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Table 4 Calculated fundamental frequencies of 2A4MP at different levels

From: Tautomerization, molecular structure, transition state structure, and vibrational spectra of 2-aminopyridines: a combined computational and experimental study

Mode of vibration

Calculated frequency (cm−1)

Vibrational assignments

HF/6-311++G(d,p)

B3LYP/6-311 ++G(d,p)

MP2/6-31G(d)

MP2/6-31G++(d,p)

Wave number

IR intensity

Raman intensity

Wave number

IR intensity

Raman intensity

Wave number

Unscaled

IR intensity

Wave number

Unscaled

IR intensity

Unscaled

Scaled

Unscaled

Scaled

1

3915

3484

35.10

43.27

3572

3429

29.12

54.97

3692

22.36

3748

28.00

NH2 asym. stretch

2

3803

3385

45.10

137.44

3449

3311

38.09

206.13

3572

30.72

3619

29.03

NH2 sym. stretch

3

3350

2982

16.54

123.71

3266

3135

14.04

149.71

3239

13.72

3265

16.47

CH stretch

4

3321

2956

9.81

90.05

3192

3064

14.35

99.14

3217

6.33

3242

1.12

CH stretch

5

3315

2950

24.65

65.81

3179

3051

22.20

98.07

3212

22.09

3240

23.15

CH stretch

6

3251

2893

24.22

55.49

3106

2982

18.00

55.85

3197

10.91

3216

12.60

CH3 asym. stretch

7

3227

2872

19.50

69.72

3078

2955

13.02

86.15

3182

12.32

3198

12.32

CH3 asym. stretch

8

3173

2824

25.08

173.18

3027

2906

21.58

228.80

3101

16.92

3112

23.71

CH3 sym. stretch

9

1800

1602

41.26

30.49

1712

1643

35.17

25.38

1703

224.65

1690

232.70

NH2 scissoring + C=C stretch

10

1786

1590

72.47

3.54

1635

1570

34.32

1.70

1684

27.56

1669

42.39

C=C stretch +NH2 scissoring

11

1750

1558

51.56

15.42

1601

1537

57.64

10.37

1646

24.71

1636

27.98

C–C stretch

12

1656

1474

19.35

1.45

1590

1526

17.05

7.38

1558

55.80

1539

44.84

CH3 asym. scissoring

13

1609

1432

1.95

3.37

1556

1493

76.44

2.69

1548

2.25

1532

18.42

C=C stretch

14

1605

1428

0.25

8.79

1512

1451

7.62

8.81

1545

7.14

1522

8.95

CH3 sym. scissoring

15

1568

1396

43.00

3.71

1454

1396

2.83

6.68

1501

76.96

1486

79.28

C=C stretch + CH3 sym. scissoring

16

1535

1366

1.95

5.46

1412

1356

3.62

9.65

1467

2.02

1451

1.16

CH3 sym. scissoring

17

1451

1291

0.25

3.07

1351

1297

5.84

9.76

1426

22.30

1420

29.75

C–NH2 stretch + CC stretch

18

1429

1272

43.00

11.87

1331

1278

29.93

10.73

1368

1.27

1357

1.36

C=N stretch

19

1288

1146

24.37

5.99

1302

1250

6.23

1.55

1351

8.57

1340

12.77

CH in-plane-bending

20

1277

1137

16.11

4.36

1224

1175

14.35

4.78

1232

7.97

1222

11.87

C–CH3 stretch

21

1243

1106

8.55

5.81

1172

1125

2.56

5.91

1185

0.94

1172

1.02

CH in-plane-bending

22

1156

1029

4.78

0.06

1081

1037

0.62

0.53

1118

0.88

1106

0.91

CH in-plane-bending

23

1139

1014

5.70

7.65

1073

1030

3.77

0.06

1081

3.27

1066

3.24

CH3 rocking

24

1105

983

0.04

0.74

1002

958

11.18

2.83

1052

5.68

1045

4.63

Ring breathing

25

1099

978

3.54

1.09

998

958

5.90

23.56

1019

3.53

1017

2.90

Trigonal bending

26

1078

959

7.91

26.89

978

939

0.43

0.26

976

7.60

968

9.54

CH out-of-plane

27

1020

908

12.26

1.48

959

921

6.84

2.83

922

3.24

902

3.29

CCC in-plane-bending

28

947

843

22.00

0.20

863

828

10.45

0.08

835

0.59

811

0.16

CH out-of-plane

29

893

795

54.97

1.40

813

780

36.36

0.69

793

45.98

783

10.41

CH out-of-plane

30

836

744

4.24

1.04

777

746

1.00

18.62

787

9.82

771

35.11

CH out-of-plane

31

827

736

0.18

16.53

759

729

1.16

0.28

728

266.44

699

276.48

CCC in-plane-bending

32

678

603

53.40

2.24

607

583

26.71

1.72

659

109.50

608

59.48

CH2 + twisting in CH3

33

623

554

16.96

8.29

759

729

2.28

8.49

579

6.33

577

13.57

CNC in-plane-bending

34

576

513

226.60

0.96

523

502

4.10

5.15

545

22.34

523

2.88

CCC in-plane-bending

35

559

498

2.48

6.74

477

457

207.64

1.28

525

4.39

476

15.88

NH2 wagging

36

496

441

44.98

0.85

454

436

55.99

0.58

443

19.25

434

1.42

C–NH2 in-plane bending

37

469

417

2.05

0.20

439

421

6.02

1.19

436

1.26

414

15.25

CCC out-of-plane + CNC out-of-plane

38

383

341

36.68

0.60

377

362

55.61

0.50

345

37.72

343

30.42

C–NH2 out-of-plane

39

313

279

2.93

0.76

294

282

2.76

0.78

294

2.89

292

2.69

C–CH3 in-plane bending + C-NH2 in-plane bending

40

241

214

4.88

0.99

210

202

2.08

0.86

211

3.83

200

3.53

C–CH3 out-of-plane + C-NH2 in-plane bending

41

210

187

5.25

0.73

197

189

5.24

0.91

196

3.64

185

3.59

CCC out-of-plane

42

71

63

0.09

0.25

147

141

0.31

0.37

36

0.17

83

0.14

CH3 torsion