Computational Chemistry Comparison and Benchmark DataBase Release 22 (May 2022) Standard Reference Database 101 National Institute of Standards and Technology
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Relative enthalpies of isomers - Comparison of 0K enthalpies (kJ mol^-1)

Isomers of C₄H₆O₂

index	Species	CAS number	Name	Relative experimental enthalpy (kJ mol-1)	sketch
a	C4H6O2	96333	2-Propenoic acid, methyl ester
b	C4H6O2	96480	γ–Butyrolactone
c	C4H6O2	107937	Crotonic Acid
d	C4H6O2	431038	2,3-Butanedione