Correlation of the effects of alkyl substituents on the basicities of indoles

1992 ◽  
Vol 70 (1) ◽  
pp. 282-284 ◽  
Author(s):  
Peter A. Cohen ◽  
Louis A. Cohen
Keyword(s):  
Free Energy ◽  
Double Bond ◽  
Substituent Effects ◽  
Energy Correlation ◽  
Linear Free Energy ◽  
Alkyl Groups ◽  
Stabilization Parameter ◽  
Opposing Effects ◽  
Isomeric Mono

Alkyl groups at C-2 of indole increase basicity at the site of protonation, C-3, while alkyl groups at C-3 decrease basicity. These opposing effects can be incorporated, for both the isomeric mono- and 2,3-dialkylindoles, into a single linear free energy correlation, pKa = −10.05Σσ −3.94, in which [Formula: see text] and Ds is the double bond stabilization parameter at C-3. An analogous correlation for N-methylindoles, pKa = −8.64Σσ −2.80, reveals that the effect of N-alkylation on basicity is predictable but not additive. Keywords: alkylindoles, carbon basicity, free energy correlation, substituent effects, N-alkyl effect.

Substituent effects on the N.M.R. spectra of carboxylic acid derivatives. III. Correlation of 13C N.M.R. spectra of para substituted acetanilides and 4'-nitrophenyl 4-substituted benzoates with infrared carbonyl stretching frequencies, 1H N.M.R., rate and equilibrium data

1984 ◽  
Vol 37 (3) ◽  
pp. 497 ◽  
Author(s):  
CJ O'Conner ◽  
DJ McLennan ◽  
DJ Calvert ◽  
TD Lomax ◽  
AJ Porter ◽  
...  
Keyword(s):  
Free Energy ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Linear Free Energy Relationships ◽  
Reactive Site ◽  
Linear Free Energy ◽  
Equilibrium Data ◽  
Energy Relationships ◽  
Monosubstituted Benzenes ◽  
Best Fit

The 13C n.m.r. spectra of 17 monosubstituted benzenes, 14 para substituted acetanilides and ten 4'-nitrophenyl 4-substituted benzoates have been measured in (CD3)2SO and the chemical shifts have been compared with the infrared carbonyl stretching frequencies of the substrates (in CCl4), the 1H n.m.r. chemical shifts of protons close to the reactive site of protonation, rates of hydrolysis or aminolysis and literature values of the corresponding basicity constants and rate constants. The observed substituent chemical shifts are non-additive and this result has been discussed in terms of the electronic properties of -NHCOCH3 and -COOC6H4NO2. The 13C n.m.r. and the i.r. data have been treated by single parameter and dual substituent parameter linear free energy relationships and σR values of best fit have been identified. Relative resonance and inductive contributions have been discussed.

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