Table 1 Main infrared peaks of fatty acids and copper carboxylates on clean/polished copper and copper-zinc alloy coupons
Fatty acids | Cu carboxylates1, cm−1 | Zn carboxylates2, cm−1 | Assignments | Notes3 |
|---|---|---|---|---|
~ 3100 (br) | – | vOH | Typically, very broad | |
2960–2956 | 2954 | 2956 | vasCH3 | Only in monoacids and their carboxylates Marginally variable, according to number of carbons in acids |
2934–2919 2977–2911 | 2930 (C6); 2920 (C8); 2014 (C10-C18) | 2940(sh), 2926–2916 (C6-C18) | vasCH2 | Generally, CuC and ZnC down-shifted with respect to parent FAs General trend: variable, according to the number of carbons |
2991, 2951, 2941, 2911 (C8di) 2977, 2937, 2915 (C9di) | 2964, 2943, 2931, 2917, 2906 (C8di) 2942, 2927, 2909 (C9di) | 2964, 2943, 2931, 2917, 2906 (C8di) 2842, 2927, 2906 (C9di) | Multiplets in diacids and corresponding carboxylates; higher multiplicity for C8di | |
2875–2872 | 2871 | 2870 | vsCH3 | Variable, according to the number of carbons |
2851 | 2853 (C6); 2851 (C8); 2848 (C10-C18) 2851 (C8di) 2849 (C9di) | 2850 | vsCH2 | Variable in CuC according to the number of carbons |
2670, 2565 (FMA) | – | – | vO-H•••O = C (dimer band stretch) | Only in FA, often used diagnostically; weak, structured with shoulders |
2759, 2676, 2599, 2534 (C8di) 2774, 2698, 2621, 2553 (C9di) | More extended in diacids | |||
1714 to 1690 (C6, C8, C10, C12) | vC = O, acidic | In C6–C12: single bands, maxima downshifted upon acid consumption and film thinning | ||
1700, 1688 (C14, C18) | In C14, C18 doublet at fixed maxima during the FA consumption | |||
1692–1690 | In C8di, C9di | |||
1616–1613 w (C6-C10) | vasCOO‒ | Intermediate band in copper carboxylates of C6-C10 | ||
1583 (C6) | 1527 (C6) | |||
1583 (C8) | 1548, 1525 (C8) | |||
1581, 1519 w (C10) | 1550, 1532–1524 (C10) | |||
1585, 1525–1519 w (C12) | 1537 (C12) | |||
1585 (C12) | 1537 (C14) | |||
1586 (C18) | 1540 (C18) | |||
1589 (C8di) | 1552, 1532 (C8di) | Diacid carboxylate bands in both substrates were observed on pre-corroded surfaces | ||
1600 (C9di) | 1552, 1527 (C9di) | |||
1465, 1416 | 1458, 1415 | 1468, 1456 | δCH2 scissoring | FA: Split into two components (two in diacids) |
1457 (?) | 1439(?) | 1439(?) | δasCH3 | Barely distinguishable in Cu and Zn carboxylates |
1436 | δipCOH | Relatively broad | ||
1440–1431 | 1400–1396 (br) | vsCOO‒ | Generally medium-weak intensity for most carboxylate bands; relatively sharp | |
1400 1395 | Intermediate (C8, C10) C8di and C9di | |||
1382 | n.d | n.d | δsCH3 (‘umbrella’ vibration) | |
1356–1347 | 1366, 1341, | 1366, 1341, | τCH2 | Splitting in progression bands for monoacids in their crystalline state (at room temperature, higher than C10); |
1318–1185 | 1312–1185 | 1312, 1207 | wCH2 | In crystalline, saturated monoacids and diacids progressions |
1108 | vC‒OH | Up shifted for longer hydrocarbon chains. Weak or not observed for diacids | ||
943–935 (br) | δoopC‒O–H•••O = C | The dimer bending band; characteristic of fatty acids | ||
720, 800–607 | 720 | 720 | ρCH2 | Stronger in long hydrocarbon chains; the 725 cm−1 peak doubly split in crystalline monoacids |
690 | δoopC‒O–H | Overlapped in unsaturated acids |