Table 5.
Experimental (Exp.) and B3LYP/6-311++G(d,p) calculated (Calc.) infrared spectra of monomeric 2,6-difluorobenzoic acid, and band assignments a.
| Exp. | Calculated | Approximate Description b |
Sym- metry |
|
|---|---|---|---|---|
| Gas Phase | B3LYP | |||
| ν | ν | I IR | ||
| 3570 | 3670 | 93.6 | ν(O–H) | A |
| n.obs. | 3143 | 0.1 | ν(CH) +++ | A |
| n.obs | 3138 | 0.7 | ν(CH) +0– | A |
| 3082 | 3118 | 3.5 | ν(CH) +–+ | A |
| 1779 | 1768 | 421.1 | ν(C=O) | A |
| 1621 | 1623 | 121.0 | ν(CC) +–++–+ | A |
| 1597/1563 c | 1585 | 80.2 | ν(CC) +0–+0– | A |
| 1472 | 1466 | 80.1 | ν(CC) 0++0– –, δ(CH) 0++ | A |
| 1472 | 1461 | 68.7 | ν(CC) ++0– –0, δ(CH) ++0 | A |
| 1363/1320 d | 1331 | 115.2 | ν(C–O), δ(COH) | A |
| n.obs. | 1304 | 0.3 | ν(CC) +–+–+– | A |
| 1295 | 1266 | 27.4 | ν(CF2) sym | A |
| 1244/1238 e | 1230 | 65.5 | δ(CH) +++ | A |
| 1182 | 1179 | 163.4 | δ(COH), ν(C–O) | A |
| 1150 | 1153 | 0.9 | δ(CH) +–+ | A |
| 1094 | 1090 | 109.6 | ν(C-O), δ(CH) +0– | A |
| 1054 | 1050 | 24.9 | δ(ring)1 | A |
| 1020 | 1002 | 146.0 | ν(CF2) asym | A |
| 964 | 956 | 0.5 | γ(CH) +–+ | A |
| n.obs. | 874 | 0.1 | γ(CH) +0– | A |
| 798 | 793 | 51.2 | γ(CH) +++, γ(C=O) | A |
| 786 | 784 | 10.3 | ν(C–C), δ(ring)2 | A |
| 763 | 763 | 19.6 | γ(C=O), γ(CH) +++ | A |
| 697 | 700 | 44.55 | τ(ring)1 | A |
| 683 | 684 | 21.7 | δ(OCO) | A |
| 611 (?) | 594 | 7.0 | τ(ring)3, γ(CF2) asym | A |
| 581 | 588 | 86.9 | τ(C–O) | A |
| n.obs | 573 | 5.2 | τ(ring)2 | A |
| 566 | 554 | 41.0 | δ(OCO), δ(ring)3 | A |
| n.i. | 509 | 2.4 | δ(CF2) asym | A |
| n.i. | 473 | 3.0 | τ(ring)3 | A |
| n.i. | 400 | 2.1 | δ(ring)4 | A |
| n.i. | 385 | 1.9 | γ(C-[CCC]) | A |
| n.i. | 283 | 0.8 | δ(CF2) sym | A |
| n.i. | 236 | 0.02 | γ(CF2) asym | A |
| n.i. | 218 | 0.9 | γ(CF2) sym | A |
| n.i. | 165 | 1.4 | w(COOH) | A |
| n.i. | 94 | 2.3 | γ(COOH) | A |
| n.i. | 44 | 1.9 | τ(C–C) | A |
a Wavenumbers (ν) in cm−1, calculated infrared intensities (IIR) 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 Fermi interaction with 2 × {γ(CH) +++, γ(C=O)}. d Fermi interaction with 2 × δ(OCO). e Fermi interaction with 2 × {τ(ring)3, γ(CF2) asym}.