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carbon double bonded to an oxygen. the double bond is shorter and stronger than the double bond of an alkene. planar stereochemistry. polar bond.
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.
enol becomes far more stable due to internal hydrogen bonding and resonance. more acidic than water or alcohol.
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.
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.
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
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.
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.
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)
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.
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.
when a carboxylic acid loses CO₂. activation energy for this reaction is usually high.
inorganic acid chlorides like SOCl₂, PCl₃, and PCl₅ each react with carboxylic acids by nucleophlic substitution to form ____ _____.
are Bronsted-Lowry acids.
carboxylic acid derivatives hydrolize to give the carboxylic acid
can occur in either acidic or basic conditions
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.
formed when an amine, acting as a nucleophile, substitutes at the carbonyl of a carboxylic acid or one of its derivatives.
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)
from highest to lowest when the functional groups are electron donating: 2°, 1°, ammonia
since amines like to donate their negative electrons...
tend to stabilized carbocations of the same molecule
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.
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 group can be easily replaced by a variety of other groups, making the the diazotization of an amine a useful reaction
cyclic amides are called lactams. greek letter refers to size. β are four membered rings.
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