Stereodynamics of isopropyldimethylamine. Carbon-13(proton) and proton dynamic NMR studies. Molecular mechanics calculations

Brown, Jay H.; Bushweller, C. Hackett

doi:10.1021/ja00047a025

Cited by 16 publications

(38 citation statements)

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“…69 % in proportion based on the free‐energy difference) has one isopropyl methyl group anti and the other gauche to the lone pair and corresponds to the AAG conformer of TEA (Figure 10). 33 The expected DMT‐IPDMA was obtained in only 48 % yield after 1 h despite the reaction proceeding via the major conformer, indicating that the reaction is significantly retarded, but not completely repressed, by the addition of one gauche β‐methyl group. In the case of TEA, the least stable conformation is AAA (7.36 kcal mol −1 ) followed by AAG (second unstable conformer; 3.35 kcal mol −1 ).…”

Section: Resultsmentioning

confidence: 99%

Study on 1,3,5‐Triazine Chemistry in Dehydrocondensation: Gauche Effect on the Generation of Active Triazinylammonium Species

Kunishima

Ujigawa

Nagaoka

et al. 2012

Chemistry A European J

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The reaction of 2-chloro-4,6-dimethoxy-1,3,5-triazine (CDMT) with various nitrogen-containing compounds, particularly tertiary amines (tert-amines), has been studied for the preparation of 2-(4,6-dimethoxy-1,3,5-triazinyl)trialkylammonium salts [DMT-Am(s)]. DMT-Ams derived from aliphatic tert-amines exhibited activity for the dehydrocondensation between a carboxylic acid and an amine to form an amide in a model reaction. Based on a conformational analysis of DMT-Ams and tert-amines by NMR and X-ray diffraction methods, we concluded that a β-alkyl group maintained in a gauche relationship with the nitrogen lone pair of tert-amines significantly hinders the approach of CDMT to the nitrogen. Thus, trimethylamine and quinuclidine without such alkyl groups readily react with CDMT whereas triethylamine, possessing two or three such gauche β-alkyl groups in the stable conformations, does not react at all. The theory of "gauche β-alkyl group effect" proposed here provides useful guidelines for the preparation of DMT-Ams possessing various tertiary amine moieties. An investigation of the dehydrocondensation activity of tert-amines in a CDMT/tert-amine system that involves in situ generation of DMT-Am, showed that the gauche effect of the β-alkyl group becomes quite pronounced; the yield of the amide decreases significantly with tert-amines possessing an unavoidable gauche β-alkyl group. Thus, the tert-amine/CDMT systems are useful for judging whether tert-amines can readily react with CDMT without isolation of DMT-Ams.

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Section: Resultsmentioning

confidence: 99%

Study on 1,3,5‐Triazine Chemistry in Dehydrocondensation: Gauche Effect on the Generation of Active Triazinylammonium Species

Kunishima

Ujigawa

Nagaoka

et al. 2012

Chemistry A European J

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“…If the major factors influencing inversion barriers in tertiary amines are angle strain, torsional strain, and steric crowding rather than a specific orbital interaction requiring appropriate alignment of certain bonds with the lone pair, then a molecular mechanics model might account for the observed trends. Nelsen 12 and others , have noted the success of Allinger's MM2 parameterization in describing ground state structures and rotational barriers of amines. Indeed, MM2 predicts that 2-endo should be 0.1 kcal mol -1 more stable than 2-exo , in close agreement with our experimental finding.…”

Section: Discussionmentioning

confidence: 99%

Nitrogen Inversion Barrier of 2-Methyl-2-azabicyclo[2.2.1]heptane. The Role of Torsional Strain in Pyramidal Inversion

1996

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Low-temperature 13C NMR measurements indicate that the endo isomer of 2-methyl-2-azabicyclo[2.2.1]heptane is about 0.3 kcal mol-1 more stable than the exo isomer. Rate constants for inversion from the endo to exo isomer were determined by NMR line shape analysis. The inversion barrier, ΔG ‡, of 7.2 kcal mol-1 is lower than that in model acyclic amines, despite an internal CNC bond angle that is less than the tetrahedral angle of 109.47°. Comparison with 7-methyl-7-azabicyclo[2.2.1]heptane that has a small internal CNC angle and an unusually high barrier, as well as other cyclic and bicyclic amines, leads to the conclusion that torsional (eclipsing) strain plays a significant role along with angle strain in determining inversion barriers. Molecular mechanics calculations of the change in energy between pyramidal ground state and planar transition state account reasonably well for the observed barriers. New measurements of inversion barriers and their dependence on solvent are also reported for 2-methyl-2-azabicyclo[2.2.2]octane and 1-methyl-4-piperidone.

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“…Usually, the only way to solve these problems is to decrease the sample temperatures below 150 K. Unfortunately, there is not a wide range of solvents available that are suitable for liquid-state NMR below 150 K. Moreover, the solvents also need to contain either deuterium or fluorine as nuclei for magnetic field locks. Examples of solvents that can be applied for such studies in the 85 to 150 K range are 1-monodeuteropropane, 7 bromotrifluoromethane and vinylchloride, 8 dimethyl ether, 9 and methylethyl ether. 10 In addition, n-propylnitrite, C 3 H 7 ONO, is a promising solvent for low-temperature studies in the future, since it remains liquid between 300 and 94 K. 11 Especially useful are solvent mixtures exhibiting lower melting points than their pure components, via the formation of eutectic mixtures.…”

Section: A-hð ð ðBmentioning

confidence: 99%

Influence of the temperature-dependent dielectric constant on the H/D isotope effects on the NMR chemical shifts and the hydrogen bond geometry of the collidine-HF complex in CDF3/CDClF2 solution

et al. 2001

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Stereodynamics of isopropyldimethylamine. Carbon-13(proton) and proton dynamic NMR studies. Molecular mechanics calculations

Cited by 16 publications

References 0 publications

Study on 1,3,5‐Triazine Chemistry in Dehydrocondensation: Gauche Effect on the Generation of Active Triazinylammonium Species

Study on 1,3,5‐Triazine Chemistry in Dehydrocondensation: Gauche Effect on the Generation of Active Triazinylammonium Species

Nitrogen Inversion Barrier of 2-Methyl-2-azabicyclo[2.2.1]heptane. The Role of Torsional Strain in Pyramidal Inversion

Influence of the temperature-dependent dielectric constant on the H/D isotope effects on the NMR chemical shifts and the hydrogen bond geometry of the collidine-HF complex in CDF3/CDClF2 solution

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