A compar tive stud y of chemical shifts in ۲-substitude pyrrole stable pho sphorus y lide: ۱۳C and ۱H N MR GIAO c.s meth ods

Theoretical calculation of N MR parameters has been under developmen t for over three decades. Quantum theory-based calculatio n of NMR parameters is now a mature approach that can significantly widen the i nterpretative and analytical power of one of the most important spectroscopic tec hniques. The gauge-including atomic orbital ( GIAO) met hod is one of the most s uccessful a pproaches fo r calculatio ns of chemic al shifts. [۱,۲] It has been show n to provide results that are often more accurate than those calculated with other approaches, at the sam e basis set size. In m ost cases, i n order to take into account correlation effects, post-Hartree–Fock calculations of organic mo lecules have been perfo rmed using (i) Møller–Plesset perturbation m ethods, which are very time cons uming and hence applicable only to small molecular system s, and (ii) d ensity functional theory (DFT) methods, which usually provide signifi cant results at a relatively low comp utational co st. In this re gard, DFT methods hav e been preferred in the study of large organic molecules, metal comp lexes and organometallic compoun ds and for GIAO ۱۳C c.s. calcula tions. Although the g eneral principles and al gorithms for computing nuclear sh ielding are widely described, ver y few papers have been focused on a comparison among different quantum chemical models, basis sets, consistent reproduction and predicti on of the experimental ۱۳C and ۱H chemical sh ifts to be app lied in the study of med ium–large o rganic compounds. [۳,۴]

کلیدواژه ها:

GIAO ، ۱۳C NMR ، ۱H NMR ، Ylide ، Chemical shift