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Papers by Marija Baranac-Stojanović
Journal of Physical Organic Chemistry
Chemistry – An Asian Journal, 2021
Chemistry, 2021
It is well known that singlet state aromaticity is quite insensitive to substituent effects, in t... more It is well known that singlet state aromaticity is quite insensitive to substituent effects, in the case of monosubstitution. In this work, we use density functional theory (DFT) calculations to examine the sensitivity of triplet state aromaticity to substituent effects. For this purpose, we chose the singlet state antiaromatic cyclopentadienyl cation, antiaromaticity of which reverses to triplet state aromaticity, conforming to Baird’s rule. The extent of (anti)aromaticity was evaluated by using structural (HOMA), magnetic (NICS), energetic (ISE), and electronic (EDDBp) criteria. We find that the extent of triplet state aromaticity of monosubstituted cyclopentadienyl cations is weaker than the singlet state aromaticity of benzene and is, thus, slightly more sensitive to substituent effects. As an addition to the existing literature data, we also discuss substituent effects on singlet state antiaromaticity of cyclopentadienyl cation.
New Journal of Chemistry, 2021
By employing DFT calculations, we show the influence of heteroatom substitution on the triplet st... more By employing DFT calculations, we show the influence of heteroatom substitution on the triplet state (anti)aromaticity of benzene, naphthalene and anthracene.
The Journal of Organic Chemistry
Chemistry - An Asian Journal
The classical textbook explanation of variations of 1 H NMR chemical shifts in benzene substitute... more The classical textbook explanation of variations of 1 H NMR chemical shifts in benzene substituted with an electrondonating (NH2) and electron-withdrawing (NO2) group in terms of substituent resonance effects was examined by an analysis of molecular orbital contributions to the total shielding. It was found that the -electronic system shows a more pronounced shielding effect on all ring hydrogen atoms, relative to benzene, irrespective of substituent R/R effects. For the latter, this is in contrast to the traditional explanations of downfield shift of nitrobenzene proton resonances, which are found to be determined by the -electronic system and oxygen in-plane lone pairs. In aniline, R effect of NH2 group can be used to explain fully the upfield position of meta-H signals and partly the upfield position of para-H signal, the latter also being influenced by the -system. The position of the lowest frequency signal of ortho-Hs is fully determined by -electrons.
The Journal of Organic Chemistry
Chemistry – A European Journal
Chemistry - An Asian Journal
We present an efficient and simple, metal-free and solvent-free silica gel-promoted synthesis of ... more We present an efficient and simple, metal-free and solvent-free silica gel-promoted synthesis of functionalized conjugated dienes by sequential aza-Michael/Michael reactions starting from commercially available primary amines and propiolic esters. The scope and usefulness of the method is demonstrated on 31 examples, including a range of propiolic esters, aliphatic amines and differently substituted aromatic amines. In the case of aliphatic amines, the products are obtanied within 0.5-4 h in 52-85% yield compared with 3.5-22 h under classical solution-phase synthesis, proceeding in similar or lower yields. Particular usefulness of the method is found in the case of weakly nucleophilic aromatic amines, which provide products in 21-73% yield during 2.5-9.5 h compared with 0-49% during 1-6 days under standard solution-phase conditions and in the case of more hydrophobic esters yielding products in 47-79% during 1-3 h compared with 0-45% during 4-114 h in the solvent.
Physical Chemistry Chemical Physics
This work was initiated by the increasing interest in BN/CC isosterism and by the long lasting in... more This work was initiated by the increasing interest in BN/CC isosterism and by the long lasting interest in the concepts of aromaticity and substituent effects. We have theoretically examined aromaticity...
Physical Chemistry Chemical Physics
DFT calculations provide insight into the factors responsible for the energy trend of two isomeri... more DFT calculations provide insight into the factors responsible for the energy trend of two isomeric dibenzopentalenes and the types of magnetically induced currents.
New Journal of Chemistry
An insight into the electronic structure changes driven by CC → BN substitution in a naphthalene ... more An insight into the electronic structure changes driven by CC → BN substitution in a naphthalene system has been given by quantum chemical calculations.
European Journal of Organic Chemistry
European Journal of Organic Chemistry
New J. Chem., 2017
The strength and origin of the azido gauche effect were studied by ab initio calculations and com... more The strength and origin of the azido gauche effect were studied by ab initio calculations and compared with the well-known fluorine gauche effect.
New J. Chem., 2016
The rotational barriers around the CC bond are efficient parameters to quantify the strength of ... more The rotational barriers around the CC bond are efficient parameters to quantify the strength of the push–pull effect in 2-alkylidene-4-oxothiazolidines.
The Journal of Organic Chemistry, 2015
The Journal of Organic Chemistry, 2015
The well-known gauche preference in FCCX systems, where X is an electronegative element from Peri... more The well-known gauche preference in FCCX systems, where X is an electronegative element from Period 2, is widely exploited in synthetic, medicinal, and material chemistry. It is rationalized on the basis of σ(C-H) → σ*(C-F) hyperconjugation and electrostatic interactions. The recent report (Thiehoff, C.; et al. Chem. Sci. 2015, 6, 3565) showed that the fluorine gauche effect can extend to Period 3 elements, such as sulfur. The aim of the present work is to disclose factors governing conformational behavior of FCCS containing systems. We examine conformational preferences in seven classes of compounds by ab initio and DFT calculations and rationalize the results by quantitatively decomposing the anti/gauche isomerization energy into contributions from electrostatic, orbital, dispersion, and Pauli interactions, and energy spent on structural changes. The results show that the fluorine/sulfur gauche effect is primarily electrostatic (63-75%), while all orbital interactions contribute 22-41% to stabilizing interactions. Stereoelectronic effects, involved in orbital interactions, also play a role in gauche conformer stabilization.
