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: PBEPBE/3-21G

formula	sketch		Energy (kJ mol-1)		Name		difference
	A	B	calculated	experiment	A	B
C3H4			9	-7	allene	propyne	16
C4H6			19	3	1,2-Butadiene	1-Butyne	16
C4H6			-8	-17	1,2-Butadiene	2-Butyne	9
C4H6			-36	-51	1,2-Butadiene	1,3-Butadiene	15
C4H6			-46	-49	Cyclobutene	1,3-Butadiene	4
C4H6			-105	-82	1-Methylcyclopropene	1,2-Butadiene	-23
C4H6			58	42	Methylenecyclopropane	1-Methylcyclopropene	17
C3H6O			-104	-110	Oxetane	Propanal	6
C4H8			-11	-33	cyclobutane	1-Butene	22
C3H4O2			5	29	2-Propenoic acid	β–Propiolactone	-23
C4H6S			4	4	Thiophene, 2,5-dihydro-	Thiophene, 2,3-dihydro-	-0
C5H8			29	25	1,3-Pentadiene, (E)-	1,4-Pentadiene	4
C5H8			46	64	1,3-Pentadiene, (E)-	1,2-Pentadiene	-19
C5H10			-10	-5	1-Butene, 2-methyl-	2-Butene, 2-methyl-	-5
C5H10			-35	-29	Cyclopropane, 1,1-dimethyl-	1-Butene, 2-methyl-	-6