Steric hindrance and the conformation of molecules

Summary

• 1. The crystal structure of 2,6-dichloro-4-nitrodimethylaniline was determined; the interatomic distances and valence angles were found with accuracies of ±0.01 A and ±2°, respectively.

• 2. Steric hindrance at CH₃... Cl leads to rotation of the dimethylamino group by 60.5° relative to the benzene nucleus and deformation of the C-C-Cl valence angles by 4°.

• 3. The loss in coplanarity disrupts conjugation in the molecule, which is reflected in the lengths of the carbon-nitrogen bonds: C-NO₂=1,43 Å; C-N(CH₃)₂=1,41 Å; N-CH₃=1,46 Å.

• 4. The actual conformation of the molecule is established as a result of a compromise between the tendencies to coplanarity, retention of normal valence angles, and minimum steric hindrance.

• 5. The structure is characterized by a high coordination number and density. Most intermolecular contacts occur at normal distances.