GIAO/DFT evaluation of ¹³C NMR chemical shifts of selected acetals based on DFT optimized geometries

Abstract

DFT/B3LYP calculations of the ground-state conformation of eight cyclic and acyclic acetals are presented and compared with experimental data. Results of single-point GIAO/DFT calculations at five different levels of theory show that isotropic shieldings need to be empirically scaled to achieve agreement with experimental chemical shifts. Statistical evaluation of data indicates that the most accurate prediction of 13C chemical shifts is achieved at the MPW1PW91/6-311G** level of theory. An empirical equation describing the relationship between delta values and shielding constants is postulated. This equation has been applied to the non-chair ground-state conformation of the six-membered acetonide and to the conformationally flexible benzodioxonine derivative. The agreement observed between the experimental and predicted chemical shifts shows that calculations at the MPW1PW91/6-311G** level of theory are adequate for addressing questions of conformation.

Psammaplin A as a general activator of cell-based signaling assays via HDAC inhibition and studies on some bromotyrosine derivatives

“…Also, the 13 C NMR shift at δ c 54.1 is not consistent with a terminal methyl sulfone substructure, such methyl carbons are usually observed in the range of δ c 37-45 33. We conducted DFT calculations34 modeling the 13 C NMR shifts of 8 and 6 (Table 4). These showed a much better fit to the observed data for the sulfinate ester structure.…”

“…The low energy conformations were imported to Gaussian03,36 and each structure was subjected to a full geometry optimization using DFT/mpw 1pw91/6-311g(d,p). After geometry optimization, NMR calculations were performed using the GIAO method using DFT/mpw 1pw91/6-311g(d,p), which has been shown to provide reliable results for 13 C calculations 34. All Gaussian calculations were performed at the Center for High Performance Computing at the University of Utah on an Opteron cluster.…”

Initial Carbon–Carbon Bond Formation during the Early Stages of the Methanol‐to‐Olefin Process Proven by Zeolite‐Trapped Acetate and Methyl Acetate

“…[1,3,14,16,22] Only at al ong mixing time,a na dditional crosspeak with 57.7 was observed at 100.1 ppm, whose corresponding 1 Hr esonates at 4.72 ppm, which can be assigned to dimethoxymethane (DMM). [41][42][43] Remarkably,asecond minor signal at 101.3 ppm is observed for the DMM-CH 2 group,that shows an exchange cross-peak with 100.1 at longer mixing times (Figure 2a). This is an indication of exchange between anomeric DMM structures on as ub-second timescale (trans, trans and gauche, gauche,F igure 2d).…”

Theoretical studies of organotin(IV) complexes derived from ONO-donor type schiff base ligands

“…On this matter two main approaches can be applied, empirical scaling [98][99][100] and multiple-reference standard methodology [101,102]. The latter is based on usage of references different from tetramethylsilane (TMS) for 1 H and 13 C-NMR GIAO calculations.…”