Understanding the Polar Character Trend in a Series of Diels-Alder Reactions Using Molecular Quantum Similarity and Chemical Reactivity Descriptors

Table 1

Reaction rate constant (𝐾) with the factor 10⁵ 𝑘 [M⁻¹S⁻¹] and activation energy (kcal/moL) for the DA reactions of cyclopentadiene (Cp) as nucleophile with dienophiles at 20°C; see [13] reported by Sauer et al. [14] and also see [15–20].

Reactions (R-V)	X^1	X^2	X^3	X^4	Dienophile	TS-Y	𝐾 (10^5 𝑘 [M^−1S^−1])^a
R-1	H	H	H	H	Et^b	TS-Et	~10^−5
R-2	H	CN	H	H	1CN	TS-1CN	1.04
R-3	CN	H	H	CN	2tCN	TS-2tCN	81
R-4	H	CN	H	CN	2cCN	TS-2cCN	91
R-5	CN	CN	H	H	2CN	TS-2CN	4.8×10^4
R-6	CN	CN	H	CN	3CN	TS-3CN	4.8×10^5
R-7	CN	CN	CN	CN	4CN	TS-4CN	4.3×10^7

aRate constant (𝐾).
bReference reaction.