Explain why the hydrogen migration shown in reaction (1) occurs readily and why the very similar migration shown in (2) does not take place even under forcing conditions. (The asterisked carbons indicate a carbon isotope present so that the rearrangement can be detected.)

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(1) (2) *CH₂ CH₂ H CH-CH₂ // *CH₂ H 195 °C 250 °C 4300 psi *CH₂ CH₂ T H CH=CH₂ T *CH₂-H