Lecture 5 Flashcards
(38 cards)
What is thermodynamics
it is a field of chemistry that describes the properties of a system at equilibrium
the relative concentrations of products and reactants in equilibrium depends on
the relative stability of the compounds, as the more stable the compound is the greater its concentration.
For example:
if Keq < 1 then the reactants are more stable in the equilibrium compared with the products
if Keq > 1then the products are more stable in the equilibrium compared with the reactants.
what is Gibbs’s free energy change
it is the difference between the free energy of the products and the free energy of the reactants under stander conditions.
G = free energy of products - free energy of reactants
what are the exogenic and endogenic reactions and which reaction is more favorable
exogenic reactions are when the reactants have more free energy than the products, where the reaction releases more energy than consumed and the Gibbs energy is negative.
Endogenic reactions are when products have more free energy than the reactants where the reactions consume more energy than released and the Gibbs energy is positive.
Exogenic reactions are more favored than endogenic reactions since the products are more stable
what is the equation that represents the relationship between Keq and the Gibbs free energy
G = -RTln Keq
what is gibbs rs with entropy and enthalpy
G = dH - T dS
what is enthalpy
it is the heat given off or consumed during a reaction dH = Heat required to break bonds - heat released to make bonds
what is Entropy
it is the measure of freedom of motion
S = freedom of movement of products - freedom of movement of reactants
when is a reaction favorable
when the products are favored and that occurs at Keq > 1 which gives a negative Gibbs energy and since G = dH - T dS the reaction is more favorable with more negative enthalpy and more positive entropy
what are the transition states for the reaction between HX and Alkenes
5.12 In the book important to make sure you know how to draw page 216 LOOK PLEASE
In the transition state atoms that either lose charge or gain charge are represented by
a partial negative charge or a partial positive charge
what is an intermediate
it is a compound that is a product for one step of the reaction and a reactant for the next step.
How is the electrophilic addition reaction between HX and Alkene look like in a reaction coordinate diagram
the first step is an endogenic reaction where the alkene acts as a nucleophile and attacks the hydrogen forming an intermediate of a carbonation that is less stable than the starting product, the second step is the reaction between the carbonation and the nucleophile of the halide where the final product is formed in a exogenic reaction where it is more stable than the reactants.
The total process is an exogenic reaction
What is the rate-determining step
if a reaction has more than 1 step the reaction that forms teh transition state with the highest point on a reaction coordinate is teh rate determining step where that reaction is what determines the overall rate of the reaction
A transition state can never be
isolated as they exist only fleetingly
what is the mechanism for the addition of hydrogen halide to an alkene
271 (pdf not on top)
what are the factors that determine the carbonation formed in addition of hydrogen halide to alkenes?
the stability of the carbocation and how it affects the rate and which it is formed
the stability of carbocations is affected by
the amount of alkyl groups attached to the positive carbon the more there are the more stable the carbonation is (Tertiary > secondary > primary)
why do alkyl groups stabilize carbocations
the alkyl groups decrease the concentration of the positive charge, as the positive charge in the carbon is due to an empty p orbital which if there is an adjacent alkyl group will result in the sigma bond formed between the adjacent carbon and hydrogen to overlap the empty p-orbital forming a partial positive charge on the adjacent hydrogen and carbon as well as a less positive charge on the carbon with the initial positive charge. This is called hyperconjugation and signifies stability as the charge is dispersed more with more alkyls attached.
hyperconjugation between the carbocation and alkyl groups only occurs when
the sigma bond on the alkyl and the empty p-orbital have proper orientation, which is easy to achieve due to free rotation.
what is a constitutional isomer?
they are isomers that have the same molecular formula but differ in the way the atoms are attached to each other
what is the regioselective reaction
a reaction in which two or more constitutional isomers could be obtained as products but one is predominant
what are the degrees of regioselectivity
- moderately regioselective
- highly regioselective
- completely regioselective - which means only one product is formed
when the possible carbocations formed are of the same order (3ani both secondary) is the reaction considered to be regioselective
no, it is not as both carbocations would form at the same rate which will cause the products to a 50% to 50% amounts