Journal of Physical Organic Chemistry
Chemistry – An Asian Journal, 2021
Chemistry, 2021
It is well known that singlet state aromaticity is quite insensitive to substituent effects, in t... more It is well known that singlet state aromaticity is quite insensitive to substituent effects, in the case of monosubstitution. In this work, we use density functional theory (DFT) calculations to examine the sensitivity of triplet state aromaticity to substituent effects. For this purpose, we chose the singlet state antiaromatic cyclopentadienyl cation, antiaromaticity of which reverses to triplet state aromaticity, conforming to Baird’s rule. The extent of (anti)aromaticity was evaluated by using structural (HOMA), magnetic (NICS), energetic (ISE), and electronic (EDDBp) criteria. We find that the extent of triplet state aromaticity of monosubstituted cyclopentadienyl cations is weaker than the singlet state aromaticity of benzene and is, thus, slightly more sensitive to substituent effects. As an addition to the existing literature data, we also discuss substituent effects on singlet state antiaromaticity of cyclopentadienyl cation.
New Journal of Chemistry, 2021
By employing DFT calculations, we show the influence of heteroatom substitution on the triplet st... more By employing DFT calculations, we show the influence of heteroatom substitution on the triplet state (anti)aromaticity of benzene, naphthalene and anthracene.
The Journal of Organic Chemistry
Chemistry - An Asian Journal
The classical textbook explanation of variations of 1 H NMR chemical shifts in benzene substitute... more The classical textbook explanation of variations of 1 H NMR chemical shifts in benzene substituted with an electrondonating (NH2) and electron-withdrawing (NO2) group in terms of substituent resonance effects was examined by an analysis of molecular orbital contributions to the total shielding. It was found that the -electronic system shows a more pronounced shielding effect on all ring hydrogen atoms, relative to benzene, irrespective of substituent R/R effects. For the latter, this is in contrast to the traditional explanations of downfield shift of nitrobenzene proton resonances, which are found to be determined by the -electronic system and oxygen in-plane lone pairs. In aniline, R effect of NH2 group can be used to explain fully the upfield position of meta-H signals and partly the upfield position of para-H signal, the latter also being influenced by the -system. The position of the lowest frequency signal of ortho-Hs is fully determined by -electrons.
The Journal of Organic Chemistry
Chemistry – A European Journal
Chemistry - An Asian Journal
We present an efficient and simple, metal-free and solvent-free silica gel-promoted synthesis of ... more We present an efficient and simple, metal-free and solvent-free silica gel-promoted synthesis of functionalized conjugated dienes by sequential aza-Michael/Michael reactions starting from commercially available primary amines and propiolic esters. The scope and usefulness of the method is demonstrated on 31 examples, including a range of propiolic esters, aliphatic amines and differently substituted aromatic amines. In the case of aliphatic amines, the products are obtanied within 0.5-4 h in 52-85% yield compared with 3.5-22 h under classical solution-phase synthesis, proceeding in similar or lower yields. Particular usefulness of the method is found in the case of weakly nucleophilic aromatic amines, which provide products in 21-73% yield during 2.5-9.5 h compared with 0-49% during 1-6 days under standard solution-phase conditions and in the case of more hydrophobic esters yielding products in 47-79% during 1-3 h compared with 0-45% during 4-114 h in the solvent.
Physical Chemistry Chemical Physics
This work was initiated by the increasing interest in BN/CC isosterism and by the long lasting in... more This work was initiated by the increasing interest in BN/CC isosterism and by the long lasting interest in the concepts of aromaticity and substituent effects. We have theoretically examined aromaticity...
Physical Chemistry Chemical Physics
DFT calculations provide insight into the factors responsible for the energy trend of two isomeri... more DFT calculations provide insight into the factors responsible for the energy trend of two isomeric dibenzopentalenes and the types of magnetically induced currents.
New Journal of Chemistry
An insight into the electronic structure changes driven by CC → BN substitution in a naphthalene ... more An insight into the electronic structure changes driven by CC → BN substitution in a naphthalene system has been given by quantum chemical calculations.
European Journal of Organic Chemistry
European Journal of Organic Chemistry
New J. Chem., 2017
The strength and origin of the azido gauche effect were studied by ab initio calculations and com... more The strength and origin of the azido gauche effect were studied by ab initio calculations and compared with the well-known fluorine gauche effect.
New J. Chem., 2016
The rotational barriers around the CC bond are efficient parameters to quantify the strength of ... more The rotational barriers around the CC bond are efficient parameters to quantify the strength of the push–pull effect in 2-alkylidene-4-oxothiazolidines.
The Journal of Organic Chemistry, 2015
The Journal of Organic Chemistry, 2015
The well-known gauche preference in FCCX systems, where X is an electronegative element from Peri... more The well-known gauche preference in FCCX systems, where X is an electronegative element from Period 2, is widely exploited in synthetic, medicinal, and material chemistry. It is rationalized on the basis of σ(C-H) → σ*(C-F) hyperconjugation and electrostatic interactions. The recent report (Thiehoff, C.; et al. Chem. Sci. 2015, 6, 3565) showed that the fluorine gauche effect can extend to Period 3 elements, such as sulfur. The aim of the present work is to disclose factors governing conformational behavior of FCCS containing systems. We examine conformational preferences in seven classes of compounds by ab initio and DFT calculations and rationalize the results by quantitatively decomposing the anti/gauche isomerization energy into contributions from electrostatic, orbital, dispersion, and Pauli interactions, and energy spent on structural changes. The results show that the fluorine/sulfur gauche effect is primarily electrostatic (63-75%), while all orbital interactions contribute 22-41% to stabilizing interactions. Stereoelectronic effects, involved in orbital interactions, also play a role in gauche conformer stabilization.