Chemistry · Ch 13 — Organic Nitrogen Compounds
Structure of Amines
Structure of Amines
Like ammonia, the nitrogen of an amine is trivalent, carries one lone pair of electrons, and is sp3-hybridised: three of the four sp3 orbitals overlap with hydrogen or alkyl-group orbitals, while the fourth holds the lone pair. This gives amines a PYRAMIDAL geometry. Because the lone pair occupies more space than a bonding pair, the C-N-H (or C-N-C) bond angle is compressed below the ideal tetrahedral angle of 109.5 degrees. Measured examples: ammonia's H-N-H angle is 107 degrees, while trimethylamine's C-N-C angle is 108 degrees -- larger than ammonia's H-N-H angle (though still below 109.5 degrees) because the three bulky methyl groups repel each other more than three hydroge …
What this figure shows. Two pyramidal nitrogen structures side by side for comparison: ammonia (N bonded to three H, N-H bond length 101 pm, H-N-H angle 107 degrees, lone pair shown as the fourth sp3 position) and trimethylamine (N bonded to three CH3 groups, C-N-C angle 108 degrees, lone pair similarly on the fourth sp3 orbital) -- both labelled sp3-sp3 hybrid overlap. …