Ch. 5: Alkenes Flashcards
An alkene is (1) ____________________ . Because alkenes contain fewer than the maximum # of hydrogens, they are called
(2) ________________________ .
(1) a hydrocarbon that contains a double bond.
(2) unsaturated hydrocarbons.
The double bond is the __________ , or center of reactivity, of an alkene.
functional group
The general molecular formula for a hydrocarbon is __________ , minus 2 hydrogens for every pi bond or ring in the molecule.
CnH2n+2
The number of pi bonds plus the # of rings is called the _______________ .
degree of unsaturation
When there are both a functional group suffix and a substituent, which one gets the lowest possible number?
The functional group suffix gets the lowest possible number.
What is the difference between the Z isomer and the E isomer? What do priorities mean in this context?
The Z isomer has the high-priority groups on the same side of the double bond.
The E isomer has the high-priority groups on opposite sides of the double bond.
The relative priorities depend on the atomic numbers of the atoms bonded directly to the sp2 carbon.
All compounds with a particular _____________ react in the same way.
functional group
Due to the cloud of electrons above and below the pi bond, an alkene is a __________.
nucleophile
What is the name for the electron-deficient species, opposite to nucleophiles?
Electrophiles are the electron-deficient species. Nucleophiles are attracted to them.
What kind of reactions do alkenes undergo?
Alkenes undergo electrophilic addition reactions.
What do curved arrows indicate in reactions?
Curved arrows show the bonds that are formed and the bonds that are broken in a reaction.
Thermodynamics vs. kinetics
Thermodynamics describes a reaction at equilibrium.
Kinetics describes how fast the reaction occurs.
What is a reaction coordinate diagram?
A reaction coordinate diagram shows the energy changes that occur during the course of a reaction.
The more stable a species, the _________ its energy.
lower
What is the state that is in limbo between reactants and products?
As reactants are converted into products, a reaction passes through a maximum-energy transition state.
What is formed between a reactant and a product?
An intermediate.
Transition state vs. intermediate
A transition state has partially formed bonds while an intermediate has fully formed bonds.
The _________________ has its transition state at the highest point on the reaction coordinate.
rate-determining step
What is Keq?
Keq represents the equilibrium constant which is found by the concentrations of the products divided by the concentrations of the reactants.
Define Le Chatelier’s principle.
Le Chatelier’s principle states that if an equilibrium is disturbed, the system will adjust to offset the disturbance.
What is the Keq value and the sign of free energy (delta G) when the reaction is exergonic? When the reaction is endergonic? What is the relationship between products and reactants in these 2 cases?
When the reaction is exergonic, Keq > 1, free energy is negative, and the products are more stable than the reactants.
When the reaction is endergonic, Keq < 1, free energy is positive, and the reactants are more stable than the products.
What is the formula for Gibbs free-energy change (delta G)?
delta G = delta H - T * delta S, where delta G = Gibbs free-energy change, delta H = change in enthalpy, T = temperature in Kelvin, delta S = change in entropy.
What does delta H stand for?
Delta H is change in enthalpy, which is the heat given off or consumed as a result of bond making and bond breaking.
What kind of reaction has a negative delta H?
What kind of reaction has a positive delta H?
An exothermic reaction has a negative delta H.
An endothermic reaction has a positive delta H.
What does delta S stand for?
Delta S is change in entropy, which is the change in the freedom of motion of the system.
What causes delta G to be negative?
The formation of products with stronger bonds and greater freedom of motion causes delta G to be negative.
What is the formula that relates delta G and Keq?
delta G = -RT (ln Keq),
where delta G is Gibbs free energy change,
R is the gas constant (1.986 x 10^-3 kcal mol^-1 K^-1 or 8.341 x 10^-3 kJ mol^-1 K^-1),
and T is temperature in Kelvins.
What does delta G double dagger represent?
Delta G double dagger represents the free energy of activation, which is the energy barrier of a reaction. It is the difference between the free energy of the reactants and free energy of the transition state.
The rate of the reaction _________ as delta G double dagger (free energy of activation) decreases.
increases
Anything that makes the reactant less stable or makes the transition state more stable ___________ the rate constant for the reaction.
increases
What kind of stability is delta G double dagger (free energy of activation)?
What kind of stability is delta G (Gibbs free energy)?
delta G double dagger is kinetic stability while delta G is thermodynamic stability.
The rate of a reaction depends on:
(1) ______________,
(2) ______________, and
(3) ______________.
(1) concentration of the reactants,
(2) temperature, and
(3) rate constant.
Define rate constant.
The rate constant for a reaction indicates how easy it is for the reactants to reach the transition state.
First-order reaction vs. second-order reaction
A first-order reaction depends on the concentration of one reactant.
A second-order reaction depends on the concentrations of 2 reactants.
How does a catalyst help expedite a reaction?
A catalyst decreases the energy barrier that has be overcome in the process of converting the reactants into products.
A catalyst is neither (1) ________ nor
(2) ________ during the reaction.
(1) consumed
(2) changed
A catalyst does not change the (1) _______ of product formed; it changes only the (2) _______ at which the product is formed.
(1) amount
(2) rate
Most biological catalysts are proteins called ________ .
enzymes
_______________ is the ability of one molecule to recognize another molecule.
Molecular recognition
