# Enthalpy of Formation of Polycyclic Aromatic Hydrocarbons and Heterocyclic Aromatic Compounds

## TL;DR

This paper calculates the enthalpy of formation for aromatic compounds using various computational methods and compares results with experimental data.

## Contribution

The study introduces benchmark calculations for PAHs and heterocyclic compounds using quasi-isodesmic reactions and cost-effective methodologies.

## Key findings

- DSDPBEP86-optimized isodesmic reactions show strong agreement with experimental data for most compounds.
- B2PLYP-D3/cc-pVTZ and B3LYP-D3/cc-pVTZ methods are effective for heterocyclic aromatic compounds.
- CBH methods with B2PLYP-D3/cc-pVTZ yield accurate enthalpies for alkyl-substituted thiophene derivatives.

## Abstract

The standard enthalpy of formation is an important indicator
of
the heat involved in a chemical reaction. In this work, benchmark
calculations with quasi-isodesmic type reactions have been performed
on 8 different polycyclic aromatic hydrocarbons (PAHs) with 9 different
methodologies. All geometry optimizations were carried out at the
B2PLYP-D3, B3LYP-D3, CAM-B3LYP-D3, LC-WPBE-D3, M05-2X-D3, M06-2X-D3,
WB97XD, DSDPBEP86, and PBE0DH levels in conjunction with the cc-pVTZ
basis set. The DSDPBEP86-optimized isodesmic reactions yield remarkably
good agreement with the experimental data for most of the compounds.
For the heterocyclic aromatic compounds, quasi-isodesmic reactions
are carried out successfully using the cost-effective B2PLYP-D3/cc-pVTZ
and B3LYP-D3/cc-pVTZ methodologies. In the case of alkyl-substituted
thiophene derivatives, quasi-isodesmic reactions and the connectivity-based
hierarchy (CBH) methods have yielded enthalpies of formation close
to those from experiments with B2PLYP-D3/cc-pVTZ.