Papers by Neda Khorshidvand
Journal of Physical Organic Chemistry
Iranian Journal of Chemistry & Chemical Engineering-international English Edition, 2020
We present electronic effects on stability (ΔES-T), nucleophilicity (N), global electrophilicity ... more We present electronic effects on stability (ΔES-T), nucleophilicity (N), global electrophilicity (ω), and band gaps (ΔEHOMO-LUMO) of 36 novel 1,4- and 1,3-tetrazole-5-ylidenes, 1 and 2, respectively. A union of three sets of "normal" 1W,W, 1D,D, and 1D,W are compared to another union of four sets of "abnormal" 2W,W, 2D,D, 2D,W and 2W,D NHCs, electron-withdrawing substituents (W) and electron-donating ones (D). Every 1 is more stable and shows a larger bandgap than its corresponding 2. In addition, philicities, N and ω, of every 2 appear larger than that of the corresponding 1 isomer. Carbenes with W groups increase electrophilicity while D ones increase nucleophilicity and in pull-push groups, W groups in carbene center increase electrophilicity. All our NHCs give doubly bonded head-to-head dimers except for 5 species.
Research on Chemical Intermediates, 2020
Laetrile (D-mandelonitrile-β-D-glucuronic acid, 1 COOH) is being promoted, more and more, as an a... more Laetrile (D-mandelonitrile-β-D-glucuronic acid, 1 COOH) is being promoted, more and more, as an alternate cancer treatment, in many countries. Here we show how intramolecular long-range hydrogen bonding (ILRHB) affects proton affinity (PA) of 1 COOH and turns it into a rather strong acid at M06/6-311 + + G(d,p) level of theory. The ILRHB between carboxylate and the-CN of 1 COOH activates the cyanide and provides a form of neighboring group participation (anchimeric assistance) in which the rate of the cyanide release is increased. The released cyanide is reported to kill cancer cells more rigorously than the normal ones. Constituents (-CN,-ph and-OH) effects on 1 COOH acidity are probed. The-OH groups show the highest impact on increasing the relative acidity in H 2 O, DMSO and gas phase. The 1 COOH and its derivatives appear more acidic in DMSO than in water. Quantum theory of atoms in molecules (QTAIM), natural bond orbital (NBO) analysis and the polarized continuum mode (PCM) are used for calculation of the pK a values.
Journal of Physical Organic Chemistry, 2020
Triplet ground state-monomeric 1,4-disubstituted-tetrazole-5-germavinylidenes (normal, 1 R) and t... more Triplet ground state-monomeric 1,4-disubstituted-tetrazole-5-germavinylidenes (normal, 1 R) and their corresponding 1,3-disubstituted-tetrazole-5-germavinylidenes (abnormal, 2 R) are computed and compared at B3LYP/6-311++G** level, with R = H, CN, CF 3 , SH, NH 2 , OMe, and OH. Every triplet germavinylidene is more stable than its corresponding singlet form (except for 1 CF3). Likewise, every triplet abnormal isomer (2 R) emerges more stable than its corresponding normal isomer (1 R). The most stable triplet monomeric species are 1 H and 2 H. All abnormal 2 R isomers show higher nucleophilicity (N) and smaller band gaps (ΔE HOMO-LUMO) than their corresponding normal 1 R isomers. Electron-donating species increase N in both 1 R and 2 R (R = H > NH 2 > SH > OCH 3 > OH > CF 3 > CN). The nuclear independent chemical shift (NICS) results indicate that every 1 R is more aromatic than its corresponding 2 R .
Journal of Physical Organic Chemistry, 2019
Following our recent steric studies on diaminocarbenes, here, electronic effects of symmetric acy... more Following our recent steric studies on diaminocarbenes, here, electronic effects of symmetric acyclic, cyclic saturated, and cyclic unsaturated 2,4-disubstituted structures (1 X , 3 X , and 5 X , respectively) are compared with their asymmetric corresponding 2,5-disubstituted isomers (2 X , 4 X , and 6 X , respectively), at B3LYP/6-311++G** level of theory (X = NH 2 , OH, OMe, SH, Ph, CN, CF 3 , NO 2). Both symmetric and asymmetric species (1 X-6 X) appear with singlet(s) ground states. These are suggested by the conductor-like polarizable continuum model (CPCM) on both gas-phase and solvent-phase optimized structures. Regardless of X, singlet-triplet energy gap (ΔE S-T) and band gap (ΔE H-L) increase in going from acyclic to cyclic saturated and cyclic unsaturated structures (except 6 X). More importantly, nucleophilicity (N) decreases (while electrophilicity, ω, increases) in going from acyclic to cyclic saturated and cyclic unsaturated structures for both symmetric and asymmetric carbenes. Acyclic 1 X and 2 X appear less stable than their corresponding cyclic 3 X and 6 X in the presence of either electron-withdrawing or electron-releasing substituents. The proton affinity (PA) increases in going from acyclic to cyclic saturated, while decreases in going to cyclic unsaturated structures for both symmetric and asymmetric carbenes. The calculated metal-ligand isodesmic complexation energies, ΔE com , indicate that 1 X-6 X complexes have very strong M─(carbene) bonds. The trend of ΔE com for symmetric series is 1 X > 3 X > 5 X , while that for asymmetric appears as 6 X > 2 X > 4 X. Atoms in molecules (AIM) wavefunction analysis shows internal hydrogen bondings for 1 OH , 1 OMe , 1 CF3 , 2 Ph , and 4 NO2. Hammett assessments are made on sensitivity of thermodynamic parameters of 1 X to 6 X toward electronic effects. Finally, basicity increases as a function of the carbenic bond angle for 1 X to 6 X. Hence, basicity increases in going from the unsaturated 5 X and 6 X (96°) to the saturated 3 X and 4 X (102°) and lastly to acyclic 1 X and 2 X (120°). KEYWORDS AIM, DFT, diaminocarbene, electronic effects, pK a , proton affinity 1 | INTRODUCTION Carbenes are important divalent reactive intermediates, which may appear acyclic, cyclic saturated, or cyclic unsaturated with two nitrogen atoms adjacent to their carbenic center. They may appear as normal, abnormal, and remote types. A normal carbene is joined by two σaccepting and π-donating heteroatoms such as nitrogen
