Organic Chemistry InternationalVolume 2013 (2013), Article ID 348379, 14 pageshttp://dx.doi.org/10.1155/2013/348379

Research Article

Molecular Structure and Vibrational Spectra of 2-Ethylhexyl Acrylate by Density Functional Theory Calculations

Ottman Belaidi,¹ Tewfik Bouchaour,¹ and Ulrich Maschke²

¹Laboratoire de Recherche sur les Macromolécules, Faculté des Sciences, Université Abou Bekr Belkaid, BP 119-13000, Tlemcen, Algeria²UMET (Unité Matériaux et Transformations), UMR CNRS No. 8207, Université Lille 1-Sciences et Technologies, 59655 Villeneuve d'Ascq Cedex, France

Received 26 February 2013; Accepted 28 April 2013

Academic Editor: Dipakranjan Mal

Copyright © 2013 Ottman Belaidi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

The Fourier transform infrared spectra (FTIR) of 2-ethylhexyl acrylate have been measured in liquid phase. The molecular geometry, vibrational frequencies, and infrared intensities have been calculated by using density functional theory. We found two local minima representing s-cis and s-trans conformations for 2-ethylhexyl acrylate molecule. The optimized geometries at DFT//B3LYP/6-311+ are in good agreement with electron diffraction data of methyl acrylate for the acrylic group. The two conformers were used for the interpretation of the experimental infrared spectrum of title compound. PED calculations are represented for a more complete and concise assignment. There is one band in the infrared spectrum at 1646 cm⁻¹ that definitely indicates the conformer with s-trans arrangement of acrylic moiety to be present or not in the liquid 2-ethylhexyl acrylate.

1. Introduction

Alkyl acrylates are important monomers used in the manufacture of polymers and copolymers. Acrylates give polymers exhibiting outstanding transparency and aging proprieties which have made them of interest in a wide variety of applications [1–4]. The structural data and the preferred molecular conformation of these acrylates molecules would be important for basic understanding of these polymers [5].

2-Ethylhexyl acrylate is used for production of paint, adhesive, and paper coating trade. This monomer imparts flexibility and water resistance to the polymers [1, 6]. It is also used for curing polymeric materials [7–15].

To our best knowledge no structural data or detailed interpretation of the vibrational spectra of 2-ethylhexyl acrylate is presented in the literature. This prompted us to look into the vibrational spectroscopy of 2-ethylhexyl acrylate more carefully.

Many reports, experimental [16–21] and theoretical [20, 22], show that acrylates and related compounds exhibit rotational isomerism with the planar s-trans and s-cis heavy-atom structures being the energetically most stable conformations. However, uncertainty continues to exist regarding the relative stability of the two conformers. Gas electron diffraction studies on methyl methacrylate [20] suggested the cis/trans ratios to be equal to 2 : 1. On the other hand, the IR spectrum of methyl methacrylate in Ar low temperature matrix suggested an inverse ratio [23]. Many experimental and theoretical studies on methyl acrylate reported that the s-cis conformer is more stable than the s-trans conformer [24–29]. However, Bowles et al. [30] assumed that the s-trans conformer is more stable.

2. Experimental

2-Ethylhexyl acrylate (purity greater than 99%) was purchased from Sigma-Aldrich and it was used as it is without further purification. The infrared spectra of liquid films placed between the KBR windows were recorded within 4000–700 cm⁻¹ range with a Perkin Elmer FTIR System-2000 model.

3. Computational

The optimizations of the stable conformers were conducted with the density functional theory using 6-311+G** basis sets. The DFT calculations were performed using Becke’s 3-parameter (local, nonlocal, Hartree-Fock) hybrid exchange functionals with Lee-Yang-Parr correlational functionals (B3LYP) [31, 32].

The harmonic vibrational frequencies of the stable conformations were calculated at the same level of theories used for the calculated optimized geometries. The calculated frequencies were scaled down by the wavenumber linear scaling procedure (WLS) of Yoshida et al. [33, 34] using the following equation:

All the calculations were carried out with the Gaussian 03 program [35]. The vibrational assignments of the normal modes were provided on the basis of the calculated PEDs by using the program GAR2PED [36].

4. Geometry Optimizations and Energies

The geometries optimizations were conducted at the B3LYP/6-311+G** assuming the s-cis and s-trans conformations. All the optimized geometries are recognized as true minima due to the lack of imaginary harmonic frequencies. The results are given in Table 1 for s-cis and s-trans conformers, respectively. For atoms numbering, see Figure 1.

Table 1: Optimized geometries of s-cis and s-trans 2-ethylhexyl acrylate conformations by DFT//B3LYP/6-311+G**.

Internal coordinates
Level of theory DFT/6-311+G**  s-cis EHA
s-cis methyl acrylatea
DFT/6-311+G**  s-trans EHA
s-trans methyl acrylateb

Bond lengths ()

    C₁H₂
1.084

1.083
1.074

    C₁H₃
1.083

1.084
1.075

    C₁C₄
1.331
1.341(7)
1.332
1.319

    C₄H₅
1.084

1.084
1.075

    C₄C₆
1.486
1.484(6)
1.484
1.484

    C₆O₇
1.210
1.211(2)
1.211
1.191

    C₆O₈
1.351
1.349(3)
1.348
1.325

    O₈C₉
1.448
1.439(3)
1.448
1.417

    C₉H₁₀
1.093

1.093

    C₉H₁₁
1.093

1.092

    C₉C₁₂
1.526

1.526

    C₁₂H₁₃
1.098

1.098

    C₁₂C₁₄
1.543

1.543

    C₁₄H₁₅
1.097

1.097

    C₁₄H₁₆
1.096

1.096

    C₁₄C₁₇
1.531

1.531

    C₁₇C₁₈
1.094

1.094

    C₁₇H₁₉
1.093

1.093

    C₁₇H₂₀
1.092

1.092

    C₁₂C₂₁
1.549

1.549

    C₂₁H₂₂
1.097

1.097

    C₂₁H₂₃
1.094

1.094

    C₂₁C₂₄
1.534

1.534

    C₂₄H₂₅
1.097

1.097

    C₂₄H₂₆
1.095

1.095

    C₂₄C₂₇
1.533

1.533

    C₂₇H₂₈
1.097

1.097

    C₂₇H₂₉
1.097

1.096

    C₂₇C₃₀
1.531

1.531

    C₃₀H₃₁
1.094

1.093

    C₃₀H₃₂
1.094

1.094

    C₃₀H₃₃
1.094

1.094

Bond angles (°)

