IONIC POLYMERIZATION. A METHOD FOR MEASURING THE RELATIVE RATES OF ATTACK OF A CARBONIUM ION PAIR ON AROMATIC COMPOUNDS IN HOMOGENEOUS SOLUTION. NUCLEOPHILICITY FACTORS

1953 ◽  
Vol 75 (24) ◽  
pp. 6349-6350 ◽  
Author(s):  
C. G. Overberger ◽  
Gerard F. Endres
Keyword(s):  
Aromatic Compounds ◽  
Homogeneous Solution ◽  
Ion Pair ◽  
Carbonium Ion

scholarly journals THE STEREOCHEMISTRY OF HALOGEN DISPLACEMENT BY NITRATE ION RACEMIZATION AND RETENTION OF CONFIGURATION IN THE SYNTHESIS OF DINITRATE ESTERS

1965 ◽  
Vol 43 (6) ◽  
pp. 1656-1660 ◽  
Author(s):  
L. D. Hayward ◽  
M. Jackson ◽  
I. G. Csizmadia
Keyword(s):  
Silver Nitrate ◽  
Steric Effect ◽  
Heterogeneous Reaction ◽  
Ion Pair ◽  
Alkyl Halides ◽  
Preferential Formation ◽  
Carbonium Ion ◽  
Carbonium Ions ◽  
And Inversion ◽  
Derivatives Of

The reaction of silver nitrate in dry acetonitrile with 2,5-dideoxy-2,5-diiodo-1,4;3,6-dianhydro-L-iditol resulted in formation of the dinitrate esters of the 1,4;3,6-dianhydrides of D-mannitol, D-glucitol, and L-iditol. Similarly both endo- and exo-nitrato groups were introduced in displacement of the endo-halogen in the 2-deoxy-2-iodo-5-O-acetyl and 2-deoxy-2-iodo-5-O-p-toluenesulfonyl derivatives of 1,4;3,6-dianhydro-L-iditol. Since both types of nitrato groups were stable to silver nitrate, the racemization occurred during the displacement and was attributed to formation of cyclic carbonium ion intermediates. The steric effect of the adjacent ring in the carbonium ions apparently suppressed the termolecular, ion-pair mechanism previously established for the metathesis of acyclic alkyl halides and caused preferential formation of the exo-nitrato derivatives.The heterogeneous reaction of meso-dibromostilbene with silver nitrate in acetic acid or acetonitrile gave meso-dihydrobenzoin dinitrate with overall retention of configuration. This result could be most readily reconciled with the contrasting sequence of retention and inversion previously reported for meso- and dl-2,3-dibromobutane if participation of neighboring phenyl groups occurred in the second displacement step.

Isoprene Polymerization by Organometallic Compounds. II

1960 ◽  
Vol 33 (3) ◽  
pp. 655-668 ◽  
Author(s):  
Arthur V. Tobolsky ◽  
Charles E. Rogers
Keyword(s):  
Heterogeneous System ◽  
Homogeneous Solution ◽  
Organometallic Compounds ◽  
Ion Pair ◽  
Heterogeneous Surface ◽  
Ionic Character ◽  
Definition Of ◽  
Clear Solution ◽  
Isoprene Polymerization ◽  
Hydrocarbon Media

Abstract From the above results it would certainly appear that the ionic character of the growing ion pair (polymer−M+) is a very important factor in governing the structure of isoprene homopolymers. Another factor which may be sufficient or necessary for the formation of the unique cis-1,4-eonfiguration is the presence of an orienting surface or complex. It is well known that organolithium compounds are associated in hydrocarbon media, whereas they are probably monomolecularly dispersed in ethers and amines. It is apparent, then, that in hydrocarbon solutions the carbon-lithium chain end may be associated with other carbon-lithium pairs from unreacted initiator molecules or even with other chain ends or, in some cases, it may be associated with the lithium atoms on the surface of lithium particles. The fact that greater than 90 per cent cis-1,4-structure is obtained in hydrocarbons by use of either an apparently clear solution of filtered n-butyllithium or a heterogeneous system of lithium dispersion suggests that the massive surface of the lithium particle is not a necessary factor for the stereospecificity of the reaction. Whether we should consider the butyllithium or the lithium-initiated polymerizations as homogeneous solution reactions or heterogeneous surface reactions depends on the definition of a surface, since an associated complex or micelle may also conceivably serve as an orienting specie in the same way as a surface does. We emphasize this since so many stereospecific polymerizations such as the Ziegler system and the Phillips system appear to occur under heterogeneous conditions, presumably on an orienting surface of rather gross dimensions.

Studies on the Decomposition of Tetra-alkylammonium Salts in Solution. IV. The α-Deuterium Secondary Isotope Effect

1971 ◽  
Vol 49 (1) ◽  
pp. 129-132 ◽  
Author(s):  
E. C. F. Ko ◽  
K. T. Leffek
Keyword(s):  
Isotope Effect ◽  
Ion Pair ◽  
Deuterium Isotope Effect ◽  
Solvent Interaction ◽  
Temperature Range ◽  
Carbonium Ion ◽  
Alkylammonium Salts ◽  
Rate Ratios

The secondary deuterium isotope effect is reported for the decomposition of benzyl-α-d2-phenyldimethylammonium bromide in both chloroform and acetone solvent, over a temperature range of 25 to 30°. The magnitudes of the rate ratios are compared to literature values for SN1 reactions, from which it is concluded that the mechanism of the decomposition involves a carbonium ion or ion-pair. The variation of the isotope effect with solvent is rationalized in terms of specific solvent interaction with the benzyl group.

REARRANGEMENT STUDIES WITH 14C: XIX. THE REACTION OF 2-PHENYL-1-14C-ETHANOL WITH THIONYL CHLORIDE

1964 ◽  
Vol 42 (5) ◽  
pp. 1130-1136 ◽  
Author(s):  
C. C. Lee ◽  
D. J. Kroeger ◽  
D. P. Thornhill
Keyword(s):  
Thionyl Chloride ◽  
Ion Pairs ◽  
Aqueous Sodium Hydroxide ◽  
Covalent Bonding ◽  
Ion Pair ◽  
Aqueous Sodium ◽  
Carbonium Ion ◽  
Partial Completion ◽  
The Stability ◽  
Excess Thionyl Chloride

The reaction of 2-phenyl-1-14C-ethanol with thionyl chloride in pyridine, dioxane, toluene, or excess thionyl chloride as solvent gave 2-phenylethyl chloride showing, respectively, about 0, 15, 44, and 48% rearrangement of the 14C-label from the C-1 to the C-2 positions. When reactions of 2-phenyl-1-14C-ethauol or 2-p-anisyl-1-14C-ethanol with thionyl chloride in dioxane or excess thionyl chloride were carried only to partial completion and the undecomposed chlorosulphites hydrolyzed by aqueous sodium hydroxide, the recovered alcohols showed only 0.1 to 0.5% isotope position rearrangement. This indicated a lack of return from ion-pairs to isotopically rearranged 2-arylethylchlorosulphite and suggested that the first stage of ionization may involve ion-pairs with structures that will not result in rearrangement on return to covalent bonding, or that the first ion-pair may decompose faster than it can return to reactant. The possibility that rearrangements via rigidly oriented ion-pairs and via the concerted SNi′ mechanism may represent the two extremes of a graded series is discussed. It is suggested that the relative contributions from the ion-pair and from the SNi′ mechanisms will depend on the stability of the carbonium ion as well as on the nature of the reaction solvent.

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