Computational Chemistry Comparison and Benchmark DataBase Release 22 (May 2022) Standard Reference Database 101 National Institute of Standards and Technology
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Tautomer energy comparison

using model chemistry: CCSD=FULL/6-31G(2df,p)

formula	sketch		Energy (kJ mol-1)		Name		difference
	A	B	calculated	experiment	A	B
C3H4			-8	-7	allene	propyne	-1
C4H6			47	42	Methylenecyclopropane	1-Methylcyclopropene	5
C4H8			-12	-33	cyclobutane	1-Butene	21