IV.A.4. (XIV.F.) 
Relative enthalpies of isomers  Comparison of 298.15K enthalpies (kJ mol^{1})
Isomers of C_{4}H_{7}NO
index  Species  CAS number  Name  Relative experimental enthalpy (kJ mol^{1})  sketch 

a  C_{4}H_{7}NO  616455  2Pyrrolidinone  0.0  
b  C_{4}H_{7}NO  79390  Methacrylamide  39.7  
c  C_{4}H_{7}NO  1120645  Oxazole, 4,5dihydro2methyl  66.9  
d  C_{4}H_{7}NO  62957602  Ethoxyacetonitrile  127.9 
semiempirical  AM1  0.0 a 52.6 b 90.2 c 363.1 d 

PM3  209.4 d 

PM6  0.0 a 44.0 b 72.5 c 140.6 d 

MNDOd  0.0 a 83.7 b 50.6 c 

composite  G1  0.0 a 27.7 b 65.1 c 119.5 d 
G2MP2  0.0 a 29.0 b 68.2 c 122.9 d 

G2  0.0 a 28.9 b 68.9 c 123.0 d 

G3  0.0 a 61.5 b 19.4 c 33.2 d 

G3B3  0.0 a 27.1 b 68.6 c 

G3MP2  0.0 a 25.2 b 68.9 c 

G4  0.0 a 26.8 b 67.8 c 120.0 d 

CBSQ  0.0 a 122.8 d 

molecular mechanics  DREIDING  c 
MM3  0.0 a 131.0 b 91.5 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 a 184.5 b 0.9 c 
0.0 a 50.7 b 97.6 c 
0.0 a 50.7 b 97.6 c 
0.0 a 27.4 b 109.6 c 
0.0 a 44.5 b 77.6 c 
0.0 a 46.5 b 76.8 c 
0.0 a 38.1 b 79.7 c 
0.0 a 43.7 b 73.7 c 
0.0 a 36.5 b 75.5 c 
0.0 a 39.9 b 77.9 c 
0.0 a 74.9 c 
0.0 a 40.5 b 78.2 c 
0.0 a 35.4 b 74.7 c 
0.0 a 74.9 c 

density functional  LSDA  0.0 a 179.1 b 13.2 c 
0.0 a 82.8 b 106.1 c 
0.0 a 82.8 b 106.1 c 
0.0 a 61.0 b 110.9 c 
0.0 a 80.6 b 75.3 c 
0.0 a 74.0 b 80.6 c 
0.0 a 69.0 b 86.0 c 
0.0 a 73.6 b 88.5 c 
0.0 a 64.3 b 91.6 c 
0.0 a 74.2 b 79.5 c 
0.0 a 73.5 b 84.8 c 
0.0 a 62.1 b 85.9 c 
0.0 a 68.5 b 88.0 c 
0.0 a 62.1 b 85.9 c 

BLYP  0.0 a 135.4 b 12.8 c 
0.0 a 43.8 b 76.6 c 
0.0 a  0.0 a 18.6 b 83.9 c 
0.0 a 29.8 b 62.6 c 
0.0 a 23.3 b 68.9 c 
0.0 a  0.0 a 20.0 b 71.8 c 
0.0 a 28.9 b 62.2 c 
0.0 a 28.8 b 67.5 c 
0.0 a 16.6 b 68.3 c 
0.0 a 24.0 b 72.4 c 
0.0 a 16.6 b 68.3 c 

B1B95  0.0 a 161.6 b 3.6 c 
0.0 a 66.6 b 95.9 c 
0.0 a 66.7 b 95.9 c 
0.0 a 42.4 b 103.2 c 
0.0 a 62.8 b 69.6 c 
0.0 a 54.4 b 74.2 c 
0.0 a 49.7 b 78.7 c 
0.0 a 55.1 b 77.9 c 
0.0 a 46.8 b 81.1 c 
0.0 a 54.5 b 71.9 c 
0.0 a 53.3 b 76.6 c 
0.0 a 47.4 b 76.9 c 
0.0 a 51.3 b 80.2 c 
0.0 a 47.4 b 76.9 c 

B3LYP  0.0 a 152.5 b 4.6 c 
0.0 a 52.9 b 87.3 c 
0.0 a 52.9 b 87.3 c 
0.0 a 28.5 b 94.9 c 
0.0 a 47.6 b 63.8 c 
0.0 a 41.1 b 69.2 c 
0.0 a 35.2 b 74.7 c 
0.0 a 39.2 b 74.1 c 
0.0 a 31.4 b 77.4 c 
0.0 a 39.7 b 68.1 c 
0.0 a 28.7 b 74.4 c 
0.0 a 39.5 b 73.1 c 
0.0 a 28.3 b 73.4 c 
0.0 a 34.9 b 77.2 c 
0.0 a 28.3 b 73.4 c 

