Mechanism of reactions of N-(methoxymethyl)-N,N-dimethylanilinium ions with nucleophilic reagents
The prediction that the oxocarbonium ion derived from formaldehyde should have a lifetime of approximately 10/sup -15/ s that gives rise to an enforced preassociation or concerted reaction mechanism has been tested by examining the reactions of N-(methoxymethyl)-N,N-dimethylanilinium ions in water in the presence of added nucleophilic reagents. These compounds undergo well-behaved second-order reactions with nucleophiles and give the amount of substitution product that is expected from the rate increase in the presence of nucleophile. Structure-reactivity correlations exhibit behavior intermediate between that expected for S/sub N/2 (Swain-Scott) and carbonium ion (N/sup +/) reactions. The small values of s = 0.3 and ..beta../sub nuc/ = 0.14 and large values of ..beta../sub lg/ = -0.7 to -0.9 indicate a transition state that can be described either as an open transition state for S/sub N/2 displacement or as an oxocarbonium ion that is stabilized by weak interactions with the entering and leaving groups. Secondary ..cap alpha..-deuterium isotope effects for the second-order reactions range from (k/sub H//k/sub D/)/D = 0.99 for fluoride ion to 1.18 for iodide ion. Solvolysis and the second-order reaction with n-propylamine exhibit values of ..delta..S/sup + +/ = -1.2 and -2.1 cal K/sup -1/ mol/sup -1/, respectively, and display similar changes in rate in mixed water-alcohol solvents. It is suggested that the lifetime of the carbonium ion species in the presence of nucleophiles is so short that the reaction mechanism must be concerted.
- Research Organization:
- Brandeis Univ., Waltham, MA
- OSTI ID:
- 6861702
- Journal Information:
- J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 102:22; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
Similar Records
Solvolytic reactivity of 1-trifluoromethyl-1-phenylethyl tosylate. Formation of a highly destabilized carbonium ion
Three component synthesis of substituted {eta}{sup 5}-cyclopentadienyltricarbonylrhenium complexes: Scope, limitations, and mechanistic interpretations
Related Subjects
400302* -- Organic Chemistry-- Isotope Effects-- (-1987)
AMINES
AROMATICS
AZIDES
CATIONS
CHARGED PARTICLES
CHEMICAL REACTION KINETICS
DEUTERIUM
HALIDES
HALOGEN COMPOUNDS
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
HYDROXIDES
IONS
ISOTOPE EFFECTS
ISOTOPES
KINETICS
LIGHT NUCLEI
NITRATES
NITROGEN COMPOUNDS
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
REACTION KINETICS
STABLE ISOTOPES