Theoretical studies on structures, 13C NMR chemical shifts, aromaticity, and chemical reactivity of finite-length open-ended armchair single-walled carbon nanotubes

Reversal of Clar's Aromatic-Sextet Rule in Ultrashort Single-End-Capped [5,5] Carbon Nanotubes

The three-fold HOMO-LUMO gap oscillation, typical of finite length armchair carbon nanotubes (CNT), has a major effect on the magnetic response of ultrashort, single-end-capped [5,5] carbon nanotubes to a perturbing magnetic field parallel to the main symmetry axis. For the CNT's containing 40, 70, and 100 carbon atoms, for which 100 % of the C=C double bonds can be grouped into aromatic-sextets, i. e., fully or complete Clar networks, large paratropic (antiaromatic) global circulations around the cylindrical axis are predicted at the DFT level of calculation. Local and semi-global diatropic (aromatic) currents of strengths not larger than that of the benzene molecule are determined for a perpendicular perturbing magnetic field. CNTs of intermediate lengths do not display this enhanced antiaromatic response. The paratropic current flow clearly shows that these complete Clar networks can be viewed as stacked cycloparaphenylene belts, each providing a double 4 n annulene circuit as a consequence of the quinoidal resonance structure that results from their closure. Paradoxically, the fully aromatic Clar structure itself is responsible for the enhanced global antiaromaticity.

Structural activity analysis, spectroscopic investigation, biological and chemical properties interpretation on Beta Carboline using quantum computational methods

In this methodological work, the structural activity analysis have been carried out on β-Carboline to study the anti cancer activity and the way of improving the biological activity. The molecular spectroscopic tools were used to evaluate all the experimental data like spectral results and data were validated by the computational, HyperChem and Osiris tools. The structural, biological and physico-chemical related analyses have been performed to interpret the properties. The GPCR ligand calculated to be 0.11 for generating pharmacokinetic process, Specified drug information for the compound, was congregated from all types of structural activity which was drawn by spectral and HyperChem data. The σ and π interaction band gap (6.18 eV) ensured the drug consistency. The Mulliken charge process distribution was mapped, the charge orientation assignment was checked; the acquired negative charge potential consignment for the cause of antibiotic impact was verified. The molecular orbital interaction study was carried out to identify the origination of degeneracy of interaction causing drug mechanism. Using NMR spectral pattern, the chemical reaction path was recognized and the nodal region dislocation was distinguished on chemical shift. The Electronegativity (χ) and Electrophilicity charge transfer found to be 3.83 and 0.215, confirmed charge complex transfer for activating drug process in the compound. The molecular nonbonding section was thoroughly observed in order to find the occupancy energy, was the key process to initiate drug activity. The bathochromic electronic shift was observed and the existence of CT complex was discussed. The hindering of toxicity was inspected on inevitable chirality of the compound by specifying VCD spectrum.

Modeling zigzag CNT: dependence of structural and electronic properties on length, and application to encapsulation of HCN and C2H2

Density functional theory (B3LYP, B3LYP-D2 and wB97XD functionals) was used in finite models of zigzag carbon nanotubes (CNT), (n,0)×k with n = 6-9 and k = 2-4, to systematically investigate the effects of size on their structural and electronic properties. We found that the ratio between the length (L _t) and the diameter (d _t) of the pristine CNT has to be larger than 2, i.e., L _t/d _t > 2, in order to provide the observed experimental trends of C=C bond distances, as well as to maintain the atomic charges nearly constant and zero around the center of the tube. Therefore, the concepts of useful length and volume were developed and tested for the encapsulation process of HCN and C₂H₂ into CNTs. The energies involved in these processes, as well as the changes in molecular structure and electronic properties of the dopants and the CNTs are discussed and rationalized by the amount of charge transferred between dopant and CNT. Graphical Abstract Illustration of zigzag CNT length and diameter ratio in order to represent C=C bond experimental trend.

A Theoretical Study on the Strain Energy of Carbon Nanobelts

A theoretical study on the strain energy of carbon nanobelts, i.e. the belt-shaped molecules representing the sidewall structures of carbon nanotubes, is reported. The strain energy of carbon nanobelts with chiral indices (n,n), (n,0), and (n,m) was determined without considering hypothetical homodesmotic reactions. The calculated difference between the strain energy of carbon nanobelts and their possible precursors is expected to be of great utility for future synthetic purposes.

A theoretical study on surface reactivity of fluorinated (n,0) and (n,n) carbon nanotubes (n = 3–6)

Density functional theory calculations are performed to investigate the surface reactivity of pristine as well as fluorine-terminated zigzag (n,0) and armchair (n,n) carbon nanotubes (n = 3–6). The properties determined include the electrostatic potential V(r) and average local ionization energy Ī(r) on the surfaces of the investigated tubes. A general feature of all of the systems studied is that stronger potentials are associated with regions of higher curvature. The results indicate that both V(r) and Ī(r) detect the effects of fluorine-terminated regions in which significant effects are observed for those atoms in the vicinity of the fluorine-terminated regions. Comparison with the Ī(r) of the pristine nanotube indicates correctly that in the fluorine-terminated models, the fluorine atoms tend to deactivate the surface toward electrophilic/radical attack.

Using the 19F NMR chemical shift anisotropy tensor to differentiate between the zigzag and chiral forms of fluorinated single-walled carbon nanotubes

The structural characterization of different kinds of zigzag and chiral single-walled carbon nanotubes (SWNTs) has been investigated theoretically using (19)F NMR spectroscopy. The chemical shift anisotropy (CSA) tensor is computed at different levels of theory for the (19)F nuclei in different forms of functionalized fluorinated carbon nanotubes (CNT). A set of fluorine CSA parameters comprising the span, skew, and isotropic chemical shift is computed for each form of the fluoronanotubes and multidimensional CSA parameter correlation maps are constructed. We show that these correlations are able to clearly distinguish between the chiral and zigzag forms of fluorinated carbon nanotubes (F-SWNTs). Implications for solid-state and liquid-state NMR experiments are discussed.