Mario Barzaghi - Academia.edu (original) (raw)
Papers by Mario Barzaghi
![Research paper thumbnail of Charge density topological approach to the dinorcaradiene .dblharw. [10]annulene equilibrium in some 11,11-disubstituted 1,6-methano[10]annulenes](https://attachments.academia-assets.com/109505993/thumbnails/1.jpg)
](Journal of the American Chemical Society, Feb 1, 1985
The topological theory of molecular structure is used to analyze the electronic charge distributi... more The topological theory of molecular structure is used to analyze the electronic charge distribution in some 1l-R-1 l-R'-1,6-methane[lO]annulenes (R = R' = H, CH3, CN, F; R = CH3, R' = CN). The presence of the c&6 bond critical point in the dicyano derivative and in the / 3 phase of the methylcyano derivative points out the dinorcaradienic character of these compounds. Of the two different molecules in the crystal unit cell of the dimethyl derivative, one has a dinorcaradienic structure (but with a very low cl-c6 bond order, n = 0.44) and the latter has an annulenic structure (since the cI-c6 bond critical point has disappeared). These facts indicate the existence of a bifurcation catastrophe point as well as a maximum in the free molecular potential, in the range of experimental geometries, along the reaction coordinate of the valence tautomerism between the dinorcaradienic and the annulenic structures. Comparison with the topological results of the related 1 ,I-disubstituted cyclopropanes allows an exhaustive description of the conjugative coupling of the cyclopropyl ring with the two butadienyl fragments linked to it. When the Ci-C6 bond length is close to the value of normal CC bonds, the r-like charge distribution of the three-membered ring system is preserved and the whole cyclopropyl ring behaves as a conjugate r bond. However, 10 2 (I)
Journal of Molecular Structure-theochem, Jun 1, 1988
Semiempirical (MINDO and MNDO) and ab initio molecular orbital calculations (using 3-21G, 6-31G, ... more Semiempirical (MINDO and MNDO) and ab initio molecular orbital calculations (using 3-21G, 6-31G, and 6-31G* basis sets and including electron correlation through second-order M~ller-Plesset calculations) have been applied in a study of the thermal rearrangements of the homotropylium cation (circumambulation, conformational ring inversion, and transannular hydride transfer). On the basis of our calculations and estimates, we conclude that the conformational ring inversion is the most facile process, with an activation energy of 28.7 kcal/mol, which is 2.2 kcal/mol lower than that for the transannular hydride transfer. The walk rearrangement is a symmetry-forbldden one-step reaction, which occurs with inversion at the migrating center and has an activation energy of 52.4 kcal/mol. The quantum theory of atoms in molecules has been applied to the chemical characterization of the transient species, through a topological analysis of the corresponding 6-31G* charge density functions. MINDO and MNDO estimates have been made of the influence that dimethyl substitution at the migrating carbon has on the activation energies. It is found that substitution makes the walk reaction energetically comparable to the ring inversion.
Journal of Molecular Structure-theochem, Jun 1, 1988
The substituent (OH, OC2H5, Cl,-CH=CH-CH-CH-) effects on the relative stabilities of Winstein and... more The substituent (OH, OC2H5, Cl,-CH=CH-CH-CH-) effects on the relative stabilities of Winstein and Mobius structures of the homotropylium cation, 1, have been investigated by the MNDO model. Electron donor substituent at C1, Cs, C&, and C7 favor Miibius structures in the order C,,C,> C3,C6, whereas Winstein structures are stabilized by electron donor substituenta at position Cz, C4, and Cs, and in the order C,,&> C1. Electron withdrawing substituents at Cs enhance stability of the homoaromatic structures, in the order OH > Cl. In any case, the substituent effect is found to be nearly additive. The reaction path for the three-carbon membered ring opening and the eight-carbon membered ring inversion has been derived for all the compounds investigated. The equilibrium populations of Winstein and Mijbius structures were then obtained from the calculated probability distribution functions along the reaction path. The unsubstituted compound 1 was found to be a non-homoaromatic cation in the gas phase, as it adopts a Miibius conformation with a large C1-C7, internuclear distance.
