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

Hybridization

Organic Chemistry

1. A Review of General Chemistry

Hybridization

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3:21 minutes

Problem 57b

Textbook Question

What orbitals contain the electrons represented as lone pairs in the structures of purine, and pyrimidine?

Verified step by step guidance

Understand the structures of purine and pyrimidine: Purine is a bicyclic aromatic compound with a six-membered pyrimidine ring fused to a five-membered imidazole ring. Pyrimidine is a six-membered aromatic ring containing two nitrogen atoms at positions 1 and 3.

Identify the lone pairs on the nitrogen atoms in purine and pyrimidine: Lone pairs are non-bonding electron pairs located on the nitrogen atoms in these structures. Each nitrogen atom in the aromatic rings contributes one lone pair.

Determine the hybridization of the nitrogen atoms: In aromatic systems like purine and pyrimidine, the nitrogen atoms are sp² hybridized. This hybridization allows the nitrogen atoms to participate in the conjugated π-system of the aromatic ring.

Assign the orbitals for the lone pairs: In sp² hybridized nitrogen atoms, one of the sp² orbitals contains the lone pair of electrons. The other two sp² orbitals are used for sigma bonding, and the unhybridized p orbital is part of the π-system.

Conclude the orbital location of the lone pairs: The lone pairs on the nitrogen atoms in purine and pyrimidine are located in sp² hybrid orbitals, which are oriented in the plane of the aromatic ring and do not participate in the π-system.

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Key Concepts

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

Lone Pairs

Lone pairs are pairs of valence electrons that are not involved in bonding and are localized on a single atom. In organic molecules, they play a crucial role in determining the molecule's geometry and reactivity. Understanding where these lone pairs are located helps in predicting molecular interactions and the overall shape of the molecule.

Hybridization

Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals that can accommodate bonding and lone pairs. In purines and pyrimidines, the hybridization of carbon and nitrogen atoms influences the arrangement of electrons and the geometry of the molecule. Recognizing the hybridization state is essential for understanding the spatial distribution of lone pairs.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule, which is influenced by the presence of lone pairs and bonding pairs of electrons. The VSEPR (Valence Shell Electron Pair Repulsion) theory helps predict the shape of molecules based on electron pair repulsion. This understanding is vital for analyzing the structures of purine and pyrimidine, as it affects their biological function.

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