有机化学英文课件chapter6
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system during the reaction
6-5
Gibbs Free Energy
Gibbs free energy change, DG0: a thermodynamic function relating enthalpy, entropy, and temperature
M a c in to s h P IC T im a g e fo r m a t
6-6
Gibbs Free Energy
• a change in Gibbs free energy is directly related to chemical equilibrium
M a c in to s h P IC T im a g e fo r m a t
is n o t s u p p o r te d
M acintosh PICT im age form at is not supported
6-2
Characteristic Reactions
M acin to sh P IC T im ag e fo rm at
is n o t su p p o rted
6-3
Characteristic Reactions
• they provide an intellectual satisfaction derived from constructing models that accurately reflect the behavior of chemical systems
• they are tools with which to search for new information and new understanding
Heat of reaction, DH0: the difference in enthalpy between reactants and products
• exothermic reaction: a reaction in which the enthalpy of the products is lower than that of the reactants; a reaction in which heat is released
• endothermic reaction: a reaction in which the enthalpy of the products is higher than that of the reactants; a reaction in which heat is absorbed
6-8
Macintosh PICT im age form at is not supported
6-9
Activation Energy
Transition state:
• an unstable species of maximum energy formed during the course of a reaction
reduction
6-15
Addition of HX
Carried out with pure reagents or in a polar solvent such as acetic acid
M a c in to s h P IC T im a g e fo r m a t
is n o t s u p p o r te d
• if DG‡ is small, many collisions occur with sufficient energy to reach the transition state; reaction is fast
6-10
Energy Diagram
• a one-step reaction with no intermediate
• this does mean that the mechanism is correct, only that it is the best explanation we are able to devise
6-13
Why Mechanisms?
• they are the framework within which to organize descriptive chemistry
• Markovnikov’s rule: in the addition of HX, H2O, or ROH to an alkene, H adds to the carbon of the double bond having the greater number of hydrogens
6-16
HBr + 2-Butene
A two-step mechanism
Step 1: proton transfer from HBr to the alkene gives a carbocation intermediate
M a c in to s h P IC T im a g e fo rm a t
is n o t s u p p o rte d
Step 2: reaction of the sec-butyl cation (an electrophile) with bromide ion (a nucleophile) completes the reaction
M a c in to s h P IC T im a g e fo rm a t
• propose a set or sets of steps that might account for the overall transformation
• a mechanism becomes established when it is shown to be consistent with every test that can be devised
6-7
Energy Diagrams
Enthalpy change, DH0: the difference in total bond energy between reactants and products
• a measure of bond making (exothermic) and bond breaking (endothermic)
Energy Diagrams
Energy diagram: a graph showing the changes in energy that occur during a chemical reaction
Reaction coordinate: a measure in the change in positions of atoms during a reaction
M a c in to s h P IC T im ag e fo rm at
is n o t su p p o rted
6-4
Reaction Mechanisms
A reaction mechanism describes how a reaction occurs
• which bonds are broken and which new ones are formed
Addition is regioselective
• regioselective reaction: an addition or substitution reaction in which one of two or more possible products is formed in preference to all others that might be formed
• the order and relative rates of the various bondbreaking and bond-forming steps
• if in solution, the role of the solvent • if there is a catalyst, the role of a catalyst • the position of all atoms and energy of the entire
is n o t s u p p o r te d
• exergonic reaction: a reaction in which the Gibbs free energy of the products is lower than that of the reactants; the position of equilibrium for an exergonic reaction favors products
6-11
Energy Diagram
A two-step reaction with one intermediate
6-12
Developing a Reaction Mechanism
How it is done
• design experiments to reveal details of a particular chemical reaction
• a maximum on an energy diagram
Activation Energy, DG‡: the difference in Gibbs free energy between reactantsபைடு நூலகம்and a transition state
• if DG‡ is large, few collisions occur with sufficient energy to reach the transition state; reaction is slow
• endergonic reaction: a reaction in which the Gibbs free energy of the products is higher than that of the reactants; the position of equilibrium for an endergonic reaction favors starting materials
Carbocation: a species in which a carbon atom has only six electrons in its valence shell and bears positive charge
6-14
Electrophilic Additions
• hydrohalogenation using HCl, HBr, HI • hydration using H2O in the presence of H2SO4 • halogenation using Cl2, Br2 • halohydrination using HOCl, HOBr • oxymercuration using Hg(OAc)2, H2O followed by
is n o t s u p p o rte d
6-17
HBr + 2-Butene
An energy diagram for the two-step addition of HBr to 2-butene
• the reaction is exergonic
6-18
Carbocations
Organic Chemistry
William H. Brown Christopher S. Foote Brent L. Iverson
6-1
M acintosh PIC T
Reactions im a g e fo rm a t is not supported
of Alkenes
Chapter 6
• summary of the relationships between DG0, DH0, DS0, and the position of chemical equilibrium
