Question

IR spectrum of maleic acid (bottom) and product of cis-trans isomerization, fumaric acid (top). Can someone help label the peaks of both? thanks!

CMNC Window File Colt View Process Analyse Report Window Help Experiment D7 ATR - Diamond (DT ATR Diamond KBS6.exp) - System Status BIG BEN WINNER Save Sick Spe Fulse Can Sel Auto AYATR Sibast Find Search i maleic acid Mon Nov 18 1551:57 2015 (GMT-0500 mnt 80- Transmittance 3081.72 2620 53 2555.79 2513.10 1318.771 1420.92 721.00 779.49 1656.37 9€ 606 127108 1227.39 88011 $77.00 3057.102 287197 2684.19 OCTOR 2377.70) 216152 1707361- 14583 peces 2016 12696 78499 859 92 LYZED 60708 84 4000 2500 1500 Wavenumbers icm-1) X12413.720) Y.191.482) ⓇOB@D$$X G NEW

Answer 1

In both maleic acid and fumaric acid the carbonyl group is conjugated with the C=C bond, so the C=O stretching band appears at a lower value (nearly 1630-1640 cm^-1).

For maleic acid (bottom) due to the intramolecular H-bonding partial formation of carboxylate anion happens, thus a peak for C=O stretching at 1561 appears but for fumaric acid (top) this peak is absent.

In fumaric acid, the C=O stretching band and C=C stretching band gives rise to broadband at 1656 cm^-1

For maleic acid, the C=O stretching band is so weak that broadband is not observed instead sharp C=C stretching band at 1703 cm^-1 is observed clearly.

CMNC Window File Colt View Process Analyse Report Window Help Experiment D7 ATR - Diamond (DT ATR Diamond KBS6.exp) - System Status BIG BEN WINNER Save Sick Spe Fulse Can Sel Auto AYATR Sibast Find Search i maleic acid Mon Nov 18 1551:57 2015 (GMT-0500 mnt 80- Transmittance 3081.72 2820 1318.77 1420.92 9€ 606 721.00 779.49 1271 De 1227.39 88011 C=C stretching peak and CEO stretching peak, resulting broad peak $77.00 3057.102 2871 97 268419 280430 C=C stretching 1560.84 peces 2016 12696 78499 859 92 LYZED 60708 84 4000 1500 c=8 stretshing...) X12413.720) Y.191.482) CEO stretching for the carboxylate group ⓇOB@D$$X el NW