Experimental and Theoretical Estimates of Sigma and Pi Electron Contributions to Long-range Spin–Spin Coupling Constants in Coumarin and its Methyl Derivatives

Abstract

A full analysis of the p.m.r. spectra of coumarin and five of its methyl derivatives allows the assignment of o and n electron components to the inter-ring proton-proton spin-spin coupling constants. Magnitudes of up to 0.3 Hz are observed over a coupling path of eight bonds. The o and n components can be combined on the basis of the appropriate valence bond structures to predict closely the observed parameters in naphthalene, suggesting only weak participation of the ether oxygen atom in the 7c electron system of coumarin. Calculations of the inter-ring coupling constants at the INDO and CNDO/2 ievels of molecular orbital theory are helpful in the interpretation of the observed data, the agreement with experiment being quantitative in many instances. Comparison of the observed coupling constants in coumarin and styrene with the ZNDO results for an assumed planar form of the latter suggests that styrene exists in a nonplanar conformation.Une Ctude complete des spectres r.m.n, du coumarin et de cinq de ses derives methyles permet I'attribution des composantes o et .rr aux constantes de couplages deduites spin-spin des interactions protonproton. Des amplitudes allant jusqu'a 0.3 Hz sont observees pour une zone de couplage inciuant huit liaisons. Les composantes o et n peuvent ktre combinCes en se basant sur les structures appropriees (obtenues par la theorie du lien de valence) pour prCdire avec precision les parametres observes pour le naphtaline suggerant une faibie participation seulement de I'atome d'oxygene du groupe ether dans le systemc d'Clectrons n du coumarin. Les calculs des constantes de couplage deduites aux niveaux INDO et CNDO/2 de la theorie des orbitales moleculaires sont utiles dans l'interpretation des donnees obtenues, l'accord avec les donnees experimentales etant tres souvent quantitatif. La comparaison des constantes de couplage observees pour le coumarin et le styrene avec les rPsultats TNDO pour une structure supposee planaire pour ce dernier suggere que le styrene existe dans une conformation non-planaire.[Traduit par Ie journal]Can. J . Chem.. 51. 953 (1973) The dependence on conformation and on bonding situation of the spin-spin coupling constants between protons on a side-chain and ring protons in benzene and pyridine derivatives has been extensively studied by experimental and theoretical methods (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Less extensive investigations of inter-ring long-range proton coupling constants in fused aromatic systems (21, 22) have been reported for naphthalene (23), acridine (24), isoquinoline (25), and for several coumarin derivatives (26). The use of the 'methyl group replacement technique' (27-29) and of approximate molecular orbital theory at the INDO and CND8/2 levels (30) is enlightening in the elucidation of the coupling mechanisms operating in the single ring compounds (7, 8, 14). In this paper we apply these methods to the interring coupling constants in coumarin (I). Com- 'Postdoctoral Fellow, 1970 parisons are made...

Patterns of phenolic compounds in leafy galls of tobacco

“…These findings are in agreement with the data published by Rowbotham and Schaefer (1973) for coumarin and some methylated derivatives thereof. Furthermore, there was a singlet (integration 3) at 6 3.92, pointing to an 0-methyl resonance linked to an aromatic system.…”

“…Since only partial 1 H-NMR data of esculin were (Lassak and Pinhey 1967), we ran the NMR spectrum of commercial esculin for comparison. In Table 1, data are given for coumarin (Rowbotham and Schaefer 1973), esculin (commercial, taken in D 20) and the product of peak d.…”

Stereospecific 5JHortho,OMe couplings in methoxyindoles, methoxycoumarins, and methoxyflavones

“…The fact that the 1 H NMR spectra of 1–17 were measured in a highly homogenized magnetic field provides the opportunity to accurately determine all chemical shifts and coupling constants, even allowing to know the small values of inter‐ring coupling constants. The pertinent values for indoles 1–4 are given in Table and include refined data for J 1,4 , J 2,6 , and J 3,7 long‐range spin‐spin interactions, while those values for coumarins 5–10 are given in Table and include the refined data for J 3,5 , J 3,7 , J 4,5 , and J 4,8 values. In turn, the chemical shifts and coupling constants for the ring‐A hydrogen atoms and H‐3 of flavones 11–17 are shown in Table , while those corresponding to ring C are found in Table .…”

Isolation and HPLC quantitation of kaurane-type diterpenes and cinnamic acid derivatives of long-term stored leaves of Mikania laevigata and Mikania glomerata

“…KA was also isolated from M. glomerata extract. Structure identifi cation of the isolated compounds was achieved by usual spectroscopic analysis and comparison with previously reported data (Kupriyanova 1997, Oliveira et al 1984, Rowbotham and Schaefer 1972, Batista et al 2005, Velandia et al 1998, Fabbri et al 1997, Vichnewski et al 1977 Development and optimization of the HPLC-DAD method comprised the evaluation of 14 different conditions. Mikania laevigata was selected for method development in view of its more complex profi le than Mikania glomerata.…”

“…PEREIRA, JOSÉ E.B.P. PINTO, ALAÍDE B. OLIVEIRA and FERNÃO C. BRAGA Spectroscopic data obtained for the isolated compounds were compared with literature records (Batista et al 2005, Kupriyanova 1997, Fabbri et al 1997, Velandia et al 1998, Oliveira et al 1984, Vichnewski et al 1977, Rowbotham and Schaefer 1972. Coumarin (CO,191 For the analysis, 1 g of dried leaves was submitted to ultrasound-assisted extraction with ethanol (2 × 30 mL), at room temperature (20 min each cycle).…”