Reaction Reagents 10

Question 1

what is the hybridization of ketones and aldehydes? what does this mean?

Answer 1

trig planar = enantiomers bc nuc attack either side

Question 2

why are aldehydes more reactive than ketones (towards nucs)?

Answer 2

1. less sterically hindered
2. aldehyde has larger delta + on carbonyl C

Question 3

What is the general mechanism for nucleophilic addition under BASIC CONDITIONS?

what should you use at nuc?

Answer 3

1. nuc attacks delta + C and e- from double bond transfers to O making O- negative intermediate
2. O- base attack a proton source

made an alcohol

use H- (LAH or NaBH4) or C- (Grignard - CMgBr)

Question 4

ketone + Grignard reaction + H2O

Answer 4

basic condition nucleophilic attack

C- of Grignard attacks C+ of carbonyl

water protonates O- intermediate in second step

C- or H- (grignard or hydride)

Question 5

when do you use acidic bs basic conditions for nuc attack?

Answer 5

strong nuc = basic conditions

weak nuc = acidic conditions

Question 6

what is the general mechanism for nuc addition at acidic conditions?

Answer 6

1. O of carbonyl attacks H of acid (this protonates the carbonyl = better electrophile) - positive intermediate
2. weak nuc attacks C of carbonyl and e- in double bond transfers to O

makes alcohol

Question 7

can nucleophilic addition be reversible?

Answer 7

yes, if nuc is a good LG

Question 8

examples of H- donors?

Answer 8

LiAlH4 or NaBH4

Question 9

can you make a racemic mixture with ketone/aldehyde + H-/C-?

Answer 9

yes! aldehydes + unsymmetrical ketones are sp2 = H-/C- attacks either side

Question 10

what is the strength of an Oxygen nucleophile?

Answer 10

strong under basic (HO-, RO-)
weak under acidic (water, ROH)

Question 11

ketone/aldehyde + water

Answer 11

equilibrium with hydrate (2OH) but generally doesn’t favour hydrate

acidic cond. = water becomes O+ = is better electrophile

basic cond. = water becomes OH- = better nuc

Question 12

under acidic conditions, a mech is reasonable if…

Answer 12

avoids use/formation of strong base

and vice versa

Question 13

what is an acetal?

Answer 13

C with 2 OR groups

Question 14

rxn to make acetals?

Answer 14

carbonyl + 2ROH under acidic conditions

acidic by TsOH or H2SO4 rep by H+

ROH is a weak nuc = acidic conditions needed to protonate first to make C a better electrophile

Question 15

mech to make acetal?

Answer 15

NEED TO PROTONATE
1. TsOH or H2O4 protonates O of carbonyl
2. C is a good electrophile = O of ROH attacks C
3. ROH deprotonates O of ROH that is attached to C of carbonyl
this is a HEMI ACETAL
1. protonate carbonyl O with H2OR generates water LG and double bond to OR and C becomes electrohphile
2. ROH attacks electrophilic C
3. ROH gets deprotonates by another ROH

this is ACETAL

all steps are reversible, need 2 ROH

acidic condtions

Question 16

how can you ensure that acetal formation occurs?

Answer 16

enough ROH alcohol present
(if too much water/proton, drives back to carbonyl) remove water as it is being generated

Question 17

carbonyl + diol under acidic conditions?

Answer 17

both equivalents of alcohol compes from same compound and a cyclic acetal is formed

Question 18

hemi acetyl under basic conditions?

Answer 18

1. base attacks C of carbonyl
2. protonate O of carbonyl

no LG = can’t make acetal

Question 19

carbonyl + 2RSH

Answer 19

thioacetal or cyclic thioacetal if acidic conditions and diol used

Question 20

acetal

acetals can be used as

Answer 20

protecting groups; protect ketone from LAH and H3O will deprotect

Question 21

how can you isolate hemiacetal?

Answer 21

make cyclic when compound contains both carbonyl and hydroxy group

electrophile and nuc in same molecule

intramolecular

Question 22

imine formation?

Answer 22

carbonyl + CH3NH2

acidic condition protonates CH3NH2

primary amine

Question 23

enamine formation?

Answer 23

carbonyl + 2º amine (R2NH)

acidic conditions

no proton to deprotonate after water leaves, so beta H is depronotated and makes double bond with C

Question 24

acetal + base

Answer 24

no rxn