Table 2.

Acid–base free main group carbonyls with key spectroscopic and DFT data.

Main group carbonyls	Spectroscopic data	DFT data
	B=O: 1.273(8) Å 11B: 20.7 ppm	WBI: 1.40 (B=O) B (+0.99), O (−1.03)
	R= i Pr Si=O: 1.533(1) Å 29Si: 38.4 ppm	R= i Pr WBI: 1.14 (Si=O) Si (+2.16), O (−1.24)
	R=Cy Si=O: 1.527(3) Å 29Si: 40.8 ppm	R=Cy N.A.
	Si=O: 1.537(3) Å 29Si: 28.8 ppm ν(Si=O): 1144 cm−1	WBI: 1.13 (Si=O) Si (+1.70), O (−1.23)
	Si=O: 1.5432(12) Å 29Si: 71.3 ppm ν(Si=O): 1130 cm−1	WBI: 1.09 (Si=O) Si (N.A.), O (−1.27)
	Si=O: 1.518(2) Å 29Si: 90.0 ppm	WBI: 1.35 (Si=O) Si (+2.08), O (−1.10)
	Ge=O: 1.6468(5) Å ν(Ge=O): 916 cm−1	WBI: 1.25 (Ge=O) Ge (+1.80), O (−1.05)
	X=N P=O: 1.4603(9) Å 31P: 59.1 ppm	X=N WBI: 1.32 (P=O) P (+2.31), O (−1.03)
	X=CH P=O: 1.463(2) Å 31P: 99.0 ppm	X=CH WBI: 1.30 (P=O) P (+2.14), O (−1.03)