有機化學 Organic Chemistry 汪炳鈞教授

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Elaine Malone
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1 有機化學 Organic Chemistry 汪炳鈞教授

2 Student Voices Bottom Line: Organic Chemistry is Intense But Doable Organic is not as terrible as the rumors say, but it s labor intensive Read the textbook. It was my best friend for the better part of the year. You have to study a little at a time; you can t cram everything in just before a test. Go to class. Go to group help sessions even if they are not mandatory. Work extra problems. Build models. Recopy your lecture notes-you may realize there are things you don t completely understand. Model sets are a great resource. They re essential to understanding stereochemistry. There s nothing better than being able to hold a model in your hand and twist it and turn it. Working on syntheses ties together everything you ve learned. If you know the underlying reasons why stuff happens, you can figure out a reaction you ve never seen before.

3 ORGANIC Compounds derived from living organisms were believed to contain an unmeasurable vital force, the essence of life 1807 Jöns Jakob Berzelius

4 INORGANIC Compounds derived from minerals those lacking vital force 1807 Jöns Jakob Berzelius

5 Organic / Inorganic? 1828 Friedrich Wöhler Definition for Organic Molecule Compounds that they contain at least one carbon atom except diamond, graphite, CO 2, CO, NH 4 OCN, NaCN, Na 2 CO 3

6 Why is an entire branch of chemistry devoted to the study of carbon-containing compound? The molecules that make life possible proteins, enzymes, vitamins, lipids, carbohydrates, nucleic acids,. Natural and unnatural compounds food, medicine, clothing, energy (gas, petroleum), synthetic fabrics, plastics, pesticides,

7 tendency to accept electron BETTER tendency to give up electron BETTER

8 Carbon neither to accept electron nor give up electron usually forms covalent bond

9 The Structure of An Atom a brief review An atom consists of a dense nucleus surrounded by electrons The nucleus contains positively charged protons and neutrons. It is positively charged. The electrons are negatively charged. An atom contains an equal amount of protons and electrons, and is neutral. Atomic number = number of protons in its nucleus Mass number protons & neutrons Isotopes: Same Atomic number but different mass number

10 Properties of Electron Dual properties of electron: particle and wave-like Quantum mechanics: Wave equation wave functions(solution of wave equation) the volume of space around the nucleus where the electron is most likely to be found Orbital: the volume of space around the nucleus where the electron is most likely to be found. atomic orbitals, degenerate orbitals s, p, d, and f orbitals

11 He Ne Ar Kr

12 Principles that Determine Which Orbitals Electrons Occupy The aufbau priciple; first thing we need to know to assign electrons to the various atomic orbitals The Pauli exclusion principle:(a) no more than two electrons can occupy each atomic orbital. (b) the two electrons must be of opposite spin. Hund s rule: When there are degenerate orbitals-- two or more orbitals with the same energy an electron will occupy an empty orbital before it will pair up with another electron.

13 The aufbau principle An electron always goes into the available orbital with the lowest energy. The relative energies of the atomic orbitals: 1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p<6s<4f<5d <6p<7s<5f 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f

15 Electron Affinity Ionization Energy

17 Ionic bond if electronegativity 2

18 Polar Covalent Bond

19 Formal charge = number of valence electrons (number of nonbonding electrons + 1/2 number of bonding electrons) methyl ammonia Ammonium anion ion Formal charge = 5-(2+6/2) 4-(2+6/2) 5-(0+8/2) = Neutral anion Cation molecule

20 More Examples on Formal Charge H 3 N-BH 3 Nitrogen: FC=5-0-8/2= +1 Boron: FC=3-0-8/2= -1 H 3 N: Nitrogen: FC=5-2-6/2= 0 BH 3 Boron: FC=3-0-6/2= 0

25 Atomic Orbitals

27 Degenerate 2p orbitals 1.6 Molecular Orbitals and Bonding

30 Ψ H2 = Ψ 1sa -Ψ 1sb Ψ H2 = Ψ 1sa +Ψ 1sb

33 Bonding in Methane and Ethane; Single Bonds Degenerate 2p orbitals

34 Orbital Hybridization p p p hybridization sp 3 x 4 s

35 Bonding in Ethane

37 hybridization s p p p sp 2 x 3 p

40 hybridization s p p p sp x 2 p p

43 How to Determine The Hybridization of A Certain Atom Hybridization SP n n = 3 empty orbital(s) π bonds BF 3 B: 2s 2 2p 1 H 2 O O: 2s 2 2p 4 NH 3 N: 2s 2 2p 3 BeH 2 Be: 2s 2 2s 2p x 2p y 2p z 2s 2p x 2p y 2p z 2s 2p x 2p y 2p z 2s 2p x 2p y 2p z n = = 2 SP 2 n = = 3 SP 3 n = = 3 SP 3 n = = 1 SP

44 2s 2p x 2p y 2p z C: 2s 2 2p 2 n = = 1 SP

46 Bonding in Ammonia and in The Ammonium Ion

47 Bonding in The Hydrogen Halides

48 Summary of Orbital Hybridization, Bond Lengths, Bond Strengths and Bond Angles

49 Dipole Moments of Molecules

51 An Introduction to Acids and Bases Arrhenius: Acid: A species that ionizes in solution to release a hydrogen ion (H + ). Base: A species that ionizes in solution to release a hydroxide ion (OH - ). HCl + H 2 O Cl + H 3 O an acid a base a base an acid Brønsted-Lowry: Acid: A species that donates a proton (H + ). Base: A species that accepts a proton (H + ). NH 3 + H 2 O HO + H 4 N a base an acid a base an acid The stronger the acid, the Conjugate weaker its base Conjugate conjugate of H 2 O acid base of NH 3

52 Organic Acids and Bases; pk a and ph Acidity: A measure of how easily a compound gives up a proton. Basicity: A measure of how well a compound shares its electron with a proton. Very strong acids pk a < 1 Moderate strong acids pk a = 1~5 Weak acids pk a = 5~15 Extremely weak acids pk a > 15 ph = -log[h 3 O + ]

55 CH 3 OH + HO CH 3 O + H 2 O an acid CH 3 OH + H 3 O a base CH 3 OH 2 + H 2 O O O CH 3 COH + HO CH 3 CO + H 2 O an acid O OH CH 3 COH + H 3 O CH 3 COH + H 2 O a base

56 CH 3 NH 2 + HO an acid pk a = 40 CH 3 NH 2 + H 3 O a base CH 3 NH + H 2 O CH 3 NH 3 + H 2 O pk a = 10.7

58 The Effect of Structure on pka

63 An Introduction to Delocalized Electrons and Resonance H H H Actual structure H H H

66 Lewis electrophile nucleophile

67 resonance structures B H B F X

Self Assessment_Ochem I

Self Assessment_Ochem I UTID: 2013 Objective Test Section Identify the choice that best completes the statement or answers the question. There is only one correct answer; please carefully bubble your choice on the scantron sheet.