Journal de chimie physique, 1987
The structures of cyclooctatrienyl cation 1a, 1,3,5-cycloheptatriene 2a, norcaradiene 2b, cyclohe... more The structures of cyclooctatrienyl cation 1a, 1,3,5-cycloheptatriene 2a, norcaradiene 2b, cyclohexadienyl anion 3a, homocyclopentadienyl anion 3b, cyclopentadiene dianion 4a, and homocyclobutadiene dianion 4c were determined by ab initio MO theory at the RHF level with use of the split-valence 3-21G basis set. All molecules, but 3a, prefer non planar structures. Homoaromaticity was found not to be important in anionic and neutral systems and has not been observed at all in cation 1. It can be concluded that Möbius aromaticity is preferred over homoaromaticity in stabilizing the investigated systems. The topological analysis of the electronic charge distribution supports this conclusion
CrystEngComm
Very low temperature can preserve the photolabile N–Cl bond in a N-chloro-N-benzamidine derivativ... more Very low temperature can preserve the photolabile N–Cl bond in a N-chloro-N-benzamidine derivative long enough to carry on an accurate experimental X-ray charge density study.
Isotopic hydronium ions DâH¹â·O/sup +/ and DHâ¹â·O/sup +/ in 1:1 (molar) HF:SbFâ/SOâ and DF:S... more Isotopic hydronium ions DâH¹â·O/sup +/ and DHâ¹â·O/sup +/ in 1:1 (molar) HF:SbFâ/SOâ and DF:SbFâSOâ solutions, respectively, at -15°C undergo slow hydrogen-deuterium exchange as monitored by ¹â·O NMR spectroscopy. The rate of such exchange increases with the increase in the acidity of the fluoroantimonic acid medium (1:2 molar composition). The previously observed lack of exchange of isotopic hydronium ions in the
Journal de Chimie Physique, 1987
The structures of cyclooctatrienyl cation 1a, 1,3,S-cycloheplatriene 2a, norcaradiene 2b, cyclohe... more The structures of cyclooctatrienyl cation 1a, 1,3,S-cycloheplatriene 2a, norcaradiene 2b, cyclohexadienyl anion 3a, homocyclopentadienyl anion 3b, cyclopentadiene dianion 4a, and homocyclobutadiene dianion tlc were determined by ab initio MO theory at the RHF level with use of the split-valence 3-21G basis set. All molecules, but 3a, prefer non planar structures. Homoaromaticity was found not to be important in anionic and neutral
systems and has not been observed at all in cation 1. lt can be concluded that Mobius aromalicity is preferred over homoaromaticity in stabilizing the investigated systems. The topological analysis of the electronic charge distribution supports this conclusion.
Molecules
The experimental electron density distribution (EDD) of 1-methyluracil (1-MUR) was obtained by si... more The experimental electron density distribution (EDD) of 1-methyluracil (1-MUR) was obtained by single crystal X-ray diffraction (XRD) experiments at 23 K. Four different structural models fitting an extensive set of XRD data to a resolution of (sinθ/λ)max = 1.143 Å−1 are compared. Two of the models include anharmonic temperature factors, whose inclusion is supported by the Hamilton test at a 99.95% level of confidence. Positive Fourier residuals up to 0.5 eÅ–3 in magnitude were found close to the methyl group and in the region of hydrogen bonds. Residual density analysis (RDA) and molecular dynamics simulations in the solid-state demonstrate that these residuals can be likely attributed to unresolved disorder, possibly dynamical and long–range in nature. Atomic volumes and charges, molecular moments up to hexadecapoles, as well as maps of the molecular electrostatic potential were obtained from distributed multipole analysis of the EDD. The derived electrostatic properties neither d...
