The theory of torsion vibration-rotation interaction as applied to high barrier to internal rotation ethanelike molecules is discussed. It is shown that the effects of internal rotation can be described by one parameter X which introduces an oscillatory behavior in subband origins. Also, the effects of xy Coriolis interaction between A and E vibrational states on the energy levels and effective band constants of the E state are discussed. The band ν11 + ν4 of ethane has been measured with high resolution and analyzed. The barrier to internal rotation in ν11 has been found to be 3330 ± 23 cal/mole.