PhOCH C-NH CH 300 CH Boiling Points COOH acylated. inactive enzyme 1°amides 200 N-methyl2°amides N.N-dimethyl 3 amides acid 100 acids chlorides nitriles R I°alcohols methyl esters 个 R -100 intermolecular attraction Even3°amides have n-alkanes 20 60 100 140 180 strong attractions. molecular weight 7 Chapter 21 16
Chapter 21 16 Boiling Points Even 3 amides have strong attractions. =>
COOH Melting Points inactive enzyme Amides have very high melting points. Melting points increase with increasing number of N-H bonds. 0 CH3 H一C-N CH,CH,-C-N< CH CH dimethylformamide N-methylacetamide propionamide m.p.-61C m.p.28C m.p.79C => Chapter 21 17
Chapter 21 17 Melting Points • Amides have very high melting points. • Melting points increase with increasing number of N-H bonds. m.p. -61C m.p. 28C m.p. 79C =>
0 PhOCH C NH CH Solubility CH COOH acylated Acid chlorides and anhydrides are too enzyme reactive to be used with water or alcohol. ·Esters,3°amides,and nitriles are good polar aprotic solvents. Solvents commonly used in organic reactions: >Ethyl acetate >Dimethylformamide (DMF) >Acetonitrile Chapter 21 78
Chapter 21 18 Solubility • Acid chlorides and anhydrides are too reactive to be used with water or alcohol. • Esters, 3 amides, and nitriles are good polar aprotic solvents. • Solvents commonly used in organic reactions: ➢Ethyl acetate ➢Dimethylformamide (DMF) ➢Acetonitrile =>
PhOCH,C IR Spectroscopy H COOH inactive TABLE 21-3 Characteristic IR Stretching Absorptions of Acid Derivatives Functional Group Frequency Comments C=0,1710cm- lower if conjugated,higher if strained ketone R C=0,1710cm-1 lower if conjugated acid OH 0-H.2500-3500cm- broad,on top of C-H stretch C=0,1735cm-1 lower if conjugated,higher if strained ester O—R C=0,1640-1680cm-1 amide N-H,3200-3500cm-I two peaks for R-CO-NH,, one peak for R-CO-NHR' C=0.1800cm-1 very high frequency acid chloride C=0,1800and1750cm-1 two peaks acid anhydride => nitrile R-CN C=N,2200cm-1 just above 2200 cm- Copyright 2005 Pearson Prentice Hall,Inc
Chapter 21 19 IR Spectroscopy =>
0 PhOCH,C- NH CH CH COOH 1H NMR Spectroscopy acylated. inactive enzyme 82.0-62.5 0 H variable,δ5-δ8.broad R-CH2-C-X R-c-0-C- R-C-N-CH2- alpha protons ester 64 amide 63 0 0 H一C一R H-C-0-R H-C-NR2 R一CH2-C=N: 69-810 68 68 62.5 aldehyde formate formamide nitrile Copyright2005 Pearson Prentice Hall,Inc. > Chapter 21 20
Chapter 21 20 1H NMR Spectroscopy =>