The most intense absorption peaks of C20, Figure 1, are found in 3342 cm−1 due to OH frequency region of intramolecular hydrogen bond vibration of secondary alcohol C3–OH⋯O5 jointly with the 3277 cm−1 peak due to the similar vibration of C2 secondary alcohol , and within the area of 1200–1000 cm−1 several absorption peaks are present due to C–O stretching vibrations from the glucose ring skeletal vibration .