Conformational Analysis. NMR Spectra of Six-Membered Cyclic Acetals.

Pihlaja, Kalevi; Äyräs, Pertti; Brohult, Sven; Ragnarsson, Ulf; Rasmussen, Svend Erik; Sunde, Erling; Sørensen, Nils Andreas

doi:10.3891/acta.chem.scand.24-0531

Cited by 53 publications

(10 citation statements)

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“…This, in turn, gives J(3a4a') = 11.7 Hz and J(3e4e') = 1.5 Hz, in excellent agreement with the model values for 2, 3, 4b and 5b, taking into account that the first substituent in the C-3-C-4 moiety, in general, tends to decrease J(aa') and increase J(ee'). 17 The values of the substituent effects on the 13C chemical shifts (Table 4) are in reasonable agreement with those of the 1,3-dioxane ring,' taking into account the differences in the ring conformations (halfchair vs chair) and the orientation of the substituents (e' vs e and a' vs a at C-1 and C-4).…”

Section: Conformational Equilibriasupporting

confidence: 60%

A ¹H and ¹³C NMR conformational study of methyl‐substituted isochromanes

Pihlaja

Mattinen

Kleinpeter

et al. 1985

Magnetic Reson in Chemistry

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The 'H and the noise-decoupled =C NMR spectra of isochromane and 13 of its methyl-substituted derivatives were recorded and analysed. The collected data were used to assign the configurations and to determine the position of the conformational equilibria based on the vicinal ' I 3 coupling constants of the aliphatic moiety of the ring system. In some cases the substitution site-dependent conformational energies of the methyl substituents were also used to estimate the conformer ratios. The primary and some vicinal methyl substituent effects on the -C chemical shifts of the oxme ring carbons were derived and compared with those of l,3-dioxanes. Their usefulness in conformational analysis is demonstrated for 1-methylipochromane.

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Section: Conformational Equilibriasupporting

confidence: 60%

A ¹H and ¹³C NMR conformational study of methyl‐substituted isochromanes

Pihlaja

Mattinen

Kleinpeter

et al. 1985

Magnetic Reson in Chemistry

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“…If one of these protons is replaced by a methyl group the former coupling decreases, in general, by ca 1 Hz whereas the latter increases similarly. [13] A similar situation prevails in trans-5-methyl-3-oxo-1,3-oxathiolane (12) where the values of coupling constants furthermore stay practically constant in CDCl 3 as compared to those obtained in C 6 D 6 (Table 2) opposite to the situation in cis-5-methyl-3-oxo-1,3-oxathiolane (11) which is a conformational mixture of HC1 and HC2 forms and shows clear changes (0.2-0.3 Hz) in the values of vicinal coupling constants when moved from CDCl 3 to C 6 D 6 solution.…”

Section: Vicinal Hh-coupling Constantsmentioning

confidence: 99%

“…In some cases, the 13 C NMR spectra were also recorded (Table 1). Teodori et al [8b] reported 13 C chemical shifts for the three isomeric 2-methyl,5-chloromethyl,3-oxo-1,3-oxathiolanes.…”

Section: Nmr Spectramentioning

confidence: 99%

“…Teodori et al [8b] reported 13 C chemical shifts for the three isomeric 2-methyl,5-chloromethyl,3-oxo-1,3-oxathiolanes. C(2) in the cisisomers (7 and 13) is ca 10 ppm more shielded than that in the trans-isomers.…”

Section: Nmr Spectramentioning

confidence: 99%

“…The preparation of several 2-aryl-3-oxo-1,3-oxathiolanes was reported in order to study the mechanism of hepatic flavin-containing monooxygenase in the enzymatic oxidation of 2-aryl-1,3-oxathiolanes. [2] In this report also the synthesis of cis- (13) and trans-2-pnitrophenyl-3-oxo-1,3-oxathiolanes (14) are described. The crystal structure of the major trans-isomer (14) was reported already much earlier [3] on a sample donated by Prof. Schank (cf Ref.…”

Section: Introductionmentioning

confidence: 98%

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3‐Oxo‐1,3‐oxathiolanes—synthesis and stereochemistry

Pihlaja

Sinkkonen

Stájer

2008

Magnetic Reson in Chemistry

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The compound 3-oxo-1,3-oxathiolane (6) and its cis - and trans - 2-methyl (7,8), 4-methyl (9,10), 5-methyl (11,12) and 2-p-nitrophenyl (13,14) derivatives were prepared by oxidizing the corresponding 1,3-oxathiolanes (1-5) with NaIO4 in water. The oxides were purified and their isomers separated using thin layer chromatography. The structural characterization was carried out with 1H NMR spectroscopy and molecular modeling. Compounds 8-10, 12, and 14 attain the half-chair type conformation with O1 above and C5 below the plane (HC1), but 6, 7, 11, and 13 are, for steric reasons, the mixtures with the alternative half-chair (HC2), where O1 is below and C5 above this plane. Accordingly, 6 appears based on the values of experimental coupling constants as an 81:19, 7 as a 37:63, 11 as a 33:67 and 13 as a 54:46 mixture of HC1 and HC2, respectively. The relative energies of these conformations, the values of the vicinal H,H-coupling constants and 1H chemical shifts were estimated for compounds 6-12 also by computational methods and they support nicely the conclusions based on experimental data.

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