Organic Chem II
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What causes a reaction involving a carbonyl group to diverge from typical addition reaction to a subsitution reaction?
when a heteroatom or chlorine is attached to the carbonyl group
Basic conditions of a reaction favor what type of nucleophile?
a strong nucleophile
Acidic conditions of a reaction favor what type of nucleophile?
In acidic conditions, what event allows the nucleophile to attach to the carbonyl group?
the c=O is protonated to become +c-O-H. The weak nucleophile can attach to the cationic carbon.
The effects that control reaction rate?
- steric effects
- inductive effects
- resonance effects
How do you produce an acyl chloride?
carboxylic acid with SOCl2 (thionyl chloride) or PCl3
The importance of an acyl chloride?
The chlorine acts as a good leaving group providing the basis needed to synthesize many compounds.
Preperation of anyhydrides
- any carboxylic acid with and acyl chloride
- in pyridine (the lone pair off the N group removes the H of the -OH)
to make an ester
acyl chloride with an alcohol in pyridine
what is the role of pyridine in ester synthesis?
the pyridine remove a H off the intermediate (once the lone pair of the ROH group attack the carbonyl)
another way to prepare an ester?
carboxylic acid reacts with an alcohol. This requires the presence of an acid.
what is a lactone?
cyclic ester, a product of intramolecular esterification when a carboxyl and a hydrox group are on the same molecule.
carbonyl (c=o) + H20
- geminal diol (hydrate)
- 2 OH groups now present on the carbonyl carbon
- in acidic or basic conditions
an aldehyde in the presence of one mol of alcohol
addition of an aldehyde + (excess) alcohol
ketone + one mole of alcohol
ketone + excess alcohol
A hemiacetal has one ______ and one _____ functional groups attached to reacted carbonyl
- OR and an OH group.
- in exess alcohol the OH group becomes an OR group as well
in words describe how a hemiketal is made
the carbonyl group is reacted, the double bonded oxygen becomes protonated from an alchol producing a formal charge of +1. Through resonance the double bond breaks to restore the charge on the oxygen and the carbon gains + charge. The alcohol (ethanol) has a lone pair of electron on the oxygen that are attracted to the cationic carbon and performs a back-side attack. The conjugate base produced from the original reaction removes a proton (H) from the alcohol group to restore the oxygens charge.
what makes a good protecting group?
acetals and ketals
how do we remove a acetal protecting group?
acid hydrolysis (HCl + H20)
carbonyl + cyanide = ?
- produces an -OH group and CN (triple bonded) group to the carbon
- a cyanohydrin
HCN in presence of carbonyl =
- no reaction
- it is a poor nucleophile but can be converted to CN- in the presence oh OH-
wanting to perform addition of cyanide to a carbonyl?
HCN in the presence of NaCN or KCN
decribe the addition of cyanide to a carbonyl group
figure out how to get CN-, its a good nucleophile. The nucleophile attacks the slightly positive carbon and gives the double bonded oxygen a single bond plus a lone pair (3) with a negative charge. The oxygen steals a (H) from HCN to make an alcohol group.
Primary amines add to carbonyl to produce
- the nitrogen maintains the double bond and rids of 2 H to produce a C=N-R and HOH
- the reaction favors the reactants because C=O is a stronger bond. Remove HOH as it is produced to shift eq. to the products.
seconday amines react with carbonyls to produce
- a single bond is formed to the N from the carbon but beta to the amine forms a double bond (removes a H) where a single bond once was
how do you reduce an imine?
- add H2/Ni
- reduces C=NR to C-NRH
The wittig reaction reacts carbonyl to produce ______
- all C=O to C=C
- produces mixtures of cis and trans products
- requires the formation of an ylide
what is an ylide?
- PH3P- CH2
- reacts with carbonyl to make PH3P=O
Will a ketone attached to a phenyl group (benzene) undergoe a Wittig Reaction?
no. The ketone is stabilized in the pi system. Only aldehydes undergoe this kind of reaction.
reduction of a ketone via hydrogenation produces first and secondary alcohols.
What 2 reactions can accomplish this?
- metal-hydride reactions
- catalytic hydrogenation - reduces all C=O and C=C
name 2 metal hydrides used to reduce the C=O group
LiAlH4 and NaBH4
the solvents used for metal-hydride reaction?
How would you prepare 3-phenyl-3-pentanol using a Grignard synthesis?
- Method 1 – react 3-pentanone with phenylmagnesium bromide in diethyl ether followed by workup with acidified water
- Method 2 – react ethyl phenyl ketone with ethylmagnesium bromide in diethyl ether followed by workup with acidified water
- Method 3 – involves benzoic acid and two moles of ethylmagnesium bromide and belongs in the next module.
a grignard reagant reacts with carbon dioxide to produce?
a carboxylic acid attached to the R group of the grignard reagant
when a carbonyl group is conjugated with a C=C addition of the nucleophile can occur in 2 ways. Explain
- The nucleophile can add to the carbonyl group (1,2-addition) or add to the C=C (1,4-addition) becuase the conjugation allows a partial positive on either carbon
- the reaction is also dependant on the nucleophile
1,2-addition occurs when a conjugated pi system reacts with 3 different things. What are these?
- reactive Nu
- Grignard reagent
1,4-addition occursw when a conjugated pi system reacts with 4 different things. What are they?
- weak nucleophile
Does NaBH4 react with a conjugated carbonyl by 1,2-addition or 1,4-addition mechanisms?
reacts to form a mixture
2RLi + CuI → R2CuLi + LiI
make a carboxylic acid from amide?
- in acid
- or in base followed by acid
- similar to ester hydrolysis
- biproduct is ammonia
describe the preperation of CA from amide in basic conditions.
The base (in H2O) backside attacks the carbonyl group(addition) forcing a pi bond to break adding a lone pair on the oxygen. Next, (elimination) the double bond re-establishes and NH2- leaves. The base steals a proton from the OH group on the carbonyl (deprotonation). A proton is regained from H20 to restore then carboxylic acid.
notes on preparation of CA from Nitriles
- can be in acid or base (in HOH)
- reaction is known as hydrolysis
- good way to turn an alkyl halide into an acid and useful in synthesis
- -CN to CA
a hydride can reduce amides and nitriles to _________
hrdride nucleophiles can reduce esters,acyl halides. amhydrides and CA to _________
special nucleophile hydrides can reduce acyl halides and anhydrides to_____
special nucleophile halides can reduce esters, CA's and nitriles to ________
how can a C(=O)-NH2 (amide) be reduced to an CH2-NH2
(rid the C=O to CH2)
- 1) LiAlH4 in ether
- 2) water
Nitriles (C triple bond N) can be reduced to CH2-NH2. How?
note: can also been done using catalytic hydrogenation
______ is the hydride nucleophile that will not reduce esters or acids. only ____ reduces these compounds.
LiAl4 reduces everything
what are the steps to reduce an acyl compound (esters,qcyl halides, anhydrides, CAs) to alcohols?
- 1)LiAl4, ether
- 2) H2O/H30+
when an intermediate of acyl reduction is an aldehyde...how can we top the reaction from further reducing the aldehyde?
- 1)use bulky hydride -- LiAlH(OtBu)3
- 2) HOH
What would you like to do?
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