P K SRIVASTAVA, D K RAI and S B RAI

Laser and Spectroscopy Laboratory, Department of Physics, Banaras Hindu University, Varanasi 221 005, India

Abstract.

Overtone spectrum of o, m and p-nitrobenzaldehydes and p-chlorobenzaldehyde has been studied in 2000-12000 cm^–1 region. Vibrational frequencies and anharmonicity constants for aryl as well as alkyl CH stretch vibrations have been determined. We have also determined the internuclear distances for the aryl CH bond in the different molecules. The small variation observed in these distances is an indication of the substitution effect.

It is observed that in the case of p-disubstituted benzenes, the shift in aryl CH bond is proportional to sum of the Hammet s of the substituents. However in thecase of o-disubstituted benzenes it is only 80% of the para- substituted shift.

Keywords: Overtone spectroscopy; aryl CH; alkyl CH; Hammet s; inductive effect.

Pacs Nos. 78.30.Jw; 33.20.Ea; 33.20.TP; 42.65.Ky