1. Chapter 2 Molecular Bonding and Acid, Base

2. Definition Intermolecular bonding （分子间作用力） is the bonding interaction which takes place between different molecules. This can take the form of ionic bonding （离子键） hydrogen bonding （氢键） dipole–dipole interactions （偶极 - 偶极作用） van der Waals interactions （范德华作用力） These bonding forces are weaker than the covalent bonds, but they have an important influence on the physical and biological properties of a compound. Strength of attractions between molecules influence m.p., b.p., and solubility; esp. for solids and liquids Chapter 2 Intermolecular Bonding

3. 2.1.1 Ionic bonding （离子键） Ionic bonding takes place between molecules having opposite charges and involves an electrostatic interaction （静电作用） between the two opposite charges.

4. Zwitterion （两性离子） Some important naturally occurring molecules contain both groups – the amino acids. electrostatic interaction 静电作用

5. 2.1.2 Hydrogen Bonding Strong dipole-dipole attraction Organic molecule must have N-H or O-H. The hydrogen from one molecule is strongly attracted to a lone pair of electrons on the other molecule. O-H more polar than N-H, so stronger hydrogen bonding =>

7. H Bonds =>

8. 2.1.2 Hydrogen bonding （氢键） Hydrogen bonding can take place when molecules have a hydrogen atom attached to a heteroatom such as nitrogen or oxygen. Hydrogen bonding is possible due to the polar nature of the N–H or O–H bond. the partially charged hydrogen of one molecule (the H bond donor) the partially charged heteroatom of another molecule (the H bond acceptor)

9. Most important noncovalent interaction in biological molecules

10. alcohols, phenols, carboxylic acids, amides, and amines donoracceptor 举一些其它氢键的例子

11. 11 2.1.2 Hydrogen Bond Forces Forces are result of attractive interaction between a hydrogen bonded to an electronegative O or N atom (or F atom) and an unshared electron pair on another O or N atom (or F atom)

12. 2.1.3 Dipole–dipole interactions （偶极 - 偶极作用） Dipole–dipole interactions are possible between polarized bonds other than N–H interactions or O–H bonds.

13. 13 2.1.3 Dipole-Dipole Occur between polar molecules as a result of electrostatic interactions among dipoles Forces can be attractive of repulsive depending on orientation of the molecules

14. 2.1.3 Dipole-Dipole => 举一些其它氢键的例子

15. 2.1.4 van der Waals interactions （范德华作用力） van der Waals interactions are the weakest of the intermolecular bonding forces interactions and involve the transient existence of partial charges in a molecule. Alkane molecules can interact in this way and the strength of the interaction increases with the size of the alkane molecule. van der Waals interactions are also important for alkenes, alkynes and aromatic rings. Hydrophobic molecules can dissolve in nonpolar, hydrophobic solvents due to van der Waals interactions Dispersion Forces （色散力）

16. 16 Occur between all neighboring molecules and arise because the electron distribution within molecules that are constantly changing Dispersion Forces （色散力）

17. 2.1.4 Dispersions =>

18. 预测一下溶解性

19. 2.1.4 Dispersions Between nonpolar molecules Temporary dipole-dipole interactions Larger atoms are more polarizable(Br,I.) Branching lowers b.p. because of decreased surface contact between molecules. => oCoC oCoC oCoC

20. 2.1 Intermolecular bonding 2.1.1 Ionic bonding 2.1.3 Dipole-Dipole 2.1.4 Dispersion Forces （ van der Waals interactions ） 2.1.2 Hydrogen Bond Forces 复习

21. 2.2 Boiling Points and Intermolecular Forces => oCoC oCoC oCoC oCoC oCoC oCoC oCoC

22. 2.3 Solubility Like dissolves like Polar solutes dissolve in polar solvents. Nonpolar solutes dissolve in nonpolar solvents. Molecules with similar intermolecular forces will mix freely. =>

23. 2.3.1 Ionic Solute with Polar Solvent Hydration releases energy. Entropy increases. =>

