UNIT 6

1. UNIT 6 Theories of Covalent Bonding and Intro to Organic Chemistry Valence Bond Theory, Multiple Bonds, and Molecular Orbital Theory

2. Identify the Functional Groups amlodipine a calcium channel blocker lysergic acid diethylamide an hallucinogen

3. Give the Systematic (IUPAC) Name A component of gasoline halothane, an anesthetic

4. Draw the 3-D Structure acetaminophen, an analgesic halothane, an anesthetic

5. Valence Bond Theory and Double Bonds Ethylene is C2H4 and has a Lewis structure of: All of the atoms of ethylene lie in a single plane. H H H H C = C The orbital diagram for each C atom is One 2p orbital remains unhybridized. 1s sp2 2p • Each C – H bond is a σ bond formed from the overlap of a C sp2 orbital with the H 1s orbital. • One of the C – C bonds is a σ bond formed from the overlap of C sp2 orbitals, but what about the second bond?

6. Valence Bond Theory and the Double Bond H H H H Ethylene C = C 3. The second C – C bond is a π bond formed from the overlap of the unhybridized C 2p orbitals.

7. Valence Bond Theory and the Double Bond H H H H Ethylene C = C The overlap in a π bond is side-to-side (NOT end-to-end like in σ bonds).

8. Valence Bond Theory and the Double Bond H H H H Ethylene C = C The electron density in a π bond is concentrated above and below the axis of the bond. (The bond has 2 lobes.) The π bond restricts the rotation around the C-C bond axis and forces the geometry around the double bond to be planar.

9. Valence Bond Descriptions H H | | H — C— C = C — H | | H H What orbitals overlap to form each of the bonds in propene? • The three C-H bonds shown in blue are each formed by the overlap of a H 1s orbital with one of the four C sp3 hybrid orbitals. • The C-C bond is formed by the overlap of the remaining sp3 orbital on the first C with one of the sp2 orbitals on the second C. • The C-H bond is formed by the overlap of a C sp2 orbital with the H 1s orbital. • The C=C bond is formed by 1) a sigma bond from the overlap of C sp2 orbitals, and 2) a pi bond from the overlap of C 2pz orbitals. • Each of the two final C-H bonds is formed by the overlap of a C sp2 orbital with a H 1s orbital.

10. Valence Bond Theory and Triple Bonds Acetylene is C2H2 and has a Lewis structure of: H - C ≡ C - H All of the atoms of acetylene lie in a single line. The orbital diagram for each C atom is Two 2p orbitals remain unhybridized. 1s sp 2p 1. Each C – H bond is a σ bond formed from the overlap of a C sp orbital with the H 1s orbital. 2. One of the C – C bonds is a σ bond formed from the overlap of C sp orbitals.

11. Valence Bond Theory and the Triple Bond Acetylene H - C ≡ C - H 3. The other two bonds are π bonds formed from the overlap of the C 2p orbitals.

12. Valence Bond Descriptions H | H — C —C ≡ C — H | H What orbitals overlap to form each of the three bonds in C≡C? The C≡C triple bond is formed by: 1) the overlap of C sp orbitals (sigma bond), 2) the overlap of C 2pyorbitals (pi bond), and 3) the overlap of C 2pzorbitals (pi bond).

13. Delocalized π Bonds 1. In a structure with alternating double bonds (cyclic or linear), there is a more universal sharing of the electrons in the π bond. 2. The electrons in the σ bonds are still localized between pairs of C atoms, but the electrons in the π bonds can actually be shared throughout the length of the alternating double bond pattern. 3. These delocalized electrons give the molecule special stability.

14. Delocalized π Bonds benzene, C6H6 The benzene molecule is planar with the π bonds above and below the plane of the molecule.

15. Molecular Orbital Theory 1. Valence bond theory says “treat a bond between two atoms as an overlap of orbitals from those two atoms.” In other words, an H 1s orbital overlaps with a Cl 3p orbital to form the bond in HCl. 2. Another way to look at bonding is to say that the molecule HCl can be treated as a single entity with its own orbitals. Since the orbitals would belong to HCl, they would be molecular orbitals (MOs).

16. Molecular Orbital Theory • A MO is a mathematical construct just like the atomic orbital. • MOs are symbolized by σ and π.

17. Molecular Orbital Theory MOs come from the mixing of two atomic orbitals. Two AOs mix to form 2 MOs, one bonding (denoted σ or π) and one antibonding (denoted σ* or π*).

18. Molecular Orbital Theory In an antibonding MO, there is a region of no electron density (a node) between the atoms. Bonding MOs are lower in energy (more stable), than antibonding MOs. In a bonding MO, the electron density is concentrated between the atoms.

19. Molecular Orbital Theory Bond order is determined by filling the MOs with the number of electrons in the molecule, then using the formula: Bond order = 0.5 x (# bonding e-s – # antibonding e-s) Bond order = 0.5 x (2-0) = 1 Bond order = 0.5 x (2-2) = 0

20. Molecular Orbital Theory Bond order = 0.5 x (4-2) = 1 Bond orders of 0.5 and 1.5 are possible (He2+ is stable).

21. Molecular Orbital Theory MO explains phenomena that VB theory cannot. Oxygen is paramagnetic, which suggests it has unpaired electrons. MOs show how this is possible.

22. Molecular Orbital Theory What is the difference in these two MO diagrams if you were using them for Period 2 compounds? For the one on the left, you would use ALL electrons. For the one on the right, you would use only the valence electrons.

23. Molecular Orbital Theory • Fill in the MO diagram for F2-. • Determine the bond order for F2-. • Is F2-more / less / as stable as F2? • Is F2- diamagnetic or paramagnetic? • Now, repeat 1-4 for F2+ .