Academic
Publications
Extension of the Karplus Relationship for NMR Spin-Spin Coupling Constants to Nonplanar Ring Systems: Pseudorotation of Tetrahydrofuran

Extension of the Karplus Relationship for NMR Spin-Spin Coupling Constants to Nonplanar Ring Systems: Pseudorotation of Tetrahydrofuran,10.3390/i40401

Extension of the Karplus Relationship for NMR Spin-Spin Coupling Constants to Nonplanar Ring Systems: Pseudorotation of Tetrahydrofuran   (Citations: 6)
BibTex | RIS | RefWorks Download
Karplus relationships for all 26 NMR spin-spin coupling constants (SSCCs) J of the pseudorotating tetrahydrofuran (THF) molecule were derived by expanding J as a function J(q,`) of the puckering amplitude q and the pseudorotational phase angle `. For this purpose, the conformational potential V(q,`) of THF was determined at the MBPT(2)/cc- pVTZ and B3LYP/6-31G(d,p) levels of theory. THF is a slightly hindered pseudorotor (MP2 barriers ¢E and ¢H are 0.1 - 0.2 kcal/mol) with a puckering amplitude q = 0.396 " A and a barrier to inversion ¢H = 4.1 kcal/mol in reasonable agreement with experimental data. The SSCCs of THF were calculated both at MBPT(2)/cc-pVTZ and B3LYP/6-31G(d,p) geometries using coupled perturbed density functional theory (CPDFT) with the B3LYP functional and a (9s,5p,1d/5s,1p)(6s,4p,1d/3s,1p) basis set. All geometrical parameters and the 26 SSCCs of THF were computed as functions of the phase angleand averaged to give <nJ> values that can be compared with measured data. The following SSCCs were obtained: <1J(CC)> = 34.2, 34.0; <1J(CO)> = 26.4; <1J(CH)> = 142.6, 130.9; <2J(CXC)> = 0.5, 0.8; <2J(OCC)> = 0.3; <2J(CCH)> = -1.5, -0.7. -2.8; <2J(OCH)> = -8.6; <2J(HCH)> = -8.7, -12.0; <3J(CXCH)> = 3.0, 4.0, 2.9; <3J(OCCH)> = -1.2; <3J(HCCH;cis)> = 7.3, 8.5; <3J(HCCH;trans)> = 5.3, 5.5; <4J(HCXCH;cis)> = -0.2, -0.2; <4J(HCXCH;trans)> = -0.5, -0.6 Hz (X = C or O). Magnitude and trends in calculated SSCCs are dominated by the Fermi contact term although other contributions are not negligible. Those SSCCs that strongly depend on the pseudorotational mode of THF were identifled as suitable descriptors for the conformation of THF in solution. THF is discussed as a suitable model for ribose.
Journal: International Journal of Molecular Sciences - INT J MOL SCI , vol. 4, no. 4, pp. 158-192, 2003
Cumulative Annual
View Publication
The following links allow you to view full publications. These links are maintained by other sources not affiliated with Microsoft Academic Search.
    • ...In previous work, we described a generalization of the Karplus relationship in the case of pseudorotating ring molecules [12]...
    • ...In this situation, however, reliable quantum chemical calculations of individual constants J [13,14] in dependence of the pseudorotational mode of a ring can be used to compliment the limited information obtained from NMR experiments to derive a Karplus relationship for the ring molecule [12]...
    • ...Our investigation of cyclopentane led to a number of interesting conclusions concerning the description of pseudorotating molecules with the help of SSCCs [12]...
    • ...However, for a given basis set of moderate size CPDFT turned out to be superior in terms of both cost and accuracy [12]...
    • ...This level of theory leads to a very accurate description in the case of cyclopentane as we showed recently [12]...
    • ...The CES function V(q;`) of any puckered flve-membered ring can be given as a Fourier expansion in the pseudorotational phase angle ` and a power series in the puckering amplitude q [25,12]:...
    • ...57). Previous investigations showed that reliable SSCC values are obtained with the B3LYP functional [12,13,57] and TZ+P or QZ+P basis sets [58]...
    • ...Although MBPT(2) covers just pair correlation efiects [43], it is known to provide an accurate account of energies and geometries along the pseudorotational path of a free (or slightly hindered) pseudorotor if carried out with a cc-pVTZ basis set [12,35]...
    • ...slightly overestimate the barrier to planarity as was also observed in the case of cyclopentane [12]...
    • ...MBPT(2), 0.396 § 0.002 ” A; Table 1), which is typical of a free or slightly hindered pseudorotor [12,25]...
    • ...In addition to bond eclipsing/bond staggering efiects, there are also anomeric interactions [12,65] involving an O electron lone pair and bonds C2H6 and C2C3...
    • ...dependence on ` than the corresponding SSCC in cyclopentane [12], adopting large values for ¿(H8C3C4H10) = 0‐ (12.1 and 10.2 Hz at ` = 0‐ and 180‐; Figure 6d) and smaller values for ¿(H8C3C4H10) = 40.7‐ (6.4 Hz for ` =90‐ and 270‐)...
    • ...[12] provided the in∞uence of the O atom is considered...

    Anan Wuet al. Extension of the Karplus Relationship for NMR Spin-Spin Coupling Const...

Sort by: