第 3 章有機化學反應種類及酸鹼有機反應. 一 ) 有機化反應的種類及有機反應機制 (organic reactions and their mechanism)

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1 第 3 章有機化學反應種類及酸鹼有機反應一 ) 有機化反應的種類及有機反應機制 (organic reactions and their mechanism) 1) a) Substitution reaction: (Saturated compound such as alkanes or alkyl halides, aromatic compounds) ne group replace another C 2 Br + NaCN C 2 CN + NaBr b) Addition reactions: Compounds with multiple bonds

2 Two molecules become one, all parts of adding reacts appear in the products R 1 R 2 R 3 R 4 2 / Pt R 1 R 2 R 3 R 4 c) Elimination reactions: used in the preparation of double bonds and triple bonds pposite to addition, a small molecule lost from one molecule

3 d) Rearrangement reactions: 3 C C 3 C 3 + cat. 3 C 3 C C 3 C 3 The molecule undergoes a reorganization of it constitutional parts 2) Mechanism of a reaction: 從分子的角度解釋由產物到生成物的過程 Briefly explain the above reactions 3) omolysis and heterolysis of covalent bond ( 共價鍵之均裂和異裂 ):

4 N C 3 hv 2 C N Curve arrow Explain eterolysis normally requires the bonds to be polarized C 2 Br + NaCN C 2 CN + NaBr Explain

5 二 ) 有機酸鹼反應 ( 瞭解用 curve arrow 表達反應機制 ; 化合物結構與反應性之間的關係 ; 用熱力學常數預測反應的平衡 ; 溶劑對反應的影響 ; 有機合成的初步概念 ) 1) Brønsted-Lowry 酸碱理論 : 酸 : 給出質子鹼 : 接受質子 ydronium (3 + ): exist in aqueous solution in significant amount

6 I I - Br Br - 2 S 4 : diprotic acid Na 2 S S 4 S S Na (aq) + (aq) exist in aqueous solution in significant amount

7 When Aqueous hydrogen chloride and aqueous sodium hydroxide are mixed, the actual reaction is between hydronium and hydroxide ions: Net reaction

8 2) Lewis 酸碱理論 ( 比 Brønsted-Lowry 酸碱理論定義更為廣泛 ): 酸 : 接受電子對鹼 : 給出電子對 Note that the proton also lose an electron pair as new bond is formed with nitrogen. Accept an electron pair without breaking any bond

9 在有機化學中普遍應用的 Lewis 酸 : Zn 2+, Fe 3+, BF 3 etc. C3 BBr 3 Br Br B Br C3 Br B Br 2

10 pposite Charges Attract and React Exercise (page 100): 1) Write the equations: C 3 + BF 3 C 3 Cl + AlCl 3 C 3 C 3 + BF 3 2) Define the Lewis acids and bases for each of the following: N C (Ph) 3 P Br - (C) 3 B -

11 正碳離子 (carbocation): 親電試劑 (electrophiles): reagents which in their reactions seek extra electrons that will give them a stable valence shell of electrons. 負碳離子 (carboanion): 親核試劑 (nucleophiles): reagents which in their reactions seek a proton or some other positive centers

12 + electrophile 2-2 nucleophile carbocation *The curved arrow begins with a covalent bond or unshared electron pair (site of higher electron density) and points toward a site of electron deficiency. *It shows the movement of electron flow but not the movement of atoms

13 Exercise (page 103):Use the curved-arrow notation to write the reaction between (C3)2N and BF3.

14 3) 酸鹼強度 Acidic constant

15 Carboxylic acid: 3~5; alcohol 15 ~ 18; ketones ~ 20.

16 Exercise (page ): 1) C2 has Ka = , in a 0.1 M solution, what is the concentration of hydronium ions? = [ 3 + ] [C - ] 0.1 2) Rationalize the Pka for 2 is 15.7: Ka = [10-7 ][10-7 ] 55.5 M = PKa = ) The Pk a of anilinium ion (C 6 5 N + 3 ) is 4.6. n this basis, decide aniline is stronger or weaker base than methylamine: C 3 N + 3 : 10.6, thus it is a weaker base than methylamine

17 3) 利用酸鹼強度判斷酸碱反應的 equilibrium: Acid base reaction favor the formation of the weaker acid and base. Equilibrium-controlled reactions: favoring the formation of more stable species. N (?) C (?)

18 Water insoluble carboxylic acids or bases can become soluble in aqueous sodium hydroxide:

19 4) 決定化合物酸鹼性強弱的因素 a) Bond strength: Bond strength decrease b) Electronegativity

20 Increasingly electronegative atoms polarize the bond and also stabilize the conjugate base better

21 verview of Acidity Trends

22 c) ybridization: s orbitals are smaller and closer to the nucleus than p orbitals Anions in hybrid orbitals with more s character will be held more closely - to the nucleus and be more stabilized d) Resonance effect stabilized by the resonance; Less potential energy than C3C2 - pka = 4.75 pka =

23 The higher the potential energy of an object the less stable it is

24 Enthalpy Δo is a measure of the change in bond energies in a reaction: Exothermic reactions: Δo is negative and heat is evolved. Potential energy in the bonds of reactants is more than that of products Endothermic reactions Δo is positive and heat is absorbed Potential energy in the bonds of reactants is less than that of products 2 2.

25 ΔGo: the standard free energy change: If ΔGo is negative, products are favored at equilibrium (Keq >1) If ΔGo is positive, reactants are favored at equilibrium (Keq<1) If ΔGo is zero, products and reactants are equally favored (Keq = 1) Entropy change ΔS o is related to the changes in relative order of the system A+B C ΔS o : negative A+B C+D ΔS 0 ~ 0 A C+D ΔS o : positive The more random a system is, the greater is its entropy A positive ΔS o means a system which is going from more ordered to less ordered A negative ΔS o :products unfavored

27 e) Inductive effect The proton is more positive

28 Indicating the stronger acid (page 120): a) CCl2C2 > C2ClC2 b) C2FC2 > C2BrC2; c) CCl3C2 > CCl2C2; d) C2FC2 > C2FC2C2 f) Solvent effect (protic solvent: is one has hydrogen attached to a strongly electronegtive element such as oxygen or nitrogen) pka = 4.75 in 2 Pka = 130 in gas phase Explain the table in page 121.

29 4) rganic compounds as bases: a) organic compound containing an atom with a lone pair (,S,N) can act as a base

30 b) π Electrons can also act as bases 5) A step-wise mechanism of a organic reaction:

32 6) Acid-base reaction in non-aqueous solution: Any base stronger than hydroxide will be converted to hydroxide in water Sodium amide can be used as a strong base in solvents such as liquid N3

33 Write the acid-base reactions (page 126): a) b) C3 + Na C NaN 2 + C 3 C 3 N 3 + C 3 C 3 - c) N 3 + C 3 C - 3 Li + gas N C 3 C 3 d) 4 + Cl + NaN 2 N 3 (l) 2 N 3 + NaCl

34 e) (C 3 )CNa + 2 (C 3 )C + - f) C 3 )C + Na (C 3 )C Na + 1) Na 2) D 2 D C 3 C 2 Li + D 2 hexane C 3 C 2 D C 3 C 2 + Na 1) hexane 2) T 2 C 3 C 2 T

35 Exercise (page 129): 3.15: what is the conjugate base of each of the following acid? (a) N 3 : N 2 - (c) 2 : - (e) C 3 : C 3 - (b) 2 : - (d) C C: - C C (f) 3 + : : List the bases you gave as answers to Problem 3.15 in order of decreasing basicity: Acidity: 3 + > 2 >C 3 > C C > 2 > N 3 Basicity: N 2 - > - > - C C> C 3 - > - > : what is the conjugate acid of each of the following bases: (a) S 4 - : 2 S 4 (c) C 3 N 2 : C 3 N 3 + (e) C 3 C 2 - : C 3 C 3 (b) 2 : 3 + (d) N 2 - :N 3 (f) C 3 C 2 - : C 3 C 2

