Carbon-13 spin relaxation and methyl rotation barriers in the methylethylenes

Collins, Scott W.; Alger, Terry D.; Grant, David M.; Kuhlmann, Karl; Smith, James C.

doi:10.1021/j100586a011

Cited by 28 publications

(5 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…where TDD is the dipole-dipole relaxation time, TSR is the spin-rotation relaxation time, and T0 is a lumped parameter for all other types of relaxation. Grant et al 13 have shown that T0 is usually negligibly small for systems like those in this study. Fortunately, TDD is directly related9 to and i?c-h (3) so that TDD can be derived from if t)C-h is available.…”

Section: Resultssupporting

confidence: 48%

Carbon-13 NMR studies on several tert-butylpyridines in alcohol-water solutions. Barriers to internal rotation and solute-solvent interactions

Hopkins¹,

Ali²

1980

J. Phys. Chem.

View full text Add to dashboard Cite

Carbon-13 NMR studies have been performed on 2-TBP, 4-TBP, 2,4-DTBP, and 2,6-DTBP in the neat phase, in 100% methanol, and in 81 wt % methanol-water to yield chemical shifts and Tx values for the majority of the carbons and jjc-h values for the methyl and methine carbons. These have been analyzed for the neutral and cationic species to provide information on the hydrogen bonding of the solvent molecules to the solute, the motion of the solute in the solvent cavity, and the extent of the internal rotation of the methyl and ferf-butyl groups in the neutral and cationic species. Employing the theoretical treatment of Woessner, we found the barriers to rotation for the methyl group to be in the 2.0-4.5 kcal mol"1 range. Small but significant changes are observed for this parameter upon protonation of 2-TBP and 2,6-DTBP. The TsR value for the methine carbons of 2,6-DTBP also increases upon protonation, indicating that the rotation of the ferf-butyl group is more hindered in the cation than the neutral species. These results support our previous contention that internal motions in 2,6-DTBP are more hindered in the cation than in the neutral species.

show abstract

Section: Resultssupporting

confidence: 48%

Carbon-13 NMR studies on several tert-butylpyridines in alcohol-water solutions. Barriers to internal rotation and solute-solvent interactions

Hopkins¹,

Ali²

1980

J. Phys. Chem.

View full text Add to dashboard Cite

show abstract

“…Theintegrationoft hese signals shows an uptake of 1.7 isobutene molecules per silver salt (Scheme 4) which is in accordance with the value described in thel iterature. [32] Ac omparison of the 13 CNMR data of the absorbed isobutenew ith values of free isobutene [34] showsasignificant shifto f+ 10 and À12 ppm for the two sp 2 carbon atoms (d = 151.4 ppm (=CMe 2 )a nd 98.4 ppm (H 2 C=)), which strongly indicates an interaction with the silver cation. The stretching vibration of the CÀNb ond in the IR spectrum is observed at 2272 cm À1 ,w hich is decreased by 15 cm À1 relative to 1g.…”

Section: Resultsmentioning

confidence: 95%

Activation of Acetonitrile with (C₂F₅)₃PF₂ and Amines

Bader

Neumann

Stammler

et al. 2018

Chemistry A European J

View full text Add to dashboard Cite

Acetonitrile is deprotonated by a combination of the strong Lewis acid (C F ) PF and triethylamine. The resulting cyanomethyl function is bound to the phosphorus moiety, affording the highly stable salt [HNEt ][P(C F ) F (CH CN)]. Salt metathesis reactions furnished the corresponding [Cu(MeCN) ] and [Ag(MeCN)] derivatives in which the CH CN substituent of the anion [P(C F ) F (CH CN)] coordinates to the metal. An investigation of the gas separation capability of the silver salt [Ag(MeCN)][P(C F ) F (CH CN)] shows an uptake of 1.7 equivalents of isobutene from a propane/isobutene mixture. The reaction of (C F ) PF with acetonitrile and diethylamine furnishes [P(C F ) F {NHC(CH )NEt }]-a phosphate featuring an amidine ligand which formally results from hydroamination of acetonitrile by HNEt . Exchange of HNEt with the primary amines H NPh and H NBu leads to comparable amidine salts that exhibit a solvent-dependent conformational isomerism.

show abstract

“…For all measurements of spin-lattice relaxation the standard 180°--90°pulse sequence was used with the phase of the 90°p ulse changed by 180°on every scan. 13 Except as noted previously2 this pulse sequence was under computer control. Magnetization was taken to be proportional to peak heights which were read manually from recorded spectra.…”

