Gear effect—10

Roussel, Christian; Balaban, Alexandrù T.; Berg, Ulf; Chanon, Michel; Gallo, R.; Klatte, Gerd; Memiaghe, Joseph A.; Metzger, Jacques; Oniciu, Daniela C.; Pierrot‐Sanders, Johanna

doi:10.1016/s0040-4020(01)88642-7

Cited by 35 publications

(17 citation statements)

References 57 publications

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“…Pyridine derivatives (3)(4)(5)(6)(7)(8)(9)(10)(11), aromatic systems (12)(13)(14), thiazoles (15,16), polymers (17), and miscellaneous nitrogen and phosphorous systems (18)(19)(20)(21)(22) all exhibit a rate change with general steric crowding. Pyridine derivatives (3)(4)(5)(6)(7)(8)(9)(10)(11), aromatic systems (12)(13)(14), thiazoles (15,16), polymers (17), and miscellaneous nitrogen and phosphorous systems (18)(19)(20)(21)(22) all exhibit a rate change with general steric crowding.…”

Section: Structure1mentioning

confidence: 99%

Effect of chain length on the rate of quaternization of alkyl amines

Friedli¹

1990

J Americ Oil Chem Soc

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Trialkyl amines from triethyl to tristearylamine were quaternized with benzyl chloride and compared for the effect of chain length on the rate of quaternization. Triethylamine reacted about twice as fast as tripropylamine with virtually no chain-length effect from propyl to stearyl. Results are compared to previous rate studies on steric hindrance and chain-length dependence.In the course of studying process improvements on alkylation of tertiary amines to quaternary ammonium salts, the reaction properties of trialkyl amines (Structure 1) were examined. R3N STRUCTURE1Industrially, amines from trimethylamine [R = Me) to tristearylamine (R --ClsH37) are readily available. Molecular models of the long-chain analogs (Structure 2) give the distinct impression of an aquatic organism. STRUCTURE 2 a 3-legged octopus.The flexibility and possible conformations are almost limitless. Depending on the conformations most favorable under a particular condition or solvent system, it is possible to theorize either equal quaternization rates for the short-and long-chain homologs of the tertiary amine series, or vastly differing rates. Three basic types of conformations seem possible in solution: (i) parallel (Structure 3): where the hydrophobic tails cling together with no solvent molecules separating them: N STRUCTURE3 (ii) separated (Structure 4): where the hydrocarbon chains are widely separated by solvent molecules: .j STRUCTURE4 (iii) ball (Structure 5): where the chains are coiled and twisted around the nitrogen: STRUCTURE 5Structures 3 and 4 should offer no particular steric hindrance to quaternization, while Structure 5 should be very slow to quaternize due to steric problems. It is known that quaternizations occur best in solvents with high dipole moments and dielectric constants {1). Acetonitrile, ethanol, or tetrahydroforan are much better reaction media than hexane or toluene. The coiled conformation should create a non-polar hydrocarbon environment around the reactive nitrogen, disfavoring formation of polar transition states typical in SN2 displacements. The effect could further slow the rate of reaction of Structure 5.While long-chain trialkyl amines do have appreciable solubility (at temperatures above their melting points) in polar organic solvents, it seems likely that they are not totally compatible on a molecular level. This conjecture is the basis for the three suggested conformation types. Rapid conversion between the types likely occurs with the important feature being the equilibrium ratio of the conformers. NMR evidence on the conformations of the amines in solution cannot be determined with certainty. The techniques are very difficult and not fully developed at this time (2).The literature shows that the effect of steric hindrance on rates of various quaternizations has been studied. Pyridine derivatives (3-11), aromatic systems (12-14), thiazoles (15,16), polymers (17), and miscellaneous nitrogen and phosphorous systems (18-22) all exhibit a rate change with general steric crowding.Berg et al. (23) discu...

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Section: Structure1mentioning

confidence: 99%

Effect of chain length on the rate of quaternization of alkyl amines

Friedli¹

1990

J Americ Oil Chem Soc

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“…The protected dithiolate ligands 2, 3 and 5, with respectively Y = S, Se, O, were prepared starting from thiazoline-2-thione 1 [9] according to the chemical pathway depicted in Scheme 1. The bis-metallation of 1 with LDA followed by the addition of S 8 and bromopropionitrile led to 2 [5].…”

Section: Synthesis and Characterization Of The Proligandsmentioning

confidence: 99%

Conformational behavior, redox and spectroscopic properties of gold dithiolene complexes: [Au(iPr-thiazYdt)2]−1 (Y = O, S, Se)

Filatre-Furcate

Barrière

Roisnel

et al. 2018

Inorganica Chimica Acta

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Three monanionic gold dithiolene complexes with different exocyclic chalcogen atoms (O, S, Se) on the N-isopropyl-1,3-thiazoline-2-chalcogenone-4,5-dithiolate ligand, have been synthetized with the aim of modulating their properties. Due to the presence of the isopropyl (iPr) group in the plane of the thiazoline-2-chalcogenone ring, different syn and anti rotamers can exist, in solution and in the solid state. Characterization of these complexes by spectroscopic and electrochemical methods was carried out in order to investigate the influence of the size, electronegativity and polarizability of the exocyclic chalcogen atom.The molecular structure of the three anionic complexes [Au(iPr-thiazYdt) 2 ] -1 , with Y = O, S, Se, were established by single crystal X-ray diffraction studies. Theoretical calculations carried out at the DFT levels were realized on the three possible rotamers, syn/syn, syn/anti and anti/anti of the trans-[Au(iPr-thiazYdt) 2 ] -1 complexes.

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“…Roussel and co-workers (17,18) have recently examined the interplay between alkyl groups attached to aromatic rings and have rationalized reactivity differences in a number of systems on the basis that adjacent methyl and similar alkyl groups prefer to avoid the interactions shown in 25 and 26. Moreover, Schug and Viers (19) have calculated the energies of the rotational conformers of 2,3-lutidine and found that the gear-clashed rotamer 27 is more stable than the two gear-meshed rotamers 28 and 29 by 0.36 and 0.59 kcal mol-', respectively; it is more stable than the gear-clashed rotamer 30, which has a frontal interaction of hydrogens, by 1 .…”

Section: Gear Effectsmentioning

confidence: 99%

Steric activation in prototropic reactions of pyrazine derivatives. I. Polar and conformational effects

Lee¹,

Stewart²

1986

Can. J. Chem.

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The rates of proton loss from methyl groups in a number of pyrazine derivatives have been measured in D2O by monitoring the replacement of protium by deuterium at the acidic sites of the substrates; they include the reaction of four methylpyrazines with NaOD/D2O and nine alkylpyrazinium ions with D2O/DCl. The reactive site, which is a methyl group conjugated to the aza or azonium group of the substrate, is in all cases activated by an adjacent alkyl group, with the greatest effect, a factor of about 30, occurring when a proton on nitrogen is replaced by a methyl group. The phenomenon is analysed in terms of polar effects, ring strain and inter-alkyl interactions (including gear effects), and hybridization changes at nitrogen.

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Gear effect—10

Cited by 35 publications

References 57 publications

Effect of chain length on the rate of quaternization of alkyl amines

Effect of chain length on the rate of quaternization of alkyl amines

Conformational behavior, redox and spectroscopic properties of gold dithiolene complexes: [Au(iPr-thiazYdt)2]−1 (Y = O, S, Se)

Steric activation in prototropic reactions of pyrazine derivatives. I. Polar and conformational effects

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