Chlorophenols their quinonoidal conjugate bases.16 Despite numerous experimental work

Chlorophenols constitute a series of
five basic compounds of covalently bonded 1-5 atomic chlorine to the five
carbons of phenyl ring (except for the carbon atom an OH group attached it). If
the positional isomerism guesstimates this number reaches to 19 different
compounds consisting of mono-, di-, tri-, and tetrachloroisomers and one
pentachlorophenol. At room temperature, excluding 2-chlorophenol which is
liquid, all of the chlorophenols are crystalline solids. Chlorophenols at least
with two chlorine atoms could be used as insecticides, herbicides, fungicides,
and precursors of other pesticides.1

It would definitely be said one of the
implications for the worthier recognition many fundamental reactions in
chemistry and biochemistry are acid dissociation constants.2-4
Therefore finding a good and easy procedure to specify the pKa
value of the compound is so important. Two very common methods used for pKa
ascertainment are potentiometric titrations or spectrophotometric measurements
in aqueous media. However, these methods require a large amount of pure sample.
Consequently, they cannot use for the acidity constant determining of compounds
in the small amounts of samples.5 Given that the determination of
acidity by experimental methods found to be difficult and may not even be
possible sometimes; therefore providing a computational method comparable to
experiment can be of great importance.

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In recent years, sweeping efforts have
been conducted to determine the acidity constant by computational approaches.6-10
Mora-Diez et al. have used the theoretical method to ascertaining of pKa
value of benzimidazoles.11 The acidity constant of the number of
organic compounds, especially carboxylic acids have determined by the Namazian
and his coworkers.12-15 Quina et al. have used DFT method for the pKa
calculation of substituted flavylium salts and their quinonoidal conjugate

Despite numerous experimental work in
the field of study of chlorophenol acidity,5,17-19 computational
calculation still has not been done in this case. Therefore, the main target of
this work is determining the pKa values of chlorinated
phenols using density functional theory methods. Fortunately, the results
obtained from theoretical method were entirely comparable experimental finding.
The difference between measured pKa value by experiment and
theory was less than 0.4 pKa unit. Consequently, it can be
said this level of computation is suitable for auspicate relative pKa
values of chlorophenols.