Ch. 6 – Organic Reactions

Question 1

T/F: When two ions with unlike charge bond, an ionic bond is always formed.

Answer 1

False. Many organic reactions involve the combination of two ions that form a covalent bond. For example, if a carbocation is attracted to an ion with a negatively charged oxygen atom, the oxygen will contribute two bonding electrons to the carbon, and a covalent bond will be formed.

Question 2

Why are reagents often drawn on top of arrow?

Answer 2

to focus on organic starting materials

Question 3

Where is the solvent or temp of a reaction added in an equation?

Answer 3

above or below arrow

Question 4

What is the symbol for light?

Answer 4

hv

Question 5

What is the symbol for heat?

Answer 5

∆

Question 6

What do numbers above or below the arrow signal?

Answer 6

sequential steps of a reaction

Question 7

T/F: Organic byproducts are often omitted.

Answer 7

True

Question 8

What occurs during a substitution reaction?

Answer 8

atom/group is replaced by another atom/group

one sigma bond breaks, another one forms

Question 9

When do substitution reactions most likely occur?

Answer 9

most commonly occur when a heteroatom more EN than carbon replaces a hydrogen

Question 10

What occurs during an elimination reaction?

Answer 10

elements of starting materials are lost

2 sigma bonds are broken, one pi bond is formed

(two groups removed)

Question 11

When does elimination reaction most commonly occur?

Answer 11

when one group is hydrogen and another group on adjacent carbon is a heteroatom more EN than carbon

Question 12

What occurs during an addition reaction?

Answer 12

elements are added to starting materials

a pi bond is broken and two sigma bonds form

Question 13

What is a reaction mechanism?

Answer 13

detailed description of how bonds are broken and formed as starting materials are converted to products

Question 14

What is a concerted reaction?

Answer 14

a one-step reaction

Question 15

What is a stepwise reaction?

Answer 15

A multiple-step reaction where starting materials are converted to unstable intermediates (reactive) and then form product

Question 16

What is bond cleavage?

Answer 16

breaking of a bond, electrons can either be divided equally or unequally between two atoms of the bond

Question 17

What is homolytic cleavage?

Answer 17

equal dividing of electrons (each atom gets one electron)

Question 18

What does homolysis generate?

Answer 18

uncharged reactive intermediates with unpaired electrons

Question 19

What is heterolytic cleavage?

Answer 19

unequal dividing of electrons (each atom gets both or none electrons)

Question 20

Where do electrons go in heterolysis?

Answer 20

usually to more EN atom

Question 21

What does heterolysis generate?

Answer 21

charged intermediates that are reactive

Question 22

What are fishhook arrows?

Answer 22

used to show movement of one electron

Question 23

What are radicals?

Answer 23

reactive intermediates with a single unpaired electron

generated by homolysis, highly unstable, no charge

Question 24

What is a carbocation?

Answer 24

electrophile carbon with plus charge (electron deficient)

result of heterolysis where electrons go to more EN heteroatom

+ intermediate, unstable, reactive

Question 25

What is a carbanion?

Answer 25

nucleophile carbon with negative charge (electron rich) has lone pair of e- (- intermediate, reactive, unstable) generated by heterolysis where two electrons are given to C and none are given to heteroatom

Question 26

Are radicals, carbocations and carbanions electrophilic or nucleophilic?

Answer 26

electrophilic: radials and carbocations nucleophilic: carbanions

Question 27

Does forming bonds absorb or release energy?

Answer 27

bond formation ALWAYS RELEASES energy

Question 28

What is bond dissociation energy? What is symbol?

Answer 28

energy needed to homolytically cleave a covalent bond ∆Hº BDE is always positive!

Question 29

What is enthalpy? What is symbol?

Answer 29

∆Hº | energy absorbed or released in a reaction

Question 30

What is a positive/negative ∆Hº indicate?

