# Selective Deuteration of Neopentyl Glycol and Its Effect on the Plastic Crystal Transformation

## TL;DR

This paper explores how deuteration affects the phase transition in neopentyl glycol, revealing how molecular structure influences thermodynamic properties for potential cooling applications.

## Contribution

The study introduces selective deuteration as a method to modulate phase transition temperatures in plastic crystals.

## Key findings

- Selective deuteration of neopentyl glycol decreases the phase transition temperature by up to ~3 K.
- Deuterated methyl groups alter rotational moments of inertia, impacting thermodynamic properties.
- The results provide bounds on how molecular shape affects phase transitions in solid-state refrigerants.

## Abstract

Transitions between rotationally ordered and disordered
states
in globular small molecules are associated with large entropy changes
and thus hold promise as solid-state barocaloric refrigerants. However,
the relationships between elements of the molecular structure and
the corresponding thermodynamic properties of the phase transformation
between ordered and disordered states remain unresolved. We hypothesize
that more spherical molecules, as measured by their rotational moments
of inertia, exhibit larger relative increases in their rotational
degrees of freedom as they transition to rotationally disordered states.
We probe this by isolating the impact of rotational moments of inertia
from more dominant factors, including intermolecular bonding, through
the selective deuteration of different functional groups of the model
plastic crystal molecule neopentyl glycol. We demonstrate a decrease
in the phase transition temperature of up to approximately 3 K associated
with the existence of deuterated methyl groups and explain this change
in terms of relative changes in the rotational moments of inertia
of the compounds. This observation places bounds on the role of rotational
moments of inertia in thermodynamic aspects of the phase transformation
and introduces a vector for subtle modulation of the transition point
for cooling applications.