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GIAO‐HDFT scaling factor for 13C NMR chemical shifts calculation

In this paper, we present a GIAO‐HDFT scaling factor study, in which we intent to investigate the ability of GIAO‐HDFT/cc‐pVDZ to achieve a high cost‐effectiveness ratio. A set of 22 small molecules providing 27 different 13C chemical shifts determined in the gas phase was used. Geometry optimizations were performed for a single molecule in a gas phase using B3LYP/cc‐pVDZ, B3LYP/aug‐cc‐pVDZ, B3PW91/cc‐pVDZ and B3PW91/aug‐cc‐pVDZ level of theory. NMR chemical shifts were computed at the B3LYP and B3PW91 with cc‐pVnZ (n = 2–3) and augment aug‐cc‐pVnZ (n = 2–3) levels using the GIAO method and are given relative to that of TMS calculated at the same level of theory. Despite the calculation approximations the chemical shifts calculated at the B3PW91/cc‐pVDZ//B3PW91/cc‐pVDZ using a simple relationship (δscalc = 1.02 δcalc − 0.92, where δcalc and δscalc are the calculated and the linearly scaled values of the 13C chemical shifts, respectively) were able to yield MAD and RMS errors as small as those obtained with other GIAO‐HDFT (B3LYP, B3PW91 and OPBE) with bigger basis sets, such as 6‐311 + G(2d,p) and cc‐pVTZ. The used approach also proved successful in distinguishing regioisomers, but, unfortunately, it lacks the ability to distinguish between diastereoisomers, a task otherwise proved to be very difficult to accomplish. Copyright © 2010 John Wiley & Sons, Ltd.13C NMR GIAO‐HDFT linear scaling factors based on “chemical shift‐chemical shift” correlation approaches were generated and provided a very attractive tool (GIAO‐ B3PW91/CC‐pVDZ//B3PW91/CC‐pVDZ‐δscale = &!thinsp;1.02 δCalc‐0.92, R2 = 0.9983) as an alternative to more computationally demanding approaches cited in literature.

Authors:   Costa, Fabio Luiz Paranhos; de Albuquerque, Ana Carolina Ferreira; dos Santos Jr., Fernando Martins; de Amorim, Mauro Barbosa
Journal:   Journal of Physical Organic Chemistry
Volume:   23
Issue:   10
Year:   2010
Pages:   972
DOI:   10.1002/poc.1749
Publication date:   01-10-2010
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