Acid SbF6 – SbF6 – F 3CSO3– –?? HClO 4 ClO4– –10 I– Increasing Acid Strength HSO 4– H 2SO 4 Br – HBr H C R H C H O+ Super Acids all too strong to measure –10 –9 sulfuric acid –9 hydrobromic acid –8 protonated aldehydes OR' C R O –7 protonated esters Cl – –7 hydrochloric acid –7 protonated ketones –6 protonated carboxylic acids –6 protonated phenols –3 sulfonic acids –3 protonated ethers –2 protonated alcohols hydronium; H +(aq) nitric acid HCl R' R' H C R O+ C O OH OH H C Comment O R OR' H C R O+ R Increasing Base Strength SO 3 / FSO 3H/SbF 5 HF / SbF5 F 3CSO3H HI R pKa Conj. Base R O+ O H O X H O O OH S O S O aka TsOH H 3C O H + X C O H 3C H + R O R' R O R' H + R O H R O H H 3O+ HNO 3 NO 3– –1.74 –1.3 HSO 4– H–F SO 42– F– 1.99 3.18 second H of sulfuric acid hydrofluoric acid HNO 2 NO 2– 3.3 nitrous acid –6 to +5 anilines; pKa very sensitive to ring substituents H 2O H +N H N H H H X X Acid O O C C O-H R C H 3C 6.35 7.00 carbonic acid hydrogen sulfide 9.00 2,4-pentandione 9.24 ammonium ion 4–11 depends on substitution plain phenol has a pka=10 R–CH–NO 2 10.0 aliphatic nitro CO3– 10.3 bicarbonate 11.0 ethyl acetoacetate 13.0 diethyl malonate 15.7 water pKa 15.0 cyclopentadiene: World's Strongest Carbon Acid!! 17.0 amides 16-19 alcohols, ethanol pKa = 16 20-21 alpha H of ketones 25 alpha H of esters O O C C H O HCO 3– HS – H 2CO3 H 2S O CH 3 H 3C O C C C H CH 3 H NH 4+ NH 3 H X X O R–CH 2 –NO2 O HCO 3– O C H 3C O H C EtO C H O O C C OEt H 3C H O O C OEt EtO C C O C H C C OH – H H H O O H N R H O C C O H C H R C H O RO C H N R O R–O–H R OEt H H–O–H R OEt O C H C Comment 4.0 to 5.0 carboxylic acids Increasing Base Strength Increasing Acid Strength R pKa Conj. Base H H O H C C H RO C H C H H R–CH 2 –CN R–CH–CN 25 alpha to nitrile R R 25 terminal alkynes. The electrons are in an sp hybridized orbital C C H C C Acid pKa Conj. Base H N N H X H C C H H C C H H H C H C C 36 hydrogen gas is a weak acid 40 amines: NH 3 pKa=38 41 benzyl hydrogens; conjugated base H C H H allyl hydrogens; conjugated conjugate base. 44 vinyl hydrogens; electrons in unconjugated sp2 orbital 44 phenyl hydrogens; electrons in unconjugated sp2 orbital, not part of aromatic π sextet 46 cyclopropane H; more vinyl than sp3 hybrid (see below.) 48 methane and hydrogens on sp3 carbons 52 cyclohexyl; weakest acid on this table. sp3 conj. base H H H C 43 H C H H Increasing Base Strength Increasing Acid Strength ((CH 3)2CH)2N – H H H anilines; pKa Depends on substitution. Low because it has a conjugated base. Plain aniline has pKa =25 H H ((CH 3)2CH)2NH H 18–28 X H2 Comment H C H C H H H C H H H 2C C H H H H H H 2C H H H H 2C H H C H C H H 2C H C H H H C H H H H H H H H H H H H H H H H H H H H H H H H updated 9/6/2016