chem test 3
nucleophile
- electron-rich species, can donate a pair of electrons - lewis bases
exergonic
- negative ΔG - reactants are higher than products
endergonic
- positive ΔG - reactants are lower than products
exothermic reaction
- the energy gained by bonds formed exceeds the energy needed for bonds broken - products are more stable than reactants
intermediate
- "middle" species formed during a reaction - observable, exist for a period of time - energy minima (troughs) on energy diagram
electrophile
- electron-deficient species, can accept a pair of electrons - lewis acids
homolytic bond cleavage
a curved arrow with a single bar showing the movement of one electron to the X and Y atoms, creating radicals
heterolytic bond cleavage
a curved arrow with two bars showing the movement of two electrons, creating ions
irreversible
carbocation rearrangements are generally ?
yes
is water a good leaving group?
hammond postulate
the transition state is more similar in structure to the species to which it is more similar in energy
ΔH = - ΔS = + ΔG = -
to be a spontaneous reaction.... ΔH = ? ΔS = ? ΔG = ?
- shifts can only occur from an adjacent carbon - shifts only occur if a more stable carbocation results
what are the two rules regarding 1,2-hydride/methide shifts?
BDE (bonds broken) - BDE (bonds formed)
what is the equation used to find ΔH?
if the pKa difference is more than 10 units, it is irreversible. if it is less than 10 units, it is reversible.
what is the rule regarding proton transfers being reversible or irreversible?
gibbs free energy
ΔG
1) when there are more moles of product than reactant 2) when a cyclic compound becomes acyclic
ΔSsys will be positive when? (2)
nucleophilic attack
nucleophile attacking an electrophile
faster
short "hump"/Ea = slower or faster rate?
a resonance stabilized cation is formed
tertiary carbocations typically will not rearrange unless what?
polarizeable
the more ? a nucleophile is, the stronger it is
endothermic reaction
- the energy needed for bonds broken exceeds the stability gained by the bonds formed - products are less stable than reactants
transition state
- the high energy state a reaction passes through - fleeting, cannot be observed - energy maxima (peaks) on energy diagram
activation energy (Ea)
- the minimum amount of energy required for a molecular collision to result in a reaction - the "hump" you must get over to convert reactants to products
ΔStot
- total entropy change - will determine whether a process is spontaneous
enthalpy
- ΔH - the heat energy exchange between the reaction and its surroundings
entropy
- ΔS - the number of vibrational, rotational, and translational states the energy of a compound is distributed into
yes
if the attacking nucleophile is a good leaving group, will the reaction be reversible?
reversible
loss of a leaving group is virtually always ?
electrophiles
are carbocations and partially-positive atoms nucleophiles or electrophiles?
decrease
as carbon count increases, does bond dissociation energy increase or decrease?
decrease
do catalysts increase or decrease the Ea?
decrease
does bond dissociation energy increase or decrease as you go down the periodic table?
decrease
does branching increase or decrease bond dissociation energy?
absorb
does breaking a bond require the system to absorb or release energy?
faster
does increased temperature produce a faster or slower rate?
loss of a leaving group
heterolytic bond cleavage, an atom or group takes the electron pair
no
if the attacking nucleophile is a poor leaving group, will the reaction be reversible?
no
is methyl a good leaving group?
endothermic
is the following describing what an exothermic or endothermic energy diagram would look like? - products are higher in energy - energy is consumed (KE --> PE) - ΔH is positive - temperature of surroundings decreases
exothermic
is the following describing what an exothermic or endothermic energy diagram would look like? - products are lower in energy - energy is released as heat (PE --> KE) - ΔH is negative - temperature of surrounds increases
Ea, ΔG
kinetics focuses on ? while thermodynamics focuses on ?
methyl, primary, secondary, tertiary
name the carbocation rearrangements in order from least to most stable
slower
tall "hump"/Ea = slower or faster rate?
