Table 2.
Main infrared peaks and assignments of monoacid and diacid metal salts.
| Peak Maxima, Wavenumbers (cm−1) | Assignment | Notes | ||
|---|---|---|---|---|
| Monoacid Metal Soaps | Octanedioate (Suberate) Metal Soaps | Nonanedioate (Azelate) Metal Soaps | ||
| 3600–3300 | 3590, 3521 Zn | 3565, 3521 Zn | vO‒H (cryst. water) | In Ca and higher Zn monoacid salts. Only in zinc diacid salts. |
| 2956 | n.a. | n.a. | vasCH3 | |
| 2940(sh), 2926–2916 | 2942, 2930, 2909 Na 2978, 2939, 2921, 2907 Ca 2939, 2927, 2905 Zn |
2943, 2936, 2921, 2907 Na 2976, 2947, 2921, 2915 Ca 2939, 2927, 291 Zn |
vasCH2 | Downshifted (3–5 cm−1) in monoacid salts, for >C16 (Ca, Na) and >C14 (Zn). Structured in diacid salts. |
| 2874–2870 | n.a. | n.a. | vsCH3 | |
| 2856–2850 Na salts 2851 Ca and Zn salts |
2863 Na 2860, 2850 Ca 2867, 2851 Zn |
2858, 2848 Na 2862, 2849 Ca 2867, 2850 Zn |
vsCH2 | Downshifted (~5 cm−1) in monoacid Na salts, for >C9. Split into two components in diacid salts |
| 1628 (br) Ca salt 1617–1619 Zn salts C12-C24 |
1607 Zn | 1616 Zn | δH-O‒H (cryst. water) | In Ca and higher Zn monoacid salts. Only in zinc diacid salts. |
| 1560 Na salts 1579, 1542 Ca salts 1551, 1532 Zn salts, C8, C9 1540 (br) Zn salts C10-C24 |
1563 Na 1581, 1544 Ca 1551, 1537 Zn |
1575 Na 1581, 1542 Ca 1556, 1534 Zn |
vasCOO- | Singlet for Na and higher Zn salts. Doublet for Ca and lower Zn salts. |
| 1472–1459 Na salts 1473 Ca salts 1467–1464, Zn salts |
1463, 14447, 1432, Na 1468, 1455, 1431, 1411 Ca 1467, 1460, 1450 Zn |
1463, 1405 Na 1468, 1434, 1420 Ca 1468, 1456 Zn |
δCH2 scissoring | Single peak, a stable frequency for Ca and higher monoacid Zn salts. Four- or three-fold structuring in diacid salts. |
| - 1458 Zn salts |
n.a. | n.a. | δasCH3 | Overlapped in Na salts; undetectable in Ca salts. Detectable as unresolved shoulder in Zn lower salts. |
| 1423 Na salts 1433, 1411 Ca salts 1410, 1399 Zn salts C8, C9 1398 Zn salts C10-C24 |
1416 Na 1436, 1405 Ca 1412, 1399 Zn |
1434 Na 1431, 1411 Ca 1407, 1398 Zn |
vsCOO- | Singlet for Na and higher Zn salts. Doublet for Ca and lower Zn salts. |
| - | n.a. | δsCH3 (‘umbrella’ vibration) | Undetectable in most monoacid salts | |
| 1400–1351 Na salts 1380–1287 Ca salts 1375–1260 Zn salts |
1356 Na 1359, 1332 Ca 1366 Zn |
1339 Na 1343, 1318 Ca 1353 Zn |
τCH2 | Progressions of 4 or 5 sub-bands in monoacid salts. Singlet or doublet in diacid salts. |
| 1341–1180 Na salts 1278–1190 Ca salts 1250–1045 Zn salts |
1293, 1200 Na 1293, 1261, 1247, 1217, 1201 Ca 1303, 1207 Zn |
1316, 1288, 1273, 1253, 1233, 1195 Na 1286, 1251, 1200 Ca 1285, 1243 Zn |
wCH2 | Progressions following the n/2 pattern (n = total carbon atoms) in Na and Ca salts. Sub-bands in Zn salts. |
| 1185–1100 Na 1114 Ca 1067–1105 Zn |
1100 | 1100 | Unassigned | Weak single band; up-shifting with longer carbon chains in monoacid Zn salts. Single band; not observed in Na and Zn C8di salts. |
| 855–849 | δCH3 + vC-C. | Not observed in monoacid zinc and diacid soaps. | ||
| 725–717, 698 721 Ca salts 747, 723 Zn salts |
ρCH2 | Doublet for Na and Zn salts; single peak for Ca salts. | ||
v: stretching vibration; vs: symmetric stretching; vas: antisymmetric stretching; δ: bending vibration; δs: symmetric bending; δas: antisymmetric bending; δip: in-plane bending; δoop: out-of-plane bending; τ: twisting vibration; ρ: rocking vibration; w: wagging vibration.