Vibrational Study and Force Field of the Citric Acid Dimer Based on the SQM Methodology

Table 1

Observed and calculated wavenumbers (cm⁻¹) and assignments for citric acid dimmer.

Experimental^a		Monomer^b			Dimer^a
IR	Raman	IR	Raman	Assignment	SQM^c	Assignment^a
	3535 vw			𝜈 O–H	3537	ν O33–H39
	3535 vw			𝜈 O–H	3527	ν O3–H4
3498 s				𝜈 O–H	3527	ν O19–H21
	3480 vw			𝜈 O–H	3525	ν O40–H42
3446 m	3446 vw				3482	ν O13–H14
3350 sh	3342 vw				3470	ν O31–H35
3291 s	3276 vw				3066	O22–H24
3247 sh
3040 sh
3035 sh					3012	νa CH2 op
2994 w	2996 w		3000	𝜈a CH2	3009	νa CH2 op
2994 w	2996 w				3006	νa CH2 ip
2994 w	2996 w		2975	𝜈a CH2	3003	νa CH2 ip
	2982 m				2952	νs CH2 ip
	2982 m		2950	𝜈s CH2	2951	νs CH2 ip
	2982 m		2934 (21)	𝜈s CH2	2946	νs CH2 op
2950 w	2961 w				2945	νs CH2 op
2933 w	2929 m				2942	O10–H12
1756 vs					1786	νs C=O1
1745 sh	1750 w				1783	νs C=O2
	1735 s				1775	νa C=O2
	1735 s				1771	νa C=O1
1708 vs	1708 w	1706 s	1736 (10)	𝜈 C=O	1726	νa C=O3
1698 sh	1693 vs	1695 sh	1693 (11)	𝜈 C=O	1677	νs C=O3
	1493 vs				1483	δs COH
	1469 w				1463	νa C–C2
1430 m	1432 m, br	1427 s	1425 m	δCH2,	1447	ν C29–C30
				δCH3
1430 m	1432 m, br				1430	δCH2 ip
	1424 sh				1426	δCH2 ip
1420 sh					1417	δCH2 op
	1413 w				1412	δCH2 op
1389 m	1391 s	1389 s	1389 (9)	δ COH,	1402	δa COH
				wag CH3
1389 m					1385	wag CH2 op
1389 m					1383	δC8–O13–H14
	1365 w				1381	wag CH2 ip
1358 w		1350 w	1350 w	τCH2	1352	ρCH2 ip
1340 sh	1347 w	1325 vw		wag CH2	1334	δs COH
1308 w					1308	δs COH
1308 w					1306	wag CH2 ip, δC38–O40–H42
1308 w	1301 vw				1303	δa COH
1292 w	1291 vw				1303	ρCH2 ip, wag CH2 ip
	1285 vw	1280 w		δ COH,	1289	ρCH2 op
				wag CH3
	1256 vw				1266	νa C–O
1242 m					1258	νs C–O
1214 m	1229 w				1219	ρCH2 ip
1214 m	1211 m	1210 w	1205 s	τCH2	1212	ρCH2 op
1199 sh	1201 w	1195 w		𝜈 C–O
1174 s	1179 w	1175 s		δ COH	1169	ν C30–O33
	1167 w				1155	ν C18–O19
1140 s		1141 s	1141 (3)	𝜈 C–O	1145	ν C38–O40
1140 s	1140 w				1140	ν C1–O3
1140 s	1130 w				1127	ν C8–O13
1081 w	1083 m	1090 w	1080 s	𝜈 C–C	1112	δa COH
	1053 m	1053 m	1053 (6)	𝜈 C–C	1059	ν C8–C5, ν C8–C15
1051 w					1057	ν C29–C32, ν C29–C26
	1036 sh				1039	wag CH2 op
	1036 sh				1036	τwCH2 op
	966 vw				926	νs C–C2
945 w	943 vs	943 m	943 (20)	𝜈 C–O	911	νs C–C1
	914 sh				886	τwCH2 op
904 w	904 m				885	τwCH2 op
904 w	904 m		900 m	𝜈 C–C	872	ν C29–O31
881 w	886 w				871	τwCH2 ip
	867 vw				865	τ(O22–H24), τ(O10–H12)
	850 vw				857	ν C32–C38
	842 vw				842	νa C–C1
	842 vw				827	γa (OH–O)^#
	807 vw				800	δCCC op
	795 sh	810 w			792	γCOO2
781 s	784 vs		786 (29)	𝜈 C–C	783	δCOO2
729 sh	723 w				735	δCOO5
	700 w				685	δCOO4
686 w			687 (6)	𝛾COO	674	γCOO5
	666 vw				672	γCOO3
	656 sh	660 sh			655	γCOO2 , τ(O3–H4),
						τwCH2 op
640 w	642 w	645 w	645 w	τ(OH)	637	τ(O40–H42)
	627 vw				631	τ(O3–H4)
	627 vw				625	τ(O19–H21)
	627 vw				621	δCOO3
599 s	597 w	598 s	598 (5)	τ(OH)	616	τ(O40–H42), δCOO5,
						δC31–C29–C30, ρCOO5
	574 w				574	δCOO6
	571 w				566	γCOO4
550 w	559 m		556 (7)	τ(OH)	544	ρCOO2
	541 w				537	δCOO1
520 sh	528 vw				519	γCOO6
	514 w				499	γCOO3 , τwCH2 ip,
						τ(O19–H21)
504 w	509 sh	503 w			496	γCOO1
	492 vw				490	τ(O33–H39)
477 sh	476 vw				485	γCOO6
438 vvw	453 w				412	ρCOO4
	415 w	420 w		δCOO	398	τ(O31–H35)
	397 w	392 s	383 (11)	τ(OH)	390	δC31–C29–C26
	382 m				387	τ(O13–H14)
	367 w				373	ρCOO3, ρCOO1
	367 w	358^b		δ COO	368	ρCOO5
	348 w	334^b		δ COO	345	ρCOO6
	323 vw	320^b		δ CCO	329	δC13–C8–C5
	306 w				294	δC13–C8–C9
	306 w				271	δC26–C29–C32
	266 w				251	δC31–C29–C30
	254 sh	255^b		ρCCC	236	δC5–C8–C15
	247 vw	245^b		δ CCC	222	δC9–C8–C5
	237 vw	223^b		δ CCC	221	δC31–C29–C32
	217 w	187^b		δ CCC	180	δC26–C29–C30
	212 w				174	δCCC op
		140^b			148	νs(O–H–O)^#
					127	τwCOO3
					122	δ(OH–O)^#
					118	τwCOO5
		105^b		δ CCC	108	νa(O–H–O)^#, δCCC ip
					99	τwCOO5
		88^b		τwCOO	92	δCCC ip
		68^b		τwCOO	72	τwCC ip
					57	τCC2
					53	τwop^#
		44^b		τwCOO	46	τwCC op
		39^b		τwCOO	38	τwCOO1
					32	τwCOO6
					30	τwCOO2
					26	τwCOO1, τwCOO2,
						τwCOO3
					25	τCC1
					11	γs (OH–O)^#
					8	τwCOO4

𝜈: stretching; δ: scissoring; wag: wagging; 𝛾: out-of plane deformation; ρ: rocking; τ: torsion, τw: twisting; a: antisymmetric; s: symmetric; s: strong; m: medium; w: weak; v: very; sh: shoulder; br: broad.
^aThis work.
^bCalculated by HF/4-21G method from [15].
^cTheoretical values from SQM/B3LYP/6-31G* calculations for citric dimer acid.
^# Intermonomer coordinates.