Synthesis and assessment of substituent effect on ( E )-1-(4-fluoro-3-methylphenyl)-3-phenylprop-2-en-1-one compounds

. In the present investigation, a series of substituted ( E )-1-(4-fluoro-3-methylphenyl)-3-phenylprop-2-en-1-one compounds were synthesized by condensation reaction of 4-fluoro-3-methyl acetophenone with substituted benzaldehydes in the presence of alkali. The yields of synthesized compounds are more than 80%. The structures of all the synthesized compounds were confirmed by their physical constants, UV, IR and NMR spectral data. All the observed spectral data of substituted ( E )-1-(4-fluoro-3-methylphenyl)-3-phenylprop-2-en-1-one compounds have been correlated with Hammett substituent constants and F and R parameters using single and multi-linear regression analyses. From the results of statistical analysis the effects of substituents have been discussed.


INTRODUCTION
Chalcones are 3-phenylprop-2-en-1-one compounds, in which two aromatic rings are linked by a three carbon α, β-unsaturated carbonyl system. These are abundant in edible plants and are considered to be precursors of flavonoids and isoflavonoids. The compounds with the backbone of chalcones have been reported to possess various properties by which they find many applications in different fields. Molecules possessing such system have relatively low redox potentials and have a greater probability of undergoing electron transfer reactions. Chalcones are one of the major classes of natural products with widespread distribution in fruits, vegetables, spices, tea and soy based foodstuff have been recently subjects of great interest for their interesting pharmacological activities [1].

1. Spectral linearity
The spectral linearity of chalcones was studied by evaluating the substituent effects [12][13] with respect to various spectral data. The assigned spectral data of all chalcones such as absorption maximum λ max (nm) of carbonyl groups, infrared carbonyl stretches of νCOs-cis and s-trans, the deformation modes of vinyl part CH out of plane, in-plane, CH=CH and >C=C< out of planes (cm -1 ), NMR chemical shifts δ(ppm) of H α , H β , C α , C β , CO are assigned and these data are correlated with various substituent constants.

2. IR spectral study
The carbonyl stretching frequencies (cm -1 ) of s-cis and s-trans conformers are shown in Fig. 2. The IR frequency values are presented in Table 2.

2. 1. IR Spectral Correlation of νCO s-cis (cm -1 )
The IR frequency νCO s-cis (cm -1 ) values of all substituted 3-phenylprop-2-en-1-one compounds have shown poor correlations (r < 0.900) with all Hammett substituent constants and F and R parameters. This is attributed to the weak polar, inductive, field and resonance effects of the substituents All the correlation have shown positive ρ values. This indicates the operation of normal substituent effect with respect to IR frequency νCO s-trans (cm -1 ) values in all substituted 3phenylprop-2-en-1-one compounds.

2. 2. IR Spectral Correlation of νCO s-trans (cm -1 )
The IR frequency νCO s-trans (cm -1 ) values of all substituted 3-phenylprop-2-en-1-one compounds except that with 3-Br and 2-Cl substituent have shown satisfactory correlations with R parameter (r=0.905). When the substituent that has been given exception is included in regression it reduces the correlations considerably. The IR frequency νCH IP (cm -1 ) values of all substituted 3phenylprop-2-en-1-one compounds have shown poor correlations (r < 0.900) with all Hammett substituent constants and F parameter. This is attributed to the weak polar, inductive, resonance and field effects of the substituents. All the correlations except Hammett substituent constants σ+, σI and F parameter have shown positive ρ values. This indicates the operation of normal substituent effect with respect to IR frequency νCO s-trans (cm -1 ) values in all substituted 3-phenylprop-2-en-1one compounds.

2. IR Spectral Correlation of νCH IP (cm -1 )
The IR frequency νCH IP (cm -1 ) values of all substituted 3-phenylprop-2-en-1-one compounds have shown poor correlations (r < 0.900) with all Hammett substituent constants and F and R parameters. This is attributed to the weak polar, inductive, field and resonance effects of the substituents. All the correlation (except F parameter) have shown positive ρ values. This indicates the operation of normal substituent effect with respect to IR frequency νCO s-trans (cm -1 ) values in all substituted 3-phenylprop-2-en-1-one compounds.

2. 4. IR Spectral Correlation of νCH OP (cm -1 )
The IR frequency νCH OP (cm -1 ) values of all substituted 3-phenylprop-2-en-1-one compounds, except that with the H(parant) and 3-Br substituents has shown satisfactory correlations with Hammett substituent constant σ R (r = 0.905). The IR frequency νCH OP (cm -1 ) values of all substituted 3-phenylprop-2-en-1-one compounds, except that with the H(parant) substituent has shown satisfactory correlations with R parameter (r = 0.905).When these substituents that have been International Letters of Chemistry, Physics and Astronomy Vol. 57 given exception are included in regression they reduce the correlations considerably. The IR frequency νCH OP (cm -1 ) values of all substituted 3-phenylprop-2-en-1-one compounds have shown poor correlations with remaining Hammett substituent constant σ, σ + , σ I , and F perameter. This is attributed to the weak polar, inductive, and field effects of the substituents. All the correlations have shown(except σ I , and F perameter ) negative ρ values. This indicates the operation of reverse substituent effect with respect to IR frequency νCH OP (cm -1 ) values in all substituted 3-phenylprop-2-en-1-one compounds .

2. 5. IR Spectral Correlation of νCH=CH OP (cm -1 )
The IR frequency νCH=CH OP (cm -1 ) values of all substituted 3-phenylprop-2-en-1-one compounds except that with the 3-Br substituent has shown satisfactory correlations with Hammett substituent constant σ (r=0.903) and σ + (r = 0.902). When these substituent that have been given exception are included in regression they reduce the correlations considerably.The IR frequency νCH=CH OP (cm -1 ) values of all substituted 3-phenylprop-2-en-1-one compounds have shown poor correlations with the remaining Hammett substituent constant σ R , σ I , and F and R parameters. This is attributed to the weak polar, inductive, field and resonance effects of the substituents. All the correlations (except σ R and σ I ) have shown positive ρ values. This indicates the operation of normal substituent effect with respect to IR frequency νCH=CH OP (cm -1 ) values in all substituted 3phenylprop-2-en-1-one compounds.

2. 6. IR Spectral Correlation of νC=C OP (cm -1 )
The IR frequency νC=C OP (cm -1 ) values of all substituted 3-phenylprop-2-en-1-one compounds except 4-Br and 3-Cl substituents has shown satisfactory correlations with Hammett substituent constants σ (r=0.903) and σ + (r = 0.903). When these substituents that have been given exception are included in regression they reduce the correlations considerably. The IR frequency νC=C OP (cm -1 ) values of all substituted 3-phenylprop-2-en-1-one compounds have shown poor correlations with the remaining Hammett substituent constants and F and R parameters. This is attributed to the inductive, field and resonance effects of the substituents. All the correlations have shown negative ρ values. This indicates the operation of reverse substituent effect with respect to IR frequency νC=C OP (cm -1 ) values in all substituted 3-phenylprop-2-en-1-one compounds . Most of the single regression analyses have shown poor correlation, it is decided to go for multi-regression analyses. The multi-regression produced satisfactory correlations with Hammett substituent constants and F and R parameters [21]. The multi correlation equations are given in (5) - (16).