Association constants (M⁻¹) for formation of 1 : 1 complexes with tri-n-butyl phosphine oxide in n-octane at 298 K^a.

X	K(Y = OH)	K′(Y = H)	K/K′
H	940 ± 140	202 ± 17	4.7
Me	650 ± 140	120 ± 20	5.4
OMe	1800 ± 300	220 ± 140	8.2
CF3	8790 ± 60	1030 ± 50	8.5
NO2	46 000 ± 8000	3840 ± 90	12.0

^aAverage values from at least 3 experiments with errors at the 95% confidence limit.