Research Article
Terahertz Absorption Spectroscopy of Benzamide, Acrylamide, Caprolactam, Salicylamide, and Sulfanilamide in the Solid State
Table 1
Calculated and experimental vibrational frequencies for salicylamide, benzamide, acrylamide, caprolactam, and sulfanilamide (cm−1)a.
| Compounds | Experiment | Calculation | Vibrational assignments | FIR | THz-TDS | 6-311++G(3df, 2pd) |
| Salicylamide | 526 | | 538 | τph | 515 | | 509 | ρNH2, ρ(C=O and OH), in-plane wagging of ph | 456 | | 439 | In-plane wagging of ph, t(C=O-NH2 and COH) | | | 419 | Out-of-plane folding of ph, νNH | 385 | | 383 | βph, τ(C=O-NH2 and COH) | 296 | | 275 | ρNH2, ρ(ph) | | | 247 | Out-of-plane wagging of whole molecule, especially ph ring | 161 | | 184 | ωNH2 | 146 | | | | 108 | | 141 | γ(whole molecule) | 94 | | | | | 80 | | | | 54 (55*) | | | | 48 (49*) | | | | 41* | 30 | t(ph-C=O-NH2) |
| Benzamide | | | 503 | In-plane wagging of ph and amide | | | 415 | Out-of-plane folding of ph ring | 412 | | 414 | Out-of-plane folding of ph ring, ρNH2 | 383 | | 375 | In-plane rocking of amide group, ωph, νCC | | | 341 | ωNH2 | 251 | | 217 | In-plane rocking of ph ring, ρ(C=O-NH2) | 178 | | | | 151 | | 152 | γph; ρNH2 | 110 | | | | 90 | | | | | 58 | | | 54 | 54 | 57 | γ(ph-CONH2), ωNH2 | | 38 | | |
| Acrylamide | 508 | | 470 | t(CH=CH2), tNH2 | | | 468 | ρNH2, ω(CH=CH2) | 314 | | 277 | ρ(CH=CH2), ρ(C=O-NH2) | 185 | | 190 | ωNH2 | 122 | | 114 | ωNH2, ω(CH=CH2) | 67 | 67 | | | | 48 | | |
| Caprolactam | 503 | | 508 | νNH; ρCH2 | 488 | | 437 | νC=O; νNH; ωCH2; | 398 | | 402 | βring | 337 | | 323 | ρCH2 | 323 | | 301 | νNH; βring | 258 | | 258 | ρCH2; ωCH2; νNH; νC=O; | 195 | | 158 | ρCH2, βring | 129 | | 107 | ωCH2; νC=O; γring | 87 | | | | 69 | 71 | | | 56 | 55 | | | | 41 | | |
| Sulfanilamide | | 73 | 85 | Out-of-plane wagging of ph, ωNH2 | | 67 | | | | 59 | | | | 54 | 15 | Out-of-plane wagging of ph, tNH2 |
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β: in-plane vibration; τ: torsion; γ: out-of-plane vibration; ν: stretching; ω: wagging; ρ: rocking; t: twisting, ph: benzene ring.
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