Barriers to nitrogen inversion in cyclic and acyclic substituted hydroxylamines. A theoretical study

Kost, Daniel; Raban, Morton

doi:10.1021/jo00872a017

Cited by 16 publications

(3 citation statements)

References 3 publications

(3 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The ratio of the isomers was solvent-dependent. The observed phenomena are accounted for by slow inversion at the N1 atom of the heterocycle. − Asymmetric centers at C2 and N1 produce two diastereomers (Chart ), which, however, cannot be separated chromatographically due to the relatively high inversion rate. Similar effect was observed earlier for some alkoxyamines of imidazoline and imidazolidine series. , …”

Section: Resultsmentioning

confidence: 99%

pH-Sensitive C–ON Bond Homolysis of Alkoxyamines of Imidazoline Series with Multiple Ionizable Groups As an Approach for Control of Nitroxide Mediated Polymerization

et al. 2011

View full text Add to dashboard Cite

Recently, a new concept of pH-switchable agents for reversible addition-fragmentation chain transfer (RAFT) polymerization has been introduced by Benaglia et al. (J. Am. Chem. Soc.2009, 131, 6914-6915). In this paper we extended the concept of pH-switchable mediators to nitroxide mediated polymerization (NMP) by employing nitroxides with basic or acidic groups as controlling agents. Four alkoxyamines, the derivatives of 2-(4-(dimethylamino)-2-ethyl-5,5-dimethyl-2-(pyridin-4-yl)-2,5-dihydro-1H-imidazol-1-oxyl and 2-(2-carboxyethyl)-5,5-diethyl-2,4-dimethyl-2,5-dihydro-1H-imidazol-1-oxyl, have been prepared. The influence of pH on alkoxyamine homolysis rate constants (k(d)) and on the nitroxide-alkyl radical recombination rate constants (k(c)) was studied. All alkoxyamines under study as well as the parent nitroxides have several basic groups, which under pH variation can undergo consecutive protonation. It was shown that the k(d) value under basic conditions are significantly (up to 15-fold) higher than in acidic solution at the same temperature, whereas the k(c) value in basic solutions decrease by a factor of 2 only. The efficiency of NMP is known to be dependent on k(d) and k(c), both constants being dependent on the monomer structure; therefore the performance of NMP of different monomers in the controlled mode requires different conditions. It is shown that the pH value crucially affects the polymerization regime, changing it from the controlled to the uncontrolled mode. The controlled regime of NMP of different hydrophilic monomers (sodium 4-styrenesulphonate and acrylamide) in aqueous solution under mild conditions (90 °C) can be achieved using the same alkoxyamine by the variation of the pH value. The chain length of polymers depends on pH value during the polymerization.

show abstract

Section: Resultsmentioning

confidence: 99%

pH-Sensitive C–ON Bond Homolysis of Alkoxyamines of Imidazoline Series with Multiple Ionizable Groups As an Approach for Control of Nitroxide Mediated Polymerization

et al. 2011

View full text Add to dashboard Cite

show abstract

“…Natural bond orbital analysis was used to calculate Wiberg bond indices 21) for the N-O and N-R bonds, and the s-character of the nitrogen lone pair for selected compounds ( Table 2). The activation energy increases with increasing s-character of the lone pair of electrons because more energy is required for the ground state to reach the p-character transition state.…”

Section: Resultsmentioning

confidence: 99%

“…The activation energy increases with increasing s-character of the lone pair of electrons because more energy is required for the ground state to reach the p-character transition state. 22) To provide a comparison, the calculated energies of several isoxazolidines are listed in Table 3. Removing the carbonyl group from the ring shifts the conformational equilibrium.…”

Section: Resultsmentioning

confidence: 99%

On the Nitrogen Inversion of Isoxazolidin-5-ones

Noda

Shibasaki

2019

CHEMICAL & PHARMACEUTICAL BULLETIN

View full text Add to dashboard Cite

The nitrogen inversion energies of a series of N-substituted isoxazolidin-5-ones were studied by density functional theory. The transition state energy was found to strongly correlate with the s-character of the lone pair of electrons on the nitrogen in the ground state. Although the activation energy trends for isxazolidin-5-ones and isoxazolidines are similar, their conformational equilibria are slightly different and the isoxazolidin-5-one inversion energies are generally higher.

show abstract

Stereochemistry and chiroptical properties

Kost

Raban

1990

Sulfenic Acids and Derivatives (1990)

View full text Add to dashboard Cite

Barriers to nitrogen inversion in cyclic and acyclic substituted hydroxylamines. A theoretical study

Cited by 16 publications

References 3 publications

pH-Sensitive C–ON Bond Homolysis of Alkoxyamines of Imidazoline Series with Multiple Ionizable Groups As an Approach for Control of Nitroxide Mediated Polymerization

pH-Sensitive C–ON Bond Homolysis of Alkoxyamines of Imidazoline Series with Multiple Ionizable Groups As an Approach for Control of Nitroxide Mediated Polymerization

On the Nitrogen Inversion of Isoxazolidin-5-ones

Stereochemistry and chiroptical properties

Contact Info

Product

Resources

About