B3LYPultrafine  0.0 a 47.6 b 63.8 c 

B3PW91  0.0 a 163.5 b 3.2 c 
0.0 a 68.1 b 98.6 c 
0.0 a 68.1 b 98.6 c 
0.0 a 43.6 b 104.2 c 
0.0 a 63.1 b 71.2 c 
0.0 a 56.1 b 76.6 c 
0.0 a 51.6 b 80.8 c 
0.0 a 56.2 b 80.3 c 
0.0 a 47.8 b 
0.0 a 55.2 b 74.4 c 
0.0 a 55.0 b 78.8 c 
0.0 a 45.8 b 78.7 c 
0.0 a 51.8 b 81.6 c 
0.0 a 45.8 b 78.7 c 

mPW1PW91  0.0 a 169.5 b 4.9 c 
0.0 a 72.6 b 100.8 c 
0.0 a 73.0 b 101.2 c 
0.0 a 48.2 b 107.0 c 
0.0 a 67.7 b 72.9 c 
0.0 a 60.5 b 78.3 c 
0.0 a 55.9 b 82.7 c 
0.0 a 61.0 b 81.6 c 
0.0 a 52.2 b 84.8 c 
0.0 a 59.6 b 75.8 c 
0.0 a 59.1 b 80.2 c 
0.0 a 45.2 b 74.9 c 
0.0 a 56.1 b 82.9 c 
0.0 a 45.2 b 74.9 c 

PBEPBE  0.0 a 153.5 b 1.2 c 
0.0 a 66.3 b 91.1 c 
0.0 a 66.3 b 91.1 c 
0.0 a 39.8 b 97.3 c 
0.0 a 58.0 b 67.7 c 
0.0 a 51.4 b 73.2 c 
0.0 a 46.0 b 78.8 c 
0.0 a 51.3 b 77.9 c 
0.0 a 42.9 b 81.3 c 
0.0 a 51.0 b 71.2 c 
0.0 a 40.9 b 78.1 c 
0.0 a 50.5 b 76.5 c 
0.0 a 40.9 b 76.9 c 
0.0 a 46.5 b 80.1 c 
0.0 a 40.9 b 76.9 c 

PBEPBEultrafine  0.0 a 58.1 b 67.8 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  
Moller Plesset perturbation  MP2  0.0 a 135.4 b 3.0 c 
0.0 a 41.6 b 83.0 c 
0.0 a 41.6 b 83.0 c 
0.0 a 16.4 b 91.6 c 
0.0 a 50.3 b 75.3 c 
0.0 a 46.2 b 83.4 c 
0.0 a 53.5 b 76.7 c 
0.0 a 47.4 b 81.0 c 
0.0 a  
MP2=FULL  0.0 a  0.0 a  0.0 a  0.0 a 55.9 b 71.5 c 
0.0 a  0.0 a  0.0 a 53.0 b 81.8 c 
0.0 a 47.1 b 84.5 c 
0.0 a  
MP3  0.0 a 52.4 b 64.4 c 

Configuration interaction  CID  0.0 a  0.0 a  
CISD  0.0 a  0.0 a  
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  
Quadratic configuration interaction  QCISD  0.0 a 78.3 c 
0.0 a  0.0 a  0.0 a  
Coupled Cluster  CCD  0.0 a  0.0 a  0.0 a  0.0 a  0.0 a  0.0 a  
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 
CEP31G  CEP31G*  CEP121G  CEP121G*  LANL2DZ  SDD  

hartree fock  HF  0.0 a 42.9 b 102.4 c 
0.0 a 68.2 b 67.9 c 
0.0 a 35.2 b 101.6 c 
0.0 a 52.4 b 69.3 c 
0.0 a 31.9 b 108.0 c 
0.0 a 32.3 b 108.2 c 
density functional  B1B95  0.0 a 61.3 b 102.0 c 
0.0 a 81.0 b 70.3 c 

B3LYP  0.0 a 42.6 b 89.6 c 
0.0 a 60.5 b 62.3 c 
0.0 a 32.9 b 88.4 c 
0.0 a 45.7 b 63.3 c 
0.0 a 32.0 b 94.6 c 
0.0 a 32.0 b 94.6 c 

Moller Plesset perturbation  MP2  0.0 a 27.7 b 88.6 c 
0.0 a 67.1 b 66.6 c 
0.0 a 18.2 b 88.1 c 
0.0 a 51.7 b 67.9 c 
0.0 a 17.3 b 95.4 c 
0.0 a 17.2 b 95.2 c 
MP2=FULL  NC 
NC 
ccpVDZ  ccpVTZ  augccpVDZ  ccpV(T+d)Z  

Moller Plesset perturbation  MP2FC// HF/631G*  0.0 a 32.0 b 133.9 c 
0.0 a 40.5 b 123.9 c 
0.0 a 40.5 b 123.9 c 

MP2FC// B3LYP/631G*  0.0 a 52.8 b 19.8 c 

MP2FC// MP2FC/631G*  0.0 a 41.4 b 81.2 c 
For descriptions of the methods (AM1, HF, MP2, ...) and basis sets (321G, 321G*, 631G, ...) see the glossary in section I.C. Predefined means the basis set used is determined by the method.
gaw refers to the group additivity method implemeted in the NIST Chemistry Webbook.
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.