The isomerization reaction of 2,4,4-trimethyl-1-pentene to 2,4,4-trimethyl-2-pentene was studied. In contrast to the general rule for alkene stability, an: excess of the or-alkene (2,(4,4-trimethyl-1-pentene) was observed in the thermodynamic equilibrium. The result is explained in terms of the molecular structure: the large and bulky substituents in 2,4,4-trimethyl-2-pentene cause steric tension and make the molecule less stable. A reaction enthalpy of 3.5 +/- 0.03 kJ mol(-1) i.e., endothermic reaction, and a reaction entropy of -0.47 +/- 0.10; J mol(-1) K-1 were determined from the experimental data of the isomerization reaction.