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1、1,Chapte 6.An Overview of Organic Reactions,proper use of curved arrows to illustrate mechanisms qualitative understanding of G the use of energy diagrams to describe reactions,Key focus:,2,6.1 Kinds of Organic Reactions 有机反应类型,Common patterns describe the changes in organic reactions.,2 reactants a
2、dd together to form a single new product.,Addition reactions 加成反应:,3,2 reactants exchange parts to give 2 new products.,Elimination reactions 消去反应:,A single reactant split into 2 products.,Substitution reactions 取代反应:,4,A single reactant undergoes a reorganization of bonds to yield an isomeric produ
3、ct.,Rearrangement reactions 重排反应:,Dihydroxyacetonephosphate,Glyceraldehyde3-phosphate,Kinds of Organic Reactions 有机反应类型,5,6.2 How Organic Reactions Occur:Reaction Mechanisms,Reactions occur in defined steps that lead from reactant to product.The mechanism describes the steps behind the observed chan
4、ges in a reaction.We classify the types of steps in a sequence.A step involves either the formation or breaking of a covalent bond.Steps can occur individually or in combination with other steps.When several steps occur at the same time they are said to be concerted 协同.,反应机理,6,Symmetrical-homolytic
5、breakage 均裂 Unsymmetrical-heterolytic breakage 异裂,Reaction Mechanisms 反应机理,Bond Breaking 键的断裂 and Bond Forming 键的形成,Bond formation or breakage can be symmetrical or unsymetrical.,Symmetrical bond-breaking(radical 自由基):one bonding electron stays with each product.,Unsymmetrical bond-breaking(polar 极性
6、):two bonding electrons stay with one product.,Symmetrical bond-making(radical自由基):one bonding electron is donated by each reactant.,Unsymmetrical bond-making(polar 极性):two bonding electrons are donated by one reactant.,7,Indicate breaking and forming of bonds:Arrowheads with a“half”head(“fish-hook
7、鱼钩”)indicate homolytic and homogenic steps radical processes Arrowheads with a complete head indicate heterolytic and heterogenic steps polar processes,Reaction Mechanisms 反应机理,Bond Breaking 键的断裂 and Bond Forming 键的形成,Curved arrows 弯曲箭头,8,6.3 Radical Reactions 自由基反应,A radical can break a bond in ano
8、ther molecule and abstract a partner with an electron,giving substitution in the original molecule.A radical can add to an alkene to give a new radical,causing an addition reaction.,Radicals react to complete electron octet of valence shell.,9,A radical can achieve a valence-shell octet in several w
9、ays.,A radical substitution reaction 自由基取代反应,A radical addition reaction 自由基加成反应,Radical Reactions 自由基反应,10,Three types of steps:Initiation 引发,Propagation 传递,Termination 终止.,Methane Chlorine Chloromethane,Radical Chlorination Reactions 自由基氯代反应,11,Initiation引发 homolytic formation of two reactive spec
10、ies with unpaired electrons.,Methane Chlorine Chloromethane,Radical chlorination reaction mechanism 自由基氯代反应机理,12,Radical chlorination reaction mechanism 自由基氯代反应机理,Methane Chlorine Chloromethane,Propagation 传递 reaction with molecule to generate new radical.,13,Termination 终止 combination of two radica
11、ls to form a stable product.,Radical chlorination reaction mechanism 自由基氯代反应机理,Methane Chlorine Chloromethane,14,+,O2,oxygenradical,carbonradical,the synthesis of prostaglandins 合成前列腺素,15,6.4 Polar Reactions 极性反应,Difference in electronegativities causes a partial negative charge on an atom and a com
12、pensating partial positive charge on an adjacent atom.The more electronegative atom has the greater electron densitybond polarity.Elements such as O,F,N,Cl more electronegative than carbon.,16,Polarity Patterns in Some Common Functional Groups,醇,烯烃,卤代烃,胺,羰基,羧酸,酰氯,醛,17,Polarity Patterns in Some Commo
13、n Functional Groups,醚,硫醚,腈,格氏试剂,烷基锂试剂,酯,酮,18,Polarization is a change in electron distribution as a response to a change in electronic nature of the surroundings.Polarizability is the tendency to undergo polarization.Polar reactions occur between regions of high electron density and regions of low e
14、lectron density.,Electronegativity values of C,S and I are all 2.5,Polarizability 极化度/可极化性,19,An electrophile 亲电试剂,an electron-poor species,combines with a nucleophile 亲核试剂,an electron-rich species.electrophile:Lewis acidnucleophile:Lewis base,Generalized Polar Reaction 极性反应,20,Some nucleophiles and
15、 electrophiles,Electrostatic potential maps identify the nucleophilic(negative)and electrophilic(positive)atoms.,21,6.5 An Example of a Polar Reaction:Addition of HBr to Ethylene,The bond is electron-rich:nucleophileH-Br is electron deficient at H:electrophile,22,electrophilic addition reaction of e
