Substituents used in this study and their corresponding Hammett constants,^90,91σ_p. The empirically derived Hammett constant (σ_p) is used to quantify the strength in which a substituent is electron withdrawing (positive) or electron donating (negative).

Substituent	Hammett constant (σp)	Classification
N(CH3)2	−0.83	Donating
CH3	−0.17
H	0
Cl	0.23	Withdrawing
NO2	0.78