CH223 Part 3/4: Organometallic & Aldehydes/Ketones (Conceptual) Flashcards
What do weakly activating substituents direct to?
ortho and para
What do strongly activating substituents direct to?
ortho and para
Who do weakly deactivating substituents direct to?
ortho para
What do strongly deactivating substituents direct to?
meta
What are some weakly deactivating substituents?
F, Cl, Br, I
What are some strongly activating substituents?
EDG
What substituent controls regioselectivity?
the most activating one
Where does substitution occur when positions are comparatively activated?
the less hindered site
What should you use when you have an ortho, para director but only want ortho?
SO3H blocking group
How are primary alkyl groups more efficiently introduced?
freidel-crafts acylation
Why are aryl halides less reactive than alkyl halides?
- carbon halogen bonds are stronger
- the backside attack is blocked
What are exceptions that allow NAS to occuer?
the presence of a strong electronegative substituent
What position(s) will NOT react in a NAS reaction?
meta
Compare the reactivity of the halogens in an NAS reaction
X=F > X=Cl > X=Br > X=I
Why are X=F more reactive than X=I in an NAS reaction?
the most electronegative atom better stabilizes the negative charge on the intermediate
What are organometallic compounds?
compounds that have a carbon-metal bond
Which way are electrons pulled when carbon is bound to a metal?
towards the carbon
Compare the rates of reaction of Grignard reagents?
R-I > R-BR > R-Cl > R-F > alkene > alkyne
Organometallic compounds are prepared in which solvent?
aprotic solvents
Why do organometallic compounds have to be prepared in aprotic solvents?
they are extremely basic’ will deprotonate any slightly acidic molecule
What functional groups can Grignard reagents not be used in the presence of?
NH, OH, and SH
What product does an aldehyde reaction with an organometallic reagent give?
secondary alcohol
What product does an ketone reaction with an organometallic reagent give?
tertiary alcohol
What product does a formaldehyde reaction with an organometallic reagent give?
primary alcohol
What are the most acidic hydrocarbons?
alkynes
What does it mean for something to act catalytically?
for as little as 1 mol % to be used
Which reaction is extremely efficient and tolerant of various functional groups?
palladium-catalyzed cross-couplings
What leaving group can be used in a Pd. catalyzed reaction?
aryl/vinyl (sp2) halides or OTf
What are the four steps of a Suzuki mechanism?
1) Oxidative Addition
2) Ligand Exchange
3) Transmetallation
4) Reductive Elimination
What happens during oxidative addition?
two groups are added to a metal
What happens during ligand exchange?
hydroxide attacks Pd and kicks out X
What happens during transmetallation?
other carbon attacks palladium, breaking bond between OH and Pd
What happens during reductive elimination?
the two Pd groups are removed from the metal
What are the three steps to the Heck mechanism?
1) Oxidative Addition
2) Migratory Insertion
3) Beta-hydride Elimination
Which Pd. catalyzed reaction should you use if you want a trans product?
Heck
What happens to the cis and trans conformation during a Pd. catalyzed reaction?
the conformation is retained
Do aldehydes/ketones or alcohols have priority?
aldehydes/ketones
Do aldehydes/ketones or halogens have priority?
aldehydes/ketones
Do aldehydes or ketones have priority?
aldehydes
What group do aldehydes contain?
formyl group
How are aldehydes names?
by replacing the -e with -al
How are ketones names?
by replacing -e with -one
What orbital do electrophiles react with?
LUMO
The presence of water in Cr-based oxidations leads to what?
the formation of a carboxylic acid
The absence of water in a Cr-based oxidation leads to what?
the formation of the aldehyde
What does hydration lead to for terminal alkynes?
ketones
What does hydroboration lead to for terminal alkynes?
aldehydes
Why are aldehydes more electrophilic than ketones?
1) lower steric hinderance
2) lower stability of partial positive charge on C
Describe the rate of hydration of an aldehyde compared to a ketone?
aldehydes are hydrated at a much higher rate
Why is HCN not often used in Cyanohydrin formation?
HCN is highly toxic
How would you push an acid-catalyzed acetal/ketal formation to the right?
the presence of a large excess of alcohol reactant
Are acetals and ketals reactive towards nucleophiles?
no
Are amines more or less nucleophilic than alcohols?
more (no need for catalyst)
Are carboxylic acids more or less electrophilic than aldehydes/ketones?
less electrophilic
How do you name a carboxylic acid?
replace the -e ending with -oic acid
True or False: carboxylic acids have priority over other functional groups
True
Why are carboxylic acids less electrophilic than ketones/aldehydes?
the lone par on the hydroxyl oxygen stabalizes the structure through resonance
Why is the melting point of carboxylic acids so high?
hydrogen-bonding between the hydroxy groups of one acid and the carbonyl oxygen of a second contribute to strong intermolecular attractive forces
What is the pKa of carboxylic acids?
around 5
What is the pKa of alcohols?
around 16
Why are carboxylic acids more acidic than alcohols?
- the conjugate base of a carboxylic acid is more stable (multiple resonance forms)
- the inductive effect
What substituents are involved in the inductive effect?
electronegative substituents such as halogens increase acidity
True or False: the inductive effect is distance dependent
true
Will a closer substituent cause a more or less significant change in pH?
more
What is the major limitation of the use of a Grignard reaction to make a carboxylic acid?
functional group incompatibility with Grignard reagents
What is another way to create a carboxylic acid?
hydrolysis of nitrile (carbon of nitrile becomes carbonyl carbon)
What are two common ways to prepare nitriles?
1) nucleophilic substitution of alkyl halides
2) addition of potassium cyanide to aldehydes and ketones