    H₂C₁H₃
118.049

117.591

    H₂C₁C₄
120.479

121.432
121.7

    C₁C₄H₅
122.220

121.739
122.1

    C₁C₄C₆
121.072
120.3(8)
124.970
124.2

    C₄C₆O₇
125.710
126.1(5)
123.066
122.9

    C₄C₆O₈
110.564
110.3(3)
113.320
113.7

    C₆O₈C₉
116.570
116.4(5)
116.493
116.8

    O₈C₉H₁₀
108.658

108.697

    O₈C₉H₁₁
108.313

108.339

    O₈C₉C₁₂
108.522

108.488

    C₉ C₁₂C₁₄
108.099

108.115

    C₁₂C₁₄H₁₅
108.729

108.720

    C₁₂C₁₄H₁₆
108.539

108.544

    C₁₂C₁₄C₁₇
115.410

115.400

    C₁₄C₁₇H₁₈
111.304

111.345

    C₁₄C₁₇H₁₉
110.477

110.478

    C₁₄C₁₇H₂₀
112.028

112.001

    C₉C₁₂C₂₁
111.382

111.384

    C₁₂C₂₁H₂₂
109.228

109.231

    C₁₂C₂₁H₂₃
109.005

109.019

    C₁₂C₂₁C₂₄
114.775

114.824

    C₂₁C₂₄H₂₅
108.695

108.731

    C₂₁C₂₄H₂₆
110.286

110.291

    C₂₁C₂₄C₂₇
113.287

113.308

    C₂₄C₂₇H₂₈
109.207

109.229

    C₂₄C₂₇H₂₉
109.217

109.208

    C₂₄C₂₇C₃₀
113.280

109.208

    C₂₇C₃₀H₃₁
111.428

111.428

    C₂₇C₃₀H₃₂
111.218

111.209

    C₂₇C₃₀H₃₃
111.189

111.202

Dihedral angles (°)

    H₃H₂C₁C₄
180

−179.908

    H₂C₁C₄H₅
−179.977

179.808

    H₂C₁C₄C₆
0.037

0.106

    C₁C₄C₆O₇
−0.166

178.652

    C₁C₄C₆O₈
179.844

−1.298

    C₄C₆O₈C₉
179.896

179.515

    C₆O₈C₉H₁₀
55.606

55.506

    C₆O₈C₉H₁₁
−61.282

−61.454

    C₆O₈C₉C₁₂
177.303

177.169

    O₈C₉ C₁₂H₁₃
55.024

54.463

    O₈C₉C₁₂C₁₄
171.114

170.547

    C₉C₁₂C₁₄H₁₅
61.844

61.568

    C₉C₁₂C₁₄H₁₆
−53.102

−53.378

    C₉C₁₂C₁₄C₁₇
−175.215

−175.516

    C₁₂C₁₄C₁₇H₁₈
56.957

57.249

    C₁₂C₁₄C₁₇H₁₉
176.491

176.782

    C₁₂C₁₄C₁₇H₂₀
−63.865

−63.596

    O₈C₉C₁₂C₂₁
−63.322

−63.915

    C₉C₁₂C₂₁H₂₂
−96.883

−97.147

    C₉C₁₂C₂₁H₂₃
18.587

18.279

    C₉C₁₂C₂₁C₂₄
139.536

139.298

    C₁₂C₂₁C₂₄H₂₅
−59.615

−59.061

    C₁₂C₂₁C₂₄H₂₆
56.214

56.717

    C₁₂C₂₁C₂₄C₂₇
178.823

179.360

    C₂₁C₂₄C₂₇H₂₈
−58.771

−58.768

    C₂₁C₂₄C₂₇H₂₉
56.758

56.753

    C₂₁C₂₄C₂₇C₃₀
179.033

179.029

    C₂₄C₂₇C₃₀H₃₁
179.693

−179.983

    C₂₄C₂₇C₃₀H₃₂
−60.205

−59.888

    C₂₄C₂₇C₃₀H₃₃
59.599

59.917

 aDetermined by a joint analysis of electron diffraction data and rotational constants [21].

bDetermined by ab initio calculation at HF/6–31G** [20].

Figure 1: 2-Ethylhexyl acrylate molecule s-cis and s-trans conformations.

In Table 1, the calculated bond lengths, bond angles, and dihedral angles have approximately the same values for the s-cis and s-trans conformers. However, some changes occur in going from the s-cis to the s-trans conformation. The bond angles C₁C₄C₆ and C₄C₆O₈ increase by 3.8° and 2.7°, respectively, while C₄C₆O₇ decreases by 2.5°.

The X ray structural data of s-cis methyl acrylate reported by Egawa et al. [21] and ab initio structure of s-trans methyl acrylate reported by Tsuji et al. [20] are very close to those we found for 2-ethylhexyl acrylate molecule.

The zero-point corrected energy of the s-cis conformation is 365.102 × 10⁶ cal/mol showing more stability than the calculated one for the s-trans conformation. The energy for the latter conformation is 365.101 × 10⁶ cal/mol.

5. Vibrational Analysis

The most stable conformers, s-cis and s-trans 2-ethylhexyl acrylate, belong to the C₁ point group. Each conformer represents 93 normal vibrational modes. We juxtaposed the experimental IR spectrum with the computed ones for both conformers and we checked whether we can recognize them or not. Tables 2 and 3 represent the calculated and scaled fundamental wavenumbers, intensities of vibrational peaks, and potential energy distribution along the internal coordinates obtained by DFT//B3LYP/6-311+G** level of theory. The corresponding experimental wavenumbers together with assignments are also reported in these tables. The potential energy distributions are given as per the internal coordinate system recommended by Pulay et al. using DFT [37].

Table 2: Frequencies and PEDs of s-cis 2-ethylhexyl acrylate.

