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

aβ: in-plane vibration; τ: torsion; γ: out-of-plane vibration; ν: stretching; ω: wagging; ρ: rocking; t: twisting, ph: benzene ring.