36 3.18 List the acids you gave as answers to Problem 3.15 in order of decreasing acidity: Acidity: 2 S 4 > 3 + > C 3 C 2 > C 3 N 3 + > N 3 > C 3 C Designate the LA and LB in each of the following reactions: a) b) Cl 3 C 2 C Cl + AlCl 3 3 C 2 C Cl Al LB LA Cl F 3 C + BF 3 3 C B F LB LA F Cl c) 3 C C 3 C 3 LA + 2 LB 3 C C 3 C 3 2

37 3.20 Rewrite each of the following reactions using curved arrows and show all non-bonding electron pairs: a) 3 C + I 3 C + I - b) c) 3 C N 2 + Cl 3 C N F + F - + Cl -

38 3.21 When C3 is treated with Na, the product is C3 - Na + and 2 and not Na + C 2 and 2, explain: Pk ac3 >Pk a Pk a C 3 ~15; Pk a 2 ~35; 3.22 What reaction will take place if liquid ammonia: Et is added to a solution of C C - Na + in Et + + Na - C C N 3 (l) Et - + C C 3.22 omitted 3.33 Acid A has a PKa = 20; acid B has a PKa = 10: a) Which is the stronger acid: B b) Na + A - + B A + Na + B -

39 3.25 Write the equation, using curved-arrow notation: a) Et Na + Et - Na PKa ~5 2 PKa ~15.7 b) Ph S + PKa ~ Ph S Na Na + c) Et - + Et + - PK aet ~16 PK a ethyne ~25

40 d) Et - Li + + hexane C 3 C PK ac3c3 ~50 PK acc ~25 e) Et - Li + + hexane Et C 3 C 3 + Et - PK ac3c3 ~50 PK aet ~ Showing the syntheses of each of the following: 1) N a) - 3 (l) Ph + N 2 2) T 2 b) 1) hexane + Na 2) D 2 c) 1) hexane + Na 2) D 2 Ph T D D

41 3.27 a) arrange the following compounds in order of decreasing acidity and explain: Et > Et N > 3 C 2 C electronegtivity decreases b) Arrange the conjugate bases in order of increasing basicity: Et - < Et N < C 3 C Arrange the following compounds in order of decreasing acidity : a) 3 C > C 3 C=C 2 >C 3 C 2 C 3 b) C 3 CClC 2 > C 3 C 2 C 2 > C 3 C 2 C 2 c) C 3 C > C 3 C 2 >C 3 C 3

42 3.29 Arrange the following compounds in order of increasing basicity: a) b) c) C 3 N + 3 < C 3 N 2 < C 3 N - C <C 3 N - C 3 C < 2 C 3 C C - <C 3 C 2 =C - <C 3 C 2 C Draw the structures of triprotic acid 3P4 and diprotic acid 3P3 P P 3.31 Supply the curved arrow necessary for the following reactions:

43 a) b), c) C C C 3

44 d) I C C 3 + I - e) 3 C C 3 C 2 Cl Cl - + 2

45 3.32 a) 2 NC 2 C 2 3 NC 2 C - 2 pka acid ~5 pka ammonium ~10 Neutral form Salt form b): salt form is dominating 3.33 a) electron-attracting inductive effect b) Two negative centers 3.34: B 3.35 mitted

46 3.36 a) Explain both protons being more acidic than acetic acid b) Explain all of the C-C bond in dianion are same length as well as all of the C- bonds

Chapter 3 An Introduction to Organic Reactions: Acids and Bases

There are 4 types of Organic Reactions Chapter 3 An Introduction to Organic Reactions: SUBSTITUTION: ADDITION: X Y + A X A + Y Example Example A B + X Y A B X Y ELIMINATION There are 4 Types of Organic