Numberb
Observed (cm⁻¹)
DFT/6-311+G**  Unscaled (cm⁻¹)
Scaled (cm⁻¹)
Intensity (kmmol⁻¹)
Assignment (%PED)a

1
—
30.5017
30,7519
0.1860
τ (O₈C₉) (63); τ (C₉C₁₂) (35);

2
—
36.7273
37,02484
1.9384
τ (C₉C₁₂) (83); τ (O₈C₉) (17)

3
—
48.2766
48,65862
1.2435
τ (C₉C₁₂) (98)

4
—
74.7391
75,29828
0.0096
ρ (C₃₀H₃) (62); τ (C₉C₁₂) (17); τ (O₈C₉) (7); ρ (C₁₄H₂) (7)

5
—
93.1493
93,81827
0.7602
τ (C₉C₁₂) (84); ρ (C₁₄H₂) (15)

6
—
99.6177
100,32262
0.6102
τ (C₉C₁₂) (76); τ (C₉C₁₂) (21)

7
—
115.9962
116,78605
0.2949
τ (C₉C₁₂) (94)

8
—
133.8201
134,69244
0.7707
τ (C₉C₁₂) (43); ρ (C₂₇H₃) (31); ρ (C₉H₂) (15)

9
—
146.1924
147,11591
0.0469
τ (C₉C₁₂) (58); ρ (C₉H₂) (17); ρ (C₁₄H₂) (16)

10
—
201.0708
202,16112
1.8808
τ (C₉C₁₂) (89); δ (C₆O₈C₉) (5)

11
—
213.9423
215,05753
2.7336
τ (C₉C₁₂) (98)

12
—
234.1345
235,27792
0.6986
ρ (C₃₀H₃) (94)

13
—
253.7618
254,91989
1.2866
ρ (C₃₀H₃) (99)

14
—
265.4468
266,60766
0.7334
τ (C₉C₁₂) (83); ρ (C₃₀H₃) (14)

15
—
285.1163
286,27176
3.5548
ρ (C₃₀H₃) (78); τ (C₉C₁₂) (18)

16
—
315.7568
316,87874
0.5814
ρ (C₉H₂) (89); ρ (C₁₇H₃) (6)

17
—
355.1126
356,14657
0.2263
ρ (C₁₇H₃) (36); ρ (C₉C₁₂C₁₄) (31); ρ (C₉H₂) (19)

18
—
375.9666
376,93349
4.3994
ρ (C₂₄C₂₇C₃₀) (27); ρ (C₉C₁₂C₁₄) (23); ρ (C₁₇H₃) (17); δ (C₂₁C₂₄C₂₇) (10); ρ (C₉C₁₂H₁₃) (10); δ (C₂₁H₂) (8)

19
—
470.318
470,80422
0.6863
ρ (C₉C₁₂C₂₁) (72); ρ (C₁₇H₃) (11); ρ (C₉H₂) (5);

20
—
512.0856
512,26637
6.2054
ρ (C₉C₁₂C₁₄) (80); ρ (C₉H₂) (7); δ (C₂₁C₁₂C₁₄) (6)

21
—
527.3488
527,40376
0.1504
ρ (C₉H₂) (87); O (C₆O₇) (9)

22
—
533.9978
533,99558
1.1100
ρ (C₉C₁₂C₁₄) (77); ρ (C₆O₈C₉) (8)

23
—
681.189
679,55184
3.1928
ρ (C₉C₁₂C₁₄) (42); δ (O₇C₆C₄) (42); ρ (C₆O₈C₉) (5)

24
731 (m)
731.2122
728,8586
4.5137
ρ (C₂₁C₂₄C₂₇) (99)

25
748 (sh)
779.5982
776,474
1.0039
ρ (C₂₇H₂) (65); ρ (C₉C₁₂C₁₄) (18); ρ (C₁₄H₂) (12)

26
770 (m)
786.3101
783,07298
1.6507
ρ (C₂₇H₂) (36); ρ (C₂₁H₂) (32); ρ (C₁₄H₂) (23); ρ (C₁₇H₃) (8)

27
811 (m)
829.5925
825,59191
24.9487
ρ (C₉H₂) (73); O (C₆O₇) (21); y (C₁H₂) (8)

28
852 (w)
852.3514
847,92486
3.0736
ρ (C₉C₁₂C₂₁) (82); ρ (C₉H₂) (16)

29
896 (w)
901.6472
896,24016
1.0870
ρ (C₉C₁₂H₂₁) (62); ω (C₂₄H₂) (16); y (C₂₁H₂) (9); δ (C₃₀H₃) (8)

30
—
906.8585
901,34317
1.0553
ρ (C₉C₁₂H₂₁) (86); ρ (C₉H₂) (10)

31
909 (w)
917.2167
911,48352
7.2928
ρ (C₉H₂) (58); ω (C₂₇H₂) (27); ρ (O₇C₆O₈) (12)

32
933 (sh)
947.8927
941,49381
5.9570
δ (C₁₄C₁₂H₃) (50); ω (C₂₇H₂) (46)

33
962 (m)
983.6705
976,45643
25.1442
ρ (C₉C₁₂H₁₃) (83); δ (C₆O₈C₉) (21); y (C₂₁H₂) (14); y (C₂₇H₂) (11); y (C₁₄H₂) (11)

34
984 (m)
1006.9955
999,22751
25.5334
ω (C₁H₂) (84); y (C₁₄H₂) (10)

35
—
1016.9241
1008,91495
5.1103
ρ (C₁₄H₂) (41); ρ (C₉C₁₂C₂₁) (24); δ (C₁₂C₂₁C₂₄) (23); ρ (C₁₇H₃) (7)

36
1015 (sh)
1023.2765
1015,11136
26.0306
ο (C₄H₅) (99)

37
—
1025.8451
1017,61651
1.9504
δ (C₉C₁₂C₁₄) (98); ν (C₉O₈) (5)

38
1025 (sh)
1045.9956
1037,26182
27.8636
y (C₂₄H₂) (42); ν (C₉C₁₂) (42); ν (O₈C₉) (6)

39
—
1062.1068
1052,95957
0.4109
ρ (C₁₄C₁₂H₁₃) (83); ν (C₂₇C₃₀) (12)

40
—
1065.9864
1056,73835
0.4863
ν (C₁₄C₁₇) (83); ν (C₂₄C₂₇) (11)

41
—
1083.5238
1073,81387
1.6531
ω (C₉H₂) (83); ω (C₂₁H₂) (15)

42
1057 (m)
1089.4787
1079,60965
2.2238
ρ (C₉H₂) (84); ω (C₂₇H₂) (14)

43
—
1150.5508
1138,98319
1.9252
ρ (C₉C₁₂H₁₃) (96)

44
1116 (w)
1168.5589
1156,46723
11.8316
δ (C₁₂C₂₁C₂₄) (67); ρ (C₁₄C₁₂H₁₃) (9); ρ (O₈C₉C₁₂) (7); δ (C₁₄C₁₂C₂₁) (67)

