Intermolecular Interactions of Linear Alkane (N ≤ 18) Dimers: A High Accuracy Theoretical Study

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Molecular Interactions

Background:

• Understanding noncovalent interactions is crucial for molecular design and predicting chemical behavior.
• n-alkanes represent fundamental building blocks in organic chemistry, and their intermolecular forces influence macroscopic properties.

Purpose of the Study:

• To systematically investigate and accurately quantify the intermolecular interactions within n-alkane dimers.
• To establish a high-accuracy benchmark for van der Waals interactions in n-alkanes.
• To develop a predictive model for interaction energy based on alkane chain length.

Main Methods:

• High-accuracy coupled-cluster calculations, specifically DLPNO-CCSD-(T1)/CBS-(aug2/3)//M05-2X-D3/6-31G**, were employed.
• Basis set superposition error (BSSE) corrections were applied to ensure accurate interaction energies.
• Thermodynamic analysis was performed to determine conditions for spontaneous dimerization.

Main Results:

• Interaction energies in n-alkane dimers range from -2.2 kJ/mol (n=1) to -62.6 kJ/mol (n=18).
• A linear relationship was established: ΔE(n) = -3.6n + 2.2 kJ/mol, offering improved accuracy over previous methods.
• Spontaneous dimerization was predicted to begin for n-alkanes with n ≥ 8 at 100 K.

Conclusions:

• The study provides a highly accurate description of intermolecular interactions in n-alkane dimers.
• The findings enhance the understanding of van der Waals forces and their dependence on molecular size.
• This research offers valuable data for molecular design and computational chemistry benchmarks.