Abstract
Ultrasonic and UV-spectral studies have been carried out for three ternary systems containing N-methylaniline (NMANI) and three structurally different aromatic aldehydes, benzaldehyde (BA), cinnamaldehyde (CA) and salicylaldehyde(SA) in n-hexane medium at 303.15 K and at atmospheric pressure. Acoustical parameters are computed from the measured values of ultrasonic velocity, density and dynamic viscosity. The variation of acoustical parameters in the concentration range investigated establishes complex formation through intermolecular hydrogen bonding between aldehyde and N-methylaniline. The existence of strong aldehyde-amine interaction is also confirmed through the recorded UV-Visible absorption spectra with Benesi-Hildebrand theory at 303.15 K. The formation constants of the hydrogen bonded complexes are determined by spectroscopic and ultrasonic methods and compared. These values computed by two different methods are comparable and follow similar trend. The trend in the formation constants is discussed based on structures of the component molecules and correlate with computed molecular properties
Highlights
In recent years, the ultrasonic technique is widely employed in the detection of charge transfer complexes [1, 2] and in the determination of stability constants and thermodynamic properties of the complexes [3,4,5]
The complexes formed between esters and amines, phenols and ketones have been attributed to the hydrogen bonding between electron-rich carbonyl oxygen and active hydrogen
The steep increase in the ultrasonic velocity may be an indication of stronger molecular interactions such as dipole-dipole or complex formation through intermolecular hydrogen bond [17]
Summary
The ultrasonic technique is widely employed in the detection of charge transfer complexes [1, 2] and in the determination of stability constants and thermodynamic properties of the complexes [3,4,5]. Organic compounds containing electronegative groups can interact with compounds containing active hydrogen through hydrogen bond [6] This type of hydrogen bond plays important role in the stability of biologically important molecules [7]. Amines in pure state are self-associated through inter molecular hydrogen bonds They are both -as well as n-electron donors which allow them to have specific interactions with other electron deficient molecules. The complexes formed between esters and amines, phenols and ketones have been attributed to the hydrogen bonding between electron-rich carbonyl oxygen and active hydrogen. Higuchi and his coworkers [8] have investigated the complex formation of caffeine with a number of acidic drugs.
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