45
1060 (sh)
1185.6606
1173,06145
0.0857
δ (C₉C₁₂C₁₄) (63); ρ (C₃₀H₃) (26); δ (C₁₂C₁₄C₁₇) (6)

46
1191
1205.1044
1191,9167
626.1232
ρ (C₆C₄H₅) (87)

47
—
1243.7853
1229,3901
0.3621
y (C₂₁H₂) (94); y (C₂₇H₂) (5)

48
—
1258.6429
1243,77093
1.0505
ρ (C₉H₂) (76); ω (C₂₁H₂) (23)

49
—
1281.7118
1266,0853
0.7178
y (C₁₄H₂) (55); ω (C₂₁H₂) (44)

50
—
1300.3301
1284,08198
1.3337
ω (C₂₁H₂) (93)

51
—
1317.9028
1301,05761
11.1581
ω (C₂₄H₂) (24); ρ (C₉C₁₂H₁₃) (17); y (C₁₄H₂) (13); ω (C₂₇H₂) (7); ρ (C₆O₈C₉) (5)

52
1272
1324.5992
1307,52384
68.3227
y (C₂₇H₂) (37); ρ (C₉C₁₂H₁₃) (29); y (C₂₁H₂) (22); y (C₁₄H₂) (6)

53
1295
1328.2386
1311,03753
6.0034
y (C₂₇H₂) (93)

54
—
1338.1682
1320,62195
0.5711
y (C₂₄H₂) (70); y (C₂₇H₂) (28)

55
1340
1361.0156
1342,66291
1.3124
ω (C₂₁H₂) (78); ω (C₉H₂) (21)

56
—
1381.2224
1362,1423
0.4732
ρ (C₉C₁₂C₂₁) (78); ω (C₂₁H₂) (21)

57
1357
1394.2309
1374,67547
3.3349
ω (C₉H₂) (95)

58
—
1404.5719
1384,63467
4.5032
ω (C₂₄H₂) (95); ω (C₂₁H₂) (5)

59
1381
1410.9338
1390,75996
7.3272
ω (C₂₁H₂) (97)

60
—
1414.1585
1393,86422
2.3703
ω (C₂₁H₂) (99)

61
—
1418.0649
1397,62426
0.4645
ω (C₂₁H₂) (93); ω (C₁₄H₂) (6)

62
1408
1437.761
1416,57487
83.1633
ω (C₉H₂) (49); ω (C₂₁H₂) (26); δ (CH₂) (20)

63
—
1486.1635
1463,09161
1.0310
δ (C₂₁H₂) (40); δ (C₂₄H₂) (20); δ (C₁₂C₂₁C₂₄) (12); δ (C₁₄H₂) (7)

64
—
1488.3957
1465,235
1.0310
δ (C₂₇H₂) (29); δ (C₂₁H₂) (28); δ (C₂₄H₂) (18); δ (C₁₂C₂₁C₂₄) (14); δ (C₁₄H₂) (10); δ (C₂₇H₂) (10)

65
—
1492.293
1468,97685
1.3617
δ (C₂₁H₂) (67); δ (C₂₇H₂) (11); δ (C₁₄H₂) (7)

66
—
1499.9113
1476,28987
8.3925
δ (C₃₀H₃) (88); δ (C₂₇H₂) (10)

67
—
1501.7672
1478,07111
4.3738
δ (C₂₁H₂) (29); δ (C₃₀H₃) (28); δ (C₂₄H₂) (15); δ (C₂₁C₁₂H₁₃) (11); δ (C₁₄H₂) (6)

68
—
1503.707
1479,93276
3.5078
δ (C₂₇H₂) (31); δ (C₂₁H₂) (29); δ (C₉H₂) (18)

69
1464
1509.3473
1485,34511
9.9123
δ (C₁₇H₃) (27); δ (C₂₇H₂) (26); δ (C₂₁H₂) (10); δ (C₁₂C₂₁C₂₄) (8); δ (C₂₄H₂) (7); δ (C₁₂C₁₄C₂₁) (6)

70
—
1510.6836
1486,62726
10.8575
δ (C₂₁H₂) (83); δ (C₂₇H₂) (10)

71
—
1515.4657
1491,21508
6.0184
δ (C₂₄H₂) (42); δ (C₂₁C₂₄C₂₇) (25); δ (C₂₇H₂) (13); δ (C₂₁H₂) (10)

72
1637
1687.5503
1655,81242
26.9151
ν (C₁C₄) (87); δ (C₁H₂) (7)

73
1727
1770.955
1735,24092
243.4946
ν (C₆O₇) (80); δ (O₈C₉H₁₂) (7); δ (C₂₁H₂) (5); ν (C₄C₆) (5)

74
—
2997.3914
2877,02371
2.7860
ν (C₂₁H₂₂) (45); ν (C₁₄H₂) (33); ν (C₁₂H₁₃) (14)

75
—
2999.8142
2879,23075
1.7988
ν (C₂₁H₂) (76); ν (C₂₄H₂) (14)

76
—
3002.0159
2881,23622
13.8469
ν (C₂₇H₂) (33); ν (C₂₄H₂) (32); ν (C₃₀H₃₁) (22); ν (C₂₁H₂) (6)

77
—
3005.8916
2884,76609
14.6381
ν (C₂₁H₂) (74); ν (C₁₄H₂) (14); ν (C₁₂H₁₃) (5)

78
2861
3014.5745
2892,67245
45.7319
ν (C₁₂H₁₃) (63); ν (C₃₀H₃₁) (31)

79
2875
3018.0275
2895,81595
55.9324
ν (C₃₀H₃₁) (98)

80
—
3023.8407
2901,10723
22.2942
ν (C₁₇H₁₉) (58); ν (C₁₇H₁₈) (29)

81
—
3026.1436
2903,20306
16.4278
ν (C₁₇H₁₉) (32); ν (C₁₄H₂) (29); ν (C₁₇H₁₈) (15); ν (C₃₀C₃₁) (8); ν (C₂₁H₂) (6)

82
—
3034.8324
2911,10906
35.1134
ν (C₁₄H₂) (96)

83
—
3041.9158
2917,55246
16.0910
ν (C₂₇H₂) (38); ν (C₉H₂) (20); ν (C₁₄H₂) (19); ν (C₂₁H₂) (6); ν (C₂₄H) (6)

84
—
3043.1697
2918,6929
14.5616
ν (C₂₇H₂) (47); ν (C₉H₂) (26); ν (C₂₄H₂) (10); ν (C₁₄H₂) (7)