Journal of Physical Organic Chemistry, 2018
Steric effects are probed on the multiplicity, stability, and reactivity of normal 2,4-disubstitu... more Steric effects are probed on the multiplicity, stability, and reactivity of normal 2,4-disubstituted and abnormal 2,5-disubstituted diaminocarbenes 1 R-3 R and 1′ R-3′ R , respectively, at B3LYP/6-311++G ** level (R = H, Me, Et, i-Pr, t-Bu). All optimized structures appear with singlet ground states. In comparison with acyclic normal (1 R) and abnormal (1′ R), one observes cyclic normal (2 R) and abnormal (2′ R) as well as cyclic-unsaturated normal (3 R) and abnormal (3′ R) exhibit a decrease in nucleophilicity (N) and proton affinity (PA) in going from 1 R → 2 R → 3 R , and in going from 1′ R → 2′ R → 3′ R (except PA in 3′ R). On the account of higher reactivity and lower stability of 3′ R , PA increases in going from 2′ R to 3′ R. The singlet-triplet energy gaps (ΔE S-T) and the energy difference between the highest occupied molecular orbital (HOMO) energy and the lowest unoccupied molecular orbital (LUMO) energy of the compound, HOMO-LUMO energy gaps (ΔE H-L) increase in going from 1 R → 2 R → 3 R , and in going from 1′ R to 2′ R. In contrast, the stability of abnormal species decreases in going from the cyclic-saturated 2′ R , to cyclic-unsaturated diaminocarbenes 3′ R. Isodesmic reactions indicate that both normal and abnormal diaminocarbenes 1 R and 1′ R , as well as 3 R and 3′ R become more stable in the presence of heteroatoms. The abnormal ones become more stable than the corresponding normal carbenes. The larger the substituent (R) the greater is the stability effect of the heteroatom.
Journal of Physical Organic Chemistry, 2020
Thermodynamic parameters (including steric effects) of 15 new pairs of singlet and triplet bis(al... more Thermodynamic parameters (including steric effects) of 15 new pairs of singlet and triplet bis(alkylthio)carbenes, R 1 − S 1 −C−S 2 − R 2 , (1 R1,R2 and 3 R1,R2 , respectively), are compared and contrasted by B3LYP and MP2/AUG-CC-PVTZ; where R 1 (or R 2) = H, Me, Et, i-Pr, and t-Bu. Among the 30 carbenes scrutinized, the lowest nucleophilicity (N) and the highest electrophilicity (ω) are displayed by singlet 1 H,H. In contract, triplet 3 i-Pr,t-Bu exhibits the highest N, while the lowest ω is demonstrated by 3 Me,Et. The maximum and minimum carbenic bond angles (S 1 −C−S 2) are displayed by singlets 1 H,H and 1 Me,Me and triplets 3 t-Bu,t-Bu and 3 H,Et , respectively. The highest and lowest stability (ΔE st) are exhibited by 1 Me,t-Bu and 1 H,H , respectively. The former may be stabilized primarily through lone pair donations from their sulfur atom into the empty p π carbenic orbital, plus the formation of a five-membered ring between hydrogen of methyl groups and the carbenic carbons. The highest and lowest band gaps (ΔE H-L) are exhibited by 3 H,H and 1 t-Bu,t-Bu , respectively. The highest and lowest chemical potentials (μ) are exhibited by 3 Et,i-Pr and 1 H,H , respectively. Moreover, second-order Møller-Plesset perturbation theory (MP2) provided a better discrimination between the scrutinized carbenes than density functional theory (DFT).
Research on Chemical Intermediates, 2020
Electronic and steric effects on singlet and triplet symmetric 2,4-diX-vinylidenes with acyclic, ... more Electronic and steric effects on singlet and triplet symmetric 2,4-diX-vinylidenes with acyclic, cyclic-saturated, and cyclic-unsaturated structures are compared and contrasted with their corresponding asymmetric 2,5-diX-vinylidenes, at B3LYP/6-311++G** level of theory (X = H, Me, i-Pr, t-Bu, NH 2 , OH, OMe, SH, Ph, CN, and CF 3). From 64 novel vinylidenes scrutinized, 45 are singlet while the other 19 show triplet ground state. These are suggested by the conductor like polarizable continuum model on both gas-phase and solvent-phase optimized structures. Regardless of X, band gap decreases in going from acyclic to cyclic-saturated and cyclicunsaturated structures. More importantly nucleophilicity decreases with the same trend for symmetric carbenes. The proton affinity decreases in going from acyclic to cyclic-unsaturated and to cyclic-saturated structures for both symmetric and asymmetric carbenes. Atoms in molecules wavefunction analysis show internal hydrogen bondings for 1 s-Me , 1 s-i-Pr , 1 s-t-Bu , 1 s-Ph , 1′ s-CF3 , 2 s-OH , 2′ s-t-Bu , and 2′ sOMe .
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Papers by Neda Khorshidvand