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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2:36 minutes

Problem 33

Textbook Question

Predict the approximate bond angles in
a. the methyl cation.
b. the methyl radical.
c. the methyl anion.

Verified step by step guidance

Step 1: Understand the hybridization of the central carbon atom in each species. The methyl cation (CH₃⁺) has a positively charged carbon atom with only three bonding pairs and no lone pairs, indicating sp² hybridization. The methyl radical (CH₃•) has three bonding pairs and one unpaired electron, also suggesting sp² hybridization. The methyl anion (CH₃⁻) has three bonding pairs and one lone pair, indicating sp³ hybridization.

Step 2: Recall the bond angles associated with each hybridization. For sp² hybridization, the bond angles are approximately 120°, as the electron pairs are arranged in a trigonal planar geometry. For sp³ hybridization, the bond angles are approximately 109.5°, as the electron pairs are arranged in a tetrahedral geometry.

Step 3: Apply the bond angle predictions to each species. For the methyl cation (CH₃⁺), the sp² hybridization leads to bond angles of approximately 120°. For the methyl radical (CH₃•), the sp² hybridization also leads to bond angles of approximately 120°. For the methyl anion (CH₃⁻), the sp³ hybridization leads to bond angles of approximately 109.5°.

Step 4: Consider any deviations from ideal bond angles due to electronic effects. In the methyl anion (CH₃⁻), the lone pair on the carbon atom may slightly compress the bond angles below the ideal tetrahedral angle of 109.5°.

Step 5: Summarize the bond angle predictions: The methyl cation and methyl radical both have bond angles of approximately 120° due to sp² hybridization, while the methyl anion has bond angles close to 109.5° due to sp³ hybridization, with potential slight compression due to the lone pair.

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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 of mixing atomic orbitals to form new hybrid orbitals that can accommodate bonding. In organic chemistry, it helps predict the geometry and bond angles of molecules. For example, sp3 hybridization leads to tetrahedral geometry with bond angles of approximately 109.5°, while sp2 and sp hybridizations correspond to trigonal planar (120°) and linear (180°) geometries, respectively.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. It is influenced by the number of bonding pairs and lone pairs of electrons around the central atom. Understanding molecular geometry is crucial for predicting bond angles, as different geometries (like tetrahedral, trigonal planar, and linear) dictate specific angles between bonds.

Charge Effects on Geometry

The presence of a charge on a molecule can significantly alter its geometry and bond angles. Cations (positively charged) tend to have smaller bond angles due to increased electron density around the central atom, while anions (negatively charged) can lead to larger bond angles due to repulsion from additional electron pairs. This concept is essential for predicting the bond angles in species like the methyl cation, radical, and anion.

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Textbook Question

Predict the hybridization and geometry of the carbon and nitrogen atoms in the following molecules and ions. (Hint: Resonance.)

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.)

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Predict the hybridization, geometry, and bond angles for the carbon and nitrogen atoms in acetonitrile (CH₃–C≡N:).

Textbook Question

Describe the orbitals used in bonding and the bond angles in the following compounds:

e. BF₃

Textbook Question

Predict the approximate bond angles for the following:

c. the C—C—N bond angle in CH₃C≡N

d. the C—C—N bond angle in CH₃CH₂NH₂

Textbook Question

Circle the coplanar atoms in the following structure:

Textbook Question

For each of the following compounds and ions,

1. Draw a Lewis structure.

2. Show the kinds of orbitals that overlap to form each bond.

3. Give approximate bond angles around each atom except hydrogen.

c. CH₂=N–CH₃

Textbook Question

You drew the Lewis structures of the following compounds and ion in Assessment 2.32. Predict their shapes around the central atom based on the Lewis structure.

(d) CO₃^2-

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Predict the approximate bond angles in a. the methyl cation. b. the methyl radical. c. the methyl anion.

Key Concepts

Hybridization

Molecular Geometry

Charge Effects on Geometry

Watch next

Predict the approximate bond angles in
a. the methyl cation.
b. the methyl radical.
c. the methyl anion.