Empirical increment system for prediction of NMR chemical shifts of methyl proton signals of sterically crowded methylbenzenes

Häfelinger, Günther; Westermayer, Gerlinde; Westermayer, Manfred

doi:10.1016/0022-2364(82)90315-8

Cited by 2 publications

(1 citation statement)

References 17 publications

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“…Finally, in Figure 11d, the plot threshold is decreased to just above the baseplane noise level. Some extremely weak contours become evident upfield of about δ C 16 and downfield of about δ H 2.1 that probably result from aromatic CH 3 groups with two ortho alkyl substitutents; 71,72 the 1 H signals are too far downfield to be from the methyl groups on adjacent carbons of an alkyl chain. 73 Some extremely weak contours also become evident downfield of about δ C 29 and downfield of about δ H 2.5 for aromatic CH 2 groups.…”

Section: Energy and Fuelsmentioning

confidence: 99%

Solid- and Solution-State Nuclear Magnetic Resonance Analyses of Ecuadorian Asphaltenes: Quantitative Solid-State Aromaticity Determination Supporting the “Island” Structural Model. Aliphatic Structural Information from Solution-State ¹H–¹³C Heteronuclear Single-Quantum Coherence Experiments

Alemany¹,

Verma²,

Billups³

et al. 2015

Energy Fuels

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Solid-and solution-state nuclear magnetic resonance (NMR) studies of six Ecuadorian asphaltenes have provided insight into using NMR to characterize asphaltenes. For these asphaltenes, free radicals prevent obtaining quantitatively meaningful 1 H− 13 C cross-polarization magic angle spinning (CPMAS) spectra but facilitate obtaining meaningful carbon aromaticity values in direct polarization with 13 C pulse excitation. The benefit of studying any asphaltene by obtaining a series of CPMAS spectra with multiple contact times, rather than just a single contact time, is demonstrated. Analyzing the CPMAS and direct 13 C pulse spectra indicates that, on average, condensed aromatic ring systems become larger as the aromaticity increases, which seems more consistent with "island" than "archipelago" aromatic structures, just as recently proposed for asphaltenes. Solution-state two-dimensional (2D) 1 H− 13 C heteronuclear single-quantum coherence (HSQC) spectra of the asphaltenes provide a wealth of structural information and are particularly useful for demonstrating that isolated methyl branches on alkyl chains are much more abundant than aromatic methyl groups. The prospect of using cryoprobes to obtain one-dimensional (1D) and 2D spectra with a much higher signal-to-noise ratio (S/N) allowing for a more detailed analysis of the less abundant structural environments is clearly attractive.

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Section: Energy and Fuelsmentioning

confidence: 99%

Solid- and Solution-State Nuclear Magnetic Resonance Analyses of Ecuadorian Asphaltenes: Quantitative Solid-State Aromaticity Determination Supporting the “Island” Structural Model. Aliphatic Structural Information from Solution-State ¹H–¹³C Heteronuclear Single-Quantum Coherence Experiments

Alemany¹,

Verma²,

Billups³

et al. 2015

Energy Fuels

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Empirisches Inkrementsystem für Methylgruppensignale sowie Ringstrombeeinflussung der Protonen‐NMR‐Spektren methylsubstituierter Biphenylderivate

et al. 1984

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Von 18 methylsubstituierten Biphenylderivaten werden 36 Methylgruppen-NMR-Signale durch multiple lineare Regressionsanalyse auf 4.4'-und 2,2'-Positions-Substituentenkonstanten analysiert. Der EinfluR des Verdrillungswinkels Q auf die o-Methylgruppensignale steigt von -0.095, -0.284, -0.345 auf -0.377 pprn fur Q = 5 8 " , 77.5'. 85" und 90". Diese Werte werden am besten durch das theoretische Ringstrommodell von Johnson und Bouey wiedergegeben. 36 methyl group NMR signals of 18 methyl-substituted biphenyl derivatives have been analyzed by multiple linear regression analysis to derive 4,4'-and 2,2'-position substitution constants. The influence of the torsional angle Q on the signals of o-methyl groups increases from -0.095, -0.284, -0.345 to -0.377 pprn for @ = 5 8 " , 77.5", 8 5 " , and 90". These values are in good agreement with the theoretical ringcurrent model of Johnson and Bouey. Insgesamt sind 209 verschiedene methylsubstituierte Biphenylderivate formulierbar '), von denen wir die bis auf 6,12 und 13 bekannten Verbindungen 1 -18 dargestellt haben, um ihre Protonen-NMR-Spektren bei 90 MHz unter vergleichbaren Bedingungen mittels Fourier-Transform-NMR-Spektroskopie (FT) zu untersuchen. FT-NMR-Daten unterscheiden sich numerisch stark von den friiher iiblichen CW-Spektrometerdaten", und zeigen den groaen Vorteil, daB unabhangige Messungen an verschiedenen Substanzen in verdiinnten CDC13-Ldsungen (2proz.) innerhalb der spektroskopischen Auflosung von 0.003 ppm reproduzierbare und somit zuverlassig vergleichbare chemische Verschiebungswerte liefern". Damit entfallt z. B. die Notwendigkeit, zur Ermittlung von Ringstromanisotropieeffekten bei benzoiden Aromaten die Aufspaltung zwischen den o,o'und p-Methylgruppensignalen eines Mesitylsubstituenten zu betrach-ten3-", wobei das p-Methylgruppensignal als internes Standardsignal gewlhlt wurde, das als unbeeinflunt vom Ringstromanisotropieeffekt des sondierten Aromaten angenommen wurde.

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Empirical increment system for prediction of NMR chemical shifts of methyl proton signals of sterically crowded methylbenzenes

Cited by 2 publications

References 17 publications

Empirisches Inkrementsystem für Methylgruppensignale sowie Ringstrombeeinflussung der Protonen‐NMR‐Spektren methylsubstituierter Biphenylderivate

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Empirical increment system for prediction of NMR chemical shifts of methyl proton signals of sterically crowded methylbenzenes

Cited by 2 publications

References 17 publications

Solid- and Solution-State Nuclear Magnetic Resonance Analyses of Ecuadorian Asphaltenes: Quantitative Solid-State Aromaticity Determination Supporting the “Island” Structural Model. Aliphatic Structural Information from Solution-State 1H–13C Heteronuclear Single-Quantum Coherence Experiments

Solid- and Solution-State Nuclear Magnetic Resonance Analyses of Ecuadorian Asphaltenes: Quantitative Solid-State Aromaticity Determination Supporting the “Island” Structural Model. Aliphatic Structural Information from Solution-State 1H–13C Heteronuclear Single-Quantum Coherence Experiments

Empirisches Inkrementsystem für Methylgruppensignale sowie Ringstrombeeinflussung der Protonen‐NMR‐Spektren methylsubstituierter Biphenylderivate

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