Stereodynamics of N-tert-butyl-N,N-dialkylamines. Experimental and theoretical evidence for a common potential surface for tert-butyl rotation and nitrogen inversion

Bushweller, C. Hackett; Anderson, Warren G.; Stevenson, Philip E.; Burkey, David L.; O’Neil, James W.

doi:10.1021/ja00819a029

Cited by 40 publications

(22 citation statements)

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“…This conformation is an exception among alkylamines, for which a staggered conformation is invariably present [5a, 8, 19, 20] (for instance, as for 1 and 2). Mechanistic considerations of nitrogen inversion show [7,12] that this is always a concerted NIR process (and not INI [12,21] ) in alkylamines. In this case, CÀN bonds are staggered with other bonds in stable conformations.…”

Section: Resultsmentioning

confidence: 99%

“…[2, 4, 5b, 13a±c] In contrast, INI was mentioned as not relevant for alkylamines. [7,12] Each of these dynamic processes may cause a splitting of peaks in the NMR spectra at low temperatures, and it is usually not possible to determine a priori which process is responsible for this peak dichotomy. [1, 2, 13a] For instance, solid arguments (including calculation results) were given in Bushwellers pioneering experimental work [7] concerning the distinction between ISR and NIR by observing the temperature-induced changes in NMR spectra of open-chain tertiary amines.…”

Section: Introductionmentioning

confidence: 99%

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Conformational Schemes: An Available Tool for the Assignment of NMR-Measured Barriers, Demonstrated with the Example of Crowded Piperidines

et al. 1999

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MM3-derived full conformational schemes are proposed as a powerful and convenient tool for the currently problematic assignment of NMR-measured barriers for flexible systems that possess more than one type of independent intramolecular motion. Hindered piperidines were chosen as a molecular model with seven possible intramolecular dynamic processes. The free energies of activation for methyl group topomerization in 1,2,2,5,5-pentamethyl-, 1-ethyl-2,2,6,6-tetramethyl-, and 1-butyl-2,2,6,6-tetramethylpiperidines were determined at different temperatures by means of line-shape analysis of 13 C NMR spectra. Schemes of conformational transformations for the N-Me and N-Et compounds were created with MM3-based methodology. These schemes permit the assignment of the measured barriers to ring inversion for the N-Me compound and to ring inversion ± nitrogen inversion, ring inversion, and CÀN rotation for the NAlk primary piperidines (for the N-Et and N-Pr derivatives the experimental barriers had previously been attributed to isolated CÀN rotation only). A unique dynamic process for tertiary amines, isolated nitrogen inversion, is described for the N-alkylpiperidines with an Nsubstituent bulkier than Me.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Conformational Schemes: An Available Tool for the Assignment of NMR-Measured Barriers, Demonstrated with the Example of Crowded Piperidines

et al. 1999

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“…Thcrefore. the process responsible for the line broadening must have a AG* less than 7 k~al,'mol.~ Such a barrier is in the range observed (14) for rotation about certain carboncarbon and carbon-nitrogen single bonds.…”

Section: Djtzcrt77ic Nuclecrr Magtletic Resot~crtlcementioning

confidence: 95%

Stereomutation of a 1,2,3-triketone: an example of an asymmetric reaction

Wolfe¹,

Berry²,

Peterson³

1976

Can. J. Chem.

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The 1,2,3-triketone PhC(Me)2COCOCOPh has been synthesized from mandelic acid in seven steps. Its proton magnetic resonance spectrum features a sharp six-proton methyl singlet at room temperature which broadens considerably at low temperatures but is not resolved into two peaks at 173 K. Similar dynamic behaviour is observed for the monoketone PhC(Me)2COPh. It is concluded that the barrier to interconversion of enantiomeric tricarbonyl helical conformations is significantly less than 7 kcal/mol. The rotation–rotation surface of the ketodialdehyde HCO—CO—CHO has been computed by the CNDO/2 method; the barrier to stereomutation of enantiomeric helical conformations of this tricarbonyl system is found to be 3.9 kcal/mol. The dynamics of this process are discussed in terms of a recently proposed definition of symmetric and asymmetric reactions.

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“…No dichotomy for the signal of the t -Bu group of the most crowded compound 1f was observed in the monitored temperature range, and only a small broadening of this signal was detected at 157 K. Thus, consideration of the parallel C−N rotation process ,,, may be excluded, and the measured values of the free energy of activation for amines 1c − f should be assigned to Δ G ⧧ for the nitrogen inversion process only.…”

Section: Resultsmentioning

confidence: 99%

Rate-Determining Role of Strain for Nitrogen Inversion in Polycyclic Tertiary Amines¹

1996

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The nitrogen inversion barriers for N-isopropyl-, N-butyl-, N-isobutyl-, and N-tert-butyl-7-azabicyclo-[2.2.1]heptanes were measured using dynamic NMR line shape analysis. These barriers as well as those for different bicyclic and tricyclic tertiary amines were analyzed Via the molecular mechanics method (MM3 force field). A new MM3 steric energy-based parameter, including the energy of substitution-induced disturbances (E sid ), is proposed for the estimation of relative strain among related compounds with one variable substituent. A linear relationship was found between N-inversion barriers and this parameter for 7-azabicyclo[2.2.1]heptanes with a -unbranched N-substituent, which allows an accurate prediction of the barrier values for these amines. For all polycyclic systems studied, the change of strain in the transition state relative to the ground state of the amine, simulated by MM3, makes up 76-106% of the experimental value of the corresponding N-inversion barrier. Among these amines some azabicycles ("bicyclic effect" systems) display the largest deviation (∼25%) from the experimental barrier value. From the point of view of the classical model, this deviation may be attributed to a bicyclic effect which would have an orbital origin.

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Stereodynamics of N-tert-butyl-N,N-dialkylamines. Experimental and theoretical evidence for a common potential surface for tert-butyl rotation and nitrogen inversion

Cited by 40 publications

References 0 publications

Conformational Schemes: An Available Tool for the Assignment of NMR-Measured Barriers, Demonstrated with the Example of Crowded Piperidines

Conformational Schemes: An Available Tool for the Assignment of NMR-Measured Barriers, Demonstrated with the Example of Crowded Piperidines

Stereomutation of a 1,2,3-triketone: an example of an asymmetric reaction

Rate-Determining Role of Strain for Nitrogen Inversion in Polycyclic Tertiary Amines¹

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Stereodynamics of N-tert-butyl-N,N-dialkylamines. Experimental and theoretical evidence for a common potential surface for tert-butyl rotation and nitrogen inversion

Cited by 40 publications

References 0 publications

Conformational Schemes: An Available Tool for the Assignment of NMR-Measured Barriers, Demonstrated with the Example of Crowded Piperidines

Conformational Schemes: An Available Tool for the Assignment of NMR-Measured Barriers, Demonstrated with the Example of Crowded Piperidines

Stereomutation of a 1,2,3-triketone: an example of an asymmetric reaction

Rate-Determining Role of Strain for Nitrogen Inversion in Polycyclic Tertiary Amines1

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Rate-Determining Role of Strain for Nitrogen Inversion in Polycyclic Tertiary Amines¹