IV.A.4. (XIV.F.) 
index  Species  CAS number  Name  Relative experimental enthalpy (kJ mol^{1})  sketch 

a  C_{4}H_{6}O_{2}  107937  Crotonic Acid  
b  C_{4}H_{6}O_{2}  96480  γ–Butyrolactone  0.0  
c  C_{4}H_{6}O_{2}  96333  2Propenoic acid, methyl ester  33.5  
d  C_{4}H_{6}O_{2}  431038  2,3Butanedione  39.7 
semiempirical  AM1  0.0 b 89.4 c 785.0 d 

PM3  0.0 b 93.0 c 506.8 d 

PM6  0.0 b 76.5 c 486.2 d 

MNDOd  0.0 b 106.1 c 

composite  G1  554.2 a 0.0 b 37.3 c 262.0 d 
G2MP2  553.3 a 0.0 b 39.5 c 261.6 d 

G2  554.0 a 0.0 b 39.5 c 261.1 d 

G3  556.6 a 0.0 b 38.4 c 262.1 d 

G3B3  2.7 a 0.0 b 55.3 c 26.7 d 

G3MP2  0.0 b 36.8 c 261.1 d 

G4  3.0 a 0.0 b 55.9 c 25.9 d 

CBSQ  NC NC 

molecular mechanics  MM3  0.0 b 56.9 c 
STO3G  321G  321G*  631G  631G*  631G**  631+G**  6311G*  6311G**  631G(2df,p)  6311+G(3df,2p)  ccpVDZ  ccpVTZ  augccpVDZ  augccpVTZ  ccpV(T+d)Z  

hartree fock  HF  0.0 b 191.3 c 
0.0 b 49.8 c 
0.0 b 49.8 c 
0.0 b 34.6 c 
0.0 b 57.7 c 
0.0 b 54.9 c 
0.0 b 51.7 c 
0.0 b 59.0 c 
0.0 b 53.2 c 
0.0 b 52.5 c 
0.0 b 52.2 c 
0.0 b 60.3 c 
0.0 b 53.1 c 
0.0 b 52.2 c 

density functional  LSDA  0.0 b 180.5 c 
0.0 b 101.0 c 
0.0 b 101.0 c 
0.0 b 86.5 c 
0.0 b 102.0 c 
0.0 b 100.8 c 
0.0 b 97.6 c 
0.0 b 97.6 c 
0.0 b 93.7 c 
0.0 b 102.4 c 
0.0 b 100.5 c 
0.0 b 93.8 c 
0.0 b 102.2 c 
0.0 b 93.8 c 

BLYP  0.0 b 137.6 c 
0.0 b 
0.0 b 34.4 c 
0.0 b 48.6 c 
0.0 b 47.6 c 
0.0 b 43.3 c 
0.0 b 39.3 c 
0.0 b 48.0 c 
0.0 b 46.7 c 
0.0 b 38.3 c 
0.0 b 49.3 c 
0.0 b 38.3 c 

B1B95  0.0 b 167.6 c 
0.0 b 78.8 c 
0.0 b 78.8 c 
0.0 b 60.3 c 
0.0 b 78.5 c 
0.0 b 75.6 c 
0.0 b 72.5 c 
0.0 b 72.8 c 
0.0 b 69.5 c 
0.0 b 77.6 c 
0.0 b 74.8 c 
0.0 b 72.3 c 
0.0 b 
0.0 b 72.3 c 

B3LYP  0.0 b 156.8 c 
0.0 b 60.7 c 
0.0 b 60.7 c 
0.0 b 44.3 c 
0.0 b 60.7 c 
0.0 b 59.5 c 
0.0 b 55.2 c 
0.0 b 54.4 c 
0.0 b 51.3 c 
0.0 b 59.6 c 
0.0 b 51.6 c 
0.0 b 57.9 c 
0.0 b 50.6 c 
0.0 b 60.6 c 
0.0 b 50.6 c 

B3LYPultrafine  0.0 b 60.6 c 

B3PW91  0.0 b 170.1 c 
0.0 b 80.9 c 
0.0 b 80.9 c 
0.0 b 62.1 c 
0.0 b 79.2 c 
0.0 b 77.8 c 
0.0 b 74.7 c 
0.0 b 74.4 c 
0.0 b 71.0 c 
0.0 b 78.3 c 
0.0 b 76.4 c 
0.0 b 71.4 c 
0.0 b 80.1 c 
0.0 b 71.4 c 

mPW1PW91  0.0 b 176.8 c 
0.0 b 85.5 c 
0.0 b 85.8 c 
0.0 b 66.9 c 
0.0 b 84.0 c 
0.0 b 82.5 c 
0.0 b 79.4 c 
0.0 b 79.3 c 
0.0 b 75.7 c 
0.0 b 83.1 c 
0.0 b 80.8 c 
0.0 b 76.3 c 
0.0 b 84.9 c 
0.0 b 76.3 c 

PBEPBE  0.0 b 159.4 c 
0.0 b 80.4 c 
0.0 b 80.4 c 
0.0 b 60.9 c 
0.0 b 76.1 c 
0.0 b 74.8 c 
0.0 b 71.4 c 
0.0 b 71.5 c 
0.0 b 68.0 c 
0.0 b 75.9 c 
0.0 b 69.2 c 
0.0 b 73.7 c 
0.0 b 68.3 c 
0.0 b 76.8 c 
0.0 b 68.3 c 

PBEPBEultrafine  0.0 b 76.1 c 

Moller Plesset perturbation  MP2  0.0 b 143.8 c 
0.0 b 55.9 c 
0.0 b 55.9 c 
0.0 b 41.8 c 
0.0 b 73.8 c 
0.0 b 75.1 c 
0.0 b 74.5 c 
0.0 b 80.1 c 
0.0 b 73.0 c 

MP2=FULL  0.0 b 74.7 c 
0.0 b 76.3 c 
0.0 b 75.7 c 

MP3  0.0 b 71.6 c 
CEP31G  CEP31G*  CEP121G  CEP121G*  LANL2DZ  SDD  

hartree fock  HF  0.0 b 46.8 c 
0.0 b 72.2 c 
0.0 b 45.7 c 
0.0 b 62.6 c 
0.0 b 41.9 c 
0.0 b 42.6 c 
density functional  B1B95  0.0 b 75.9 c 
0.0 b 94.4 c 

B3LYP  0.0 b 54.8 c 
0.0 b 71.8 c 
0.0 b 49.5 c 
0.0 b 61.5 c 
0.0 b 51.4 c 
0.0 b 51.2 c 

Moller Plesset perturbation  MP2  0.0 b 48.8 c 
0.0 b 85.3 c 
0.0 b 43.8 c 
0.0 b 75.6 c 
0.0 b 41.9 c 
0.0 b 42.3 c 
ccpVDZ  ccpVTZ  augccpVDZ  ccpV(T+d)Z  

Moller Plesset perturbation  MP2FC// HF/631G*  0.0 b 190.7 c 
0.0 b 168.9 c 
0.0 b 168.9 c 

MP2FC// B3LYP/631G*  0.0 b 73.1 c 

MP2FC// MP2FC/631G*  0.0 b 75.2 c 
See section III.C.1 List or set vibrational scaling factors
to change the scale factors used here.
See section III.C.2
Calculate a vibrational scaling factor for a given set of molecules
to determine the least squares best scaling factor.