Chapter 2 STRUCTURE AND PROPERTIES OF ORGANIC MOLECULES

1. Chapter 2STRUCTURE AND PROPERTIES OF ORGANIC MOLECULES Helpful web site: http://cw.prenhall.com/bookbind/pubbooks/wade/ Chapter 2: Structure and Properties of Organic Molecules

2. LINEAR COMBINATION OF ATOMIC ORBITALS (LCAO) • Atomic orbitals can combine via addition or subtraction (hence, linear combination) and form: • MOLECULAR ORBITALS, if the starting atomic orbitals • belong to different atoms • HYBRID ORBITALS, if the starting atomic orbitals • belong to the same atom • GENERAL RULE:The number of new orbitals (molecular or hybrid) is ALWAYS EQUAL to the number of starting orbitals Chapter 2: Structure and Properties of Organic Molecules

3. s- ands*- molecular orbitals Chapter 2: Structure and Properties of Organic Molecules

4. s-BONDS AND p-BONDS • s-bonds can form by the combination of: • Two s-orbitals: b. Two p-orbitals: c. One s- and one p-orbital: Chapter 2: Structure and Properties of Organic Molecules

5. s-BONDS AND p-BONDS 2. p-bonds form via interaction of p-orbitals only. Chapter 2: Structure and Properties of Organic Molecules

6. s-BONDS AND p-BONDS • IMPORTANT NOTES: • s-orbitals, due to their spherical symmetry, cannot participate in the formation of p-orbitals. • The first bond between any pair of atoms is • ALWAYS a s-bond. • 3. Only ONE s-bond can be formed between any pair of two atoms. The rest (if any) are p-bonds. Chapter 2: Structure and Properties of Organic Molecules

7. PREDICTIONS BASED ON ELECTRONIC STRUCTURE OF CARBON • There is one 2s and three 2p orbitals, to form four bonds total. It would be therefore expected that one of the bonds would be different from the other three. • The 2s orbital is spherical (non-directional). The 2p orbitals are perpendicular to each other. One would therefore expect that the newly formed bonds would be at a 90o angle. • BOTH PREDICTIONS ARE FALSE!!!!! Chapter 2: Structure and Properties of Organic Molecules

8. HYBRIDIZATION AND MOLECULAR SHAPES 121.7o 109.5o 116.6o ethylene planar methane tetrahedral 180.0o acetylene linear Chapter 2: Structure and Properties of Organic Molecules

9. SEVERAL WAYS TO REPRESENT METHANE Chapter 2: Structure and Properties of Organic Molecules

10. ETHANE Chapter 2: Structure and Properties of Organic Molecules

11. ISOMERS • Constitutional (structural) isomers. Same molecular formula, but different structures. • Stereoisomers. Same molecular formula, same structure, different orientation of atoms or groups in space. Chapter 2: Structure and Properties of Organic Molecules

12. THE IMPORTANCE OF SHAPE IN INTERMOLECULAR INTERACTIONS Chapter 2: Structure and Properties of Organic Molecules

13. THE IMPORTANCE OF SHAPE IN INTERMOLECULAR INTERACTIONS Chapter 2: Structure and Properties of Organic Molecules

14. THE HYDROGEN BOND Chapter 2: Structure and Properties of Organic Molecules

15. THE HYDROGEN BOND Chapter 2: Structure and Properties of Organic Molecules