85
—
3062.906
2936,63657
46.5673
ν (C₂₁H₂) (55); ν (C₂₇H₂) (25); ν (C₂₄H₂) (9); ν (C₁₂H₁₃) (5)

86
2931
3078.8255
2951,10087
85.8987
ν (C₂₇H₂) (62); ν (C₂₇H₃₀) (10); ν 2955,03236 (C₃₀H₃) (9); ν (C₉H₂) (6); ν (C₁₇H₁₉) (6)

87
—
3083.1541
2955,03236
45.5349
ν (C₃₀H₃₁) (99)

88
—
3084.5244
2956,27682
35.1235
ν (C₁₇H₁₉) (67); ν (C₁₇C₁₉) (67); ν (C₁₇C₁₈) (17); ν (C₃₀H₃₁) (15)

89
—
3087.9105
2959,3517
19.5239
ν (C₉H₂) (63); ν (O₈C₉) (16); ν-(C₁₂H₁₃) (11); ν (C₁₇C₁₉) (6)

90
2961
3093.1423
2964,10191
56.1433
ν (C₁₇H₁₉) (38); ν (C₉H₂) (26); ν (C₁₇H₂₀) (12); ν (C₁₄H₂) (10); ν (C₁₇H₁₈) (9)

91
3038
3142.8663
3009,20422
5.1952
ν (C₁C₄) (45); ν (C₁H₂) (38); ν (C₁H₃) (9)

92
—
3185.092
3047,44188
3.2650
ν (C₁H₂) (95)

93
3104
3235.9105
3093,38372
2.3617
ν (C₄H₅) (67); ν (C₁H₂) (22); ν (C₁H₃) (6)

 aAssignments and potential energy distribution (PED) (contributing ≥ 5%) for vibrational normal mode. Types of vibration: ν: stretching; δ: deformation; ο: out-of-plane bending; ω: wagging; y: twisting; ρ: rocking; τ: torsion; w: weak; m: medium; sh: shoulder.

bNormal mode number.

Table 3: Frequencies and PEDs of s-trans 2-ethylhexyl acrylate.

Numberb
Observed (cm⁻¹)
DFT/6-311+G**  Unscaled (cm⁻¹)
Scaled (cm⁻¹)
Intensity (kmmol⁻¹)
Assignment (%PED)a

1
—
29.5569
29,79981
1.3888
τ (C₂₁C₂₄) (95)

2
—
31.2922
31,54848
1.2915
τ (C₂₁C₂₄) (100)

3
—
45.3002
45,66086
0.0227
τ (C₂₁C₂₄) (91); τ (O₈C₉) (6)

4
—
69.075
69,59818
0.0113
τ (C₂₁C₂₄) (98)

5
—
91.6561
92,31657
0.7304
ρ (C₁₄H₂) (64); τ (C₉C₁₂) (19); τ (C₂₄C₂₁) (15)

6
—
106.795
107,53821
0.0788
τ (C₁₂C₁₄) (92)

7
—
116.406
117,19786
0.4606
τ (O₈C₉) (90); τ (C₂₁C₂₄) (7)

8
—
128.002
128,84855
0.7652
τ (C₂₁C₂₄) (99)

9
—
137.7311
138,62015
0.0737
τ (C₂₄C₂₁) (94)

10
—
188.6176
189,67867
2.4795
τ (C₂₄C₂₁) (53); O (O₈C₉) (44)

11
—
196.4898
197,56995
2.2280
ρ (C₉H₂) (82); τ (C₉C₁₂) (13)

12
—
234.6
235,74391
1.7535
ρ (C₃₀H₃) (90); τ (C₂₁C₂₄) (7)

13
—
249.5865
250,74252
3.2507
ρ (C₃₀H₃) (78); τ (C₁₂C₂₁) (19)

14
—
262.3636
263,52416
1.2259
ρ (C₉H₂) (72); ρ (C₁₇H₃) (22)

15
—
274.1636
275,32362
0.5126
τ (C₁₂C₂₁) (96)

16
—
335.2283
336,31302
0.4554
δ (C₂₁C₁₂C₁₄) (93)

17
—
354.6136
355,649
0.1655
δ (C₂₁C₁₂C₂₄) (95)

18
—
406.411
407,25451
2.5402
δ (C₉C₁₂C₁₄) (92)

19
—
471.3032
471,78287
1.0320
ρ (C₉C₁₂C₁₄) (70); δ (C₉C₁₂C₂₁) (12); ρ (C₁₄H₂) (11)

20
—
509.8943
510,09251
0.4733
y (C₁H₂) (86); O (C₆O₈) (12)

21
—
514.0157
514,18098
7.3067
ρ (C₁₂C₁₄C₁₇) (38); ρ (C₉C₁₂C₂₁) (15); ρ (C₁₂C₂₁) (14);ρ (C₁₄C₁₂H₁₃) (13); ρ (C₁H₂) (8); δ (C₁₂C₂₁C₂₄) (7);

22
—
550.859
550,70531
2.2808
ρ (C₉C₁₂C₁₄) (78); ρ (C₆O₈C₉) (9); ρ (C₁H₂) (6);

23
—
636.0175
634,9572
1.9146
ρ (O₈C₉C₁₂) (97);

24
727 (m)
728.4338
726,12214
4.3677
ρ (C₉C₁₂C₂₁) (92);

25
—
778.027
774,92902
0.6843
ρ (C₉C₁₂C₂₁) (98);

26
770 (m)
785.397
782,17532
1.8732
ρ (C₂₁H₂) (59); ρ (C₁₄H₂) (36);

27
811 (m)
832.1364
828,08904
21.5147
y (C₁H₂) (94); ρ (C₉H₂) (5);

28
852 (w)
850.1904
845,80503
3.4731
ρ (C₉C₁₂C₂₁) (47); ρ (C₉H₂) (27); ρ (C₁H₂) (15); ν (C₁₄C₁₇) (5);

29
896 (w)
901.7561
896,3468
0.9206
ρ (C₉C₁₂C₂₁) (73); ρ (C₂₁C₂₄C₂₇) (14);

30
909 (w)
906.5632
901,05403
1.3451
ρ (C₉C₁₂C₂₁) (46); ρ (C₉H₂) (35); ρ (C₁₂C₁₄C₁₇) (9);

31
933 (sh)
917.0283
911,29911
7.6343
ρ (O₇C₆O₈) (86); ρ (C₉H₂) (10);

