Table 1 FTIR signatures and assignment of FTIR signals of VNLAC

610–700

–C–H bend, –C–S stretching of sulphoxides

1150

–C–O stretching vibration of alcohol

1260, 1211

–C–O–C stretching vibration of ether

1360

–S=O stretching of sulphoxides

1370

–C–H stretching vibration of gem dimethyl group

1460

–C–H in plane bending vibration of allylic group

1627

C=C ring skeletal stretching vibration of aromatic structure

1650–1580

NH bending, O–H bending vibrations of absorbed water with some carboxyl groups

1720

–C=O stretching vibration of carbonyl group

2260–2220

–C≡N stretching

3500–3300

–NH stretching of amino group

3700

OH stretching