Nesrin Tokay

Quantum chemical studies on tautomerism of 2-, 3- or 4-hydroxyquinoline derivatives along with their thio and azo analogs

The geometries, relative stabilities and proton affinities for the different tautomers of 2-, 3- and 4-hydroxyquinoline derivatives and their thio and azo analogs along with their fixed forms (i.e. model molecules in which the proton migration is eliminated) were calculated with full geometry optimization using AM1, PM3 and MNDO methods. The predominance of oxo forms over hydroxy forms were confirmed with all three methods both in gas and liquid phases, as cited in the literature, with the exception of 3-hydroxyquinoline for which the AM1 and MNDO methods both in gas and liquid phases suggest the predominance of the hydroxy form. For the thio analogs the predominance of thione forms over mercapto forms and for the amino analogs the predominance of the amino forms over imino forms were confirmed both in gas and liquid phases with all three methods as indicated in the literature.

Synthesis, spectroscopy, and quantum-chemical calculations on 1-substituted phenyl-3,5-diphenylformazans

In this study 1-substituted phenyl-3,5-diphenylformazans were synthesized from benzaldehyde-N-phenylhydrazone and appropriate phenyldiazonium salts having CH(3), Br, and Cl at the o-, m-, and p-positions of 1-phenyl ring. Their structures were determined by infrared and ultraviolet-visible spectra. Bathochromic effect in accordance with the electron-donating effect of CH(3), Br, and Cl group and its magnitude were dependent upon type and position of substituent on the ring. The ground-state geometries and absorption wavelengths for 1-phenyl substituted formazans were studied with density functional theory and time-dependent density functional theory. The calculations were carried out by using PBE1PBE functional with 6-311G(2d,2p) basis set for lambda(max) of the UV-vis spectra for the studied formazans. A good agreement was obtained between the experimental and computed values.

Spectral and electrochemical behavior of 1-[(NO2, COOH)-substituted phenyl]-3,5-diphenylformazans

Abstract1-[(NO2, COOH)-substituted phenyl]-3,5-diphenylformazans were synthesized. The compounds were characterized by infrared (IR), ultraviolet–visible (UV–vis), 1H nuclear magnetic resonance (NMR), 13C NMR spectra, elemental analysis, and cyclic voltammetry. From the UV–vis spectra of substituted formazans it was seen that λmax values were shorter than the λmax value of unsubstituted formazan. It was observed that the shift values were dependent on the type and position of the substituents. A correlation between Hammett substituent coefficients and λmax values was obtained. The oxidation peak potentials of substituted formazans were found more anodic than that of unsubstituted formazan. The oxidation mechanism was a single step for the NO2-substituted formazans, and two steps for COOH-substituted formazans.Graphical abstract

Investigation of structure–activity relationship on 17-spirolactone derivatives: the electronic-topological approach

Sixty steroid homologues belonging to a series of 17-spirolactone derivatives such as aldosterone antagonists were investigated by electronic-topological method (ETM). Activity features Ph1-Ph3 that also are called pharmacophores were revealed. The pharmacophore Ph1 consists of two oxygen atoms and four carbon atoms. The mineralocorticoid activity appeared to be affected by the distance between the two oxygen atoms. Features AP1-AP3 that are characteristic of inactive compounds (or anti-pharmacophores) were also revealed. Comparative analysis of molecules that include either pharmacophores or anti-pharmacophores was carried out.

A theoretical approach to experimental nitration of phenyl and benzyl substituted pyridine derivatives

Abstract Quantum chemical calculations of 2-, 3-, and 4-phenyl substituted pyridine derivatives reveal that 2-phenylpyridine nitrates via conjugated acid mechanism whereas 3- and 4-phenylpyridine molecules may nitrate via free base or more correctly an ipso attack to ring nitrogen atom followed by migration of nitronium ion to different positions of the phenyl ring to gain thermodynamic stability. Calculations for 2-, 3-, and 4-benzylpyridines revealed that all three compounds nitrate via the conjugated acid forms. Attempts to search correlations between the experimental acidity constants, p K a , and computed acidity constants were successful.

Conformational and structural analysis of acrylamido-4-(2-aminoethyl)morpholine

Abstract The temperature-sensitive monomer, acrylamido-4-(2-aminoethyl)morpholine (C9H16N2O2), has been synthesized and its crystal structure has been investigated by X-ray analysis and PM3 method. The compound crystallizes in monoclinic space group P21/c with a=4.830(1), b=23.940(3), c=9.048(2) A , β=91.35(2)°, V=1045.9(3) A 3 , Z=4, and D calc =1.17 mg m −3 . The title structure was solved by direct methods and refined to R=0.0542 for 1834 reflections by full-matrix anisotropic least-squares methods. The conformational study was carried out using PM3 semi-empirical method while rotating the torsion angle [N1–C1–C2–O1] in 10° steps.

MNDO, AM1, and PM3 study of the protonation tautomerization and valence tautomerization equilibria of some pyrrole macrocycles

Abstract The geometries, relative stabilities, proton affinities for tautomers of 1,3,6,10,12,15-hexamethyl-6,7,15,16-tetrahydropyrrolo[3,4- a ]pyrrolo[3,4- i ][16]annulene ( 1 ) and its possible fixed models (in which proton migration is eliminated) of 1,2,3,6,10,11,12,15-octamethyl-6,7,15,16-tetrahydropyrrolo[3,4- a ]pyrrolo[3,4- i ][16]annulene, of 1,2,3,6,8,10,12,15-octamethyl-6,7,8,15,16-pentahydro-2H-pyrrolo[3,4- a ]pyrrolo[3,4- i ][16]annulene, 1,3,5,7,10,12,14,16-octamethyl-5,6,7,14,15,16-hexahydro-2H-pyrrolo[3,4- a ]2H-pyrrolo[3,4- i ][16]annulene, molecules ( 2 ) were calculated with fully geometry optimization using MNDO, AM1 and PM3 methods in the gas and aqueous phases. A parallelism between the experimental acidity constant values p K a and of the computed acidity constants, p K a was search to clearing the tautomeric forms.