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
