Midterm 1 Flashcards
What are substitution reactions?
One functional group substitutes for another
What is an elimination reaction?
Atoms or groups of atoms in adjacent carbons are eliminated as a small molecule
Saturated become unsaturated
What are addition reactions?
Opposite of elimination reactions
Double becomes single
What are nucleophiles and electrophiles?
Nucleophiles: attracted to positive charges (negatively charged)
Electrophiles: attracted to electrons (positively charged)
Most reactions happen when a nucleophile and electrophile interact
What are nucleophilic centres?
Lone pairs, negative charges, and multiple bonds
What are electrophilic centres?
Positive charges and positively polarized atoms
What are the two ways movement of electrons cause reactions?
1) a bond forms as a nucleophile and an electrophile interact (electrons in centre become barn)
2) bonding electrons move to an atom, breaking the bond, and the atom leaves
What occurs in nucleophilic substitution reactions?
A nucleophile attacks a substrate and creates a product and a leaving group
What are the two mechanisms of substitution reactions?
Sn2 - one step reaction where rate depends on concentrations of both
Sn1 - two step reaction. First step creates an intermediate carbocation which then reacts with the nucleophile. Rate is based on slowest step
What factors affect the SN1 reaction rate?
- Stability of the intermediate: tertiary is fastest
2. Strength of the leaving group: stronger bases = poor leaving group,
What are the two elimination mechanisms?
E2: rate depends on concentration of both, 1 step
E1: two steps, slow and fast
What is regioselectivity?
Placement of double bond
One is preferred over the other
Creates a major and a minor
The more highly substituted alkene is the major
What is stereo selectivity?
Cis or trans
Trans is generally major
How do you determine where the electronegative atom goes in an addition reaction?
Use markovnikovs rule: the less electronegative atom bonds to the C atom that have the greater number of H atoms
What occurs when you have chirality with addition reactions?
Nucleophile can attack from front or back so end up with 50/50 split S/R
Define spontaneous change
No action from outside the system is necessary
Occurs on it’s own
Naturally move only in spontaneous direction
Does spontaneous change = heat released?
Not always
Spontaneous change = energy released always
Define entropy
A measure of the disorder or randomness in a closed system
A quantitative measure of the amount of thermal energy not available to do work
The tendency for all matter and energy in the universe to evolve towards a state of inert uniformity
What is the Boltzmann equation?
S = k ln W K= 1.38 x 10^ -23 j/k W= number of ways that state can be achieved
Why is low energy less probable?
Nature is striving towards a state of high entropy
Is entropy a state or path function?
State function
Path taken and rate are irrelevant
When is entropy greater than 0?
Increase in enthalpy Melting Vaporizing Making a solution A reaction that produces an increased number of moles Heating a substance
Why is the entropy of melting greater than 0?
As goes from solid to liquid, becomes more disordered
Why is the entropy of vaporizing greater than 0?
When going for liquid to gas, disorder increases
Why is the entropy of making a solution greater than 0?
It is far more likely that the solutions mix evenly than layered as it has a higher entropy
Why is the entropy of a redaction that produces an increased number of moles greater than 0?
More bonds are broken than made
What is the equation for calculating 🔺S of a solution?
🔺S rxn = E(vi Si)
Vi = stochiometric coefficient of species i
Si = absolute entropy of species i
When can the entropy of a system decrease?
Only if the entropy of the surroundings increases even more
What must the entropy be for the reaction to be spontaneous?
🔺S > 0
What is needed for a nonspontaneous process to take place?
Need outside action such as a change in p, T concentrations
Possibly but only if changing conditions
What is the equation for 🔺S of the surroundings?
-🔺H system / T
What is Gibbs free energy?
The maximum non-pV energy obtained from a system
🔺G = 🔺H - T🔺S
When is Gibbs free energy greater than 0?
H S G spontaneous - + - always \+ - + never - - +- at lower T \+ + +- at higher T
Is free energy a state or path function?
State function
Path and rate is irrelevant
What is Q?
Reaction quotient
🔺G = 🔺Go + RT ln Q
What happens to vapour pressure at equilibrium?
Rate of evaporation = rate of condensation
What is a Clausius-Clapeyron?
ln(pvap)=-(🔺Hvap/R)(1/T)+(🔺Svap/R)
What is a Clausius-Clapeyron pressure equation?
ln(p2) = ln(p1) + 🔺Hvap/R (1/t1-1/t2)
What is troutons rule?
🔺S’vap = 🔺H’vap/Tb
What is pyro metallurgy?
Production of metals from ores using heat
What are elementary reactions?
The simplest steps in a reaction
Each involved bond making and breaking
Usually unimolecular or bimolecular
What is the rate determining step?
The slowest elementary reaction in a multistep reaction
Determines overall rate of reaction
What does a catalyst do?
Speeds up a reaction but is not consumed itself
Provides a different mechanism for the reaction to proceed
What are the steps to heterogeneous catalysis?
- Absorption
- Migration across surface
- Reaction
- Desorption
What is a thermal explosion?
As reaction proceeds T rises, k rides
Reaction goes faster t rises, k rises
BOOM
releases a large pressure wave
What is a chain explosion?
Radicals contain unpaired electrons which are very reactive
1. Initiation step: radicals are produced
2. Propagation steps: no net radical production than branching occurs, number of radicals increases
More radicals = higher rates = more radicals = BOOM
What is the rate law?
Expresses how the rate varies with concentrations of reactants
Rate = k[reactant]^n
First order k= s^-1
2nd order k= M^-1 s^-1
What is the integrated rate law?
1st order: ln([A]/[A]o) = -kt
2nd order: 1/[A] = kt + 1/[A]o
What is the half life?
1st order: t1/2 = 0.693/k
2nd order: t1/2 = 1/k[A]o
What affects the reaction rate?
- Rate of collisions between A and B
- Fraction of collisions having correct orientation
- Fraction of collisions having sufficient energy to cause reaction
What is the activation energy?
The energy required for a reaction to go to completetion
What so the Arrhenius equation?
K = Ae^-Ea/RT
What are the three most important types of organic reaction?
Substitution, elimination, addition
