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: HF/6-31G*

formula	sketch		Energy (kJ mol-1)		Name		difference
	A	B	calculated	experiment	A	B
C3H4			-7	-7	allene	propyne	0
C4H6			48	42	Methylenecyclopropane	1-Methylcyclopropene	7
C4H6			-84	-82	1-Methylcyclopropene	1,2-Butadiene	-2
C4H6			-57	-49	Cyclobutene	1,3-Butadiene	-8
C4H6			-50	-51	1,2-Butadiene	1,3-Butadiene	1
C4H6			3	3	1,2-Butadiene	1-Butyne	-0
C4H6			-25	-17	1,2-Butadiene	2-Butyne	-8
C3H6O			-121	-110	Oxetane	Propanal	-10
C3H4O2			36	29	2-Propenoic acid	β–Propiolactone	8
C4H6S			6	4	Thiophene, 2,5-dihydro-	Thiophene, 2,3-dihydro-	2
C5H8			-48	-52	1,2-Butadiene, 3-methyl-	1,3-Butadiene, 2-methyl-	4
C5H8			29	25	1,3-Pentadiene, (E)-	1,4-Pentadiene	4
C5H8			65	64	1,3-Pentadiene, (E)-	1,2-Pentadiene	1
C5H10			-31	-29	Cyclopropane, 1,1-dimethyl-	1-Butene, 2-methyl-	-2
C5H10			-7	-5	1-Butene, 2-methyl-	2-Butene, 2-methyl-	-2