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71 terms

Orgo Lecture 3-Carbonyls and Amines

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carbonyl
carbon double bonded to an oxygen. the double bond is shorter and stronger than the double bond of an alkene. planar stereochemistry. polar bond.
aldehyde
formaldehyde (methanal)
ketone
acetone (2-propanone)
physical properties of aldehydes and ketones
more polar and have higher boiling points than alkanes and alkenes of similar molecular weight. cannot hydrogen bond with each other so have lower boiling points than corresponding alcohols. do not accept hydrogen bonds with water and other compounds that can hydrogen bond. makes them excellent solvents for these substances. soluble in water with up to four carbons.
chemical properties of aldehydes and ketones
most of the time will be acting either as the substrate in nucleophilic addition or as a Bronsted-Lowry acid by donating one of its α-hydrogens.
enolate ion
an enolate ion is stabilized by resonance
β-dicarbonyl
enol becomes far more stable due to internal hydrogen bonding and resonance. more acidic than water or alcohol.
keto-enol tautomerization
both aldehydes and ketones are less acidic than alcohols. any electron withdrawing groups attached to the α-carbon or the carbonyl tend to stabilize the conjugate base and thus increase acidity.
tautomerization
involves a proton shift, in this case, from the α-carbon position to the carbonyl oxygen position. is a reaction at equilibrium, not a resonance.
formation of acetals
aldehydes and ketones react with alcohols to form _______.
blocking groups
because acetals and ketals are unreactive towards bases, they are often used as _____ ______
aldehydes or ketones are dissolved in aqueous solution, they establish an equilibrium with their hydrate, a geminal diol
aldol condensation
occurs when one aldehyde reacts with another, when one ketone reacts with another, or when an aldehyde reacts with a ketone. catalyzed by an acid or base.
1) base abstracts an α-hydrogen leaving an enolate ion.
2)the enolate ion acts as a nucleophile and attacks the carbonyl carbon to form an alkoxide ion.
the alkoxide ion is a stronger base than a hydroxide ion and thus removes a proton from water to complete the aldol.
the aldol is unstable and is easily dehydrated by heat or a base to become an enal. the enal is stabilized by its conjugated double bonds.
aldol condensation reaction
halogenation
halogens add ketones at the alpha carbon in the presence of a base or an acid. when a base is used, it is difficult to prevent halogenation at more than one of the alpha positions. the base is also consumed by the reaction with water as a by-product, whereas the acid acts as a true catalyst and is not consumed.
haloform reaction
when a base is used with a methyl ketone, the alpha carbon will become comletely halogenated. this trihalo product reacts further with teh base to prdouce a carboxylic acid and a haloform (CHCl₃, CHBr₃, CHI₃)
Wittig reaction
converts a ketone to an alkene. a phosphorous ylide (a neutral moelecule with a negatively charged carbanion) is used. when possible, both cis and trans isomers are formed by the Wittig reaction.
α-β unsaturated carbonyl, conjugate addition
α-β unsaturated carbonyl, other mechanism
carboxylic acid
formic acid (methanoic acid)
acetic acid (ethanoic acid)
benzoic acid
alipathic acids
carboxylic acids where the R group is an alkyl group.
resonance stabilization of carboxylate ion
sodium acetate (sodium ethanoate)
a salt of acetic acid
carboxylic acid hydrogen bonded dimer
the dimer significantly increases the boiling point of cabroxylic acids by effectively doubling the molecular weight of the molecules leaving the liquid phase. saturated carboxylic acids with more than 8 carbons are generally solids.

carboxylic acids with four carbons or less are miscible with water.
decarboxylation
when a carboxylic acid loses CO₂. activation energy for this reaction is usually high.
decarboxylation stabilized by hydrogen bond
acyl group
derivatives of carboxylic acids contain the ____ ____
acyl chlorides
inorganic acid chlorides like SOCl₂, PCl₃, and PCl₅ each react with carboxylic acids by nucleophlic substitution to form ____ _____.
are Bronsted-Lowry acids.
acid chlorides
the most reactive of the carboxylic acid derivatives. love nucleophiles.
carboxylic acid derivatives hydrolize to give the carboxylic acid
can occur in either acidic or basic conditions
alcohols and carboxylic acid to form esters
transesterification
watch for the β-dicarbonyl compounds, which increase the acidity of the alpha hydrogens between the carbonyls.
acetoacetic ester synthesis
the production of a ketone from acetoacetic ester due to the strongly acidic properties of the alpha hydrogen.
base is added to remove the alpha hydrogens. resulting enolate ion is alkylated by an alkyl halide or tosylate leaving teh alkylacetoacetic ester.
amides
formed when an amine, acting as a nucleophile, substitutes at the carbonyl of a carboxylic acid or one of its derivatives.
carboxylic acid derivative reactivity
ammonia
primary amine
secondary amine
tertiary amine
qauternary amine
3 important considerations with nitrogen containing compounds
1) they may act as a Lewis base donating their lone pair of electrons
2) they may act as a nucleophile where the lone pair of electrons attacks a positive charge; and
3) nitrogen can take on a fourth bond (becoming positively charged)
ammonia and amines act as weak bases
by donating their lone pair of electrons.
amine basicity
from highest to lowest when the functional groups are electron donating: 2°, 1°, ammonia
aromatic rings
electron withdrawing and make amine a weaker base.
since amines like to donate their negative electrons...
tend to stabilized carbocations of the same molecule
amines react with aldehydes and ketones...
to produce imines and enamines.
Schiff bases
substituted imines
imine-enamine tuatomerization
Wolf-Kishner Reduction
Wolf-Kishner explanation
possible to replace the oxygen of a ketone or aldehyde with two hydrogens by adding hot acid in the presence of amalgamated zinc (zinc treated with mercury); however, some ketones and aldehydes may not be able to survive such a treatment.
___ ____ ____ adds a hydrazine to a ketone or aldehyde.
a hot strong base is added to the hydrazone to deprotonate the nitrogen and produce the desired product with water and nitrogen gas as by products. high boiling solvent is usually used to facilitate the high temperature.
amines can be alkylated with alkylhalides
nucleophilic substitution with the amine acting as a nucleophile.
elimination of a quaternary ammonium salt
usually follows an E2 mechanism requiring a strong base. the quaternary alkyl halide is converted to quaternary ammonium hydroxide using silver oxide.
Hoffman elimination
heating the quaternary ammonium hydroxide results in the ____ ___ to form an alkene. the LEAST stable alkene is the major product (Hoffman product)
nitrous acid is a weak acid. a strong acid can dehydrate nitrous acid to produce nitrosonium ion and water.
most reactions with amines and nitrous acid involve the introsonium ion.
diazonium salts
primary amines react with nitrous acid to form ____ ____.
diazotization of an amine
diazonium group can be easily replaced by a variety of other groups, making the the diazotization of an amine a useful reaction
amides basicity
less basic than amines
amides are hydrolized
by either strong acids or strong bases
amide hydrogen bonding
acetamide
N-ethylacetamide
β-Lactams
cyclic amides are called lactams. greek letter refers to size. β are four membered rings.
Hoffman degradation
phosphoric acid
phosphoric anhydrides