Knowledge Bank

Raman spectra have been obtained for 2-methyl butane and 2,3-dimethyl-butane in the vapor, liquid and solid $(-196\circ C$) phases. The low temperature spectra of the solids undergo a marked simplification due to the disappearance of all but one of the rotational isomers. In the case of amorphous solid, 2,3-dimethyl-butane at liquid nitrogen temperature, all the bands observed in the liquid or vapor phases are present, but, after annealing several times, many strong bands disappear due to the stabilization of only one rotational isomer. The enthalpy difference between the rotational isomers has been measured for each compound in the vapor phase. The unanswered problem concerning these energy differences has now been resolved.