Final Exam: Addition and Synthesis

Question 1

why are alkene and alkyne addition rxns called ‘addition’ rxns?

Answer 1

Because a pi bond is broken and something new is added to the molecule in its place

Question 2

why are addition rxns usually exothermic?

Answer 2

because the resulting sigma bonds are stronger than the pi bonds they came from

Question 3

what is syn addition?

Answer 3

when both of the elements being added to a molecule are on the same face (both dashed or both wedged)

Question 4

what is anti addition?

Answer 4

when elements being added to a molecule are on DIFFERENT faces (one is dashed and the other is wedged)

Question 5

when does syn and anti apply to addition reactions?

Answer 5

when the starting material/molecule being added to is asymmetrical

Question 6

what is Markonikov addition?

Answer 6

when a nucleophile attacks the most substituted carbon

Question 7

what is ANTI markonikov addition?

Answer 7

when a nucleophile attacks the LESS substituted carbon

Question 8

what’s the difference between halogenation and halohydrin rxn?

Answer 8

halogenation will have X2 but halohyrin will have X2 AND H2O

Question 9

what are the reactants for hydroboration-oxidation rxns?

Answer 9

BH3 (with THF, NaOH, and/or H2O)

Question 10

does the presence of a hydrogen peroxide reactant (H2O2) indicate Markonikov addition or ANTI Markonikov addition?

Answer 10

the presence of hydrogen peroxide tells you there will be ANTI Markonikov addition

Question 11

what 3 metals are used for hydrogenation rxns?

Answer 11

Pd, Pt, or Ni

Question 12

which rxns give you H and OH across the double bond?

Answer 12

acid catalyzed hydration, hydroboration-oxidation, and oxymercuration-demercuration

Question 13

of the 3 rxns that give you H and OH across the double bond, which one DOES do rearrangement?

Answer 13

acid catalyzed hydration

Question 14

which 4 alkene rxns make triangle/square intermediates instead of doing rearrangement?

Answer 14

halogenation, halohyrin, hydroboration-oxidation, and oxymercuration-demercuration

Question 15

how many of the alkene rxns make triangle/square intermediates instead of doing rearrangement?

Answer 15

4

Question 16

do triangle/square intermediates result in syn addition or anti addition?

Answer 16

anti

Question 17

what does dihydroxyllation add across the double bond?

Answer 17

two OH groups

Question 18

does the presence of carbocation indicate syn addition, anti addition, or both?

Answer 18

both

Question 19

when do you have to worry about showing dashes and wedges?

Answer 19

When the molecule is asymmetrical

Question 20

what characteristics do you need to know to predict hydroboration oxidation products?

Answer 20

1. ultimately add H and OH across pi bond
2. ANTI Mark
3. Syn addition
4. ring intermediate instead of carbocation; no rearrangement

Question 21

which carbon is the alpha carbon?

Answer 21

the carbon bearing the leaving group

Question 22

what are the 3 categories of stereoselectivity?

Answer 22

non-selective (rxn will do syn and anti)
syn selective
anti selective

Question 23

which reagents are stereoselective?

Answer 23

Hydrobromation (BH3) is syn
Hydrogenation (H2) syn
Bromation (Br2) anti

Question 24

when do we have to care about stereoselectivity (syn/anti addition)?

Answer 24

when the reaction is concerted AND the products have any chirality centers??

Question 25

which rxns add water across the pi bond?

Answer 25

hydration, oximercuration-demercuration, hydro-bromation oxidation

Question 26

when does Mark's rule NOT matter?

Answer 26

when you're adding two of the same thing across a pi bond exp. hydrogenation H2 or Bromination Br2

Question 27

when do you have to care about rearrangement?

Answer 27

when there's a carbocation

Question 28

what does it mean to say that a structure is geminal dihalide?

Answer 28

it has two halogens connected to the same carbon

Question 29

what does it mean to say that a structure is vicinal dihalide?

Answer 29

it has two halogens connected to two different, adjacent carbons

Question 30

what do elimination (eviction) rxns do?

Answer 30

take a H that results in the adding of a pi bonds, which evicts the leaving group

Question 31

what do addition rxns do?

Answer 31

break a pi bond in order to add a nucleophile

Question 32

what do substitution rxns do?

Answer 32

take leaving group away and replace it with something else/a nucleophile

Question 33

is it really important to show all of your hydrogens in alkyne reactions?

Answer 33

Yes! in particular, show your alpha carbon and ALL of you beta hydrogens

Question 34

what is tautomerization (in an alkyne hydration rxn)?

Answer 34

when the enol part of the rxn intermediate is converted to a carbonyl

Question 35

what are the two main steps of enol tautomerization?

Answer 35

protonate, then deprotonate

Question 36

what do alkyne hydration and hydroboration oxidation rxns have in common?

Answer 36

they both have unstable enol intermediates that have to be tautomerized

Question 37

what does acetylene look like?

Answer 37

H-CtriplebondC-H