Organic Chemistry

138 CHAPTER 3 Alkenes• Thermodynamics and Kinetics

place in a reaction. The more stable the species, the lower is

its energy. As reactants are converted into products, a reac-

tion passes through a maximum energy transition state. An

intermediateis the product of one step of a reaction and

the reactant for the next step. Transition states have partial-

ly formed bonds; intermediates have fully formed bonds.

The rate-determining stephas its transition state at the

highest point on the reaction coordinate.

The relative concentrations of reactants and products at

equilibrium are given by the equilibrium constant The

more stable the compound, the greater is its concentration

at equilibrium. If products are more stable than reactants,

is is negative, and the reaction is exergonic;

if reactants are more stable than products,

is positive, and the reaction is endergonic.

is the Gibbs free-energy change.

is the change in enthalpy—the heat given off or consumed

as a result of bond making and bond breaking. An

exothermic reactionhas a negative an endothermic

reaction has a positive ¢H°. ¢S° is the change in

¢H°;

¢H°-T¢S°;¢G° ¢H°

¢G° ¢G° =

Keq 6 1,

Keq 7 1,¢G°

Keq.

entropy—the change in the degree of disorder of the sys-

tem. A reaction with a negative has a favorable equi-

librium constant: The formation of products with stronger

bonds and greater freedom of motion causes to be

negative. and are related by the formula

The interaction between a solvent and a

species in solution is called solvation.

The free energy of activation, is the energy barri-

er of a reaction. It is the difference between the free energy

of the reactants and the free energy of the transition state.

The smaller the the faster is the reaction. Anything

that destabilizes the reactant or stabilizes the transition state

makes the reaction go faster. Kinetic stabilityis given by

thermodynamic stabilityby The rateof a re-

action depends on the concentration of the reactants, the

temperature, and the rate constant. The rate constant,

which is independent of concentration, indicates how easy

it is to reach the transition state. A first-order reactionde-

pends on the concentration of one reactant, a second-order

reactionon the concentration of two reactants.

¢G‡, ¢G°.

¢G‡,

¢G‡,

• RT ln Keq.

¢G° Keq ¢G°=

¢G°

¢G°

Key Terms

acyclic (p. 112)

addition reaction (p. 124)

alkene (p. 111)

allyl group (p. 115)

allylic carbon (p. 115)

Arrhenius equation (p. 133)

cis isomer (p. 117)

cis–trans isomers (p. 117)

degree of unsaturation (p. 112)

Eisomer (p. 120)

electrophile (p. 122)

electrophilic addition reaction (p. 124)

endergonic reaction (p. 127)

endothermic reaction (p. 128)

enthalpy (p. 128)

entropy (p. 128)

exergonic reaction (p. 127)

exothermic reaction (p. 128)

experimental energy of activation (p. 133)

first-order rate constant (p. 132)

first-order reaction (p. 132)

free energy of activation (p. 131)

functional group (p. 121)

geometric isomers (p. 117)

Gibbs free-energy change (p. 126)

intermediate (p. 136)

kinetics (p. 131)

kinetic stability (p. 131)

mechanism of the reaction (p. 123)

nucleophile (p. 122)

rate constant (p. 132)

rate-determining step (p. 136)

rate-limiting step (p. 136)

reaction coordinate diagram (p. 125)

saturated hydrocarbon (p. 112)

second-order rate constant (p. 133)

second-order reaction (p. 132)

solvation (p. 130)

thermodynamics (p. 126)

thermodynamic stability (p. 131)

trans isomer (p. 117)

transition state (p. 125)

unsaturated hydrocarbon (p. 112)

vinyl group (p. 115)

vinylic carbon (p. 115)

Zisomer (p. 120)

Problems

27. Give the systematic name for each of the following compounds:
    a. c.

b. d.

CH 2 CH 3

CH 2 CH 2 CH 2 CH 3

C

H 3 C

C

H 3 C

CH 3

CH 2 CH 3

CH 2 CH 2 CHCH 3

C

CH 3 CH 2

C

H 3 C

CH 3

CH 3

CH 3 CH 2 CHCH CHCH 2 CH 2 CHCH 3

Br Br

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