Journal of Molecular Catalysis
J. Am. Chem. Soc., 1982
The barrier to rotation about the carbonyl carbon-phenyl carbon bond of 3-nitrobenzaldehyde anion... more The barrier to rotation about the carbonyl carbon-phenyl carbon bond of 3-nitrobenzaldehyde anion radical in N,N-dimethylformamide solution has been determined by a detailed line-shape analysis of the corresponding electron paramagnetic resonance (EPR) spectra at different temperatures. At 25 °C the cis conformation is favored by 0.98 kcal mol-l in free energy,
and the free-energy barrier to the cis-trans conversion amounts to 9.35 kcal mol-'. Both enthalpy and entropy contributions to the free-energy profile are accurately evaluated (AH* = 3.91, AH° = -1.13 kcal mol-'; AS* = -18.2, AS° = -7.1 cal mol-I K-1). The effects of ionic association and solvation on the barrier are discussed. The EPR spectra of 4-nitrobenzaldehyde and 2-nitrobenzaldehyde anion radicals are also reported as a function of temperature. In these cases, the barriers to internal rotation are too high to be surmounted on the EPR time scale. STO-3G ab initio MO calculations are given for benzaldehyde, 3-nitrobenzaldehyde, 4-nitrobenzaldehyde, and the corresponding anion radicals. The spin distribution in the anion radicals is calculated by McLachlan and INDO methods.
Http Dx Doi Org 10 1080 01442358709353197, Aug 8, 2008
International Journal of Quantum Chemistry
Journal of the American Chemical Society
The topological theory of molecular structure is used to analyze the electronic charge distributi... more The topological theory of molecular structure is used to analyze the electronic charge distribution in some 1l-R-1l -R’-1,6-methane[lO]annulenes( R = R’ = H, CH3, CN, F; R = CH3,R ’ = CN). The presence of the c&6 bond critical point in the dicyano derivative and in the /3 phase of the methylcyano derivative points out the dinorcaradienic character of these compounds. Of the two different molecules in the crystal unit cell of the dimethyl derivative, one has a dinorcaradienic structure (but with a very low cl-c6 bond order, n = 0.44) and the latter has an annulenic structure (since the cI-c6 bond critical point has disappeared). These facts indicate the existence of a bifurcation catastrophe point as well as a maximum in the free molecular potential, in the range of experimental geometries, along the reaction coordinate of the valence tautomerism between the dinorcaradienic and the annulenic structures. Comparison with the topological results of the related 1 ,I -disubstituted cyclop...
The electrostatic properties of crystals of α-glycine have been obtained from extensive X-ray dif... more The electrostatic properties of crystals of α-glycine have been obtained from extensive X-ray diffraction data collected at approximately 23 K and carefully processed, including corrections for scan truncation losses, anisotropic extinction, and multiple reflection. From a multipole parameterization of the X-ray intensities we have obtained an unusually preciseand we are confident, accuratemodel of the total electron distribution in the crystal including the topological features, atom and group charges, the dipole moment for the glycine zwitterion, electrostatic potentials, electric field gradients at the nucleii of the three hydrogen atoms of the ammonium group, and intermolecular electrostatic energies within the crystal. We have also calculated the total interaction energies involving the six distinct types of intermolecular pairings and examined these energies in terms of the molecular arrangement.
Advanced Magnetic Resonance Techniques in Systems of High Molecular Complexity. In: Advanced Magnetic Resonance Techniques in Systems of High Molecular Complexity (Progress in inorganic biochemistry and biophysics; 2.) Edited by:Niccolai N, Valensin G. 437-461 Boston: Birkhauser Verlag. , 1986
This volume records the proceedings of an international symposium on 'Advanced Magnetic Resonance... more This volume records the proceedings of an international symposium on 'Advanced Magnetic Resonance Techniques in Systems of High Molecular Complexity', held in May 1985 in Siena, Italy. The meeting was attended by internationally acknowledged leaders in the various fields of magnetic resonance. The scientific discussion which followed the various lectures and presentations pointed to how magnetic resonance spectroscopies could be used to investigate physical, chemical and biological problems at all levels of complexity and molecular organization. Particular emphasis was placed on nuclear magnetic resonance dispersion. In vivo and in vitro applications of NMR techniques where discussed. EPR advances - particularly with respect to variable magnetic fields and the analysis of linewidth - were among the many other subjects treated in depth.
