Non-Planar Structures of Sterically Overcrowded Trialkylamines

Area of Science:

• Organic Chemistry
• Structural Chemistry
• Computational Chemistry

Background:

• Trialkylamines are fundamental organic compounds with diverse applications.
• Steric hindrance around the nitrogen atom significantly influences amine properties and reactivity.
• Understanding the structural consequences of extreme steric crowding is crucial for designing new molecules.

Purpose of the Study:

• To synthesize and characterize novel sterically hindered amines exceeding the crowding of triisopropylamine.
• To elucidate the molecular structures and conformations of these highly crowded amines using X-ray diffraction and computational methods.
• To investigate the relationship between steric crowding, molecular geometry, and electronic interactions in these unique amine structures.

Main Methods:

• Synthesis of sterically hindered amines via reactions of N-chlorodialkylamines with Grignard reagents.
• X-ray diffraction studies on single crystals of six synthesized amines to determine precise molecular structures.
• Quantum chemical calculations to determine gas-phase structures and preferred molecular conformers.

Main Results:

• Four noncyclic amines adopted flatter, triskele-like conformations with C-N-C angles summing to ~351-352°, resulting in shorter NC3 pyramids (0.241-0.259 Å).
• Heterocyclic amines displayed different conformations due to reduced steric stress.
• Computational results closely matched experimental X-ray diffraction data for gas-phase structures and conformers.

Conclusions:

• Sterically overcrowded amines exhibit significantly flattened structures compared to less hindered counterparts.
• Molecular conformations are influenced by a balance of steric repulsion and dispersion interactions.
• Experimental and computational methods provide consistent insights into the structural characteristics of highly hindered amines.