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Volumn 71, Issue 8, 2006, Pages 3103-3110

Accuracy vs time dilemma on the prediction of NMR chemical shifts: A case study (chloropyrimidines)

Author keywords

[No Author keywords available]

Indexed keywords

CHLOROPYRIMIDINES; NMR CHEMICAL SHIFTS; QUANTUM CHEMISTRY; REGIOISOMERIC MIXTURE; SOLVENT EFFECT;

EID: 33645778479     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo0600149     Document Type: Article
Times cited : (16)

References (69)
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    • note
    • Users can add their own data into the commercially supplied database. For instance, in our database most of Pfizer and intermediate compounds are included. However, in this paper and in order to reproduce the results in other laboratories we explicitly excluded the Pfizer database.
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    • note
    • cal - b)/a)) and STEYX function is the standard error of the regression. See Supporting Information for full details.
  • 35
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    • note
    • 13C atoms, respectively.
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    • note
    • 13C chemical shifts at different DFT levels. BLYP is a pure DFT method where the coupled-perturbed Hartree-Fock equations are avoided; therefore nuclear magnetic shielding calculations are faster with this method than with HF and B3LYP variants. For the size of this study, the relative speed was about B3LYP=1.25*HF and BLYP=0.75*HF.
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    • Significant underestimation of the paramagnetic terms has been generally observed. See: Wiberg, K. B. J. Comput. Chem. 1999, 20, 1299-1303.
    • (1999) J. Comput. Chem. , vol.20 , pp. 1299-1303
    • Wiberg, K.B.1
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    • The NICS values are -6.4 (-5.6) and -5.9 (-5.4) ppm for B3LYP and HF geometries respectively for compound 1 (2), calculated at the (3,+1) ring point of electron density according to Bader at the GIAO-B3LYP/6-31G(d.p) level. See: Morao, I.; Cossio, F. P. J. Org. Chem. 1999, 64, 1868-1874.
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  • 52
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    • note
    • The CSD search provides 23 and 29 entries for 1 and 2, respectively, using the corresponding C4N3C1 scaffold. The experimental C-C1 bond length is found to be ca. 1.73 Å. See Figure 3 for comparison with computed values at different levels of theory. Indeed, a partial optimization at the same level of theory of compound 1 restraining the C-C1 distance to the experimental value showed a better agreement (168.2 vs 166.3 ppm).
  • 53
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    • GIAO-PCM methodology also fails if the solute-solvent system exhibits cooperative charge transfer, see: Klein, R. A.; Mennucci, B.; Tomasi, J. J. Phys. Chem. 2004, 108, 5851-5863.
    • (2004) J. Phys. Chem. , vol.108 , pp. 5851-5863
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    • note
    • 13C chemical shifts in both solvents (DFT(bs1)s1 -2//DFT-(bs1)s1-2) is shown in this table (entries 20 and 21). See the Supporting Information for the data of all 27 methodologies computed.
  • 65
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    • note
    • We have used the scaled mean absolute error (CMAE) as the parameter to quantify the residuals between prediction and experiment. For proton chemical shifts the mean absolute error (MAE) was used instead as only two hydrogen atoms (aromatic) are analyzed.
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    • note
    • 1/2- 1
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    • note
    • As a metric rule of thumb, if the value of interclass distance between categories is over 3 these classes are considered well classified. We here propose a much less strict criterion. It would be the hypothetical case where both cross errors are ca. double their own errors. The higher the number (we suggest here 3 as a minimum) the higher is the confidence in the assignation.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.