M acin to sh P IC T im ag e fo rm at
is n o t su p p o rted
6-5
Gibbs Free Energy
Gibbs free energy change, DG0: a thermodynamic function relating enthalpy, entropy, and temperature
M a c in to s h P IC T im a g e fo r m a t
6-6
Gibbs Free Energy
• a change in Gibbs free energy is directly related to chemical equilibrium
M a c in to s h P IC T im a g e fo r m a t
is n o t s u p p o r te d
M acintosh PICT im age form at is not supported
6-2
Characteristic Reactions
M acin to sh P IC T im ag e fo rm at
is n o t su p p o rted
6-3
Characteristic Reactions
• they provide an intellectual satisfaction derived from constructing models that accurately reflect the behavior of chemical systems
• they are tools with which to search for new information and new understanding
Heat of reaction, DH0: the difference in enthalpy between reactants and products
• exothermic reaction: a reaction in which the enthalpy of the products is lower than that of the reactants; a reaction in which heat is released
• endothermic reaction: a reaction in which the enthalpy of the products is higher than that of the reactants; a reaction in which heat is absorbed
6-8
Macintosh PICT im age form at is not supported
6-9
Activation Energy
Transition state:
• an unstable species of maximum energy formed during the course of a reaction
reduction
6-15
Addition of HX
Carried out with pure reagents or in a polar solvent such as acetic acid
M a c in to s h P IC T im a g e fo r m a t
is n o t s u p p o r te d
• if DG‡ is small, many collisions occur with sufficient energy to reach the transition state; reaction is fast
6-10
Energy Diagram
• a one-step reaction with no intermediate
• this does mean that the mechanism is correct, only that it is the best explanation we are able to devise
6-13
Why Mechanisms?
• they are the framework within which to organize descriptive chemistry
• Markovnikov’s rule: in the addition of HX, H2O, or ROH to an alkene, H adds to the carbon of the double bond having the greater number of hydrogens
6-16
HBr + 2-Butene
A two-step mechanism
Step 1: proton transfer from HBr to the alkene gives a carbocation intermediate
M a c in to s h P IC T im a g e fo rm a t
is n o t s u p p o rte d
Step 2: reaction of the sec-butyl cation (an electrophile) with bromide ion (a nucleophile) completes the reaction
M a c in to s h P IC T im a g e fo rm a t
• propose a set or sets of steps that might account for the overall transformation
• a mechanism becomes established when it is shown to be consistent with every test that can be devised
6-7
Energy Diagrams
Enthalpy change, DH0: the difference in total bond energy between reactants and products
• a measure of bond making (exothermic) and bond breaking (endothermic)
Energy Diagrams
Energy diagram: a graph showing the changes in energy that occur during a chemical reaction
Reaction coordinate: a measure in the change in positions of atoms during a reaction
M a c in to s h P IC T im ag e fo rm at
is n o t su p p o rted
6-4
Reaction Mechanisms
A reaction mechanism describes how a reaction occurs
• which bonds are broken and which new ones are formed
Addition is regioselective
• regioselective reaction: an addition or substitution reaction in which one of two or more possible products is formed in preference to all others that might be formed
• the order and relative rates of the various bondbreaking and bond-forming steps
• if in solution, the role of the solvent • if there is a catalyst, the role of a catalyst • the position of all atoms and energy of the entire
is n o t s u p p o r te d
• exergonic reaction: a reaction in which the Gibbs free energy of the products is lower than that of the reactants; the position of equilibrium for an exergonic reaction favors products
6-11
Energy Diagram
A two-step reaction with one intermediate
6-12
Developing a Reaction Mechanism
How it is done
• design experiments to reveal details of a particular chemical reaction
• a maximum on an energy diagram
Activation Energy, DG‡: the difference in Gibbs free energy between reactantsபைடு நூலகம்and a transition state
• if DG‡ is large, few collisions occur with sufficient energy to reach the transition state; reaction is slow
• endergonic reaction: a reaction in which the Gibbs free energy of the products is higher than that of the reactants; the position of equilibrium for an endergonic reaction favors starting materials
Carbocation: a species in which a carbon atom has only six electrons in its valence shell and bears positive charge
6-14
Electrophilic Additions
• hydrohalogenation using HCl, HBr, HI • hydration using H2O in the presence of H2SO4 • halogenation using Cl2, Br2 • halohydrination using HOCl, HOBr • oxymercuration using Hg(OAc)2, H2O followed by
is n o t s u p p o rte d
6-17
HBr + 2-Butene
An energy diagram for the two-step addition of HBr to 2-butene
• the reaction is exergonic
6-18
Carbocations
Organic Chemistry
William H. Brown Christopher S. Foote Brent L. Iverson
6-1
M acintosh PIC T
Reactions im a g e fo rm a t is not supported
of Alkenes
Chapter 6
• summary of the relationships between DG0, DH0, DS0, and the position of chemical equilibrium
M acin to sh P IC T im ag e fo rm at
is n o t su p p o rted