Notes: ISBN:3-7643-3340-5
Journal of the American Chemical Society, Feb 1, 1985
The topological theory of molecular structure is used to analyze the electronic charge distributi... more The topological theory of molecular structure is used to analyze the electronic charge distribution in some 1l-R-1 l-R'-1,6-methane[lO]annulenes (R = R' = H, CH3, CN, F; R = CH3, R' = CN). The presence of the c&6 bond critical point in the dicyano derivative and in the / 3 phase of the methylcyano derivative points out the dinorcaradienic character of these compounds. Of the two different molecules in the crystal unit cell of the dimethyl derivative, one has a dinorcaradienic structure (but with a very low cl-c6 bond order, n = 0.44) and the latter has an annulenic structure (since the cI-c6 bond critical point has disappeared). These facts indicate the existence of a bifurcation catastrophe point as well as a maximum in the free molecular potential, in the range of experimental geometries, along the reaction coordinate of the valence tautomerism between the dinorcaradienic and the annulenic structures. Comparison with the topological results of the related 1 ,I-disubstituted cyclopropanes allows an exhaustive description of the conjugative coupling of the cyclopropyl ring with the two butadienyl fragments linked to it. When the Ci-C6 bond length is close to the value of normal CC bonds, the r-like charge distribution of the three-membered ring system is preserved and the whole cyclopropyl ring behaves as a conjugate r bond. However, 10 2 (I)
Journal of Molecular Structure-theochem, Jun 1, 1988
Semiempirical (MINDO and MNDO) and ab initio molecular orbital calculations (using 3-21G, 6-31G, ... more Semiempirical (MINDO and MNDO) and ab initio molecular orbital calculations (using 3-21G, 6-31G, and 6-31G* basis sets and including electron correlation through second-order M~ller-Plesset calculations) have been applied in a study of the thermal rearrangements of the homotropylium cation (circumambulation, conformational ring inversion, and transannular hydride transfer). On the basis of our calculations and estimates, we conclude that the conformational ring inversion is the most facile process, with an activation energy of 28.7 kcal/mol, which is 2.2 kcal/mol lower than that for the transannular hydride transfer. The walk rearrangement is a symmetry-forbldden one-step reaction, which occurs with inversion at the migrating center and has an activation energy of 52.4 kcal/mol. The quantum theory of atoms in molecules has been applied to the chemical characterization of the transient species, through a topological analysis of the corresponding 6-31G* charge density functions. MINDO and MNDO estimates have been made of the influence that dimethyl substitution at the migrating carbon has on the activation energies. It is found that substitution makes the walk reaction energetically comparable to the ring inversion.
Journal of Molecular Structure-theochem, Jun 1, 1988
The substituent (OH, OC2H5, Cl,-CH=CH-CH-CH-) effects on the relative stabilities of Winstein and... more The substituent (OH, OC2H5, Cl,-CH=CH-CH-CH-) effects on the relative stabilities of Winstein and Mobius structures of the homotropylium cation, 1, have been investigated by the MNDO model. Electron donor substituent at C1, Cs, C&, and C7 favor Miibius structures in the order C,,C,> C3,C6, whereas Winstein structures are stabilized by electron donor substituenta at position Cz, C4, and Cs, and in the order C,,&> C1. Electron withdrawing substituents at Cs enhance stability of the homoaromatic structures, in the order OH > Cl. In any case, the substituent effect is found to be nearly additive. The reaction path for the three-carbon membered ring opening and the eight-carbon membered ring inversion has been derived for all the compounds investigated. The equilibrium populations of Winstein and Mijbius structures were then obtained from the calculated probability distribution functions along the reaction path. The unsubstituted compound 1 was found to be a non-homoaromatic cation in the gas phase, as it adopts a Miibius conformation with a large C1-C7, internuclear distance.
