Long but Strong C-C Single Bonds: Challenges for Theory

Area of Science:

• Organic Chemistry
• Computational Chemistry
• Physical Chemistry

Background:

• Molecules with anomalously long single carbon-carbon (C-C) bonds present theoretical challenges in chemical bonding descriptions.
• Traditional theories often attribute instability in crowded molecules to steric hindrance.

Purpose of the Study:

• To analyze the theoretical challenges in describing molecules with unusually long C-C bonds.
• To investigate the role of intramolecular interactions in stabilizing such molecules.
• To reconsider the concept of steric effects in highly crowded molecular systems.

Main Methods:

• Analysis of theoretical models describing molecular interactions.
• Examination of stabilizing and destabilizing intramolecular forces, including London dispersion forces.
• Case studies of diamondoid dimers and tert-butyl-substituted hexaphenylethanes.

Main Results:

• Diamondoid dimers exhibit stability with C-C bonds up to 1.7 Å, stabilized by intramolecular noncovalent interactions.
• Bulky molecules can be stabilized by significant London dispersion forces.
• The stability of highly crowded molecules challenges the conventional understanding of steric effects.

Conclusions:

• The unexpected stability of sterically overloaded molecules suggests that "steric attraction" may be a more appropriate concept than "steric hindrance."
• Accurate theoretical descriptions of noncovalent interactions are crucial for understanding bonding in crowded molecules.
• Revisiting steric effects is necessary for advancing the field of molecular structure and stability.