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1、Organic Chemistry, 6th EditionL. G. Wade, Jr.Chapter 1Structure and BondingAcids and BasesYunfeng ChenSchool of Chemical Engineering & Pharmacychyfch第1页Atomic Structureprotons, neutrons, and electronsisotopes第2页Atomic Orbitals2s orbital (spherical)2p orbital 第3页Electronic Configurations Aufbau princ

2、iple: electrons occupy the orbitals with the lowest energy firstHunds rule: electrons will occupy empty degenerated orbitals before pairing up in the same orbitalPauli principle: only two electrons can occupy one atomic orbital and the two electrons have opposite spin.第4页Electronic Configurations of

3、 the Elements of the First and Second Rows第5页Bond FormationIonic bonding: electrons are transferred.Covalent bonding: electron pair is shared. 第6页Lewis StructuresBonding electronsNonbonding electrons or lone pairsSatisfy the octet rule! 第7页Practice: write the Lewis structures for the below molecules

4、第8页Multiple Bonding第9页Dipole MomentAmount of electrical charge x bond length.Charge separation shown by electrostatic potential map (EPM).Red indicates a partially negative region and blue indicates a partially positive region.第10页Electronegativity and Bond PolarityGreater EN means greater polarity第

5、11页Calculating Formal ChargeFor each atom in a valid Lewis structureCount the number of valence electronsSubtract all its nonbonding electronsSubtract half of its bonding electrons第12页Ionic Structures第13页Chemical FormulasFull structural formula (no lone pairs shown)Line-angle formulaCondensed struct

6、ural formulaMolecular formulaEmpirical formulaCH3COOHC2H4O2CH2O 第14页ResonanceOnly electrons can be moved (usually lone pairs or pi electrons).Nuclei positions and bond angles remain the same.The number of unpaired electrons remains the same.Resonance causes a delocalization of electrical charge.第15页

7、Resonance ExampleThe real structure is a resonance hybrid.All the bond lengths are the same.Each oxygen has a -1/3 electrical charge. 第16页Major Resonance Formhas as many octets as possible.has as many bonds as possible.has the negative charge on the most electronegative atom.has as little charge sep

8、aration as possible.第17页Major Contributor?majorminor, carbon doesnot have octet.第18页ResonanceDelocalization of the negative charge on the conjugate base will stabilize the anion, so the substance is a stronger acid.More resonance structures usually mean greater stabilization.第19页Practice: 第20页Arrhen

9、ius Acids and BasesAcids dissociate in water to give H3O+ ions.Bases dissociate in water to give OH- ions.Kw = H3O+ OH- = 1.0 x 10-14 at 24CpH = -log H3O+ Strong acids and bases are 100% dissociated.第21页BrnstedLowry Acids and Bases Acid donates a proton Base accepts a proton Strong reacts to give we

10、ak The weaker the base, the stronger is its conjugate acid Stable bases are weak bases1 Conjugate acid-base pairs.第22页 An Acid/Base EquilibriumKa: The acid dissociation constant1第23页Acid and Base StrengthAcid dissociation constant, KaBase dissociation constant, KbFor conjugate pairs, (Ka)(Kb) = KwSp

11、ontaneous acid-base reactions proceed from stronger to weaker.pKa 4.74pKb 3.36pKb 9.26pKa 10.64第24页Determining Relative AcidityElectronegativity Size Resonance stabilization of conjugate base 第25页ElectronegativityAs the bond to H becomes more polarized, H becomes more positive and the bond is easier

12、 to break.第26页SizeAs size increases, the H is more loosely held and the bond is easier to break.A larger size also stabilizes the anion.第27页 When atoms are similar in size, the stronger acid will have its proton attached to the more electronegative atom Inductive electron withdrawal increases the ac

13、idity of a conjugate acid1第28页Acetic acid is more acidic than ethanolThe delocalized electrons in acetic acid are shared by more than two atoms, thereby stabilizing the conjugated base1第29页Lewis Acids and BasesAcids accept electron pairs = electrophileBases donate electron pairs = nucleophilenucleop

14、hileelectrophile第30页 Lewis acid: non-proton-donating acid; will accept two electrons Lewis base: electron pair donors Most of organic reactions can be considered as acid-base reaction, the curve is very important for reaction mechanism.Keep in mind (curve)1第31页Practices:1. Ammonia, has pKa = 36 and acetone has pKa = 19. Will the following reaction take place? Explain.2. Is the