Hammett substituent constants

Hammett substituent constants

Introduction

Hammett substituent constants are used in LFER. Depending on the reaction or equilibrium under examination one of several sets of constants can be used. Here the two original constants, σm and σp, derived from the ionization of benzoic acids, are given together with constants for the use when there is resonance between the substituent and the reaction centre.

σm - for meta-substituents
σp - for para-substituents
σ⁺ - for para-substituents with resonance with a positive reaction centre
σ⁻ - for para-substituents with resonance with a negative reaction centre


Hammett substituent constants
NameSymbolσmσpσ⁺σ⁻
1-methylpropyl‐‐CH(CH3)CH2CH3
1-phenylethyl‐‐CH(CH3)C6H5
1-phenylpropyl‐‐CH(CH2CH3)C6H5
1-tert-butylethyl‐‐CH(CH3)C(CH3)3
2-chloroethyl‐‐CH2CH2Cl
2-phenylethyl‐‐CH2CH2C6H5
3-phenylpropyl‐‐(CH2)2C6H5
acetamido‐‐NHCOCH30.17-0.06
acetoxy‐‐OCOCH30.360.28
acetoxymethyl‐‐CH2OC(=O)CH30.05
acetyl‐‐COCH30.370.500.87
acetylmethyl‐‐CH2C(=O)CH3
amino‐‐NH2-0.08-0.65-1.30
azido‐‐N30.290.18
benzyl‐‐CH2C6H5-0.08-0.11
bromo‐‐Br0.400.230.15
bromomethyl‐‐CH2Br0.110.12
butyl‐‐(CH2)3CH3
carbamoyl‐‐CONH20.31
carboxy‐‐COOH0.370.450.42
chloro‐‐Cl0.370.230.11
chloromethyl‐‐CH2Cl0.090.12
cyano‐‐CN0.620.830.660.90
cyanomethyl‐‐CH2CN0.150.17
cyclohexylmethyl‐‐CH2C6H11
cyclopropyl‐‐CH(CH2)2-0.07-0.21
dibutylphosphoryl‐‐P(=O)((CH2)3CH3)20.380.52
dichloromethyl‐‐CHCl2
dimethoxyphosphoryl‐‐P(=O)(OCH3)20.420.55
dimethylamino‐‐N(CH3)2-0.21-0.37
diphenylmethyl‐‐CH(C6H5)2
diphenylphosphoryl‐‐P(=O)(C5H6)20.440.58
ethoxy‐‐OCH2CH30.10-0.25
ethoxycarbonyl‐‐COOCH2CH30.360.45
ethyl‐‐CH2CH3-0.06-0.15
ethynyl‐‐C≡CH0.140.07
fluoro‐‐F0.340.06-0.07-0.02
hydrogen‐‐H0.000.00
hydroxy‐‐OH0.08-0.36-0.92
hydroxy(phenyl)methyl‐‐CH(OH)C6H5
hydroxymethyl‐‐CH2OH0.07-0.01
iodo‐‐I0.350.240.13
iodomethyl‐‐CH2I0.070.09
isobutyl‐‐CH2CH(CH3)2
isocyanomethyl‐‐CH2NC
isopropyl‐‐CH(CH3)2-0.08-0.15
isothiocyanato‐‐NCS0.480.49
mercapto‐‐SH0.25
methoxy‐‐OCH30.14-0.27-0.78-0.20
methoxycarbonyl‐‐COOCH30.340.450.480.68
methoxymethyl‐‐CH2OCH30.020.03
methyl‐‐CH3-0.06-0.17-0.31
methylsulfanyl‐‐SCH30.13-0.16
methylsulfinyl‐‐S(=O)CH30.500.50
methylsulfonyl‐‐S(=O)2CH30.680.72
neopentyl‐‐CH2C(CH3)3
nitro‐‐NO20.720.880.791.24
pentafluorosulfur‐‐SF50.610.69
phenoxy‐‐OC6H50.26
phenoxymethyl‐‐CH2OC6H5
phenyl‐‐C6H50.060.06-0.17
phenylazo‐‐N2C6H50.64
phenylsulfonyloxy‐‐OS(=O)2C6H50.360.33
propyl‐‐CH2CH2CH3
styryl‐‐CH=CHC6H5
sulfamoyl‐‐SO2NH20.530.58
tert-butyl‐‐C(CH3)3-0.07
trichloromethyl‐‐CCl3
trifluoromethoxy‐‐OCF30.390.36
trifluoromethyl‐‐CF30.440.53
trifluoromethylsulfanyl‐‐SCF30.400.50
trifluoromethylsulfinyl‐‐S(=O)CF30.670.73
trifluoromethylsulfonyl‐‐S(=O)2CF30.800.96