高等有机化学chapter i

1、Advanced Organic ChemistryTuesday, 8:30-11:00 amLocation:上海市岳阳路319号8号楼2F16Required Text: “Advanced Organic Chemistry: Part A: Structure and Mechanisms”, Carey, F. A.; Sundberg, R. J., Fifth Ed.; Springer; 2007.Optional Texts:1. “Modern Physical Organic Chemistry”, Anslyn, E. V.; Dougherty, D. A.; Il

2、lustrated Ed.; University Science; 20052. “现代物理化学”, Anslyn, E. V.; Dougherty, D. A. 著; 计国楨, 佟振合等译; 高等教育出版社; 20083. “Marchs Advanced Organic Chemistry: Reactions, Mechanisms, and Structure”, Smith, M. B.; Seventh Ed.; Wiley-Interscience; 2013The electronic versions of the English books are available

3、at SIOC library.Chemical Bonding and Molecular StructureChapter 1Stereochemistry, Conformation, StereoselectivityChapter 2 Structural Effects on Stability and ReactivityChapter 3Nucleophilic SubstitutionChapter 4 Addition and Elimination Chapter 5 CarbanionChapter 6Carbonyl ChemistryChapter 7Aromati

4、cityChapter 8Aromatic SubstitutionChapter 9Concerted Pericyclic ReactionsChapter 10 Free Radical ReactionChapter 11 Photo ChemistryChapter 12 汤文军丁奎岭胡金波Chapter 1-7: Sept 9- Nov. 15 (9 weeks); No course on Oct. 1stChapter 8-10: Nov 18- Dec. 13 (4 weeks) Chapter 11-12: Dec. 16- Jan. 3 (3 weeks)Final Ex

5、am: 2014.1.8-2014.1.173Chapter 1: Chemical Bonding and Molecular StructureValence bond (VB) theoryA covalent bond is formed between the two atoms by the overlap of half filled valence atomic orbitals of each atom containing one unpaired electron.Lewis Structures: shared electron-pair bondOctet rule

6、“rule of 8”Orbital: The area of space occupied by electronsHybridization: Linus PaulingThe molecule adopts a particular shape because it maximizes bonding interactions and minimizes electron-electron and other repulsive interactions.ethyleneacetylyneformaldehydeAlleneCyclopropanenot only two bonds p

7、erpendicular, but also the two methene groupsPauli exclusion principleOnly two electrons can occupy the same point in space They must have opposite spin quantum number Valence shell electron-pair repulsion rule (VSEPR): (价层电子对互斥规则) Bonds and unshared electron pairs assume the orientations that permi

8、ts maximum seperation.Electronegativity:The power of an unequal atom in a molecule to attract electron to itselfPauling scaleDifferences in electronegativity between bonded atoms1.9: ionicMulliken scale: The average of ionization potential and electron affinity Group Electronegativity:Hybridization

9、effect:pKa: Bond strength:Increased by electronegativity differences Polarizability: (hardness and softness)The ability of the electron cloud to distort in response to an external field.Ethaneetheneenthyne 12ResonanceABDCEApproximations and/or parameters are necessary.The output of MO calculations:1

10、) Molecular structure; b) Energy; c) electron density2. Molecular Orbital TheoryTheoretical foundation: Quantum MechanicsThe Hckle MO method;Semiempirical method;Ab initio methodsRef: Fleming, Ian, Molecular Orbitals and Organic Chemical Reactions : Reference Edition, John Wiley & Sons, 2010 .2.1 Th

11、e Hckle MO methodSevere approximationRestricted to planar conjugated systems (i.e. polyenes, aromatics)The energy levels are given by the equation: E = + mj Coulomb integral Resonance integralOutput of HMO:The frontier MOs are identified and described.highest occupied MO (HOMO)Lowest upoccupied MO (

12、LUMO)Orbital symmetryRelative atomic contribution2. The approximate HOMO-LUMO gap An indicator of reactivity in terms of softness and hardness The smaller the gap, the softer the molecule.3. The overall stabilization of the moleculeStabilization: delocalization energy (DE)However, DE is not a reliab

