety, the corresponding DeltaG++ values being 9.4 and 8.8 kcal mol(-1) for the sc- and ap-atropisomer, respectively.