Ch. 17 - Intro to Carbonyl Chemistry Flashcards
What is an acyl group?
RC=O
What are the two classifications of carbonyl compounds?
acyl groups that have a LG (attached to another EN atom group that can be replaced) [includes Cl, OC=O, OH, OR, NH2/R/R2]
acyl group without a LG (aldehydes/ketones)
Rank the following in order of LG ability: OR, NH2, Cl, OC=O, OH,
worst to best
NH2, OR, OH, OC=O, Cl
Can aldehydes and ketones undergo nucleophilic substitution?
no, they do not have a leaving group
Is the carbon of a carbonyl nucleophilic or electrophilic? Why?
electrophilic because oxygen is more EN than carbon and pulls e- density
Why can’t H or R group be a LG?
H and R groups are weak acids so their conjugate bases are hydride and -R which are strong bases; this is not favored in equilibirum
Is an aldehyde or ketone more reactive? Why?
aldehyde
1) ketone is more sterically hindered (bigger R groups decrease reactivity)
2) ketone has electron donating groups which decrease carbon electrophilicity
Does NaBH4 and LAH reduce alkenes or alkynes?
No, NaBH4 is more selective. It only reduces aldehydes, ketones and acid chlorides
Does water have to be added separately in a reaction with NaBH4 or LAH?
LAH, it could be explosive
What carbonyl compounds with LAH reduce?
LAH is a strong reductant, it will reduce all carbonyl compounds
What does H2 Pd/C or Raney Nickel reduce? Which of these groups will it reduce first?
Reduces aldehydes, ketones and alkenes; will reduce alkenes first
What is LiAlH(OtBu)3 used to reduce? What is the reduction product? Finally, why does this work?
Used to reduce acid chlorides to product aldehydes. This reductant works for reducing to an aldehyde because it only has one H source and has three bulky groups.
Does Lindlar’s cat or NaNH3 reduce aldehydes or ketones?
No, just alkynes
What is DIBAL-H used to reduce? What is the reduction product and why does this reductant work?
Reduces esters and carboxylic acids to aldehydes. Reduces to an aldehyde and not fully to an alcohol because DIBAL-H only has one hydride source and also has two bulky groups.
In order to “stop at the aldehyde” what must be used?
A milder reducing agent
What are examples of milder reducing agents?
LiAlH(OtBu)3 (less nucleophilic) and DIBAL-H (bulky groups)
What is a lactone?
A cyclic ester
What happens when cyclic ester (lactone) reacts with DIBAL-H? What happens when a cyclic ester reacts with LAH?
DIBALH: Gives a chain with an aldehyde on one end and an alcohol on the other
LAH: Gives a chain with alcohols on either end
What is a lactam?
a cyclic amide
What is an important intermediate of reduction of amides?
Imine
Can NaBH4 reduce carb acids, esters and amides?
No, LAH is needed for these compounds because they have worst leaving groups and NaBH4 is too weak
What will happen to CN (has triple bond) if it reacts with H2 Pd/C or NaBH4 and water?
It is reduced all the way to CH2NH2
What are organometallic compounds?
Reagents that contain carbon bonded to a metal and sort of act like carbanions
Is the metal-adjacent carbon of an organometallic reagent nucleophilic or electrophilic?
Nucleophilic, the metal is less EN then the carbon and therefore has a partial positive charge.
How are organolithium compounds made?
halide + 2Li and hexanes
Li replaces halide
How are organomagnesium (Grignard) compounds made?
halide + Mg(s) and ether
Mg inserts btw halide and R
How are organocuprate compounds made?
halide + CuI and THF
two halid groups add to Cu
What does the reactivity of organometallic reagents depend on? What are the reactivities of the organometallic reagents studied?
More polar = more reactive
Most to least reactive: R-Li, R-MgX, R2-CuLi
Why can organocuprates hold two R groups?
They have a more accommodating valence shell.
Are organometallic reagents acids or bases?
Can act as strong bases and therefore can readily abstract a proton from water or OH group
What are alpha-beta unsaturated carbonyl compounds?
conjugated molecules with a carbonyl group and a C=C that is alpha to the carbonyl group
How many reactive sites does an alpha-beta unsaturated compound have?
two electrophilic sites; one at the carbonyl carbon and one on the beta carbon (far end of alkene pi bond)
Why must protective groups be used for some reactions?
Rapid acid-base reactions can occur between certain reagents (esp organometallics) and OH groups. If this group is not desired to be reduced, a protective group can be used to keep it from interacting.
What is the most common protector group and accompanying deprotector?
protector: TBDMSCl with imidazole
deprotector: TBAF
When reacting with Grignard reagents, does an acyl chloride or ester have a fast collapse?
acyl chloride; has better LG
What carbon is attacked by the nucleophile for an epoxide in acidic and basic conditions?
acidic: most sub’d carbon
basic: least sub’d carbon
What are alpha hydroxy alkynes?
Alkyne functional group that is bonded to a carbon bearing an OH group