Answer 30

``` positive = endothermic negative = exothermic ```

Question 31

How does BDE change with bond strength?

Answer 31

as bond strength increases, BDE increases

Question 32

How does BDE change with ptable?

Answer 32

going down ptable, atom size increases and BDE decreases

Question 33

How does BDE change with % s character?

Answer 33

as % s character increases, so does BDE

Question 34

How is BDE determined for a reaction?

Answer 34

∆Hº = (sum of bonds broken) + (sum of bonds formed (-))

Question 35

What are the limitations of BDE?

Answer 35

only give overall energy change don't give info about reaction mechanism only for gas phase

Question 36

What is thermodynamics?

Answer 36

relation of energy and equilibrium

Question 37

What is kinetics?

Answer 37

reaction rates

Question 38

How is Keq calculated?

Answer 38

[products]/[reactants]

Question 39

What does Keq>1 mean?

Answer 39

products are favored

Question 40

What does Keq<1 mean?

Answer 40

reactants favored

Question 41

What determines the positive of equilibrium?

Answer 41

relative energies of reactants and products

Question 42

What is Gibbs Free Energy?

Answer 42

free energy in a molecule (Gº)

Question 43

What does ∆Gº represent?

Answer 43

overall E difference between R and P

Question 44

How is ∆Gº calculated?

Answer 44

Gº products – Gº reactants or -2.303RT log Keq

Question 45

What does it mean if ∆Gº is positive or negative?

Answer 45

positive: Keq < 1, endothermic, reactants favored negative: Keq > 1, exothermic, products favored

Question 46

When does equilibrium favor products?

Answer 46

when Keq > 1 and when products are more stable (have less E) than reactants

Question 47

What is entropy?

Answer 47

measure of a system's disorder

Question 48

What causes higher entropy? (five factors)

Answer 48

1) more freedom of motion 2) more disorder 3) gas > liquid > solid 4) acyclic > cyclic 5) more than one product

Question 49

What is ∆Sº?

Answer 49

change in disorder/entropy between R and P

Question 50

What does positive/negative ∆Sº mean?

Answer 50

positive: products more disordered negative: reactants more disordered

Question 51

Is positive or negative ∆Sº reaction favored?

Answer 51

positive, nature favors disorder

Question 52

How is ∆Gº calculated including entropy?

Answer 52

∆Gº = ∆Hº – T∆Sº

Question 53

What contributes to total energy change for reaction?

Answer 53

change in bonding E, change in disorder

Question 54

How does temperature affect ∆Sº?

Answer 54

at high T, entropy is small compared to ∆Hº and can be neglected

Question 55

What does negative/positive ∆Hº signal?

Answer 55

positive: starting materials favored (endothermic) negative: products favored (exothermic)

Question 56

What is an energy diagram?

Answer 56

represents E change when R becomes P

Question 57

What is a transition state?

Answer 57

unstable energy max where bonds are partially broken and formed; can never be isolated, caused by e-e repulsion in cloud when atoms get too close (high energy)

Question 58

What is activation energy?

Answer 58

E difference between starting materials and transition state (minimum amount of energy needed to break R bonds)

Question 59

How are transition states drawn?

Answer 59

in brackets, partial bonds and charges, add double dagger to outside bracket

Question 60

How many humps are in a multistep reaction?

Answer 60

humps = number of steps

Question 61

In energy diagram, what is rate-determining step?

Answer 61

step with highest Ea

Question 62

What is the reaction rate?

Answer 62

how fast a reaction proceeds

Question 63

What does a larger Ea mean for reaction rate?

Answer 63

larger Ea = slower reaction

Question 64

How does concentration affect reaction rate?

Answer 64

higher concentration = faster rate

Question 65

How does temp affect reaction rate?

Answer 65

higher temp = faster rate

Question 66

How many degrees increase (in ºC) are needed to double reaction rate?

Answer 66

10 ºC

Question 67

What is a rate law?

Answer 67

shows relationship between reactant concentration and reaction progress

Question 68

What is rate law equation?

Answer 68

rate = k[reactants]

Question 69

How does size of k affect rate?

Answer 69

large k = fast | small k = slow

Question 70

For multistep reaction, which reactants should be put in rate law?

Answer 70

those included in rate-determining step

Question 71

What is a bimolecular reaction?

Answer 71

reaction with 2 reactants

Question 72

What is the order of a reaction (kinetics)?

Answer 72

sum of exponents of concentration terms

Question 73

How are exponents determined for rate law?

Answer 73

experimentally

Question 74

What is a unimolecular reaction?

Answer 74

reaction involving only one reactant

Question 75

What is a catalyst?

Answer 75

a substance that speeds up a reaction rate and does not change during a reaction, not a product

Question 76

Where are catalysts written in rxn equation?

Answer 76

above or below arrow

Question 77

Does a catalyst affect Keq?

Answer 77

nope

Question 78

What are enzymes?

Answer 78

biochemical catalysts composed of amino acids held together in very specific 3D shape, have active site