Kaplan MCAT OChem Ch. 9: Carboxylic Acids

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carb acid

pKa 3-6

alcohol

pKa = 16

carb acid

H bond donor and acceptor in same functional group => large intermolecular forces and high BP

carb acid

highest priority

formic acid

methanoic aci


http://upload.wikimedia.org/wikipedia/commons/5/58/Formic-acid-2D.png

acetic acid

ethanoi acid


http://upload.wikimedia.org/wikipedia/commons/f/fd/Acetic-acid-2D-flat.png

propionic acid

propanoic acid

http://upload.wikimedia.org/wikipedia/commons/b/b4/Propionic_acid_chemical_structure.png

cyclic carboxylic acid

cycloalkane carboxylic acids

salts of carb acids

cation + acid ending w/ -ate

oxalic acid (2C)

IUPAC: ethanedioic acid

malonic acid (3C)

IUPAC: propanedioic acid

succinic acid (4C)

IUPAC: butanedioic acid

glutaric acid (5C)

IUPAC: pentanedioic acid

adipic acid (6C)

IUPAC: hexanedioic acid

pimelic acid (7C)

IUPAC: heptanedioic acid

phys. properties of carb acids

H-bonding

acidity

H-bonding of carb acids

polar and form really well H bonds w/ each other since two diff. points participating in H bonding => dimers (pairs of molecules connected by two H bonds)

H-bonding of carb acids

multiple H bonding:
1. elevate BP (also inc. w/ MW) and MP (higher than alcohol)

acidity of carb acids

due to resonance stabilization of carboxylate anion (conjugate base)

acidity of carb acids

more stable conj. base => proton likely leaves => stronger acid

acidity of carb acids

sub. near this influence its acidity

acidity of carb acids

EW groups => absorb neg. charge => inc this

acidity of carb acids

EDG => donate add. electron density => destabilize neg charge => less this

acidity of carb acids

closer the sub gruop => great its effect on this

acidity of dicarb acids

more acidic than carb acids

acidity of dicarb acids

proton leaves => carboxylate anion formed => second carb group less acidic (since double neg species is unfavorable is second proton is deprotonated)

beta-dicarb acids

notable for high acidity of alpha carbon between two carbonyls (pKa = 10)

beta-dicarb acids

loss of acidic H atom => carbanion => stabilized by EWG effect of two carboxyl groups

this also applies to molecules that shared this structure

types of synthesis of carb acids

oxidation rxns

carboxylatin of organometalic reagents

hydrolysis of nitriles

oxidation rxns (carb acids)

these are prepared via oxidation of aldehydes, primary alcohols and certain alkylbenzenes

carb acids

most oxidized func group

oxidation rxns (carb acids)

oxidant usually KMnO4

oxidation rxns (carb acids)

2ndary and 3rd alcohols can't be oxidized to carb acids because of valence limitations

carboxylation of organometallic reagents

like Grignard reagents, react w/ CO2 to form this

carboxylation of organometallic reagents

conversion of tertiary alkyl halides into this

carboxylation of organometallic reagents

rxns adds one caron atom to the chain

carboxylation of organometallic reagents

in 2nd rxn, Nu is a carbanion that's coordinated w/ pos. charged Mg and electrophile is carbon of CO2

hydrolysis of nitrile

AKA cyanides, func group -C≡N

-C≡N (cyanide) (hydrolysis of nitrile)

carries neg charge on carbon atom => great Nu but not great base

-C≡N (cyanide) (hydrolysis of nitrile)

displaces primary and secondary halides in Sn2

hydrolysis of nitrile

can do this under either acidic or basic conditions => carb acids and ammonia (ammonium salts)

NOTE: all carb acid derivatives may be hydrolyzed to their parent carb acid

hydrolysis of nitrile

allows for conversion of alkyl halides into carb acids

hydrolysis of nitrile

additional carbon is introduced into the chain

rxns w/ carb acids

soap formation

Nu Acyl Sub

Decarboxylation

types of Nu Acyl Sub rxns (rxns w/ carb acids )

reduction

ester formation

acyl halide formation

soap formation (rxns w/ carb acids)

long chain carb acid + NaOH or KOH => RCOO-(Na+ or K+)(soap) + water

soap formation (rxns w/ carb acids)

can solvate nonpolar organic compounds in aq. sol since possess nonpolar tail and polar carboxylate head

soap formation (rxns w/ carb acids)

soap molecules placed in aq. sol => arrange themselves into micelles

micelles

spherical structures where polar heads outwards (solubilized by water) and nonpolar hydrocarbon chains oriented toward inside of sphere (protected from solvent, nonpolar molecules can dissolve in hydrocarbon interior of this)

reduction (Nu Acyl Sub rxns)

this by LAH => alcohols

reduction (Nu Acyl Sub rxns)

aldehyde can be intermediate but eventually goes to alcohols

reduction (Nu Acyl Sub rxns)

occurs by Nu add. of H- to carbonyl group

carb acids

can't be further oxidized, but can be reduced

ester formation

hybrid between carb acid and ether

ester formation

make this when carb acid + alcohols under acidic conditions

ester formation

condensation rxn, so water is a side product

ester formation

in acidic conditions, O in carbonyl is protonated => enhance polarity of bond => more positive C => able to be attacked by Nu

ester formation

condensation occurs most pardily w/ primary alcohols

ester formation (common name)

named as same manner as carb salts (cation + acid ending w/ -ate)

acyl halides

also called acid halides

acyl halides formation

carbonyl groups bonded to halides

acyl halides formation

reagents used is SOCl2 (thionyl chloride)

acid chlorides

reactive; EWG power of Cl- => carbonyl attacked more

acid chlorides

used as intermediates from carb acid to esters and amides

acid chlorides

among the highest energy (least stable and most reactive) members of carbonyl family

decarboxylation

loses a carbon in form of CO2

decarboxylation

B-keto acids may spon. decarboxylate when heated => carboxyl group is lost and replaced w/ hydrogen

decarboxylation

electrophile and Nu in same molecule => rxn proceeds through a six membered ring transition state

decarboxylation

initial enol form tautomerizes to the more stable keto form

more stable the CB

more likely the proton will leave

stability of CB (3 factors)

1. periodic trends (EN, thus induction)
2. size of anion
3. resonance

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