24. 2.3.2 Ionic Solute with Nonpolar Solvent =>

25. 2.3.3 Nonpolar Solute with Nonpolar Solvent =>

26. 2.3.4 Nonpolar Solute with Polar Solvent =>

27. 复习 2.2 Boiling Points and Intermolecular Forces 2.3 Solubility 2.3.1 Ionic Solute with Polar Solvent 2.3.2 Ionic Solute with Nonpolar Solvent 2.3.3 Nonpolar Solute with Nonpolar Solvent 2.3.4 Nonpolar Solute with Polar Solvent

28. 2.4 Acids and Bases: The Brønsted– Lowry Definition The terms “acid” and “base” can have different meanings in different contexts For that reason, we specify the usage with more complete terminology( 术语 ) The idea that acids are solutions containing a lot of “H + ” and bases are solutions containing a lot of “OH - ” is not very useful in organic chemistry Instead, Brønsted–Lowry theory defines acids and bases by their role in reactions that transfer protons (H + ) between donors and acceptors 勃朗斯特 - 劳里

29. 2.4 Brønsted Acids and Bases “Brønsted-Lowry” is usually shortened to “Brønsted” A Brønsted acid is a substance that donates a hydrogen ion (H + ) A Brønsted base is a substance that accepts the H + “proton” is a synonym for H + - loss of an electron from H leaving the bare nucleus—a proton

30. The Reaction of HCl with H 2 O Acids are shown in red, bases in blue. Curved arrows go from bases to acids

31. 2.4.1 Quantitative Measures of Acid Strength Stronger acids have larger K e Note that brackets [ ] indicate concentration, moles per liter, M.

32. pK a – the Acid Strength Scale pK a = -log K a A larger value of pK a indicates a stronger acid and is proportional to the energy difference between products and reactants The pK a of water is 15.74

33. pKapKa Acids can be described as being weak or strong and the pKa is a measure of this. K eq is normally measured in a dilute aqueous solution of the acid and so the concentration of water is high and assumed to be constant. Therefore, we can rewrite the equilibrium equation in a simpler form where Ka is the acidity constant and includes the concentration of pure water (55.5 M).

35. pK a =- log 10 K a pKapKa The strongest acid has the lowest pK a value. the stronger the acid, the higher the value of K a, and the lower the value of pK a

36. 2.4.2 Predicting Acid–Base Reactions from pK a Values

37. CH 3 CH 2 NH 2 pK a = 40 CH 3 CH 2 OH pK a =16 Acid ? Ethanoic acid (4.76), ethanol (16), and phenol (10) Acid ?

38. 38 2.4.2 Predicting Acid–Base Reactions from pK a Values pK a values are related as logarithms to equilibrium constants Useful for predicting whether a given acid-base reaction will take place The difference in two pK a values is the log of the ratio of equilibrium constants, and can be used to calculate the extent of transfer The stronger base holds the proton more tightly

39. 39 2.4.2 Organic Acids and Organic Bases Organic Acids: - characterized by the presence of positively polarized hydrogen atom

40. Inductive electron withdrawal increases the acidity of a conjugate acid; Inductive effect: shifting of electrons in a bond in response to EN of nearby Atoms. 2.4.3 Predicting Acid Strength from Inductive effect 诱导效应

41. Ka & pKa & relative strength of acid

42. 42 Organic Acids Those that lose a proton from O–H, such as methanol and acetic acid Those that lose a proton from C–H, usually from a carbon atom next to a C=O double bond (O=C–C–H)

43. a simple acid/base reaction Acid ? base? Nucleophile? Electrophile?

44. Mineral acids( 无机酸）

45. Functional groups contain hydrogens which are potentially acidic

46. >> 1.electronegative F > O > N Fluorine strongly polarizes the H–F bond such that the hydrogen becomes highly electron deficient and is easily lost. Once the proton is lost, the fluoride ion can stabilize the resulting negative charge. nitrogen which is less electronegative than fluorine.

