Effect of Ph and Ultravoilet Spectral Studies of 2,5- Dimethoxy Thio Phenol

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Effect of Ph and Ultravoilet Spectral Studies of 2,5- Dimethoxy Thio Phenol

1Dr. Pradeep Kumar

1,2,3Department of Applied Science, Mangalmay Institute of Engineering and Technology,

Greater Noida,(U.P.) India

2Dr. Ishwar Singh

1,23Department of Applied Science, Mangalmay Institute of Engineering and Technology,

Greater Noida,(U.P.) India

3Dr. Jyotsna Pandit

3Department of Applied Science, Mangalmay Institute of Engineering and Technology,

Greater Noida,(U.P.) India

4Dr. Deepak Dubey

4Deptt. of Physics,Baba Tikam Singh Kanya Mahavidhyalaya,

Khairgarh Firozabad (U.P.) India

Abstract:- The ultravoelet spectra of 2,5-dimethoxy thio phenol has been recorded in the region 2000-3500Ã….The electronic absorption spectra has been recorded in various solvents (viz. ethanol, methanol and water). The effect of substituents has been discussed. The effect of pH variation in ethanol solvent is also studied and discussed.

Keywords: electronic absorption spectra, pH effect and solvent effect.


Spectroscopic studies of phenol and its derivatives recieved considerable attention in the recent years [13]. The studies of phenol derivatives have become quite interesting because they are the constituents of DNA & RNA and hence play a central role in the structure and properties of the nucleic acids. Also phenol derivatives like chlorophenol, aminophenol and marceptophenol etc. are widely used as drugs in certain diseases. Phenol and its derivative are extensively used as a solvent as a synthetic intermediate in analytical chemistry. So, the knowledge of the molecular structure, physio-chemistry properties and vibrational properties of phenol and its derivatives is helpful for a better understanding of their function in several biological processes and analysis of the complex systems. Sunderaganeshan [4] have shown that the phenol molecule has planer structure in the ground state and a quasi planer one in the excited state.

The absorption spectra of phenol and its derivatives have been predicted theoretically and practically by various workers [5.6] have found the evidence of the

electronic transitions as n *, n * and

n *. This the detailed study of the electronic

transitions of substituted phenols is of importance in order to check the presence of n *, * and n *. Thus the detailed study of the electronic

transitions of substituted phenols is of importance in order to check the presence of n *, * and n * transition [7,8].

In view of the above discussion, the ultraviolet spectra in different solvents (viz., ethanol methanol and water) of the 2,5dimethoxy thio phenol is reported and discussed [5,9].


98% spec-pure grade sample of 2,5dimethoxy thio phenol (abbreviated as 2,5DMTP) was obtained from M/s Sigma Aldrich Chemic, West Germany and used as such without further purification. However, their purity was confirmed by elemental analysis and melting point determination [120124o]. The experimental technique in the ultraviolet spectra of 2,5DMTP was recorded on Beckman Spectrophotometer model35 in the region 20003500Ã…. The spectra have been recorded in various solvents (viz. ethanol, methanol and water). The concentration of the solution in all the cases was kept constant (8 x 103 gm/liter). All the solvents used was of spectroscopic grade. The ratio of pure solvent was obtained at 9:1 by volume.


The molecular structure of 2,5dimethoxy thio phenol

is given in fig.-1.






Fig. 1 : Molecular structure of 2,5DMTP

The observed ultraviolet bands of said molecule are given in Table1. The ultraviolet absorption spectra of the

said compound in different solvents (viz. ethanol, methanol and water) are shown in fig.2 and fig.-3.


Some investigator [10-13] have suggested, in phenol the introduction of OH group replaced of H atom in benzene, exhibits a red shift in * and n *

transition and blue shift in n * transition. In the

present study, the UV spectra of the molecule 2,5DMTP was recorded in different solvents (viz. ethanol methanol and water) but the band system which corresponds to 1A 1U transitions n * has been observed between 29503100Ã…. The band system, which corresponds to 1A1g 1B2u transition ( *) has

been observed between 23002500Ã… for the molecle 2,3

dihydroxy pyridine, while the band system which

methanol water) as shown in Table2. It is evident that the blue shift has been observed in n * transitions of the molecule with increasing of refractive index of the solvents [66]. A red shift has been observed in the * and n * transitions around 2240 and 2070 Ã… in the 2,5 DMTP with increasing the polarity of the solvents (ethanol methanol water) which is identical to the trend reported for these transition in the literature value [9,11,19]. The shift is

due to momentary polarization of the solvents by the transition dipole of the solute. The polarity of the solute also plays an important role in the electronic transition. In the present study the molecule 2,5DMTP is non-polar, the shift of absorption spectra of slightly polar solute are predominantly due to the dipoledipole interactions the solute and solvent in the ground and excited state respectively.

The hydrogen bonding will lower the energy of ground state more then that of excited state, which consequently



1 1

corresponds to 1g 2u

transition has

increase the excitation energy in a blue shift. High dielectric constant leads to a higher transition energy and

been observed between 20002100Ã… for the molecule

2,3dihydroxy benzaldehyde.

In view of this, the n * Transition observed at 2960Ã… in 2,5DMTP is taken to represent out-of-plane transition, while * and n * transition around 2240 and 2070Ã… in-plane transition originated

from A1g B2u transition respectively. In which the later one derives from A1 B1

transitions [14,15].


The electronic spectra of a molecule when recorded in a solvent generally shift the band in comparison to those obtained in the vapour phase. This is called the solvents shift effect and is due to the weak physical interaction between solute and solvents atoms. This interactions may be generally classified into specific and non-specific solvents effect on the electronic state of solute. Specific solvents effects include ionisation charge transfer, aggregation phenomenon and hydrogen bonding of molecule. Non-specific effect is due to the depressive induction electro-state forces that may occur between solute and the surrounding solvents molecule. Solvent polarity effects the electronic transitions and this depends on whether the solute becomes more or less polar after excitation polar solvent. This change of charge distribution in the molecule and result increases

delocalization [16-18] for *transitions, both the

ground and excited states are stabilized and the absorption moves towards longer wavelength. For n * transitions, the ground state is more stabilized

then the excited state and consequently absorption to the shorter wavelength.

In the present investigation, it is clearly observed that the n * transitions around 3100 Ã… is blue shifted in 2,5 DMTP with increasing polarity of the solvent (ethanol

an emergence of a short wavelngth band would be expected. During the present study in the said molecule, the shortest wavelength system 2070 Ã… has been observed in 2,5DMTP [20-24].

Furthermore, the greater the polarity of the solvent, the greater the attraction between solute and solvent molecule. Thus, the system would be more stable [15]. Also with increasing dielectric constant of the solvent the ionising potentiality of the solute molecule is increased.


The absorption spectra of the compound in different solvents at various pH are shown in Fig. [3] and in Table – 2.Yadav [15] suggested that in phenol , the substituent is of acidic nature like OH , the molecule may exist in neutral , cationic or anionic form depending upon the pH of the solution, and the wavelength of the band around 3000 Ã… increasees in the sequence neutral moleculecationanion [25,26].

In the present study, there is a blue shift in the position of entire band with the decrease in pH , the n * band is

reported to shifted towards shorter wavelength [70]. These are in accordance with the trend observed during the present investegation [18,27].


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n *


n *















Where, DC = Dielectric constant RI = Refractive index




n *


n *



Ethanol + Hcl



Ethanol + NaOH



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