Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

1. A Review of General Chemistry

Molecular Geometry

Organic Chemistry

1. A Review of General Chemistry

Molecular Geometry

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3:38 minutes

Problem 53

Textbook Question

In most amines, the nitrogen atom is sp³ hybridized, with a pyramidal structure and bond angles close to 109°. In urea, both nitrogen atoms are found to be planar, with bond angles close to 120°. Explain this surprising finding. (Hint: Consider resonance forms and the overlap needed in them.)

Verified step by step guidance

Identify the structure of urea: Urea has the formula (NH2)2CO, with two nitrogen atoms bonded to a central carbonyl carbon.

Recognize the typical hybridization of nitrogen in amines: In most amines, nitrogen is sp3 hybridized, leading to a pyramidal shape with bond angles around 109°.

Consider the resonance in urea: Urea can exhibit resonance, where the lone pair on the nitrogen can delocalize and form a double bond with the carbon, while the double bond between carbon and oxygen can shift to give oxygen a negative charge.

Analyze the effect of resonance on hybridization: The resonance form where nitrogen forms a double bond with carbon requires the nitrogen to be sp2 hybridized, which results in a planar structure with bond angles close to 120°.

Conclude the reason for planarity: The ability of nitrogen's lone pair to participate in resonance with the carbonyl group stabilizes the planar structure, making the sp2 hybridization more favorable in urea compared to the typical sp3 hybridization in amines.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Hybridization

Hybridization is the concept that describes the mixing of atomic orbitals to form new hybrid orbitals, which can explain the geometry of molecular structures. In most amines, nitrogen is sp³ hybridized, resulting in a tetrahedral arrangement with bond angles around 109°. However, in urea, the nitrogen atoms are involved in resonance, leading to a different hybridization state.

Resonance

Resonance is a phenomenon in which a molecule can be represented by two or more valid Lewis structures, known as resonance forms. In urea, the resonance between the nitrogen and carbonyl oxygen allows for delocalization of electrons, which stabilizes the molecule and results in a planar structure with bond angles close to 120°, deviating from the typical sp³ hybridization of amines.

Planarity and Bond Angles

Planarity in molecular structures refers to the arrangement of atoms in a single plane, which affects the bond angles between them. In urea, the presence of resonance and the sp² hybridization of the nitrogen atoms lead to a planar configuration, resulting in bond angles of approximately 120°. This contrasts with the pyramidal shape of typical amines, where bond angles are closer to 109°.