Table 3.
Experimental (Exp.) and B3LYP/6-311++G(d,p) calculated (Calc.; cis-II conformer) infrared spectra of monomeric 2-fluorobenzoic acid, and band assignments a.
| Exp. | Exp. (This Work; Also [16]) | Cal. | Approximate Description b |
Sym- metry |
|
|---|---|---|---|---|---|
| Gas Phase | Ar Matrix, 10 K | B3LYP | |||
| ν | ν | ν | I IR | ||
| 3576 | 3558/3555 | 3676 | 96.4 | ν(O–H) | Aτ |
| 3100 | 3069 | 3137 | 4.9 | ν(CH) ++++ | A′ |
| n.obs | n.obs. | 3132 | 1.1 | ν(CH) +0– – | A′ |
| 3087 | 3026 | 3121 | 6.7 | ν(CH) +– –+ | A′ |
| 3060 | n.obs. | 3107 | 2.8 | ν(CH) 0+–+ | A′ |
| 1765/(1778) c | 1748/1747/1745/1744 | 1736 | 407.6 | ν(C=O) | A′ |
| 1611 | 1619/1618/1617 | 1613 | 79.9 | ν(CC) +–++–+ | A′ |
| 1582 | 1593/1591/1590/1588 | 1581 | 16.0 | ν(CC) +0–+0– | A′ |
| 1490 | 1506/1504/1493/1489/1487 | 1482 | 46.6 | ν(CC) 00+00–, δ(CH) ++– – | A′ |
| 1458 | 1464/1463/1461 | 1452 | 88.5 | ν(CC) 00+00–, δ(CH) 0++0 | A′ |
| 1340 | 1395/1390/1388/1361/1360 | 1348 | 131.3 | ν(C–O), δ(COH) | A′ |
| n.obs. | 1346/1344/1343 | 1312 | 9.6 | ν(CC) +–+–+– | A′ |
| 1278 | 1284/1283/1282/1280 | 1259 | 38.9 | δ(COH), δ(CH) +0++ | A′ |
| 1238/(1245) c | 1240/1239/1235 | 1217 | 63.0 | ν(CF) | A′ |
| 1184/(1162) c | 1193/1192/1191/1188 | 1182 | 149.7 | ν(C–O), δ(COH) | A′ |
| 1155/1149 d | 1158/1155 | 1152 | 26.4 | δ(CH) +–+– | A′ |
| 1111/1105 e | 1116/1115/1113/1110/1106/1103 | 1105 | 137.0 | ν(C–O), δ(CH) 0++– | A′ |
| n.obs. | 1093/1091 | 1086 | 14.1 | ν(C–O), ν(CC) 0+00–0 | A′ |
| 1030/(1059) c | 1032/1031 | 1031 | 22.7 | δ(ring)1 | A′ |
| 973 | n.obs. | 974 | 0.6 | γ(CH) +–+0 | A″ |
| 952 | 960 | 958 | 1.8 | γ(CH) +0–+ | A″ |
| 865 | 869 | 865 | 2.3 | γ(CH) ++0– | A″ |
| 835/(845) c | 841 | 832 | 23.6 | δ(ring)2 | A′ |
| n.obs. | n.obs. | 788 | 0.002 | γ(C=O) | A″ |
| 755 | 762/761/760/759/758 | 756 | 93.8 | γ(CH) ++++ | A″ |
| 744 | 741/740/739/738/734/733 | 730 | 12.2 | ν(C–C), δ(ring)3 | A′ |
| 696 | 698/697/696 | 689 | 40.8 | τ(ring)1 | A″ |
| 625 | 626 | 623 | 44.1 | δ(OCO) | A′ |
| 575 | 587/586/585 | 576 | 69.7 | τ(C–O) | A″ |
| 552 | 538 | 548 | 17.3 | δ(ring)3 | A′ |
| 525 | 528 | 531 | 6.8 | δ(ring)3, δ(CF) | A′ |
| n.obs. | 517 | 516 | 0.3 | τ(ring)2, γ(CF) | A″ |
| n.i. | 429 (?) | 425 | 7.6 | γ(C-[CCC]), τ(ring)3 | A″ |
| n.i. | n.i. | 369 | 2.9 | δ(ring)4 | A′ |
| n.i. | n.i. | 344 | 0.03 | δ(CF) | A′ |
| n.i. | n.i. | 244 | 0.7 | γ(CF) | A″ |
| n.i. | n.i. | 208 | 3.5 | γ(COOH) | A′ |
| n.i. | n.i. | 127 | 0.8 | w(COOH) | A″ |
| n.i. | n.i. | 28 | 2.4 | τ(C–C) | A″ |
a Wavenumbers (ν) in cm−1, calculated infrared intensities (I IR) in km·mol−1; n.obs., not observed; n.i., not investigated; ?, uncertain. b Approximate description was obtained using the vibrations animation module of Chemcraft [63]; ν, stretching; δ, bending; w, wagging; γ, rocking; τ, torsion; the symbols +, – and 0 placed in front of the ν(CC), ν(CH), δ(CH) and γ(CH) ring coordinates indicate the movement (distending, compressing, staying, respectively) of the related bonds, starting from that located ortho to the C=O bond of the carboxylic group and proceeding anti-clockwise through the ring. c Band due to conformer cis-I. d Fermi interaction with 2 × τ(C-O). e Fermi interaction with 2 × τ(ring)3.