Chapter 4- Analyzing Organic Reactions

Question 1

Lewis acid/base

Answer 1

acid- electron acceptor

base- electron donor

Question 2

lewis acid

Answer 2

• electron acceptor
• electrophile
• positive charge

Question 3

lewis base

Answer 3

• electron donor
• nucleophile
• anions (negative charge)

Question 4

coordinate covalent bonds

Answer 4

formed when lewis acids and bases interact. they are covalent bonds in which both electrons in the bond came from the same starting atom (Lewis base)

Question 5

bronsted-lowry acid/base

Answer 5

acid- donates H+

base- accepts H+

Question 6

acid dissociation constant (Ka)

Answer 6

Ka = [H+][A-] / [HA]

Question 7

pKa

Answer 7

pKa = -log(Ka)

• acidic molecules: smaller pKa
• basic molecules: larger pKa

Question 8

electronegativity and acidity

Answer 8

the more electronegative an atom the higher the acidity

Question 9

functional groups that act as acids

Answer 9

alcohols, aldehydes, ketones, carboxylic acids, most carboxylic acid derivatives

Question 10

functional groups that act as bases

Answer 10

amines and amides

Question 11

nucleophiles

Answer 11

BASES ARE NUCLEOPHILES.
ex: look for C, H, O, N with a minus sign or lone pair to identify most nucleophiles. (amines groups make good nucleophiles)

“nucleus-loving”
-with either lone pairs or pi bonds that can form new bonds to electrophiles

Question 12

typical trends that determine nucleophilicity

Answer 12

1. charge- increases with a more negative charge
2. electronegativity- decreases as this increases
3. steric hinderance- bulkier molecules are less nucleophilic
4. solvent- explained in another flashcard

Question 13

solvent effects

Answer 13

polar protic solvents (can H bond)

• ex: carboxylic acids, ammonia/amines, water/alcohols
• nucleophilicity increases down the periodic table

aprotic solvents (cannot H bond)

• ex: DMF, DMSO, acetone
• nucleophilicity increases up the periodic table

Question 14

electrophiles

Answer 14

+ charge or positively polarized atom that accepts electron pair when forming new bonds with a nucleophile. typically lewis acids

-ex (in order from most electrophilic to least): anhydrides, carboxylic acids, esters, amides

-carbocations are very electrophilic
“electron-loving”

Question 15

leaving groups

Answer 15

molecular fragments that retain electrons after heterolysis.

heterolytic reactions: a bond is broken and both electrons are given to one of the two products.

best leaving groups will be able to stabilize the extra electrons. (ex: weak bases and halogens)

Question 16

substitution reactions

Answer 16

weaker base (leaving group) is replaced by the stronger base (nucleophile)

Question 17

commonalities between Sn1 and Sn2 reactions

Answer 17

a nucleophile forms a bond with a substrate carbon and a leaving group leaves.

Question 18

Sn1

Answer 18

2 steps (first-order reaction depending on reactants from step 1)

1. rate limiting step- leaving group leaves generating a positively charged carbocation
   * note: the more substituted this carbocation is the more stable it is
2. nucleophile then attacks the carbocation resulting in the substitution product.

*note: typically a racemic mixture is produced in Sn1 reactions

Question 19

Sn2

Answer 19

1 step (aka. concerted reaction)
1. nucleophile attacks the compound at the same time the leaving group leaves 

backside attack- nucleophile actively displaces the leaving group. MUST be a strong nucleophile to do this.

typical substrates: alkyl halide, tosylate, mesylate AND a nucleophile (second order reaction because it depends on both of these)

-wont occur with tertiary carbons

Question 20

oxidation and reduction in O.Chem

Answer 20

OIL RIG

oxidation: increase in oxidation state

reduction: decrease in oxidation state
reduction = increasing the number of bonds to hydrogen

Question 21

list of good oxidizing agents

Answer 21

high affinity for electrons (O2, O3, and Cl2)

unusually high oxidation states (Mn7+, permanganate MnO4-, and Cr6+ in chromate CrO4 2-)

Question 22

what are primary alcohols oxidized to?

Answer 22

one level to become aldehydes and another level to become a carboxylic acid

Question 23

what are secondary alcohols oxidized to?

Answer 23

ketones

Question 24

typical trend in redox reactions

Answer 24

oxidation reactions- increase in number of bonds to oxygen

oxidizing agents- contain metals bonded to a large number of oxygen atoms

Question 25

if the reagent is PCC whats typically gonna happen

Answer 25

alcohol turning into aldehyde or ketone

Question 26

if the reagent is KMnO4 or H2CrO4 whats typically gonna happen

Answer 26

carboxylic acid forms onto the substrate

Question 27

if the reagent is O3 whats typically gonna happen

Answer 27

double or triple bond will split into two separate molecules both with a double bond to oxygen where they were originally bonded to each other

Question 28

list of good reducing agents

Answer 28

sodium, magnesium, aluminum, zinc (low electronegatvity)

metal hydrides (NaH, CaH2, LiAlH4, NaBH4) b/c they all contain a H- ion

Question 29

aldehyde and ketone reduction

Answer 29

aldehydes- primary alcohol

ketones- secondary alcohol

Question 30

general trend with reactivity in both nucleophile-electrophile and oxidation-reduction reactions

Answer 30

the more oxidized the functional gorup the more reactive it is

Question 31

in a redox reaction AND nucleophile-electrophile reaction what part of the reagent is most likely to be part of the reaction

Answer 31

for BOTH it is the highest-priority functional group

Question 32

common reactive site on MCAT

Answer 32

carbon on a carbonyl due to the positive polarity (negative polarity on the oxygen group)

Question 33

protecting group

Answer 33

if a molecule contains multiple reactive functional groups then some of them will first be converted to a nonreactive group and serve as a protecting group then the reaction will proceed.