Table 2. HOMO Energies (ε_HOMO, eV) and Global Nucleophilicity Indices (N, eV) for the [ECX]⁻ Anions and MeC≡P, Calculated at the M06-2X/aug-cc-pVTZ Level of Theory.

dienophile	εHOMO	N
[PCO]−	–1.54	9.50
[PCS]−	–1.83	9.21
[PCSe]−	–1.90	9.14
[AsCO]−	–1.44	9.60
[AsCS]−	–1.76	9.28
[AsCSe]−	–1.87	9.17
P≡CMe	–8.69	2.35