Correlation Of 13C Chemical Shifts Research Articles

ChemInform Abstract: Definitive Structural Assignment of Condensation Products from Anthranilamide and 3-Amino-2-carbamoylthiophene with Ketones. Formation of Tetrahydroquinazolinones and Their Thiophene Isosteres.

Products formed from dehydrative cyclization of cyclopentanone, cyclohexanone, and cycloheptanone with anthranilamide (2) under neutral or acidic conditions are established as the spiro compounds 2,2-polymethylene-1,2,3,4-tetrahydroquinazolin-4-ones 6 by means of (a) the presence of a 13C nmr signal at 66–79 ppm for atom C-2 and (b) X-ray crystallography on the tetramethylene compound 6a. Analogously, products from reactions of these cycloalkanones with 3-amino-2-carbamoylthiophene are now shown by 13C nmr spectra to have structures isosteric to 6, i.e. 5,5-polymethylene-4,5,6,7-tetrahydrothieno[2,3-e]pyrimidin-7-ones 5, rather than the chelate ring structures previously proposed. Additionally, conflicting literature reports on product 3 from reaction of acetone with 2 are partially clarified. Correlation of 13C chemical shifts in systems 3, 5, and 6 is presented.

Definitive structural assignment of condensation products from anthranilamide and 3‐amino‐2‐carbamoylthiophene with ketones. Formation of tetrahydroquinazolinones and their thiophene isosteres

AbstractProducts formed from dehydrative cyclization of cyclopentanone, cyclohexanone, and cycloheptanone with anthranilamide (2) under neutral or acidic conditions are established as the spiro compounds 2,2‐polymethylene‐1,2,3,4‐tetrahydroquinazolin‐4‐ones 6 by means of (a) the presence of a 13C nmr signal at 66–79 ppm for atom C‐2 and (b) X‐ray crystallography on the tetramethylene compound 6a. Analogously, products from reactions of these cycloalkanones with 3‐amino‐2‐carbamoylthiophene are now shown by 13C nmr spectra to have structures isosteric to 6, i.e. 5,5‐polymethylene‐4,5,6,7‐tetrahydrothieno[2,3‐e]pyrimidin‐7‐ones 5, rather than the chelate ring structures previously proposed. Additionally, conflicting literature reports on product 3 from reaction of acetone with 2 are partially clarified. Correlation of 13C chemical shifts in systems 3, 5, and 6 is presented.

1H,13C and17O NMR study of substituent effects in 4-substituted phenylthiol esters

The 1H and 13C NMR spectra of 4-substituted phenylthiol acetates, benzoates and cinnamates and the 17O NMR spectra of a few thiol acetates were measured. The 13C chemical shifts of C-1 of the thiol esters when correlated with appropriate substituent-induced chemical shifts (SCS) of monosubstituted benzenes reveal an enhancement of substituent effect at C-1. Several good dual substituent parameter (DSP) correlations of 13C chemical shifts with σ1 and σR parameters were obtained for the carbons para to the substituent and the carbonyl carbons of all the three series of thiol esters display inverse substituent effects, indicating π-polarization of the thiol ester functionality by the dipole of the substituent. © John Wiley & Sons Ltd.

Correlation of 13C chemical shifts with torsional angles from high-resolution, 13C-C.P.-M.A.S. N.M.R. studies of crystalline cyclomalto-oligosaccharide complexes, and their relation to the structures of the starch polymorphs

The chemical shifts and multiplicities of the resonances in high-resolution, 13C-c.p.-m.a.s. n.m.r. spectra of cyclomalto-oligosaccharide inclusion complexes are characteristic of the crystalline structure of the different complexes. In particular, the 13C chemical shifts of C-1 and C-4 correlate with the torsion angles φ' 2and φ 1 respectively (related to Ψ and φ, respectively, in an alternative terminology), which describe the orientation of the D-glucosyl residues about the α-D-(1→ 4) glycosidic linkage. The 13C chemical shift of C-6 correlates with the torsion angle x, which describes the orientation of O-6 about the exocyclic, C-5-C-6 bond. The cyclomalto-oligosaccharide inclusion complexes are good models for the interpretation of the characteristic chemical shifts and multiplicities previously observed in the 13C-c.p.-m.a.s. n.m.r. spectra of the natural starch polymorphs. From these chemical-shift correlations, values for the torsion angles φ' 2, φ 1 and X are predicted for starches that crystallize as “A” and “B” structures. These predicted values are in agreement with the limited data currently available from X-ray fiber diffraction studies.

Synthesis of 6,9‐Dipropyl‐1,4‐Dioxaspiro[4.5] Deca‐6,8‐Diene‐2,10‐Dione and its Diels‐Alder Reactions with Substituted Acetylenes

AbstractThe title compound, a masked 3,6‐di‐n‐propyl‐o‐benzoquinone, was synthesized from 3,6‐di‐n‐propylcatechol in 82% yield. Its Diels‐Alder reactions with methyl propiolate, phenylacetylene, 1‐octyne, dimethyl acetylenedicarboxylate, diphenylacetylene and 3‐hexyne were studied. The yields of the adducts were excellent except for the last two cases in which the unimolecular decomposition of the title compound to generate 3,6‐di‐n‐propylcatechol methylene ether predominates. The regiochemistry of the adducts derived from monosubstituted acetylenes were determined by the correlation of 13C chemical shifts of the adducts and the corresponding bicyclo[2.2.2]octa‐5,7‐diene‐2,3‐diones obtained from the hydrolysis of the spirolactone ring of the Diels‐Alder adducts. Photolysis of these α‐diketones gave the corresponding aromatic compounds in high yields. These synthetic sequences provide an effective entry to bicyclo[2.2.2]octa‐5,7‐diene‐2,3‐diones and polysubstituted benzene derivatives.

Carbon-13 N.N.R. studies of carbocations. VII. 3,4-Ethyleneoxyphenyl(2,3-dihydrobenzofuran-5-yl), a powerful electron-donating group for use in Hammett correlations of 13C chemical shifts of aryldialkyl carbocations with increasing electron demand

Carbon-13 N.N.R. studies of carbocations. VII. 3,4-Ethyleneoxyphenyl(2,3-dihydrobenzofuran-5-yl), a powerful electron-donating group for use in Hammett correlations of 13C chemical shifts of aryldialkyl carbocations with increasing electron demand

Correlations of13C chemical shifts and geometry modifications

The effect of geometry modifications of13C chemical shifts has been investigated in a small subset of molecules using both LO-INDO and Gaussian 70 (4–31) calculations. The Gaussian calculations, while known to give poor absolute shifts, compare well to the reparameterized semi-empirical INDO determinations in calculated shift changes. In virtually all cases the signs of the shift changes were found to be opposite to that of the changes in the calculated electronic energy.

13C NMR study of 3-(X-benzal)phthalides and 2-(X-benzal)-1,3-indanediones

13C NMR spectra of 14 derivatives of 3-(X-benzal)phthalides (I) and 10 derivatives of 2-(X-benzal)-1,3-indanediones (II) were investigated. The correlation of 13C chemical shifts of carbon atoms of the phthalide ring with σ-constants showed that the electronic effect of substituents was transmitted from the benzylidene group of 3-(X-benzal)phthalides on the chemical shift of the carbonyl group not only through oxygen, but also through the aromatic ring of the phthalide moiety. The transmission of substituent effects in 2-(X-benzal)-1,3-indanediones on the chemical shift of the carbonyl groups was more pronounced on the carbonyl, which is in the trans-arrangement with respect to the aryl group. This phenomenon was also observed at carbon atoms of the benzene ring of the indanedione moiety closer to the trans-CO group.