Aldehydic C-H Vibrations

Benzaldehydes with bulky ortho- substituents such as nitro-, halogen or methoxy groups absorb at 2900-2800cm (3.45-3.57 pm) and 

The presence of a sharp band at about 2720cm (3.68pm) and a band due to the carbonyl stretching vibration in the region 1740-1685 cm (5.75-5.95 pm) may usually be taken as indicating the presence of an aldehyde. 

The CH stretching band, although weak, is useful for characterisation purposes. However, the overtone of the CH in-plane deformations may disturb the position of the CH stretching band or result in some confusion. The presence of two bands in the region 2895-2650cm (3.45-3.77 pm) is due 

A weak-to-medium intensity band due to the aldehydic C-H deformation vibration is found in the region 975-780 cm (10.26-12.82 pm). However, because of its variable position and intensity, this band may be difficult to identify. 

---