32
962 (m)
947.0255
940,64585
6.0649
ρ (C₆O₈C₉) (99);

33
—
972.6775
965,71834
7.0484
ρ (C₆O₈C₉) (99);

34
984 (m)
1001.2212
993,59199
34.4957
ω (C₁H₂) (52); ν (C₁C₄) (15); δ (C₄C₆O₈) (15); ν (C₁₂C₂₁) (15)

35
1015 (sh)
1017.1676
1009,15249
7.0006
ν (C₁₂C₂₁) (92)

36
—
1021.9635
1013,83071
3.5045
ν (C₂₁C₂₄) (85); δ (C₉C₁₂O₁₄) (9)

37
1025 (sh)
1029.9052
1021,57589
18.5130
y (C₁H₂) (97)

38
—
1040.755
1032,15388
0.3554
ν (C₂₁C₂₄) (70); ν (C₉C₁₂) (14); y (C₂₁H₂) (5)

39
—
1060.8287
1051,71458
5.5936
y (C₂₁H₂) (58); ρ (C₁₄C₁₂H₁₃) (29); ρ (C₁₄H₂) (7)

40
—
1064.0573
1054,85945
18.8097
ν (C₂₁C₂₄) (88); ν (C₁₄C₁₇) (8)

41
1057 (m)
1076.7989
1067,26727
192.6571
ν (C₉O₈) (82); ν (C₁₄C₁₇) (13)

42
1060 (sh)
1089.5069
1079,6371
4.6500
ρ (C₉H₂) (40); δ (C₉C₁₂C₂₁) (30); ω (C₂₇H₂) (25)

43
1116 (w)
1150.6075
1139,03825
1.4631
ρ (C₉C₁₂H₁₃) (51); δ (C₉C₁₂C₂₁) (42)

44
1191
1168.2621
1156,17915
3.2253
ρ (C₁₄C₁₂H₁₃) (72); ω (C₂₁H₂) (16); ρ (O₈C₉C₁₂) (9)

45
—
1185.0265
1172,44634
0.1695
δ (C₉C₁₂C₁₄) (94)

46
—
1242.923
1228,55525
1.7298
y (C₂₁H₂) (89)

47
—
1258.238
1243,37912
1.1546
ρ (C₉C₁₂C₂₁) (35); ω (C₂₁H₂) (35); ω (C₉H₂) (27)

48
—
1280.1017
1264,52842
77.9146
ω (C₂₁H₂) (47); ρ (C₉C₁₂C₂₁) (37); ρ (C₉H₂) (27);

49
1272
1283.202
1267,52616
351.6365
ω (C₂₁H₂) (60); y (C₁₄H₂) (27); y (C₉H₂) (10)

50
—
1299.1286
1282,92094
4.4292
y (C₉H₂) (72); y (C₂₁H₂) (26);

51
1295
1311.7811
1295,14505
7.2842
y (C₁₄H₂) (99)

52
—
1318.75
1301,87577
6.8204
y (C₁₄H₂) (100)

53
—
1326.4691
1309,3292
0.1479
y (C₂₁H₂) (97)

54
—
1336.2199
1318,74163
0.4090
y (C₂₄H₂) (94); y (C₂₁H₂) (5)

55
1340
1359.997
1341,68063
1.0793
ω (C₂₁H₂) (86); ρ (C₂₁C₁₂C₁₄) (7); ω (C₉H₂) (5)

56
—
1380.0145
1360,97825
0.4801
ρ (C₉C₁₂C₂₁) (43); δ (C₉H₁₂) (28); ω (C₂₁H₂) (25)

57
1357
1393.1134
1373,59902
2.8872
ω (C₉H₂) (50); ω (C₁₄H₂) (23); δ (C₂₁C₁₂H₁₃) (12); ω (C₂₁H₂) (86)

58
—
1404.3849
1384,45461
0.9476
ω (C₂₁H₂) (86); ω (C₉H₂) (12)

59
—
1411.9509
1391,73911
0.8054
ω (C₉H₂) (85); ω (C₂₁H₂) (14)

60
1381
1414.5333
1394,225
5.0233
ω (C₂₁H₂) (54); ω (C₉H₂) (45)

61
—
1417.3104
1396,89807
0.8100
ω (C₂₁H₂) (89); ω (C₉H₂) (8)

62
1408
1441.4398
1420,11302
30.5726
ω (C₉H₂) (93); ω (C₂₁H₂) (5)

63
—
1483.1028
1460,15241
2.0326
δ (C₉H₂) (38); δ (C₂₁C₁₂H₁₃) (18); δ (C₂₄C₂₁C₁₂) (15); δ (C₁₄H₂) (13); δ (C₂₄H₂) (7); δ (C₂₁H₂) (6)

64
—
1487.6468
1464,51591
0.4300
δ (C₂₁C₁₂H₁₃) (33); δ (C₂₇H₂) (28); δ (C₂₄H₂) (20); δ (C₂₁H₂) (10)

65
—
1491.6884
1468,3964
1.2432
δ (C₂₁H₂) (54); δ (C₉H₂) (21); δ (C₂₇H₂) (11)

66
—
1500.0764
1476,44833
2.4692
δ (C₂₄H₂) (32); δ (C₂₁C₁₂H₁₃) (24); δ (C₂₇H₂) (8); δ (C₃₀H₃) (8); δ (C₂₁H₂) (6)

67
—
1500.718
1477,06413
7.0795
δ (C₃₀H₃) (75); δ (C₉H₂) (11); δ (C₂₇H₂) (6)

68
—
1502.5266
1478,79993
8.9950
δ (C₉H₂) (74); δ (C₁₇H₃) (21)

69
1464
1508.1671
1484,21269
9.8400
δ (C₂₇H₂) (26); δ (C₃₀H₃) (22); δ (C₂₁H₂) (14); δ (C₁₇H₃) (14); δ (C₂₄H₂) (11)

70
—
1511.6225
1487,52807
10.5533
δ (C₂₁H₂) (73); δ (C₂₁C₁₂H₁₃) (6); δ (C₂₄H₂) (5); δ (C₁₇H₃) (5)

71
—
1514.069
1489,8752
5.6625
δ (C₂₄H₂) (30); δ (C₂₁H₂) (29); δ (C₂₁C₂₄C₂₇) (20); δ (C₂₇H₂) (9)

72
1619
1678.7098
1647,38009
28.7096
ν (C₁C₄) (52); ν (C₄C₆) (22); δ (C₉C₁₂H₁₃) (11); δ (C₂₁H₂) (8)

