Quantification of the Nucleophilicities of 3-X-Thiophenes: Highlighting the Hyperortho Correlation

Table 2

Second-order rate constants k₁ (M⁻¹·s⁻¹) and selectivity parameters (ρ and pK_a) of the reactions of 3-X-thiophene 1 with the electrophiles 2a and 3a-c.

Thiophene	Ν/s	σ^+b	k1 (M^−1s^−1)
			2a	3a	3b	3c
	2.38/1.09	−0.31	4.08 × 10^−3	2.76 × 10^−3	1.23 × 10^−3	4.10 × 10^−5
	1.79/1.06	0.00	1.28 × 10^−3	7.18 × 10^−4	3.39 × 10^−4	1.35 × 10^−5
	1.20/1.03	0.15	3.41 × 10^−4	2.22 × 10^−4	1.08 × 10^−4	4.36 × 10^−6
ρ			−2.23	−2.27	−2.22	−2.03
pKa			0.30	2.95	3.75	5.86

^bRef [18].