Carboxylic Acids Carboxyl group: -CO 2 H, -COOH Pure carboxylic acids form hydrogen bonded dimers very high boiling points (higher than alcohols) H-bond donor H-bond acceptor ++ −− −− ++ Intermolecular forces: dipole-dipole, H-bonding

Carboxylic Acid Nomenclature Parent chain: longest containing carboxyl group (COOH) Name of parent: replace “–e” with “–oic acid” Numbering starts at carboxyl carbon –Priority: Carboxylic acid > aldehydes > ketones > alcohols  “hydroxy” substituent “oxo” substituents trans-3-methyl-2-hexenoic acid (human armpits) 3-oxobutanoic acid (diabetes) propanedioic acid (apples)

Carboxylic Acid Acidity +H2OH2O ⇌ H3O+H3O+ + K a = [RCO 2 - ][H 3 O + ] [RCO 2 H]  1  Weak acids pH  2.5 for a 1 M solution Anion is stabilized by resonance Delocalized negative charge [A - ][H 3 O + ] [HA] = HA + H 2 O ⇌ A - + H 3 O +

aspirin Tylenol Can irritate your stomach Gentle on the stomach A carboxylic acidJust an alcohol

Carboxylic Acid Reactions Acid-Base reactions (formation of carboxylate salts) Reduction to 1° alcohols –Only LiAlH 4 reduces carboxylic acids (not NaBH 4 or H 2 /Pt) carboxylic acidstrong basecarboxylate saltwater Naming: cation, then anion (regular ionic compound) Anion name: replace “–oic acid” with “–oate” sodium hexanoate butanoic acid1-butanol NaOHH2OH2O ++ +  + LiAlH 4

What are the products? 3-oxo-4-pentenoic acid LiAlH 4 H 2 /PtNaBH 4 3-hydroxypentanoic acid 4-pentene-1,3-diol 3-hydroxy-4-pentenoic acid

Carboxylic Acid Reactions Certain molecules can attack the carboxyl carbon and replace the –OH group H−Nu H-OR′ Alcohol H-NH 2 Amine Product Ester Amide ++ H 2 O H−Nu OH H

What do these flavors/smells have in common? Esters Made from a carboxylic acid and an alcohol banana apricot pear grape rum wintergreen orange pineapple apple raspberry

What do these flavors/smells have in common? Esters Made from a carboxylic acid and an alcohol banana apricot pear grape rum wintergreen orange pineapple apple raspberry

Esters from Carboxylic Acids & Alcohols Nucleophilic substitution – a condensation reaction +H2OH2O H+H+ + carboxylic acidalcoholesterwater ++ Reverse reaction = hydrolysis (“water-splitting”) H+H+ +H2OH2O esterwater + + carboxylic acidalcohol +  

Esters An ester is similar to a carboxylic acid, but the acidic hydrogen has been replaced by an alkyl group (R) H O CCC H H OH H H a carboxylic acid H O CCC H CH 3 OH H H an ester methyl propanoate methyl group propanoic acid from propanoic acid R – C – O – R’ O

Naming Esters Named as “alkyl alkanoates” –Alkyl group first (from alcohol) –Acid name: “-oic acid” changed to “-oate” ethylbutanoate pentylbutanoate 3-methylbutylethanoate (pineapple) (apricot) (banana)

Naming Esters Name the following ester: CH 3 CH 2 CH 2 C-O-CH 2 CH 3 O Step 1) the ester alkyl group (R’) = ethyl Step 2) the acid (R) = butanoic acid Step 3) the name = ethyl butanoate R – C – O – R’ O

Esters – Physical Properties H-bond acceptors No H-bond donors Only dipole-dipole interactions Low boiling points (“volatile” compounds) Oxygen atoms are H-bond acceptors Esters are soluble in water (up to 4 or 5 carbon atoms) ++ -- --

Formation of an Ester H OH CCC H O HH H C H H+ H CH H H C H HO H O CCC H O HH H C H H + H CH H H C H H butyric acid (butanoic acid) ethyl alcohol ethyl butanoate or ethyl butyrate (tastes and smells like pineapple)  water

Ester H CCH 3 O HC O O RC O R' Raspberry CH 2 H O CC H OH CH Banana CH 2 (CH 2 ) 6 H O CC H OH CH 3 Orange CH 3

Ester O RC O R' CH 2 H O CC H OH CH 3 Pear Peach CH 2 H O CC H OH C C CC CC H H H H H

Structural Isomers Draw all possible isomers of C 3 H 6 O 2 Two oxygen's → carboxylic acids and esters