Unexpected multiplet patterns induced by the Haupt-effect.

An NMR polarization up to a factor of 100 compared to the room temperature signal of a fully equilibrated sample and up/down multiplets are observed when 4-methyl-pyridine or toluene are taken rapidly from liquid helium temperatures to room temperature by dissolving in acetone-d6. These findings result from the inherent coupling between rotational and nuclear spin states in methyl groups which can act as quantum rotors. The temperature jump causes changes in rotational and spin energy level population due to symmetry rules that is known as the Haupt-effect.