Five and nine membered (heteronines) heterocyclic molecules. Theoretical approach (original) (raw)

A Study on Aromatic Heterocyclic Organic Compounds

Journal of Pharmaceutical Research International, 2022

The synthesis of newer and more novel molecules has always been a goal for research in organic chemistry. Heterocyclic compounds are those in which the fundamental compound structure contains an element other than carbon. These molecules may also be aromatic, which means they have a distinct odor. The composition of heterocyclic compounds will be discussed in depth in this study. The paper will also go through the synthesis and application methodologies. The pharmaceutical sector makes substantial use of these chemicals. It is largely employed in histamine and serotonin-related medications in that country. These chemicals are also used in the cosmetics and DNA vaccine industries, as well as in genetic research. Advancements in organic chemistry are allowing for a more thorough investigation of aromatic heterocyclic compounds in order to get a better knowledge of their structural and chemical compatibility with other molecules.

The electronic structure of heteroaromatic molecules. Part 3. A comparison of benzene, borazine, and boroxine

Journal of the Chemical Society, Perkin Transactions 2, 1989

The UV photoelectron spectra are reported for isoxaxde and 1,3,4oxadiaxole (He(I) region), oxazole and 1.2.5-oxadiazole (He(I) and He(H) regions). Marked fine structure is apparent on some of the spectra. The spectra have been assigned on the basis of ab initio calculations, and by comparison with the azoles and thiazoles. Variations in the lone pairs levels at 0-, S-and N-across the azoles, oxazoles, thiazoles and azines are discussed. It is suggested that "through-bond"

Influence of building block aromaticity in the determination of electronic properties of five-membered heterocyclic oligomers

Physical Chemistry Chemical Physics, 2002

With the aim of exploring the electronic and optical properties of some interesting conductive copolymers in view of potential applications, a regular oligomer systems made of aniline and three reference heterocyclic compounds (pyrrole, thiophene and furan) are studied using density functional theory (DFT) and time dependent DFT (TDDFT) calculations at B3LYP/6-31+G(d,p) level. It was found that poly (aniline-co-pyrrole) has the lowest ionization potential (4.48 eV) and electro affinity (0.77 eV) while poly (aniline-co-thiophene) has the lowest band gap and longest (3.21 eV) wavelength of absorption (and therefore the highest electronic conjugation) among the studied molecules. Comparison of the theoretical data and spectroscopic results obtained by DFT calculations with those experimentally obtained show very good agreement.

Polycyclic Aromatic Compounds Synthesis, Structural Characterization, Spectroscopic Properties, and Theoretical Investigations of Aminoacridine Derivatives

Synthesis of four N-(heterocyclic)-9-aminoacridine derivatives was investigated. The synthesized compounds, N-thiazolyl-9-aminoacridine (AC1), N-(1,3,4-thiadiazolyl)-9-aminoacridine (AC2), N-(5-methyl-1,3,4- thiadiazolyl)-9-aminoacridine (AC3), and N-(5-phenyl-1,3,4-thiadiazolyl)- 9-aminoacridine (AC4) were characterized by FT-IR, 1H NMR, massspectral, and elemental analysis. Amine-imine tautomerism was suggested by density functional theory (DFT) calculations. The optimized structures were obtained using B3LYP/6–311++G(d,p) level of theory. The UV–Vis absorption spectra were measured in various organic solvents. The synthesized compounds AC1–AC4 exhibit absorption spectra characteristic of typical donor–acceptor compounds. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) analysis have been used to explain the internal charge transfer (ICT) phenomena within the molecules. Also, simulated UVspectrawere calculated using TD-DFT (B3LYP/6–311++G(d,p) and the results were compared with the experimental values.

Substituent effects and aromaticity of six-membered heterocycles

Structural Chemistry, 2013

Structure, aromaticity, relative stability, and conformational flexibility of nitro and amino substituted monoheterocyclic analogous of benzene were studied by ab initio quantum-chemical method at MP2/aug-cc-pvDZ level of theory. Amino derivatives were found to be slightly less aromatic than nitro derivatives. Strong push-pull interactions were found in aand c-aminochalcogenopyrylium cations and, in less extent, in aand c-aminopyrydines. These molecules are less aromatic but more stable, as compare to their b-isomers. All heterocycles with 3rd and 4th row heteroatoms reveal C-NO 2 bond elongation accompanied by C-Heteroatom bond shortening in b-nitro isomers, and strong inequality of two endocyclic C-Heteroatom bonds in a-amino isomers.

Computational assessment of the electronic structures of cyclohexa-1,2,4-triene, 1-oxacyclohexa-2,3,5-triene (3delta(2)-pyran), their benzo derivatives, and cyclohexa-1,2-diene. An experimental approach to 3delta(2)-pyran

Journal of the American Chemical Society, 2002

Treatment of a solution of 3-bromo-1-methyl-1,2-dihydroquinoline (9) and [18]crown-6 in furan or styrene with KOtBu followed by hydrolysis afforded a mixture of 1-methyl-1,2-dihydroquinoline (10) and 1-methyl-2-quinolone (11). If the reaction was performed in [D 8 ]THF and the mixture was immediately analysed by NMR spectroscopy, 2-tert-butoxy-1-methyl-1,2-dihydroquinoline (17) was shown to be the precursor of 10 and 11. The structure of 17 is evidence for the title cycloallene 7, which arises from 9 by b elimination of hydrogen bromide and is trapped by KOtBu to give 17 so fast that cycloadditions of 7 with furan or styrene cannot compete. Since this reactivity is unusual compared to the large majority of the known six-membered cyclic allenes, we performed quantum-chemical calculations on 8, which is the parent compound of 7, and the corresponding isopyridine 6 to assess the electronic nature of these species. The ground state of 6 was no longer an allene (6 a) but the zwitterion 6 b. In the case of 8, the allene structure 8 a is more stable than the zwitterionic form 8 b by only % 1 kcal mol À1. These results suggest a high reactivity of 6 and 8 towards nucleophiles and explains the behaviour of 7. In addition to the ground states, the low-lying excited states of 6 and 8 were considered, which are represented by the diradicals 6 c and 8 c and, as singlets, lie above 6 b and 8 a by 19.1 ± 24.8 and 14.4 ± 17.7 kcal mol À1 , respectively.

Investigation of the electronic structures of 1,4,5-substituted derivatives of 1H-pyrimidin-2-thione

Monatshefte für Chemie - Chemical Monthly, 1996

Conformational analyses and quantum chemical calculations were carried out for 1,4,5substituted derivatives of 1H-pyrimidin-2-thione with the common skeleton I by means of the methods MMP2 and SCF MO LCAO in the CNDO/2 and MNDO approximations. The analysis of the electron density distribution as a function of the nature of the substitutents was performed on the basis of the data obtained.