Journal de chimie physique, 1987
The structures of cyclooctatrienyl cation 1a, 1,3,5-cycloheptatriene 2a, norcaradiene 2b, cyclohe... more The structures of cyclooctatrienyl cation 1a, 1,3,5-cycloheptatriene 2a, norcaradiene 2b, cyclohexadienyl anion 3a, homocyclopentadienyl anion 3b, cyclopentadiene dianion 4a, and homocyclobutadiene dianion 4c were determined by ab initio MO theory at the RHF level with use of the split-valence 3-21G basis set. All molecules, but 3a, prefer non planar structures. Homoaromaticity was found not to be important in anionic and neutral systems and has not been observed at all in cation 1. It can be concluded that Möbius aromaticity is preferred over homoaromaticity in stabilizing the investigated systems. The topological analysis of the electronic charge distribution supports this conclusion
CrystEngComm
Very low temperature can preserve the photolabile N–Cl bond in a N-chloro-N-benzamidine derivativ... more Very low temperature can preserve the photolabile N–Cl bond in a N-chloro-N-benzamidine derivative long enough to carry on an accurate experimental X-ray charge density study.
Isotopic hydronium ions DâH¹â·O/sup +/ and DHâ¹â·O/sup +/ in 1:1 (molar) HF:SbFâ/SOâ and DF:S... more Isotopic hydronium ions DâH¹â·O/sup +/ and DHâ¹â·O/sup +/ in 1:1 (molar) HF:SbFâ/SOâ and DF:SbFâSOâ solutions, respectively, at -15°C undergo slow hydrogen-deuterium exchange as monitored by ¹â·O NMR spectroscopy. The rate of such exchange increases with the increase in the acidity of the fluoroantimonic acid medium (1:2 molar composition). The previously observed lack of exchange of isotopic hydronium ions in the
Journal de Chimie Physique, 1987
The structures of cyclooctatrienyl cation 1a, 1,3,S-cycloheplatriene 2a, norcaradiene 2b, cyclohe... more The structures of cyclooctatrienyl cation 1a, 1,3,S-cycloheplatriene 2a, norcaradiene 2b, cyclohexadienyl anion 3a, homocyclopentadienyl anion 3b, cyclopentadiene dianion 4a, and homocyclobutadiene dianion tlc were determined by ab initio MO theory at the RHF level with use of the split-valence 3-21G basis set. All molecules, but 3a, prefer non planar structures. Homoaromaticity was found not to be important in anionic and neutral
systems and has not been observed at all in cation 1. lt can be concluded that Mobius aromalicity is preferred over homoaromaticity in stabilizing the investigated systems. The topological analysis of the electronic charge distribution supports this conclusion.
Molecules
The experimental electron density distribution (EDD) of 1-methyluracil (1-MUR) was obtained by si... more The experimental electron density distribution (EDD) of 1-methyluracil (1-MUR) was obtained by single crystal X-ray diffraction (XRD) experiments at 23 K. Four different structural models fitting an extensive set of XRD data to a resolution of (sinθ/λ)max = 1.143 Å−1 are compared. Two of the models include anharmonic temperature factors, whose inclusion is supported by the Hamilton test at a 99.95% level of confidence. Positive Fourier residuals up to 0.5 eÅ–3 in magnitude were found close to the methyl group and in the region of hydrogen bonds. Residual density analysis (RDA) and molecular dynamics simulations in the solid-state demonstrate that these residuals can be likely attributed to unresolved disorder, possibly dynamical and long–range in nature. Atomic volumes and charges, molecular moments up to hexadecapoles, as well as maps of the molecular electrostatic potential were obtained from distributed multipole analysis of the EDD. The derived electrostatic properties neither d...
