Enthalpies of transfer from methanol to protic and aprotic solvents of the transition state in the reaction of benzenesulphonyl chloride with imidazole

1973 ◽  
pp. 1760 ◽  
Author(s):  
Otto Rogne
Keyword(s):  
Transition State ◽  
Aprotic Solvents ◽  
Enthalpies Of Transfer

Rate of enhancement of S N2 reactions in dipolar aprotic solvents. The importance of transition-state solvation

1968 ◽  
pp. 194 ◽  
Author(s):  
Paul Haberfield ◽  
Abraham Nudelman ◽  
Allen Bloom ◽  
Richard Romm ◽  
Henry Ginsberg ◽  
...  
Keyword(s):  
Transition State ◽  
Aprotic Solvents ◽  
Dipolar Aprotic Solvents

Thermodynamics and structures in solvents coordinating through nitrogen. I. Enthalpies of transfer from water to pyridine and acetonitrile for some monovalent cations and anions

1983 ◽  
Vol 36 (9) ◽  
pp. 1805 ◽  
Author(s):  
S Ahrland ◽  
S Ishiguro ◽  
R Portanova
Keyword(s):  
Hydrogen Bonding ◽  
Dimethyl Sulfoxide ◽  
Aprotic Solvents ◽  
Protic Solvent ◽  
Monovalent Cations ◽  
Enthalpies Of Transfer ◽  
C 30 ◽  
Tetraalkylammonium Ion

The enthalpies of transfer ΔHtr�, between water and the aprotic solvents pyridine and acetonitrile have been determined for a number of 1-1 electrolytes. To calculate ΔHtr� for the single ions, the tatb assumption that ΔHtr�,(Ph4As+) = ΔHtr�BPh4-) for all solvents has been applied. The results are compared with those found earlier for the transfer between water and dimethyl sulfoxide. The values of ΔHtr�, differ widely between different ions, from exothermic by c. 30 kJ/mol to endothermic by about the same amount. Endothermic values are found for Cl- and, though much smaller, for Br-, and also for the large tetraalkylammonium ion Bu4N+. Compared to the differences in ΔHtr�, found between the various ions, the differences found for a certain ion between different solvents are small. The decrease of AH,", in the sequence Cl- > Br- > I- runs almost parallel in the three aprotic solvents, and is much less steep than in water. This reflects the influence of ligand hydrogen bonding in the protic solvent.

Heterocyclic Ambident Nucleophiles. V. Alkylation of Benzimidazoles

1993 ◽  
Vol 46 (8) ◽  
pp. 1177 ◽  
Author(s):  
JR Howell ◽  
M Rasmussen
Keyword(s):  
Transition State ◽  
Electrostatic Field ◽  
Alkyl Halides ◽  
Proximity Effects ◽  
Aprotic Solvents ◽  
Control Factors ◽  
Transition State Structures

Alkylation of 5-substituted benzimidazole anions with a variety of primary alkyl halides in both protic and aprotic solvents showed only small regioselectivity , with a slight preference for reaction at N1 for 5-nitro and N3 for 5-methoxy systems. With 4-substituted benzimidazole anions, alkylation gave more divergent results with the N1 to N3 regioselectivity varying between 100:0 and 29:71. These alkylation patterns are interpreted as deriving from an interplay of electrostatic, thermodynamic, steric and associative control factors within the variable SN2 transition state structures involved. In the 4-substituted series, proximity effects, both electrostatic field and steric non-bonded, are clearly dominant.

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