Section: Methodsmentioning

confidence: 96%

“…Accurate utilization of data gathered from biophysical application of l3C methyl probes will potentially require consideration of auto-and cross-correlation effects in both the dipolar and spin-rotation interactions, since spin-rotation frequently plays a role in methyl relaxation. 13 In such a situation analysis of the relaxation is not straightforward, and in the present publication we illustrate an attack on the problem utilizing both and 13C relaxation data.…”

mentioning

confidence: 99%

Cross correlation and spin-rotation effects on methyl spin-lattice relaxation in peptides. Tetragastrin

Cutnell¹,

Glasel²

1976

J. Am. Chem. Soc.

View full text Add to dashboard Cite

I H and "C relaxation data relating to the methionine methyl group i n the peptide tetragastrin are reported. An analysis of methyl spin-lattice relaxation times and the heteronuclear Overhauser effect is presented. This analjsis illustrates an approach to the determination of motional information when dipolar and spin-rotation interactions dominate the relaxation mechanism and when the effect of cross correlations must be considered. The importance of these effects in studies of peptides in solution by N M R relaxation is emphasized.We have recently reported the existence of nonexponential relaxation behavior for the protons of the methyl group of tetragastrin2 (I) and have attributed this behavior to cross cor-H-Trp-Met-Asp-Phe-NHl I relations between the relaxing spin pairs. In addition, we have presented a detailed account of the relaxation of 'H and I3C nuclei in other groups of this molecule and have emphasized the conformation information implicit in the proper use of both ' H and 13C relaxation times and the 'H-I3C heteronuclear Overhauser e f f e~t .~ This paper is an amplification of our original report,2 and its importance stems from theoretical and experimental ~o r k~-~ which indicates that accurate measurements of cross-correlation effects may be an aid in determining the nature of overall anisotropic molecular tumbling in molecules of the size with which we are dealing. Moreover, we recently have found nonexponential spin-lattice relaxation for the methionyl methyl protons of another peptide, the pharmacologically active pentapeptide, "methionine enkephalin".lO.l Thus, nonexponential methyl proton relaxation and observable cross-correlation effects may be a general feature of methionine containing peptides. Also, specific I3C enrichment of S -C H j sites has recently been reported,I2 and thus the increased use of methyl carbons as NMR probes of protein conformation seems likely. Accurate utilization of data gathered from biophysical application of I 3C methyl probes will potentially require consideration of auto-and cross-correlation effects in both the dipolar and spin-rotation interactions, since spin-rotation frequently plays a role in methyl relaxation.I3 In such a situation analysis of the relaxation is not straightforward, and in the present publication we illustrate an attack on the problem utilizing both IH and I3C relaxation data.The approach taken here utilizes analysis of the two different spin systems '*CH3 and I3CH3, the former relating to the proton spin system and the latter relating to the proton decoupled I3C system. An alternative method involves analyzing the ' H and I3C relaxation directly in the fully coupled I3CH3 specie^,^ which has the advantage of potentially providing a complete description of the relaxation kinetics and thereby providing additional information from which motional parameters may be obtained. However, full utilization of this alternative method requires that I3C enriched species be available and that facilities exist with which various kinds of spin system ...

show abstract

Carbon-13 spin relaxation and methyl rotation barriers in the methylethylenes

Cited by 28 publications

References 8 publications

Carbon-13 NMR studies on several tert-butylpyridines in alcohol-water solutions. Barriers to internal rotation and solute-solvent interactions

Carbon-13 NMR studies on several tert-butylpyridines in alcohol-water solutions. Barriers to internal rotation and solute-solvent interactions

Activation of Acetonitrile with (C₂F₅)₃PF₂ and Amines

Cross correlation and spin-rotation effects on methyl spin-lattice relaxation in peptides. Tetragastrin

Contact Info

Product

Resources

About

Carbon-13 spin relaxation and methyl rotation barriers in the methylethylenes

Cited by 28 publications

References 8 publications

Carbon-13 NMR studies on several tert-butylpyridines in alcohol-water solutions. Barriers to internal rotation and solute-solvent interactions

Carbon-13 NMR studies on several tert-butylpyridines in alcohol-water solutions. Barriers to internal rotation and solute-solvent interactions

Activation of Acetonitrile with (C2F5)3PF2 and Amines

Cross correlation and spin-rotation effects on methyl spin-lattice relaxation in peptides. Tetragastrin

Contact Info

Product

Resources

About

Activation of Acetonitrile with (C₂F₅)₃PF₂ and Amines