Journal of Molecular Catalysis
J. Am. Chem. Soc., 1982
The barrier to rotation about the carbonyl carbon-phenyl carbon bond of 3-nitrobenzaldehyde anion... more The barrier to rotation about the carbonyl carbon-phenyl carbon bond of 3-nitrobenzaldehyde anion radical in N,N-dimethylformamide solution has been determined by a detailed line-shape analysis of the corresponding electron paramagnetic resonance (EPR) spectra at different temperatures. At 25 °C the cis conformation is favored by 0.98 kcal mol-l in free energy,
and the free-energy barrier to the cis-trans conversion amounts to 9.35 kcal mol-'. Both enthalpy and entropy contributions to the free-energy profile are accurately evaluated (AH* = 3.91, AH° = -1.13 kcal mol-'; AS* = -18.2, AS° = -7.1 cal mol-I K-1). The effects of ionic association and solvation on the barrier are discussed. The EPR spectra of 4-nitrobenzaldehyde and 2-nitrobenzaldehyde anion radicals are also reported as a function of temperature. In these cases, the barriers to internal rotation are too high to be surmounted on the EPR time scale. STO-3G ab initio MO calculations are given for benzaldehyde, 3-nitrobenzaldehyde, 4-nitrobenzaldehyde, and the corresponding anion radicals. The spin distribution in the anion radicals is calculated by McLachlan and INDO methods.
Http Dx Doi Org 10 1080 01442358709353197, Aug 8, 2008
International Journal of Quantum Chemistry
Journal of the American Chemical Society
The topological theory of molecular structure is used to analyze the electronic charge distributi... more The topological theory of molecular structure is used to analyze the electronic charge distribution in some 1l-R-1l -R’-1,6-methane[lO]annulenes( R = R’ = H, CH3, CN, F; R = CH3,R ’ = CN). The presence of the c&6 bond critical point in the dicyano derivative and in the /3 phase of the methylcyano derivative points out the dinorcaradienic character of these compounds. Of the two different molecules in the crystal unit cell of the dimethyl derivative, one has a dinorcaradienic structure (but with a very low cl-c6 bond order, n = 0.44) and the latter has an annulenic structure (since the cI-c6 bond critical point has disappeared). These facts indicate the existence of a bifurcation catastrophe point as well as a maximum in the free molecular potential, in the range of experimental geometries, along the reaction coordinate of the valence tautomerism between the dinorcaradienic and the annulenic structures. Comparison with the topological results of the related 1 ,I -disubstituted cyclop...
The electrostatic properties of crystals of α-glycine have been obtained from extensive X-ray dif... more The electrostatic properties of crystals of α-glycine have been obtained from extensive X-ray diffraction data collected at approximately 23 K and carefully processed, including corrections for scan truncation losses, anisotropic extinction, and multiple reflection. From a multipole parameterization of the X-ray intensities we have obtained an unusually preciseand we are confident, accuratemodel of the total electron distribution in the crystal including the topological features, atom and group charges, the dipole moment for the glycine zwitterion, electrostatic potentials, electric field gradients at the nucleii of the three hydrogen atoms of the ammonium group, and intermolecular electrostatic energies within the crystal. We have also calculated the total interaction energies involving the six distinct types of intermolecular pairings and examined these energies in terms of the molecular arrangement.
Advanced Magnetic Resonance Techniques in Systems of High Molecular Complexity. In: Advanced Magnetic Resonance Techniques in Systems of High Molecular Complexity (Progress in inorganic biochemistry and biophysics; 2.) Edited by:Niccolai N, Valensin G. 437-461 Boston: Birkhauser Verlag. , 1986
This volume records the proceedings of an international symposium on 'Advanced Magnetic Resonance... more This volume records the proceedings of an international symposium on 'Advanced Magnetic Resonance Techniques in Systems of High Molecular Complexity', held in May 1985 in Siena, Italy. The meeting was attended by internationally acknowledged leaders in the various fields of magnetic resonance. The scientific discussion which followed the various lectures and presentations pointed to how magnetic resonance spectroscopies could be used to investigate physical, chemical and biological problems at all levels of complexity and molecular organization. Particular emphasis was placed on nuclear magnetic resonance dispersion. In vivo and in vitro applications of NMR techniques where discussed. EPR advances - particularly with respect to variable magnetic fields and the analysis of linewidth - were among the many other subjects treated in depth.
Notes: ISBN:3-7643-3340-5