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?