有机化学（英文讲义）Chapter 3.pptVIP

Chapter 3 Orbitals and Valence Bond Theory 3.2 Atomic orbitals (AO) The shapes of AOs s--sphere (positive phase sign) px, py, pz--two lobes (one with a positive phase sign, and another with a negative phase sign) The energy of atomic orbitals 1s 2s 2px,py,pz 3s 3px,py,pz (degenerate orbitals, 简并轨道) How to fill electrons into AOs 3 principles: i. The Aufbau principle (能量最低原理): Orbitals with lowest energy are filled first. ii. The Pauli exclusion principle (鲍利不相容原理) A maximum of 2es can be placed into each orbital and the spins of the two es must be paired. iii. Hund’s rule (洪特规则): For degenerate orbitals, one e should be filled to each orbital with their spins unpaired, until each orbital has one e, then the left es can be filled to each degenerate orbital in a way of spin paired with the first e. e.g. C (6e) O (8e) S (16e) 3.3 Molecular orbitals ◆The formation of molecular orbitals (MO) bonding MO: 2AOs of the same phase sign overlap with each other. pA pB ?pApB antibonding MO: 2AOs of opposite phase sign overlap with each other. pA pB ◆The type of MOs in organic compounds i. ? bonds (single bonds, head to head overlap): ii. ? bonds (double or triple bonds, shoulder to shoulder overlap) 3.4~3.6, 1.11, 4.8 valence bond theory and shapes of molecules important pointshybrid orbitals (杂化轨道) the type and the shape of hybrid orbitals: sp3, sp2, sp i. sp3tetrahedron, 109°, single bond, 4 hybrid orbitals, each hybrid orbital comprises 1/4 SO and 3/4 PO. e.g. CH4 (methane) In CH4: CH2Cl2 has no stereoisomer. other examples: NH3 or NR3 N(7e, 5es in its valence shell)