The last globally stable extended alkane.

Area of Science:

• Physical Chemistry
• Molecular Spectroscopy
• Computational Chemistry

Background:

• Linear alkanes (C(n)H(2n+2)) are fundamental molecules with simple structures.
• Understanding their conformational preferences is key to molecular self-assembly and material properties.
• At low temperatures, intermolecular forces can influence molecular conformations.

Purpose of the Study:

• To investigate the conformational behavior of isolated linear alkanes at low temperatures.
• To determine the critical chain length at which alkanes transition to a folded structure.
• To elucidate the role of cohesive forces in inducing molecular folding.

Main Methods:

• Raman spectroscopy was employed to study alkane conformations at 100-150 K.
• High-level quantum-chemical calculations were performed to model molecular structures and energies.
• Analysis focused on the transition from extended all-trans to folded hairpin conformations.

Main Results:

• Isolated linear alkanes prefer an extended all-trans conformation in the absence of strong cohesive forces.
• A folded hairpin structure becomes more stable for alkanes with a critical chain length (n(C)) of 17 or 18 carbon atoms.
• Quantum-chemical calculations corroborate this critical chain length, yielding n(C) = 17 ± 1.

Conclusions:

• Cohesive forces between chain ends are responsible for inducing a folded hairpin structure in longer alkanes.
• The transition to a folded state is a critical phenomenon occurring around n(C) = 17.
• This study provides fundamental insights into the self-assembly behavior of long-chain molecules.