Sharif Digital Repository

Hartree-Fock and density functional theory methods at gauge invariant atomic orbital approach with different simplest basis sets were employed for the computation of chemical shifts. The wave functions for calculating gas-phase 1H and 13C chemical shifts have been optimally selected using empirical models. The effects of electron correlation treatment, triple-ξ valance shell, diffuse function, and polarization function on calculated chemical shifts have been discussed. Through empirical scaling of shielding, accurate predictions of 1H chemical shifts are achieved for the molecules studied, when considering small Pople basis sets. Gas phase experimental 1H chemical shifts in alcohols, amines... 

The wave functions for calculating gas-phase 13C nuclear magnetic shielding constants of 22 molecules have been optimally selected using factorial design as a multivariate technique. GIAO and CSGT methods were used for computation of shielding constants. Different wave functions for different types of carbons were recommended. A wave function as the best level of the theory is proposed for almost similar carbons. ONIOM approach for molecules with different types of carbons is applied. The results of GIAO method using the proposed wave function are in very good agreement with the experimental values. An additional series (21 carbons) were used as test sets and their results confirmed the... 

The wave functions for calculating gas phase 1H chemical shifts of primary and secondary alcohols have been optimized using factorial design as multivariate technique. Gas-phase experimental 1H chemical shifts of 18 alcohols were used to establish the best levels of theory for obtaining 1H chemical shift, among them the new experimental values of 1H chemical shifts of 10 alcohols were obtained in our laboratory. HF/6-31G(d,p) wave function is proposed as the best level of theory for calculating 1H chemical shifts of primary alcohols. For secondary alcohols, ONIOM(B3LYP/6-31G(d,p): HF/6-31G(d,p)) are recommended. An additional series of primary and secondary alcohols were used as test sets... 

The experimental 13C NMR chemical shift components of uracil in the solid state are reported for the first time (to our knowledge), as well as newer data for the 15N nuclei. These experimental values are supported by extensive calculated data of the 13C, 15N and 17O chemical shielding and 17O and 14N electric field gradient (EFG) tensors. In the crystal, uracil forms a number of strong and weak hydrogen bonds, and the effect of these on the 13C and 15N chemical shift tensors is studied. This powerful combination of the structural methods and theoretical calculations gives a very detailed view of the strong and weak hydrogen bond formation by this molecule. Good calculated results for the...