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IV.A.4. (XIV.F.)

Relative enthalpies of isomers - Comparison of 298.15K enthalpies (kJ mol-1)

Isomers of C3H4N2

index Species CAS number Name Relative experimental enthalpy (kJ mol-1) sketch
a C3H4N2 9000162 4H-Imidazole   sketch of 4H-Imidazole
b C3H4N2 9000173 2H-Imidazole   sketch of 2H-Imidazole
c C3H4N2 288324 1H-Imidazole 0.0 sketch of 1H-Imidazole
d C3H4N2 288131 1H-Pyrazole 46.5 sketch of 1H-Pyrazole
The calculated enthalpies include the calculated and scaled vibrational zero-point energy.
Methods with predefined basis sets
semi-empirical AM1 49.4 a
0.0 c
61.6 d
PM3 -124.5 a
0.0 c
73.7 d
PM6 77.5 a
0.0 c
37.7 d
MNDOd
0.0 c
50.8 d
composite G1 NC
G2MP2 NC
G2 NC
G3 -342.3 a
0.0 c
47.2 d
G3B3 -123.1 a
0.0 c
46.8 d
G3MP2 -342.7 a
0.0 c
46.6 d
G4 -121.8 a
0.0 c
46.2 d
CBS-Q -132.8 a
0.0 c
46.5 d
molecular mechanics MM3
0.0 c
39.4 d

Methods with standard basis sets
STO-3G 3-21G 3-21G* 6-31G 6-31G* 6-31G** 6-31+G** 6-311G* 6-311G** 6-31G(2df,p) 6-311+G(3df,2p) cc-pVDZ cc-pVTZ aug-cc-pVDZ aug-cc-pVTZ cc-pV(T+d)Z
hartree fock HF
0.0 c
28.2 d