13、le indicator of stablization.HOMOLUMOBenzene is 1.012 more stable than 1,3,5-hexatriene: AROMATICITYOutput of HMO:Huckels ruleHigh stablization is found for systems with (4n+2) electrons but not for systems with (4n) electron.2 or 6 cations or anions are stablized systems.2.2 Semiempirical MO method

14、sExtended Huckel theory (EHT)Complete neglect of differential overlap (CNDO)Modified neglect of differential overlap (MNDO)AM1PM32.3 Ab Initio MethodsIterative calculation of a self-consistent electronic field (SCF)Provide improved reliability and applicabilityGaussian basis functions are commonly u

15、sedBasis setSplit valence sets: two or more components in the outer shellPolarization function: include p function on H, d or f functions on other atomsDiffuse function: extend farther from the nuclear centerOutputAtomic coordinates at the minimum energyTotal energyGeometry et al.2.4 Pictorial Repre

16、sentation of Molecule Orbitals for MoleculesAufbau principle (构造原理）：Electron occupy the MOs of lowest energyPauli exclusion principle: Any MO can have only two electrons, one of each spinMethane: CH4It has one carbon 2s, 2px, 2py, 2pz atomic orbitalsIt has four hydrogen 1s atomic orbitalsSo it shoul

17、d have 8 molecule orbitalsWhat about ethane?Ethylene MOs232.5 Perturbational MO theory and Frontier Orbitals qualitative applications of MO theory to reactivityIn MO, reactivity is related to the relative energies and shapes of the orbitals.Symmetry of molecular orbitalsShape of the orbitals (define

18、d by the atomic coefficient)Purturbation molecular orbital theory (PMO):The MO characteristic of the new system are reduced by analyzing LUMO or HOMOInteractions are strongest between orbitals that are close in energy.Only Mos of matching symmetry can interact and lead to bond formation.Focus on rel

19、ative energy and symmetryEthylene vs. Formaldeyde: ReactivityWhy nucleophilic attack on formaldehyde and electrophilic attack on ethylene? Relative energy of the and * orbitals in ethene and formaldehyde.Energies values in au are from W.L.Jorgensen and L.Salem,The Organic Chemistry Book of Orbitals,

20、Academic Press,New York,1973.Interaction of formaldehyde frontier orbital with E+ and Nu-Interaction of ethene frontier orbitals with E+ and Nu-PMO description of interaction of ethylene and formaldehyde with an electrophile(E+)and a nucleophile(Nu-)Trajectory of the approachSubstituents: MO energy

21、levels for ethene with a -donor substituentCharge distributionCharge distribution in butadiene,acrolein,and aminoethylene based on HF/6-31G*calculation.From .Chem.,59,4506(1994)Case 1:bonding interactionantibonding interactionComparison of FMO interactions of ethene with allyl anion and ozoneHard ha

22、rd and soft soft reactions A large separation between the HOMO and LUMO orbitals: hard-hard reactionThe electrostatic term is dominant.The HOMO and LUMO are close: soft soft reaction, the perturbational stablization is the key.Hard-hard pertubation is small.Electrostatic factors are dominant.Orbital

23、 stabilization is small.Soft-soft pertubation is large.Mutual polarizability factors are dominant.Orbital stabilization is large.2.6 Numerical Application of MO theory ElectronicVibrational rotational energy levelsNMR spectraElectron Density Functionals Founded by Hohenberg and KohnThe exact energy

24、for a ground state system is defined entirely by the electron density that links it to the energy.Most commonly approximation: B3 LYPDFT computation uses less computer time than ab initio.B3: Beckes hybrid exchange funtionalLYP: Lee, Yang, and ParrSummaryChemical Bonding and Molecular StructureElect

25、ronegativityDelocalizationPolarizability4) Molecular orbital (MO)5) Density Functional Theory (DFT)TOPIC 1: Rotational barrier (Tosional)-delocalization(hyperconjugation)6 kcal/molTOPIC 1: Heteroatom hyperconjugation (Anomeric Effect)If one atom with an unshared electron pair is a particularly good electron donor and another a good * acceptor, the n * contribuation should be enhanced.Anomeric effect (heteroatom hyperconjugation)Corr