NMR‐Untersuchungen an Piperidinen—IV.<sup>13</sup>C‐NMR‐Messungen an stereoisomeren Dimethylpiperidinen

Wendisch, Detlef; Feltkamp, Herbert; Scheidegger, Mitarbeit von Ueli

doi:10.1002/mrc.1270050305

Cited by 12 publications

(5 citation statements)

References 6 publications

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“…The 2,6-dimethylpiperidine was shown to be exlusively the cis-or (R,S)-isomer by "C nmr spectroscopy (24). The 2-methylpiperidine was resolved as described below.…”

Section: Methodsmentioning

confidence: 99%

Conformational analysis of chiral hindered amides

Rauk¹,

Tavares²,

Khan³

et al. 1983

Can. J. Chem.

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The static and dynamic structures of the amide derivatives of racemic and (R)-(+)-2-methoxy-2-phenyl-3,3,3-trifluoropropanoic acid (MPTA) with diisopropyl amine (1), meso-2,6-dimethylpiperidine (2), (R)-(−)- and (S)-(+)-2-methylpiperidine (3 and 4, respectively) were investigated by proton nmr spectroscopy. The piperidine rings adopt a single dominant conformation in which the substituent methyl groups occupy axial positions. One of the isopropyl groups of 1 is oriented in the same way as the corresponding side of the piperidine ring of 2–4 but the other (syn to carbonyl oxygen) is turned so that the methyl groups are toward the carbonyl oxygen and the oxygen lies in the plane bisecting the C—C—C angle. Rotation about the amide C(O)—N bond of 1 is accompanied by concurrent rotation about each of the N—iPr single bonds. The free energies of activation of the hindered rotation about the C(O)—N bond in 1–4, 81 kJ/mol, 77 kJ/mol, 77 kJ/mol, and 79 kJ/mol, respectively, are higher than found in most other hindered amides, suggesting that buttressing due to the steric crowding around the amide functionality is felt throughout the rotational pathway.

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“…The 2,6-dimethylpiperidine was shown to be exlusively the cis-or (R,S)-isomer by "C nmr spectroscopy (24). The 2-methylpiperidine was resolved as described below.…”

Section: Methodsmentioning

confidence: 99%

Conformational analysis of chiral hindered amides

Rauk¹,

Tavares²,

Khan³

et al. 1983

Can. J. Chem.

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“…C-methylpiperidines with highly hindered cyclic inversion (3,7,6) or with easy cyclic inversion (1,2,5,8) and their salts (NH case).…”

Section: Resultsmentioning

confidence: 99%

“…C-methylpiperidines with highly hindered cyclic inversion (3,7,6) or with easy cyclic inversion (1,2,5,8) and their salts (NH case). The most abundant isomer of the N-methyl-Cmethylpiperidinium salts with highly hindered cyclic inversion (IIIm+, VUAH+, VIM+), i.e., with the N-Me in equatorial position, or, with easy cyclic inversion (k, IIm+, VIII,+), i.e.…”

Section: Resultsmentioning

confidence: 99%

Carbon‐13 nuclear magnetic resonance spectroscopy of methyl‐substituted piperidines and their hydrochloride salts

et al. 1978

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Carbon-13 chemical shifts and 'J(CH) coupling constants of pipendine, 4-t-butylpiperidine, five C-methyl substituted piperidines and of the corresponding N-methyl compounds have been measured. These NMR parameters have also been determined for the fourteen corresponding hydrochlorides. The N-methy1-Cmethyl pipendinium salts showed two stereoisomers on the positive nitrogen atom. The effect of protonation is discussed in relation to charge and steric effects and the methyl substituent effects are compared with those of methyl-substituted cydohexanes. Deviations from the general tendencies in the series are correlated with changes in r h g conformations around the highly crowded substituted carbons.

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“…The 2,6-dimethylpiperidine (Aldrich Chemical Co.) is the cis-or ( R , S ) -isomer as verified by I3C nmr spectroscopy (14). No trace of the trcrt~s-or (d,l)-isomer is detectable in the ambient temperature I3C spectrum.…”

Section: Mnteriulsmentioning

confidence: 93%

“…4 (R1 $ RZ $ H), present complications for the deterrnination of absolute configurations or optical purities which arise from the fact that, in general, pairs of geometric diastereomers as well as configurational diastereomers are evident in the 'H nmr spectrum (13,14), at ambient temperature. Indeed, the room temperature I9F nmr spectrum of amide 5, prepared in connection with another study, shows two broad, unequal, overlapping absorptions.…”

Section: Introductionmentioning

confidence: 99%

Magnetic non-equivalence of fluorine atoms of a trifluoromethyl group

Khan¹,

Tavares²,

Rauk³

1982

Can. J. Chem.

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The three fluorine atoms of N,N-dialkyl amide and chloride derivatives of 2-methoxy-2-phenyl-3,3,3-trifluoropropanoic acid are magnetically nonequivalent below –60 °C and exhibit a clear ABC coupling pattern from which chemical shifts and geminal coupling constants are readily derived. The chemical shifts span a range of about 10 ppm and the geminal coupling constants average about 110 Hz. A five bond coupling of about 5 Hz is observed between the hydrogens of the methoxy group and one of the nonequivalent fluorine atoms of the trifluoromethyl group. Barriers to the hindered rotation about the single bond to the trifluoromethyl group are in the range 36–46 kJ/mol.

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NMR‐Untersuchungen an Piperidinen—IV.¹³C‐NMR‐Messungen an stereoisomeren Dimethylpiperidinen

Cited by 12 publications

References 6 publications

Conformational analysis of chiral hindered amides

Conformational analysis of chiral hindered amides

Carbon‐13 nuclear magnetic resonance spectroscopy of methyl‐substituted piperidines and their hydrochloride salts

Magnetic non-equivalence of fluorine atoms of a trifluoromethyl group

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NMR‐Untersuchungen an Piperidinen—IV.13C‐NMR‐Messungen an stereoisomeren Dimethylpiperidinen

Cited by 12 publications

References 6 publications

Conformational analysis of chiral hindered amides

Conformational analysis of chiral hindered amides

Carbon‐13 nuclear magnetic resonance spectroscopy of methyl‐substituted piperidines and their hydrochloride salts

Magnetic non-equivalence of fluorine atoms of a trifluoromethyl group

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NMR‐Untersuchungen an Piperidinen—IV.¹³C‐NMR‐Messungen an stereoisomeren Dimethylpiperidinen