0.0 c
61.3 d

0.0 c
61.3 d

0.0 c
50.7 d
 
0.0 c
55.3 d
 
0.0 c
54.7 d

0.0 c
55.3 d

0.0 c
55.6 d

0.0 c
57.7 d

0.0 c
54.2 d

0.0 c
55.7 d

0.0 c
55.2 d

0.0 c
56.3 d

0.0 c
55.7 d
density functional LSDA
0.0 c
18.1 d

0.0 c
47.2 d

0.0 c
47.2 d

0.0 c
38.4 d

0.0 c
39.4 d

0.0 c
39.6 d

0.0 c
40.1 d

0.0 c
41.1 d

0.0 c
41.6 d

0.0 c
39.8 d
 
0.0 c
39.4 d

0.0 c
40.9 d

0.0 c
40.3 d
 
0.0 c
40.9 d
BLYP
0.0 c
14.6 d

0.0 c
42.2 d

0.0 c
42.2 d

0.0 c
35.4 d

0.0 c
38.7 d

0.0 c
38.9 d

0.0 c
39.8 d

0.0 c
40.0 d

0.0 c
40.4 d

0.0 c
39.8 d
 
0.0 c
38.4 d
 
0.0 c
39.6 d
   
B1B95
0.0 c
19.3 d

0.0 c
48.3 d

0.0 c
48.3 d

0.0 c
39.7 d

0.0 c
43.0 d

0.0 c
42.7 d

0.0 c
43.3 d

0.0 c
43.8 d

0.0 c
44.3 d

0.0 c
43.2 d
 
0.0 c
42.2 d

0.0 c
44.3 d

0.0 c
43.4 d
 
0.0 c
44.3 d
B3LYP
0.0 c
18.5 d

0.0 c
47.0 d

0.0 c
47.0 d

0.0 c
39.1 d

0.0 c
42.2 d

0.0 c
42.5 d

  d

0.0 c
43.3 d

0.0 c
43.8 d

0.0 c
43.1 d

0.0 c
45.5 d

0.0 c
41.7 d

0.0 c
44.0 d

0.0 c
42.9 d
 
0.0 c
44.0 d
B3LYPultrafine        
0.0 c
42.2 d
                     
B3PW91
0.0 c
17.9 d

0.0 c
46.9 d

0.0 c
46.9 d

0.0 c
38.5 d

0.0 c
41.1 d

0.0 c
41.4 d

0.0 c
42.0 d

0.0 c
42.3 d

0.0 c
42.9 d

0.0 c
41.8 d
 
0.0 c
40.8 d

0.0 c
42.5 d

0.0 c
41.6 d
 
0.0 c
42.5 d
mPW1PW91
0.0 c
18.6 d

0.0 c
48.0 d

0.0 c
48.0 d

0.0 c
39.2 d

0.0 c
41.8 d

0.0 c
42.0 d

0.0 c
42.6 d

0.0 c
42.9 d

0.0 c
43.5 d

0.0 c
42.5 d
 
0.0 c
41.5 d

0.0 c
43.1 d

0.0 c
42.2 d
 
0.0 c
43.1 d
PBEPBE
0.0 c
14.5 d

0.0 c
42.8 d

0.0 c
42.8 d

0.0 c
35.1 d

0.0 c
37.3 d

0.0 c
37.5 d

0.0 c
38.2 d

0.0 c
38.8 d

0.0 c
39.2 d

0.0 c
38.1 d

0.0 c
40.5 d

0.0 c
37.2 d

0.0 c
39.0 d

0.0 c
37.8 d
 
0.0 c
39.0 d
Moller Plesset perturbation MP2
0.0 c
19.0 d

0.0 c
43.1 d

0.0 c
43.1 d

0.0 c
35.8 d
 
0.0 c
41.6 d
 
0.0 c
41.2 d

0.0 c
42.2 d

0.0 c
42.0 d
 
0.0 c
40.8 d

0.0 c
42.4 d
   
0.0 c
42.4 d
MP2=FULL        
0.0 c
41.7 d

0.0 c
42.0 d

0.0 c
42.8 d

0.0 c
41.3 d

0.0 c
42.4 d
             
MP3        
0.0 c
45.4 d
                     
Configuration interaction CID        
0.0 c
49.1 d
                     
CISD        
0.0 c
49.2 d
                     
Quadratic configuration interaction QCISD  
0.0 c
47.5 d
     
0.0 c
46.3 d

0.0 c
47.3 d
 
0.0 c
46.4 d
             
Coupled Cluster CCD        
0.0 c
45.8 d
                     

Methods with effective core potentials (select basis sets)
CEP-31G CEP-31G* CEP-121G CEP-121G* LANL2DZ SDD
hartree fock HF
0.0 c
48.3 d

0.0 c
58.5 d

0.0 c
47.0 d

0.0 c
55.5 d

0.0 c
46.0 d

0.0 c
46.0 d
density functional B1B95
0.0 c
42.0 d

0.0 c
49.6 d
       
B3LYP
0.0 c
39.7 d

0.0 c
47.8 d

0.0 c
37.2 d

0.0 c
44.0 d

0.0 c
37.9 d

0.0 c
38.0 d
Moller Plesset perturbation MP2
0.0 c
33.8 d

0.0 c
45.2 d

0.0 c
33.1 d

0.0 c
42.0 d

0.0 c
33.5 d

0.0 c
33.4 d

Single point energy calculations (select basis sets)
6-311+G(3df,2p) cc-pVDZ cc-pVTZ aug-cc-pVDZ cc-pV(T+d)Z
Moller Plesset perturbation MP2FC// HF/6-31G*  
0.0 c
41.8 d

0.0 c
43.9 d
 
0.0 c
43.9 d
MP2FC// B3LYP/6-31G*  
0.0 c
41.0 d
     
MP2FC// MP2FC/6-31G*
0.0 c
44.7 d
   
0.0 c
42.2 d
 
MP4// HF/6-31G*  
0.0 c
45.3 d
     
MP4// MP2/6-31G*
0.0 c
50.4 d
       
Coupled Cluster CCSD// HF/6-31G*  
0.0 c
45.4 d

0.0 c
48.2 d
 
0.0 c
48.2 d
CCSD(T)// HF/6-31G*  
0.0 c
43.8 d

0.0 c
46.2 d
 
0.0 c
46.2 d
CCSD(T)//B3LYP/6-31G(2df,p)    
0.0 c
45.3 d
 
0.0 c
45.3 d
CCSD// MP2FC/6-31G*
0.0 c
50.3 d
       
CCSD(T)// MP2FC/6-31G*
0.0 c
47.8 d
       
NC = not calculated
For descriptions of the methods (AM1, HF, MP2, ...) and basis sets (3-21G, 3-21G*, 6-31G, ...) 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.