Chemical reactivity and mechanisms

Question 1

Heterolytic bond cleavage

Answer 1

Results in forming ions & use only a single head curved arrow

Question 2

Bond dissociation energy

Answer 2

The energy required to break a covalent bond through hommolytic bond cleavage

Question 3

Homolytic Bond cleavage

Answer 3

Results in forming two uncharged radicals (Use two half curved arrows)

Question 4

Enthaply (ΔH)

Answer 4

Heat at constant pressure

Question 5

The ΔH⁰ is known as the ______________

Answer 5

Standard bond dissociation (under standard conditions like 1 atm)

Question 6

Heat of reaction

Answer 6

The total change in enthaply for a reaction

Question 7

Entropy

Answer 7

Measure of disorder associated with a system

Question 8

Spontaneous reaction

Answer 8

Increases total entropy (ΔS_tot = S_sys + S_surr) (ΔS_total has to be positive for a reaction to be spontaneous)

Question 9

Between liquids, solids, & gases list it in increasing entropy

Answer 9

S_solid < S_liquid gas (from least to greatest)

Question 10

Under constant pressure what is the equation used for ΔS_surr ?

Answer 10

ΔS_surr = -ΔH_sys / T

Question 11

What is the equation for Gibbs free energy?

Answer 11

ΔG = ΔH - TΔS (ΔG must be negative for a reaction to be spontaneous)

Question 12

Exergonic

Answer 12

A reaction where ΔG is negative

Question 13

Endergonic

Answer 13

A reaction where ΔG is positive

Question 14

Equilibrium constant (K_eq)

Answer 14

K_eq = [Products] /[Reactants]

Question 15

Equation relating equilibrium constant to ΔG

Answer 15

ΔG = -RTlnK_eq

Question 16

With the equation relating ΔG & K_eq if ΔG is negative then the __________ are favored (K_eq > 1) & if ΔG is positive the _________ will be favored (K_eq < 1)

Answer 16

Products, Reactnats

Question 17

What is the rate equation?

Answer 17

R = k[Reactants] (R = k[A] ^*[B]^*)

Question 18

What are the factors that affect the rate constant?

Answer 18

1. Energy Activation (E_a)
2. Temperature
3. Steric Considerations

Question 19

How does E_a (activation energy) affect the rate of a reaction?

Answer 19

The activation energy is the minium energy required for a reaction to occur so the lower the E_a the faster the reaction & the larger the E_a the slower the reaction

Question 20

How does the temperature affect the rate of a reaction?

Answer 20

The rate constant (k) is directly proportional to temp. & the rate of a reaction so increase the temp will increase the rate constant & speed up the rate of the reaction & vis versa when decreased

Question 21

Catalysts

Answer 21

Speeds up the reaction without being consumed (Enzymes are a type of calalysts)

Question 22

Transition state on a energy diagram

Answer 22

Highest peaks on the graph

Question 23

Intermediate on a energy diagram

Answer 23

Peaks where it concaves up on the graph

Question 24

The transition state is where the ____________ occurs where bonds are broken & formed

Answer 24

Reaction

Question 25

What is the Hammond Postulate?

Answer 25

States that if the reactants are close in energy to the transition state then the transition state will look like the reactants (exothermic reaction) & if the products are close in energy to the transition state then the transition state will look like the products (endothermic reaction)

Question 26

Nucleophile

Answer 26

Reacts with a positive charged atom & donates electrons (has a high electron density)

Question 27

Electrophile

Answer 27

Reacts with a negative charged atom & accepts electrons (Low electron density)

Question 28

A ____________ shows how a reaction takes place using a curved arrows to show the flow of electrons (The tail shows where the electrons coming from & the head shows where its going to)

Answer 28

Mechanism

Question 29

What are the patterns of a mechanism?

Answer 29

1. Nucleophilic Attack 2. Loss of a leaving group 3. Proton Transfer 4. Rearrangments

Question 30

Nucleophilic Attack

Answer 30

A nuclepphile attacking (donating electrons) to an electrophile

Question 31

Loss of a leaving group

Answer 31

Question 32

Proton Transfer

Answer 32

For a compound to lose a proton (transfer a proton (H) a base must be present to deprontonate the compound)

Question 33

Rearrangment (Carbocation arrangement)

Answer 33

Carbocation are stabilized by neigboring alkyl groups & a prcoess calles hyperconjugation- stablizes the P orbitial

Question 34

What are the two types of rearrangments to stablize the carbocations?

