Ch 20 - Carbonyl Chem, Organometallic Reagents, Oxi & Red

Question 0

General reactions of 2 carbonyl classes?

Answer 0

• aldehydes & ketones: nucleophilic addn

* with LG: nucleophilic substitution (Nu replaces Z)

Question 1

Two classes of carbonyl compounds? (and types in each class)

Answer 1

• only C & H bonded to carbonyl C (aldehydes, ketones - NO LG)
• EN atom bonded to carbonyl C (carboxylic acids, acid chlorides, esters, amides)

Question 2

Steps of nucleophilic addn to aldehydes & ketones?

Answer 2

1) nucleophilic attack at carbonyl C (Nu = H- or C-)

2) protonation of carbonyl O by water

Question 3

Steps of nucleophilic substitution of RCOZ?

Answer 3

1) nucleophilic attack at carbonyl C (Nu = H- or C-)

2) loss of LG (Z)

Question 4

Order of reactivity of RCOZ compounds?

Answer 4

(best) acid chlorides➡carboxylic acids & esters➡amides (worst)

Question 5

3 main redox reaction?

Answer 5

• red aldehydes & ketones ➡alcohols (primary for aldehydes, secondary for ketones)
• red RCOZ➡aldehydes or primary alcohols
• oxi aldehydes➡carboxylic acids

Question 6

Metal reagents used to reduce aldehydes & ketones?

Answer 6

• NaBH4 - more selective
• LiAlH4 - more reactive
C=C bonds inert

Question 7

Catalytic hydrogenation of aldehydes and ketones (red): reagents? Effects?

Answer 7

• H2/Pd-C

* reduces C=C faster than C=O (both reduced w/excess H2➡alcohols)

Question 8

Stereochemistry of hydride red of achiral ketone?

Answer 8

Racemic mix of 2 alcohols (new stereogenic ctr formed, H behind & H in front, vice versa w/OH ➡ 2 enantiomers)

Question 9

Activity of metal hydride reagents in RCOZ red?

Answer 9

• NaBH4 - not used (selective for aldehydes and ketones)
• LiAlH4 - gives 2 H-, more reactive➡alcohols
• R2AlH (DIBAL-H) - gives one H-, less reactive➡aldehydes
• LiAlH(OR)3 - gives one H-, less reactive➡aldehydes

Question 10

Steps of acid chloride & ester red mechanism? 1)➡aldehyde, 2)➡primary alcohol

Answer 10

1) nucleophilic substitution - attack of Nu at carbonyl C, loss of LG
2) nucleophilic addn - Nu attack at carbonyl C, protonation of carbonyl O by water

Question 11

Reagents for red of carboxylic acids➡primary alcohols & amides➡amines?

Answer 11

•LiAlH4/H2O

Both C-O bonds red➡C-H bonds

Question 12

Reagents used to oxi aldehydes to carboxylic acids?

Answer 12

• CrO3/H2SO4, H2O
• Na2Cr2O7/H2SO4, H2O
• Ag2O/NH4OH - selectively oxi aldehydes if compound contains other FGs

Question 13

3 types of organometallic reagents? Materials used to form them?

Answer 13

• R-Li (organolithium) - more reactive; RX + 2Li
• R-Mg-X (Grignard) - more reactive; RX + Mg
• R2CuLi (organocuprates) - less reactive; 2RLi + CuI

Question 14

Ways to form acetylide anions from terminal alkynes?

Answer 14

• H extraction w/NaH➡acetylide anion + Na+ + H2

* H extraction w/CH3Li➡acetylide anion + Li+ + CH4

Question 15

How do organometallic reagents act as strong bases?

Answer 15

• Abstract H+ from water➡hydrocarbons

* RLi rxt with any OH & NH (esp ROH, RCOOH, RNH2)

Question 16

4 rxns of organometallic reagents as nucleophiles?

Answer 16

• w/aldehydes & ketones (H2O)➡any alcohol
• w/esters & acid chlorides (H2O)➡ketones or tertiary alcohols
• w/CO2 (H3O+)➡carboxylic acids
• w/epoxides (H2O)➡primary alcohols

Question 17

Mechanism for RMX w/aldehydes & ketones?

Answer 17

Exactly follows 2 steps of nucleophilic addn (nucleophilic attack & protonation)

Question 18

RMX w/aldehydes & ketones: what SM to make 1)primary 2)secondary 3)tertiary alcohols?

Answer 18

1) formaldehyde
2) aldehyde
3) ketone

Question 19

Stereochemistry of RMX rxn w/aldehydes & ketones?

Answer 19

Racemic mix of 2 alcohols (new stereogenic ctr formed, R behind & R in front, vice versa w/OH ➡ 2 enantiomers)

Question 20

RMX w/carbonyl compds w/NH or OH: w/protecting group➡? W/out protecting group➡?

Answer 20

• w/PG - 2OHs (C=O➡OH)

* w/out PG - anion (RMX deprotonates interfering OH)

Question 21

3 Steps for using a PG? (RMX w/carbonyl only)

Answer 21

1) protection OH w/silyl ether (R-O-TBDMS) & imidazole
2) rxn (RMX, then H2O)
3) deprotect w/Bu4NF

Question 22

esters & acid chlorides➡tertiary alcohols. Reagent?

Answer 22

• 2 RMX/H2O
• 2 RLi/H2O
Both very reactive

Question 23

Mechanism for RMX or RLi rxn w/esters & acid chlorides?

Answer 23

1) nucleophilic substitution of R w/Z
2) nucleophilic addn of R and H (protonation)
2 R added are the same

Question 24

Rxn acid chlorides ➡ ketones?

Answer 24

R2CuLi/H2O (less reactive, don’t rxt w/esters)

Question 25

Stereochemistry of RMX/H2O rxn w/epoxides➡alcohols?

Answer 25

Nu attacks at backside of less sub corner of epoxide➡anti, trans OH & R

Question 26

What is an alpha-beta unsaturated carbonyl compd?

Answer 26

Conjugated molecules w/carbonyl group (C=O) and C=C, w/single bond in between

Question 27

2 types of rxns of an alpha-beta unsaturated carbonyl compd? Reagents for each?

Answer 27

• 1,2 addn: H & Nu added across C=O➡allylic alcohol (RMgX and RLi, more reactive)
• 1,4 addn: Nu added to beta C➡carbonyl compd (R2CuLi), less reactive)

Question 28

Mechanisms to know for exam!

Answer 28

• reduction of acid chlorides & esters

* rxn of RLi or RMgX w/esters & acid chlorides