47. 2 完全电离 部分电离

48. 复习 A Brønsted acid is a substance that donates a hydrogen ion (H + ) 2.4.1 Quantitative Measures of Acid Strength 2.4.2 Predicting Acid–Base Reactions from pK a Values 2.4.3 Predicting Acid Strength from Inductive effect

49. 2.5 Organic Bases A Brønsted base is a substance that accepts the H+ “proton” is a synonym for H + - loss of an electron from H leaving the bare nucleus— a proton

50. Bronstered-Lowry definition Donates/accepts a hydrogen ion (H + ) Conjugate A/B

51. 51 The Reaction of Acid with Base Hydronium ion, product when base H 2 O gains a proton HCl donates a proton to water molecule, yielding hydronium ion (H 3 O + ) [conjugate acid] and Cl  [conjugate base] The reverse is also a Brønsted acid–base reaction of the conjugate acid and conjugate base

52. 2.6 Acids and Bases: The Lewis Definition Lewis acids are electron pair acceptors and Lewis bases are electron pair donors

53. 2.6.1 Illustration of Curved Arrows in Following Lewis Acid-Base Reactions

54. 2.6.2 Organic bases (red) Have an atom with a lone pair of electrons that can bond to H + -O & -N

55. Base is a molecule which can form a bond to a proton. include negatively charged ions with a lone pair of electrons

57. Electronegativity( 电负性） Electronegativity has an important influence to play on basic strength. C N O F<<< Electronegativity: Strongly electronegative atoms are able to stabilize a negative charge making the ion less reactive and less basic.

58. These neutral molecules are much weaker bases than their corresponding anions.

59. Anitrogen atom can stabilize a positive charge better than a fluorine atom since the former is less electronegative amines act as weak bases in aqueous solution and are partially ionized. Alcohols only act as weak bases in acidic solution. Alkyl halides are essentially nonbasic even in acidic solutions.

60. pKbpKb pK b is a measure of basic strength. If methylamine is dissolved in water, an equilibrium is set up Acid ? base? Nucleophile? Electrophile? the equilibrium constant

61. K eq is normally measured in a dilute aqueous solution of the base and so the concentration of water is high and assumed to be constant. K b is the basicity constant and includes the concentration of pure water (55.5 M).

62. pK b =- Log 10 K b Alarge pKb indicates a weak base. Ammonia 4.74 methylamine 3.36 basicities ？ pK a + pK b = 14

63. Definition an acid is a molecule which can provide a proton. a base is a molecule which can accept that proton. 复习

64. 2.6.3 Lewis Acids The Lewis definition of acidity includes metal cations, such as Mg 2+ : They accept a pair of electrons when they form a bond to a base Group 3A elements, such as BF 3 and AlCl 3, are Lewis acids because they have unfilled valence orbitals and can accept electron pairs from Lewis bases Transition-metal compounds, such as TiCl 4, FeCl 3, ZnCl 2, and SnCl 4, are Lewis acids Organic compounds that undergo addition reactions with Lewis bases (discussed later) are called electrophiles and therefore Lewis Acids 亲电试剂

65. 65 Lewis Acids and the Curved Arrow Formalism （格式，形式） The Lewis definition of acidity includes metal cations, such as Mg 2+ They accept a pair of electrons when they form a bond to a base Group 3A elements, such as BF 3 and AlCl 3, are Lewis acids because they have unfilled valence orbitals and can accept electron pairs from Lewis bases Transition-metal compounds, such as TiCl 4, FeCl 3, ZnCl 2, and SnCl 4, are Lewis acids Organic compounds that undergo addition reactions with Lewis bases (discussed later) are called electrophiles and therefore Lewis Acids The combination of a Lewis acid and a Lewis base can shown with a curved arrow from base to acid

66. 66 Illustration of Curved Arrows in Following Lewis Acid-Base Reactions

67. Lewis Bases

68. 复习 Acids and Bases: The Lewis Definition Lewis acids are electron pair acceptors and Lewis bases are electron pair donors 2.6.1 Illustration of Curved Arrows in Following Lewis Acid-Base Reactions