Theoretical study of oxocarbons: structure and vibrational spectrum of the D6h and C2 forms of the rhodizonate ion

A comparison of chitosan properties after extraction from shrimp shells by diluted and concentrated acids

Chitosan and chitin are mainly extracted from shells of fish such as lobsters, crabs or shrimps. Originally, the raw material and the two compounds are identical. This study aims to show the acid concentration effect on chitosan extraction from shrimp shells between concentrated and diluted acid; on surface morphology, thermal resistance, structural, elemental composition, optical and opto-electronic properties. It also aims to reduce the production time and increase the quantity. We focused mainly on comparing between Physico-chemical properties of chitosans extracted by diluted (1M) and concentrated (20%) Chloric acids, and sometimes we compare by other concentrated acids like nitric acid (70%) and sulphuric acid (98%). We performed the product's characterization by various tools such as: X-ray diffraction (XRD) spectroscopy, X-ray fluorescence (XRF) analysis, UV-Visible spectroscopy, Fourier Transformed Infra-Red (FTIR), Raman Spectroscopy, Thermogravimetry and Derivative Thermogravimetry (TG/DTG), Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX) analysis. The elemental analysis (XRF and EDX). The results showed that all chitosan samples we gained are good about 80% degree of deacetylation, and pure mostly composed by carbon between (15,02% - 45.55%), nitrogen (4,17% - 12.28%) and oxygen (42.16% and 81.25%), with appearance of essential peaks for chitosan in Raman analysis: 470 cm⁻¹ → ν(C-C(=O)-C), 1000 cm⁻¹ → ν(C-H), 1800 cm⁻¹ → δ(C=CCOOR), δ(C=O), 2630 cm⁻¹ → δ(CH) rings, 3250 cm⁻¹ → ν(NH₂). All our chitosan particles are ultrafine nanoscale between 8 and 34 nm.

On the Lack of Ring-Current Aromaticity of (Heteroatom) [N]Radialenes and their Dianions

Current-density maps, calculated at the ab initio RHF//6-31G**/CTOCD-DZ level, show no significant pi ring current in planar equilateral geometries of neutral and dianionic [N]radialenes, oxocarbons and thiocarbons C(N)Y(N) (q-) (Y=CH(2), O, S; N=4, 5, 6; q=0 (1 a-12 a), 2 (1 b-12 b)). Only the N=3 deltate dianions C(3)Y(3) (2-) (Y=CH(2), O, S (1 b, 5 b and 9 b)) have discernible pi ring current, and then with at most 20-25 % of the strength of the standard benzene current. On the magnetic criterion, lack of current is definitive evidence against aromaticity. Pictorial molecular-orbital analysis within the ipsocentric approach shows this to be an inevitable consequence of the nodal structure of the pi and pi* orbitals of [N]radialene-like systems. On grounds of angular-momentum symmetry, spatial distribution, or both, the HOMO-LUMO excitation does not contribute a significant central diamagnetic ring current.