Number Of Five-membered Rings Research Articles

Exploration for the Optical Properties and Fluorescent Prediction of Nitrotriazole and Nitrofurazan: First-Principles and TD-DFT Calculations.

High-energy materials containing azole and furazan have revealed numerous properties; however, the underlying optical properties need to be solved. Meanwhile, the uncertainty for the choice of fluorescent matrix materials and the flexible situational conditions prompted us to estimate the optical and fluorescent properties of 5,5′-dinitro-2H,2H′-3,3′-bi-1,2,4-triazole (DNBT), 4,4′-dinitroazolefurazan (DNAF), and 4,4′-dinitro-3,3′-4,3′-ter-1,2,5-oxadiazole (DNTO). The first-principles calculation with improved dispersion correction terms and time-dependent density functional theory were utilized to calculate the absorbance and excitation energy of DNBT, DNAF, and DNTO, as well as characterization for their crystal structure, electronic structure, molecular orbitals, and so forth, synchronously. In this work, the absorbance anisotropy of DNBT and DNTO is stronger than that of DNAF. The absorbance for each of the (0,0,1) crystal planes in the three compounds is greater than that of the other two crystal planes. Moreover, DNBT has the maximum absorbance on the (0,0,1) crystal plane. The N–N–H from DNBT and N–O–N from DNTO and DNAF are responsible for these results, while N=N in DNAF weakens the performance of N–O–N. UV–vis spectra show that the maximum absorption wavelengths λmax for DNBT, DNAF, and DNTO are 225, 228, and 201 nm, respectively. The number of five-membered rings and the coplanarity of groups in the intermolecular non-conjugation interaction potentially improve this ability due to the results from the crystal diffraction analysis. In addition, the polarization rate DNBT > DNTO > DNAF based on the molecular orbital analysis and the electrostatic potential calculation implies that the excitation energy of DNBT is less than DNTO, and the excitation energy of DNTO is less than DNAF. This work is beneficial to the expansion of energetic materials into the optical field and the accelerated application process of the related industry.

Theoretical study on aromatic and open-shell characteristics of carbon nanobelts composed of indeno[1,2-b]fluorene units: dependence on the number of units and charge states.

In this study, we theoretically investigate the aromatic and open-shell characteristics of carbon nanobelts (CNBs) composed of five- and six-membered rings. We have designed nanobelts composed of indeno[1,2-b]fluorene ([1,2-b]IF) units, which are referred to as [N]IF-CNB (N: the number of five-membered rings). The number of π-electrons, nπ, in neutral [N]IF-CNB is 7N, and thus depending on N and charge states, nπ can be 4n + 2 and 4n. Quantum chemical calculations on neutral [6]IF-CNB and [8]IF-CNB and dicationic [8]IF-CNB2+ have revealed that they are expected to exhibit unique aromatic and open-shell characteristics depending on nπ, there are several analogies of the electronic structures in [N]IF-CNB to those in [N]annulene. Delocalized and intermediate open-shell electronic structures of [N]IF-CNB are also useful to drastically change the third-order nonlinear optical properties. These results suggest that theoretically designed [N]IF-CNB can be attractive and challenging targets of organic synthesis for realizing novel open-shell functional conjugated macrocycles.

Synthetic, Crystallographic, and Computational Study of Copper(II) Complexes of Ethylenediaminetetracarboxylate Ligands

Copper(II) complexes of hexadentate ethylenediaminetetracarboxylic acid type ligands H(4)eda3p and H(4)eddadp (H(4)eda3p = ethylenediamine-N-acetic-N,N',N'-tri-3-propionic acid; H(4)eddadp = ethylenediamine-N,N'-diacetic-N,N'-di-3-propionic acid) have been prepared. An octahedral trans(O(6)) geometry (two propionate ligands coordinated in axial positions) has been established crystallographically for the Ba[Cu(eda3p)]·8H(2)O compound, while Ba[Cu(eddadp)]·8H(2)O is proposed to adopt a trans(O(5)) geometry (two axial acetates) on the basis of density functional theory calculations and comparisons of IR and UV-vis spectral data. Experimental and computed structural data correlating similar copper(II) chelate complexes have been used to better understand the isomerism and departure from regular octahedral geometry within the series. The in-plane O-Cu-N chelate angles show the smallest deviation from the ideal octahedral value of 90°, and hence the lowest strain, for the eddadp complex with two equatorial β-propionate rings. A linear dependence between tetragonality and the number of five-membered rings has been established. A natural bonding orbital analysis of the series of complexes is also presented.