73
1727
1766.8533
1731,34006
315.5882
δ (C₉C₁₂C₂₁) (63); ν (C₄C₆) (16); δ (C₂₁H₂) (6); ν (C₆O₇) (6)

74
—
2995.932
2875,69419
2.0873
ν (C₂₄H₂) (35); ν (C₁₄H₂) (34); ν (C₂₁H₂) (25)

75
—
2998.467
2878,00355
0.6759
ν (C₂₄H₂) (40); ν (C₁₂H₁₃) (29); ν (C₂₁H₂) (12); ν (C₁₄H₂) (10)

76
—
3001.649
2880,90203
13.5187
ν (C₂₁H₂) (92)

77
—
3005.3152
2884,24116
13.2101
ν (C₂₄H₂) (87); ν (C₂₄H₂) (8)

78
2861
3013.385
2891,58948
58.5964
ν (C₂₁H₂) (45); ν (C₃₀C₃₂) (36); ν (C₁₂H₁₃) (12)

79
2875
3017.8939
2895,69433
47.2871
ν (C₃₀C₃₂) (96)

80
—
3023.6248
2900,91073
21.1397
ν (C₁₄H₁₂) (46); ν (C₁₇H₁₉) (32); ν (C₁₇H₁₈) (17)

81
—
3026.0401
2903,10887
15.9088
ν (C₁₂H₁₃) (30); ν (C₁₇H₁₉) (27); ν (C₁₇H₁₈) (13); ν (C₃₀C₃₂) (12)

82
—
3034.55
2910,85214
32.9164
ν (C₂₁H₂) (66); ν (C₁₄H₂) (28)

83
—
3040.4085
2916,18149
4.0314
ν (C₂₁H₂) (55); ν (C₃₀H₃₂) (27); ν (C₁₂H₁₃) (7)

84
—
3043.7899
2919,25696
26.3738
ν (C₂₁H₂) (98)

85
—
3060.9167
2934,82854
50.3404
ν (C₂₁H₂) (85); ν (C₃₀C₃₂) (12)

86
2931
3078.6333
2950,92629
82.4131
ν (C₃₀C₃₂) (95)

87
—
3083.3975
2955,25341
44.1245
ν (C₃₀C₃₂) (93)

88
—
3084.2781
2956,05315
36.9537
ν (C₁₇H₁₉) (67); ν (C₁₇H₁₈) (18); ν (C₂₁H₂) (9)

89
—
3088.9498
2960,29541
15.1201
ν (C₂₁H₂) (52); ν (C₉H₂) (14); ν (C₁₂H₁₃) (14); ν (C₁₄H₂) (8); ν (C₁₇H₁₉) (7)

90
2961
3093.0704
2964,03663
59.5099
ν (C₁₇H₁₉) (36); ν (C₁₄H₂) (28); ν (C₁₇H₂₀) (10); ν (C₂₁H₂) (10); ν (C₁₇H₁₈) (8); ν (C₉H₂) (6)

91
3038
3146.2567
3012,27655
5.2018
ν (C₁C₄) (50); ν (C₁H₂) (31); ν (C₁H₃) (10)

92
3069
3185.7999
3048,08243
3.4136
ν (C₄H₅) (57); ν (C₄C₆) (23); ν (C₁C₄) (14)

93
3104
3237.707
3095,00628
4.4771
ν (C₁H₂) (70); ν (C₁H₃) (11); ν (C₄H₅) (7)

 aAssignments and potential energy distribution (PED) (contributing ≥ 5%) for vibrational normal mode. Types of vibration: ν: stretching; δ: deformation; ο: out-of-plane bending; ω: wagging; y: twisting; ρ: rocking; τ: torsion; w: weak; m: medium; sh: shoulder.

bNormal mode number.

5.1. The CH Stretching Vibrations Region (3200–2800 cm⁻¹, Figure 2)

(a)

(b)

(c)

Figure 2: Comparison of the experimental IR (a) CH stretching region (3200–2800 cm⁻¹) with the appropriate theoretical DFT//B3LYP/6-311+G** spectra ((b) and (c)) for s-cis and s-trans 2-ethylhexyl acrylate, respectively.

In this region, the calculations reveal the existence of 20 vibrational normal modes for both the s-cis and s-trans conformers. These normal modes are of approximately the same energies and intensities for both conformers. In the IR spectrum in this region (Figure 2(a)) there are three groups of bands, two groups of strong bands and one group of a very weak band. In the latter there are three bands of very weak intensity at 3104, 3069, and 3038 cm⁻¹ which are well reproduced by the theoretical bands 3093, 3047, and 3012 cm⁻¹, respectively. These bands are ascribed to the C₁H and C₄H stretching modes of vibrations of the vinyl group. The second group is composed of the strongest peaks at 2961 and 2931 cm⁻¹. These two bands are well reproduced by the theoretical bands 2963 and 2953 cm⁻¹, respectively. The third group is composed of one peak slightly asymmetric at 2875 cm⁻¹ in the experimental IR spectrum; this band is reproduced at 2903 cm⁻¹ in the theoretical calculations. The remaining bands below 2900 cm⁻¹ with higher intensity in these series of CH stretching vibrational modes may be assigned to reproduce the broad shoulder at 2861 cm⁻¹. All the theoretical peaks located between 3000 and 2860 cm⁻¹ are ascribed to CH stretching of the methylene groups in the butyl and the ethyl sides of the 2-ethylhexyl acrylate molecule.

5.2. The C=O and C=C Stretching and CH Bending Vibrations (1800–1200 cm⁻¹, Figure 3)

(a)

(b)

(c)

Figure 3: Comparison of the experimental IR (a) C=O and C=C stretching and CH bending region (1800–1200 cm⁻¹) with the appropriate theoretical B3LYP/6-311+G** spectra ((b) and (c)) for s-cis and s-trans 2-ethylhexyl acrylate, respectively.

In the IR spectrum (Figure 3(a)), a very strong peak at 1727 cm⁻¹ represents the C=O stretching band. The simulated peaks are at 1735 and 1731 cm⁻¹ for the s-cis and s-trans conformations; these two frequencies contribute to the experimental C=O stretching band.