Answer 34

1. Hydride shift (involves moving a hydrogen) 2. Methyl shift (involves moving a methyl group)

Question 35

The terms primary, secondary, tertiary, represents the number of ________ groups attached directly to the positively charged atom

Answer 35

Alkyl

Question 36

\_\_\_\_\_\_\_\_\_\_\_ carbocation are the most stable, & __________ are the least stable (secondary carbocation is in between the two)

Answer 36

Tertiary, primary

Question 37

For a mehyl or hydride shift to occur they must be attacthed to a carbon atom that is ____________ to the carbocation

Answer 37

Adjacent

Question 38

All mechanism are just a combination of the \_\_\_\_\_\_\_\_\_\_

Answer 38

4 patterns

Question 39

When drawing the curved arrow the tail must either be on a bond or _________ & can never be on a \_\_\_\_\_\_\_\_\_\_

Answer 39

Lone pair, positive charge

Question 40

The head of the curved arrow shows where the electrons are going to form a _________ or \_\_\_\_\_\_\_\_\_

Answer 40

Bond or lone pair (Have to make sure dont break the octect rule)

Question 41

When predicting if a carbocation rearrangement (shift) can occur must determine wheteher the carbocation can become more ________ if a methyl or hydride shift was to occur

Answer 41

Stable

Question 42

Reversible arrows

Answer 42

Equilibrium arrows

Question 43

Irreverisble reaction arrows

Answer 43

Forward arrows

Question 44

A reversible arrow is used if the nucleophile is capable of functioning as a _____________ after the nucleophilic attack

Answer 44

A good leaving group

Question 45

A irrversible arrow is used if the nucleophile is a \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Answer 45

Poor leaving group

Question 46

For a loss of a leaving group a reversible arrow is mostly used for the reaction but its used only if the leaving group is capable of functioning as a \_\_\_\_\_\_\_\_\_\_\_\_\_

Answer 46

Good nucleophile

Question 47

For a proton transer they are mostly drawn with a reversible arrow if the ________ difference is low

Answer 47

pKa

Question 48

Irreversible arrows are used for a proton transfer when the pKa difference is greater than \_\_\_\_\_\_

Answer 48

10 pKa

Question 49

Carbocation rearrangment are always drawn with an __________________ arrow

Answer 49

Irreversible arrow (Beacuse stabilzing a secondary carbocation into a tertiary one)

Question 50

Free energy diagram gives us information on the ____________ & ________ of a reaction

Answer 50

Spontaneity & Rate of reaction

Question 51

Stability & reactivity have a ___________ relationship

Answer 51

Inverse relationship (increase the stability decreases the reactivity & vis versa)

Question 52

What are the 4 common indicators of a compound being reactive?

Answer 52

1. Formal charges 2. net dipoles (partial charges) 3. π bonds (have a good source of free electrons & wants give away) 4. Steric affect (Ring strains)

Question 53

Negative charged atoms are called \_\_\_\_\_\_\_\_\_\_\_\_\_

Answer 53

Nucleophiles (donates electrons)

Question 54

Positive charged atoms are called \_\_\_\_\_\_\_\_\_\_\_

Answer 54

Electrophiles (Accepts electrons)

Question 55

The side of the dipole with the _______________ preference can be used to predict nucleophile or electrophile whenever there is no formal charges present

Answer 55

Highest bond (whatever atom can form the most bonds)

Question 56

If a compound is not __________ then its neither nucleophile or electrophile

Answer 56

Reactive

Question 57

\_\_\_\_\_\_\_\_\_\_\_\_\_ can be both a nucleophile or electrophile depending on the atom its reacting with

Answer 57

Water

Question 58

Reactive molecules react to become more ___________ & share two electrons

Answer 58

Stable

Question 59

Electrons flow from regions of ____________ electron denisty to regions of \_\_\_\_\_\_\_\_\_\_\_\_\_\_electron denisty

Answer 59

High electron denisty (Nucleophile) , low electron density (Electrophile)

Question 60

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ always attacks ___________ & the curved arrows shows 2 electrons being shared & an arrow will then be repalced with a sigma bond & bond breaking is only needed to protect the octect rule

Answer 60

Nucleophile, electrophile

Question 61

Ring expansion (a type of carbocation rearrangment)

Answer 61

Occurs when a carbocation is adjacent to a 3,4,5 or small ring & turns it into a larger ring