A nitrogen atom can undergo sp2 hybridization when it becomes part of a carbon-nitrogen double bond, as in H2C=NH (a) Using a sketch , show the electron configuration of sp2 hybridized nitrogen just before the overlapping occurs to make this double bond (b) Using sketches (and the analogy to the double bond in C2H4), describe the two bonds of the carbon-nitrogen double bond (c) Describe the geometry of H2C=NH (using a sketch that shows all expected bond angle)
The Correct Answer and Explanation is:
Hybridization and Bonding in H₂C=NH (Iminomethane or Methanimine)
(a) Electron Configuration of sp² Hybridized Nitrogen Before Overlap
The ground-state electron configuration of nitrogen (atomic number 7) is:
1s² 2s² 2p³
In sp² hybridization, one 2s orbital mixes with two 2p orbitals, leaving one unhybridized 2p orbital:
- sp² hybrid orbitals: 3 orbitals (used for σ bonding and lone pair)
- Unhybridized 2p orbital: 1 orbital (used for π bonding)
Sketch (conceptual, text description):
yamlCopyEditBefore hybridization: After sp² hybridization:
2s ↑↓ sp² ↑ ↑ ↑ (3 hybrid orbitals)
2p ↑ ↑ ↑ 2p ↑ (1 unhybridized p orbital)
- One sp² hybrid orbital contains the lone pair.
- Two sp² orbitals form σ bonds (one with C, one with H).
- The unhybridized 2p orbital participates in π bonding with carbon.
(b) Description of the Two Bonds in the C=N Double Bond
The carbon in H₂C=NH is also sp² hybridized:
- σ bond: Formed by overlap of carbon’s sp² hybrid orbital with nitrogen’s sp² hybrid orbital.
- π bond: Formed by sideways overlap of unhybridized 2p orbitals from both carbon and nitrogen.
Analogy to C₂H₄ (Ethene):
Just as in ethene, where each carbon forms a σ bond with one another using sp² orbitals and a π bond with p orbitals, here nitrogen and carbon behave similarly.
Sketch (conceptual):
mathematicaCopyEdit π overlap (p orbital on N and C)
↑ ↑
C (sp²) — σ — N (sp²)
|
H H
(c) Geometry of H₂C=NH
Because both carbon and nitrogen are sp² hybridized, the geometry around both atoms is approximately trigonal planar.
- Bond angles: ~120°
- The lone pair on nitrogen slightly compresses the H–N–C angle to slightly less than 120°.
Sketch (conceptual):
mathematicaCopyEdit H
\
C = N — H
/
H
Bond angles ~120°
Summary Explanation (300 words)
In H₂C=NH, the carbon atom forms a double bond with nitrogen, requiring both atoms to adopt sp² hybridization to maximize orbital overlap and minimize electron repulsion. Nitrogen’s electron configuration of 1s² 2s² 2p³ is modified during hybridization: one 2s orbital and two 2p orbitals combine to form three sp² hybrid orbitals, while one 2p orbital remains unhybridized. One sp² hybrid orbital holds the nitrogen’s lone pair, while the remaining two form sigma (σ) bonds: one with carbon and one with hydrogen.
Simultaneously, carbon, which also undergoes sp² hybridization, uses one sp² orbital to form a σ bond with nitrogen. The unhybridized p orbitals on both carbon and nitrogen lie parallel and overlap sideways, forming a pi (π) bond. This π bond constitutes the second bond in the C=N double bond, analogous to the bonding in ethene (C₂H₄).
The molecular geometry around both carbon and nitrogen is approximately trigonal planar due to sp² hybridization, with ideal bond angles of 120°. However, the lone pair on nitrogen exerts greater repulsion, slightly decreasing the H–N–C bond angle. The planar structure allows maximum p orbital overlap, stabilizing the π bond. This hybridization and bonding arrangement account for both the structure and reactivity of imines like H₂C=NH.
