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

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

Isomers of C8H18

index Species CAS number Name Relative experimental enthalpy (kJ mol-1) sketch
a (CH3)3CC(CH3)3 594821 tetramethylbutane 0.0 sketch of tetramethylbutane
b C8H18 111659 Octane 17.8 sketch of Octane
The calculated enthalpies include the calculated and scaled vibrational zero-point energy.
Methods with predefined basis sets
semi-empirical AM1
373.7 b
PM3
395.5 b
PM6 0.0 a
-563.8 b
composite G1
NC
G2MP2
NC
G2
NC
G3
NC
G3B3 0.0 a
669.2 b
G3MP2
NC
G4 0.0 a
25.4 b
CBS-Q
NC

Methods with standard basis sets
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.