There are two C=C stretching bands in the experimental spectra located at 1637 and 1619 cm⁻¹, of medium intensity. These bands are well reproduced by the theoretical bands at 1655 cm⁻¹ for s-cis conformer (Figure 3(b)) and 1647 cm⁻¹ for the s-trans conformer (Figure 3(c)). The band at 1637 cm⁻¹ may be used to definitely indicate that conformer with s-trans arrangement of acrylic moiety is present or not in the liquid 2-ethylhexyl acrylate.

In the region from 1500 to 1200 cm⁻¹, in the experimental spectrum (Figure 3), there are four bands of medium intensity located at 1464, 1408, 1295, and 1272 cm⁻¹. The bands of weak intensity of account of three are located at 1381, 1357, and 1340 cm⁻¹. The calculated frequencies in this region for the s-cis and s-trans conformations have close energies for each normal mode, and the differences do not exceed 5 cm⁻¹. Based on the assignments reported by Dulce et al. [28] and our PED calculations, we have ascribed the theoretical frequencies 1485 cm⁻¹ (s-cis) and 1484 cm⁻¹ (s-trans) to the experimental band at 1464 cm⁻¹ and they are representing a C₁₇H₃ symmetric bending. The calculated frequencies at 1479, 1478, and 1476 cm⁻¹ may be contributed to the experimental band at 1464 cm⁻¹ due to its relatively large middle width of about 75 cm⁻¹. Mishra et al. [38] have reported the experimental and the theoretical IR spectra of γ form of oleic acid, many peaks reported in the region 1370 to 1220 cm⁻¹ for the CH₂ carboxyl-sided chain correspond approximately to those we found in our spectrum from 1400 to 1200 cm⁻¹, and all of them may be assigned to CH₂ deformation. The assignment is based on the bands intensities; we found a good correlation between the experimental and the theoretical spectra. One should point out that the very intense bands predicted at 1267 and 1264 cm⁻¹ for s-trans form reproduce well the asymmetric shape of the experimental band at 1272 cm⁻¹. For bands assignment, see Tables 2 and 3.

5.3. The CO Stretching and CH Bending Vibrations (1200–700 cm⁻¹, Figure 4)

(a)

(b)

(c)

Figure 4: Comparison of the experimental IR (a) CO stretching and CH bending region (1200–700 cm⁻¹) with the appropriate theoretical B3LYP/6-311+G** spectra ((b) and (c)) for s-cis and s-trans 2-ethylhexyl acrylate, respectively.

In this region, in the IR spectrum, there is one very strong band at 1192 cm⁻¹ with weak shoulder at 1160 cm⁻¹ and four medium intensity bands 1057, 984, 962, shoulder at 933 and 811 cm⁻¹. The bands at 1116, 1025, 909, 896, 852, 770, and 727 cm⁻¹ (shoulder at 748 cm⁻¹) are of weak intensity (Figure 4). Based on PEDs and intensities of the calculated frequencies, we correlate the two intense bands at 1192 and 1156 cm⁻¹ for the more stable and the less stable conformers to the band at 1191 cm⁻¹ in the experimental IR spectrum. The medium bands in IR spectrum are well reproduced by the calculated peaks at 1079, 999, 976, 941, and 811 cm⁻¹ for the s-cis conformer and 1067, 993, 940, 911, and 828 cm⁻¹ for the s-trans conformer. They may be ascribed to CH₂ rocking, C₁H₂ wagging, CCH rocking O₈C₉, and C₁H₂ twisting. The peaks predicted by DFT at 728 and 783 cm⁻¹ in s-cis form and the peaks at 726 and 782 cm⁻¹ in the s-trans form may be correlated to the bands at 727 and 770 cm⁻¹ and they are assigned to the CH₂ deformations of the alkyl sides of the title molecule.

In the IR spectra of 2-ethylhexyl acrylate, reported in this work, there are a few bands with weak to very weak intensity which do not appear in the IR spectra of methyl acrylate reported by Dulce et al. [28] and George et al. [39]. These bands appear at 1157, 1120, 1052, and 1022 cm⁻¹, and they are well correlated to the calculated peaks in DFT for both conformers; see Tables 2 and 3.

The shoulders in the infrared spectrum at 1025, 1015 cm⁻¹ of weak to medium intensities may be correlated to the bands 1037, 1015 cm⁻¹ for s-cis and 1015, 988 cm⁻¹ for the s-trans conformer. These bands are ascribed to the CH out-of-plane bending modes of the vinyl group.

The remaining bands of weak intensity in the experimental IR spectrum are 909, 896, and 852 cm⁻¹. These bands are close to the ones at 911, 996, and 847 cm⁻¹ for the s-cis conformation of the title molecule. All the vibrational normal modes in this region are not pure and the majority of them were ascribed according to PED calculations to CH bending (for more details see Tables 2 and 3).

5.4. Region below 700 cm⁻¹

This spectral region includes the bands associated with C=C–C, C–O–C, O=C–O, O–C–C, C–C–C, and C–C–C bending and torsion modes about the single bonds O–C and C–C. The frequencies and PED calculations are presented in Tables 2 and 3. Comparing the 23 first normal modes for the two conformers, we notice that they have the same type of vibrational modes. However, the normal modes 16, 17, and 18 represent CCC bending in the s-trans and CH and CCC rocking modes in the s-cis conformer.

Due to the lack of experimental data on this region, we compare our calculated frequencies to some experimental IR bands of related molecules presented in the literature. The bands at 356, 254, 116, and 100 cm⁻¹ are close to the bands at 349(A′), 244(A′′), 114(A′′), and 114 cm⁻¹ (A′′) reported by Dulce et al. [28]. From the same work the bands at 530, 244, 114, and 114 cm⁻¹ belonging to A′′ symmetry, for the s-trans methyl acrylate in liquid state, are close to our calculated bands in DFT at 542, 244, 116, and 106 cm⁻¹.

6. Conclusions

The mid-IR spectrum of 2-ethylhexyl acrylate was measured and interpreted with support of the DFT//B3LYP/6-311+G** calculated vibrational spectra followed by potential energy distribution analysis. Assuming the s-cis and s-trans conformations, we found two stable conformations, close in their energies. The fully optimized geometries of s-cis and s-trans conformations by DFT//B3LYP/6-311+G** were compared with the experimental and theoretical data presented in the literature on the methyl acrylate molecule. The comparison shows a good agreement. The experimental vibrational spectrum is in good agreement with the theoretical spectra calculated for the two conformations. Two neighbor bands in the IR spectrum at 1619 and 1637 cm⁻¹ may be used as characteristic bands to locate and distinguish the existence of one or both conformations.

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