Can Ring Strain Be Realized in Momentum Space?

An increased electron momentum density (EMD) at low momentum is proposed to be an indicator of ring strain, with the nature of the function tending toward a maximum. A p-space Hirshfeld atomic partitioning scheme is applied for analyzing the effect of strain on molecular EMDs. The Hirshfeld momentum densities for a strained system show an increase in the population for the carbons with the hydrogens becoming more positive in comparison with an unstrained reference molecule. The manifestation of strain in cage-like hydrocarbons such as tetrahedrane, cubane, prismane, etc. as well as their nitrogen-substituted analogues is clearly seen in terms of EMDs.