A solid-state NMR study of the carbonization of polyaniline

15N-labeled polyaniline (PANI) is heat treated at temperatures from 200 to 1000°C in a nitrogen atmosphere. The carbonization of PANI is determined using solid state (SS) 13C and 15N NMR. In an attempt to accurately assign the experimentally observed 15N NMR chemical shift, theoretical nitrogen shielding is calculated using ab initio MO calculations. The SS NMR results imply that the reconstruction of the polymer backbone occurs in the temperature range 400–600°C and the nitrogen of Phe-NH-Phe amino group changes to pyrrolic or tertiary nitrogen and the imine nitrogen changes to pyridinic nitrogen. Heat-treatment above 700°C leads to a decrease in the number of five-membered rings containing nitrogen atoms (pyrrolic), while the number of six-membered rings containing nitrogen (pyridinic, pyridineoxide and pridinium) increases.

A Density Functional Investigation of Fluorinated Silicon Clusters

Density functional calculations have been carried out on a series of fluorinated empty cages XnFn(n=2–20) with XSi, Ge, and Sn. It indicates that the fullerene-like cage structure with pentagons turns out to be the most stable with n increasing, and the stability of the XnFn isomers increases with the number of five-membered rings. The HOMO-LUMO gap for Ge (n=6, 10) cages is found to be even larger than the values for Si cages, though in bulk Ge has a smaller band gap than Si. Moreover, calculation of the Gibbs free energy of oligomerization reaction of SiF1/n (SiF)n showed that this reaction is exothermic even at 900 K, indicating the favorability of their formation from the SiF monomer.

Strain Energies Due to Nonplanar Distortion of Fullerenes and Their Dependence on Structural Motifs

Accurate strain energies due to nonplanar distortion of 114 isolated pentagon rule (IPR) fullerenes with 60-102 carbon atoms have been calculated based on B3LYP/6-31G(d) optimized structures. The calculated values of strain energy due to nonplanar distortion (Enp) are reproduced by three simple schemes based upon counts of 8, 16, and 30 distinct structural motifs composed of hexagons and pentagons. Using C180 (Ih) and CN (Ih) (N is very large) as test molecules, the intrinsic limitations of the motif model based on six-membered rings (6-MRs) as the central unit have been discussed. On the basis of the relationship between the contributions of motifs to Enp and the number of five-membered rings (5-MRs) in motifs, we found that IPR fullerenes with dispersed 5-MRs present smaller nonplanar distortions.

Multivariate characterization of polycyclic aromatic hydrocarbons using semi-empirical molecule orbital calculations and physical data.

Multivariate characterization of 60 polycyclic aromatic hydrocarbons (PAHs) was performed using data from literature and semi-empirical molecular orbital calculations. This dataset was analyzed by principal component analysis and projections to latent structures by means of partial least square. The PAHs were found to distribute in the chemical domain in several groups mainly governed by the number of aromatic rings and the number of five-membered rings. The multivariate model and training set was used to predict GC retention times on a non-polar column (DB-5). Using a 2(4) experimental design on the principal components of the chemical characterization model, a test set of PAHs was selected dependent on the distribution in the chemical domain of the PAHs. Such a test set is expected to improve selection of PAHs for future testing and modeling of both biological and chemical responses. Although the model of GC retention times was good, the precision was however not good enough for practical use.

Geodesic polyarenes with exposed concave surfaces

Abstract

Molecular Size and Pyramidalization: Two Keys for Understanding the Reactivity of Fullerenes

The large electron affinity of fullerenes such as C~O or C~O has been rationalized by taking into account the effects of molecular size, the number of five-membered rings, and pyramidalization on their LUMO energy. The study of conjugated cyclopolyenes having different size and pyramidalization has shown an enhancement of their electron affinity upon an increase in these two factors and with the presence of pentagonal instead of hexagonal rings. It has also been found that pyramidalization has an effect which is almost constant for all the systems studied, namely, a reduction of the LUMO energy by a similar extent. The stabilization of the LUMO orbital due to an increase in the molecular size is normally more determining than the effect of pyramidalization. The results obtained indicate that fullerenes exhibit enhanced electron-withdrawing character upon increase of their molecular size and pyramidalization. After the discovery' and synthesis in macroscopic quantities2 of c60 and (270, it was initially assumed that fullerenes exhibited extremely stable aromatic character. This initial hypothesis was soon rejected in the light of the numerous chemical reactions undergone by C60 and C703-8 (see ref 3 for recent reviews on chemical reactivity of fullerenes).

Effect of the composition and structure of cobalt(III) complexes on their RF values obtained by partition paper chromatography : I. Effect of the position of nitro groups and the chelate ring size

R F values of 41 cobalt(III) complexes were determined by partition paper chromatography using 15 solvent systems. It was established that cis-NO 2 isomers always exhibit higher R F values than the corresponding trans-isomers, even when a complex has several cis- and trans-isomers. It has been found that an increase in the chelate ring size gives rise to higher R F values and that there is a linear dependence between the R M values observed and the number of five-membered rings that are substituted by the corresponding six-membered rings.