Magnetic Properties of Cyclo[n]Carbons (n = 10–34)

Abstract

Quantum-chemical calculations of the magnetic properties (magnetically induced ring-current strength, magnetizability) of even- and odd-number cyclo[n]carbons (n = 10–34) were carried out. The total energy of the studied molecules as a function of the external magnetic field was found for the first time. The obtained dependences predict correctly the magnetic nature of cyclo[n]carbons. For even-number aromatic cyclo[n]carbons the energy of the system increases with increasing magnetic field, while for antiaromatic systems, the energy decreases. Such behavior indicates that aromatic even-number cyclo[n]carbons (n = 4k+2) are diamagnetic, whereas antiaromatic even-number cyclo[n]carbons (n = 4k) are paramagnetic. These results are confirmed by the previously calculated average magnetizability values. In the case of odd-number cyclo[n]carbons, all structures except C13 are diamagnetic. Antiaromatic C13 is paramagnetic according to average magnetizability calculations. It was shown that nonaromatic cyclo[n]carbons (n = 28–34) at high magnetic fields (B > 300 T) possess a nonlinear effect of the increase in the energy of the system with increasing magnetic field. This effect can be observed experimentally in NMR spectra at a magnetic field greater than 300 T. The performed calculations demonstrate that the HF method correctly predicts the magnetic and aromatic properties of cyclo[n]carbons (n = 10–34).