Domain Based Pair Natural Orbital Coupled Cluster Studies on Linear and Folded Alkane Chains

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Molecular Modeling

Background:

• Understanding alkane conformations is crucial for various chemical applications.
• Previous theoretical studies have yielded varying predictions for the longest linear alkane conformer.

Purpose of the Study:

• To theoretically determine the last unbranched alkane that prefers a linear over a folded conformation.
• To refine energetic predictions using high-level computational methods.

Main Methods:

• Geometry optimization using doubly hybrid density functional theory with quadruple-ζ basis sets.
• Accurate electronic energy calculations with domain local pair natural orbital coupled cluster method with single-, double-, and triple substitutions (DLPNO-CCSD(T)).
• Thermodynamic corrections using PW6B95-D3 functional and def2-QZVP basis set.

Main Results:

• Geometries and energetics differ significantly from previous theoretical results.
• Calculations up to C19H40 were performed with high accuracy, approaching the canonical coupled cluster basis set limit.
• The last linear conformer is predicted to be C16H34 or, more likely, C17H36.

Conclusions:

• C18H38 is unlikely to be the most stable linear isomer at 100 K.
• The findings align with recent experimental observations.
• This study provides a more accurate theoretical benchmark for alkane conformational preferences.