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Ab initio Optimizations of Molecular Structures and GIAO NMR Calculations of Chemical Shieldings of [8]- and [10]Paracyclophane and of [8](1,4)Naphthalenophane. Basis Set Dependence in Relation to Experimental 2D-NMR-Spectra and to Our APUDI Ring Current

Dietrich F., Zuschneid T., Ritter G., Regelmann C., Kaiser D., Häfelinger G.

Polish Journal of Chemistry

2007

Vol. 81, nr 5-6

1159-1190

The molecular structures of the minimum energy conformations of [8]- and [10]paracyclophanes (1) and (2) have been calculated by full gradient optimizations using the ab initio HF method with four Pople basis sets and by the DFT/B3LYP method with two split-valence basis sets under the constraint of assumed C2symmetry. The calculation for [8](1,4)naphthalenophane (3) was performed in the HF/6-31G*method in comparison to a force-field PIMM calculation. For each final geometry, 1H and 13C chemical shieldings have been calculated by theGIAOMOmethod and converted to chemical shifts by calculated TMSvalues for geometries optimized in the corresponding method/basis set combination. Compounds 1 to 3 have been synthesized by known procedures and their experimental NMR chemical shifts were measured at 400 MHz. 2D homo- and heteronuclear chemical shift correlations allow non arbitrary signal assignments. The calculated shift values have been correlated with experimental shifts by linear least squares regressions for proton and carbon NMR data. Best statistical parameters are obtained for 1H NMR values by HF/6-31G* calculations but for 13C NMR shifts from HF/6-311G* data. Surprisingly, regressions with our APUDI geometric factors lead to similar accuracy if the point dipoles are located at the carbon atom positions (p = 0.0 ) for both 1H and even 13C NMRvalues. These regressions show clearly that not only the 1HNMRdata but also 13C NMR values in the vicinity of a benzene ring are determined by a long range ring current anisotropy effect reproduced by the GIAO and the APUDI calculations.

Physical Image vs. Structure Relation. 9. Synthesis and Structural Study of Some 2,5-Bis-alkoxysubstituted 3-Oxolenes and Oxolanes: An Experimental and Theoretical Approach

Nazarski R., Skowroński R.

Polish Journal of Chemistry

2003

Vol. 77 / nr 4

415-426

Two 2,5-bis-substituted 3-oxolenes 2 stable only in anhydrous, acid-free solutions were obtained in the Clauson-Kaas reaction. An immediate catalytic hydrogenation of theE/Z isomeric mixture of oxolene 2a, followed by chromatography, afforded one geometrical form of oxolane diol 4 (isomer I), which was subsequently submitted to several attempts of cyclization to an unknown bis-spiroacetal of succinic anhydride (6). Arationalization of this process failure and the Z geometry of product I exhibiting interesting spectroscopic features were inferred from theoretical results (HF/6-31G** calculations) and experimental data for solution (NMR, IR). Some additional ab initio GIAO-CPHF NMR computations concerning relevant model bis-acetals 3 and 5 were performed, as well.