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Flashcards in Final Exam: Addition and Synthesis Deck (37)
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1

why are alkene and alkyne addition rxns called 'addition' rxns?

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

2

why are addition rxns usually exothermic?

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

3

what is syn addition?

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

4

what is anti addition?

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

5

when does syn and anti apply to addition reactions?

when the starting material/molecule being added to is asymmetrical

6

what is Markonikov addition?

when a nucleophile attacks the most substituted carbon

7

what is ANTI markonikov addition?

when a nucleophile attacks the LESS substituted carbon

8

what's the difference between halogenation and halohydrin rxn?

halogenation will have X2 but halohyrin will have X2 AND H2O

9

what are the reactants for hydroboration-oxidation rxns?

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

10

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

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

11

what 3 metals are used for hydrogenation rxns?

Pd, Pt, or Ni

12

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

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

13

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

acid catalyzed hydration

14

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

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

15

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

4

16

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

anti

17

what does dihydroxyllation add across the double bond?

two OH groups

18

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

both

19

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

When the molecule is asymmetrical

20

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

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

21

which carbon is the alpha carbon?

the carbon bearing the leaving group

22

what are the 3 categories of stereoselectivity?

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

23

which reagents are stereoselective?

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

24

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

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

25

which rxns add water across the pi bond?

hydration,
oximercuration-demercuration,
hydro-bromation oxidation

26

when does Mark's rule NOT matter?

when you're adding two of the same thing across a pi bond

exp. hydrogenation H2 or Bromination Br2

27

when do you have to care about rearrangement?

when there's a carbocation

28

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

it has two halogens connected to the same carbon

29

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

it has two halogens connected to two different, adjacent carbons

30

what do elimination (eviction) rxns do?

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