Table 1 Most important absorption bands of the mid-infrared spectra of winter wheat straw

1

3380

O-H stretching of bonded and non-bonded hydroxyl groups

Included water ⁱ; lignin ^e

2

2920

Asymmetric C-H stretching

Aliphatic methylene ^{b, e, g, k}

3

2850

Symmetric C-H stretching

4

1735

Un-conjugated C = O stretching

Xylan (hemicellulose) ^{a–c, e, f, i, j}

5

1650

O-H bending

Absorbed water ^{a, i}

Conjugated C-O stretching

Carboxylates ^{a, i}

6

1600

Aromatic ring vibration

Lignin ^{a, c, g, j}

C = C skeletal vibration

C = O stretching

7

1510

Aromatic ring vibration

Lignin ^{a, c, d, g, j}

8

1460

C-H deformation

Lignin ^{a, c}; xylan ^j

9

1429

C-H deformation

Lignin ^{a, g, I, j}

CH₂ scissoring

Crystalline cellulose ^b

10

1370

Symmetric C-H deformation

Crystalline cellulose ^k; hemicellulose ^{a, i}

11

1320

C-H vibration

Cellulose, hemicellulose, lignin ^a

CH₂ wagging

Cellulose, hemicellulose ^c

12

1240

C-O stretching

Xylan (hemicellulose) ^{a, i}

13

1160

C-O-C asymmetric stretching

Crystalline cellulose ^{b, j, k}; hemicellulose ^{a, h}

14

1111

In-plane ring stretching

Crystalline cellulose ^{b, h, j}

15

1053

C-O stretching

Crystalline cellulose; hemicellulose ^{a, b, h, k}

16

898

C-O-C stretching

Amorphous cellulose ^k