16、thylene and HBr乙烯与氢溴酸的亲电加成反应,23,Reaction Mechanisms 反应机理,CH2=CH2+HBr CH3CH2Br,24,6.6 Using Curved Arrows in Polar Reaction Mechanisms 极性反应机理,Curved arrows are a way to keep track of changes in bonding in polar reaction.The arrows track“electron movement”.Electrons always move in pairs.Charges change
17、 during the reaction.One curved arrow corresponds to one step in a reaction mechanism.,25,Electrons move from a nucleophilic source to an electrophilic sinki.e.Electrons would“want”to flow from region of high electron density to region of low electron density.Arrows will always point away from negat
18、ive charges and toward positive ones.,Some guidelines,26,The rules and common patterns,Rule 1.Electrons move from a nucleophilic source(Nu:or Nu:-)to an electrophilic sink(E or E+).,The nucleophilic source must have an electron pair available,usually either as a lone pair or in a multiple bond.,The
19、electrophilic sink must be able to accept an electron pair,usually because it has either a positively charged atom or a positively polarized atom in a functional group.,Electrons usually flow from one of these nucleophiles 亲核.,Electrons usually flow to one of these electrophiles 亲电.,27,Rule 2.The nu
20、cleophile 亲核试剂 can be either negatively charged or neutral.,The total charge on one side of the transformation arrow must be the same as on the other side.,28,Rule 3.The electrophile 亲电试剂 can be either positively charged or neutral.,The total charge on one side of the transformation arrow must be th
21、e same as on the other side.,29,Rule 4.The octet rule 八隅律 must be followed.,30,Additional points to note,McMurry:,Preferred:,Wrong:,31,position of arrows:,32,6.7 Describing a Reaction:Equilibria,Rates,and Energy Changes,The ratio of products to reactants is dependent on their relative“energy content
22、”.Mathematically,For a reaction:,for example,33,Enthalpy（焓）changeenergy of:bonds broken-bonds formed(-ve:exothermic,+ve:endothermic),Entropy（熵）change:molecular disorder 混乱度 of:products-reactants,G（自由能）is the energy difference between reactants 反应物 and products 产物(-ve:exergonic 放热,+ve:endergonic 吸热).
23、,34,NOTE:equilibrium position of a reaction rate of a reaction,Explanation of Thermodynamic Quantities:DG=DHTDS,Rate Is the reaction fast or slow?Equilibrium In what direction does the reaction proceed?,35,The ratio of products to reactants is controlled by their relative Gibbs free energy 自由能.The c
24、hange in Gibbs free energy between products and reactants is written as“G”.,Gibbs Free Energy and K,36,The energy from forming a bond can be described by its bond dissociation energy（BDE，键离解能）.,Gibbs Free Energy and K,Example,37,6.8 Describing a Reaction:Bond Dissociation Energies 键离解能,Bond dissocia
25、tion energy(D):amount of energy required to break a given bond to produce two radical fragments when the molecule is in the gas phase at 25 C.,The energy is mostly determined by the type of bond,independent of the molecule.Changes in bonds can be used to calculate net changes in heat.,38,Some Bond D
26、issociation Energies,D,39,Some Bond Dissociation Energies,D,40,6.9 Describing a Reaction:能量图和过渡态 Energy Diagrams and Transition States,G,G,A good way to visualize the energy changes throughout the course of a reaction.,41,6.10 Describing a Reaction:Intermediates 中间体,Recall:,If a reaction occurs in m
27、ore than one step,it must involve species that are neither the reactant nor the final product.These are called reaction intermediates or simply“intermediates 中间体”.Each step has its own free energy of activation活化自由能.The complete diagram for the reaction shows the free energy changes associated with
28、an intermediate.,42,43,44,5.11 A Comparison between Biological Reactions and Laboratory Reactions,Laboratory reactions usually carried out in organic solvent.Biological reactions in aqueous medium inside cells.They are promoted by catalysts that lower the activation barrier.The catalysts are usually
29、 proteins,（蛋白质）called enzymes 酶.Enzymes provide an alternative mechanism that is compatible with the conditions of life.,45,Biological Reactions,46,Summary,Four common kinds of reactions,Addition reactions 加成反应,Elimination reactions 消除反应,Substitution reactions 取代反应,Rearrangement reactions 重排反应,Mecha
30、nism,Polar mechanism 极性机理,Radical mechanism 自由基机理,Transition state 过渡态,DG=DH-TDS,Energy diagram,Exergonic or endergonic reactions 放热或吸热反应,Activation energy 活化能,Reaction intermediate 反应中间体,47,作 业,6.19,6.20,6.21,6.22,6.23,6,26,6.32,6,33,6.34,6.39,6.40，6.41,48,有机化学教学计划,第二阶段：时间2013-9-30至2013-11-29（第513周）教 师：汪志勇 内 容：chapter 716教 室：五教 5305 周三（1,2）、周五（3,4）,第三阶段：时间2013-12-2至2014-1-3（第1418周）教 师：罗德平 内 容：chapter 1719&2223教 室：二教 2503 周三（1,2）、周五（3,4）,电教中心崔建生老师电话：63606483,
