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How to determine the order of acidity of the following dimethyl nitrophenols
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Marek Svrcina
How to determine the order of acidity of the following dimethyl nitrophenols
$\ce{-NO2}$ is an electron-withdrawing group and $\ce{-CH3}$ is an electron-donating group and the effect of these groups can be observed at ortho- and para- position of the ring with respect to the functional group attached to the ring.
in the above resonating structure of toluene you can see -ve charge in o-, p- position, similarly in nitrobenzene you can see positive charge in o-, p- positions, and $\ce{-OH}$ group attached to electron deficient carbon or positively charged carbon release $\ce{H+}$ more easily. Considering all this condition second option is the only option where carbon to which $\ce{-OH}$ is attached is getting positive charge and not getting a negative charge, so $\ce{-OH}$ is ready to loose $\ce{H+}$.
$\ce{-NO2}$ is an electron-withdrawing group and $\ce{-CH3}$ is an electron-donating group and the effect of these groups can be observed at ortho- and para- position of the ring with respect to the functional group attached to the ring.
in the above resonating structure of toluene you can see -ve charge in o-, p- position, similarly in nitrobenzene you can see positive charge in o-, p- positions, and $\ce{-OH}$ group attached to electron deficient carbon or positively charged carbon release $\ce{H+}$ more easily. Considering all this condition second option is the only option where carbon to which $\ce{-OH}$ is attached is getting positive charge and not getting a negative charge, so $\ce{-OH}$ is ready to loose $\ce{H+}$.
The right answer should be 3 as the $\ce{NO2}$ group has a negative mesomeric effect, which is only possible with 3. In 2, due to steric inhibition of resonance, it exhibits only -I effect, and although 3 contains H-bonding, it slightly affects acidity.
The right answer should be 3 as the $\ce{NO2}$ group has a negative mesomeric effect, which is only possible with 3. In 2, due to steric inhibition of resonance, it exhibits only -I effect, and although 3 contains H-bonding, it slightly affects acidity.
So hydrogen bonding is less effective than the -M effect, you say? Can we say that although the hydrogen bonding decreased the acidity slightly, it is still greater than the -I effect groups due to the -M effect? However, this answer doesnt match with the given answer either...More
Turns out that 2 is slightly more acidic than 3. $\ce{pKa(2) = 8.25 @ 25 ºC}$ source:10.1021/ja01187a054 $\ce{pKa(3) = 8.55 @ 28 ºC}$ source:10.1021/ja01161a043 I could not find data for compounds 1 and 4.More
$\ce{-NO2}$ is an electron-withdrawing group and $\ce{-CH3}$ is an electron-donating group and the effect of these groups can be observed at ortho- and para- position of the ring with respect to the functional group attached to the ring.
in the above resonating structure of toluene you can see -ve charge in o-, p- position, similarly in nitrobenzene you can see positive charge in o-, p- positions, and $\ce{-OH}$ group attached to electron deficient carbon or positively charged carbon release $\ce{H+}$ more easily. Considering all this condition second option is the only option where carbon to which $\ce{-OH}$ is attached is getting positive charge and not getting a negative charge, so $\ce{-OH}$ is ready to loose $\ce{H+}$.
$\ce{-NO2}$ is an electron-withdrawing group and $\ce{-CH3}$ is an electron-donating group and the effect of these groups can be observed at ortho- and para- position of the ring with respect to the functional group attached to the ring.
in the above resonating structure of toluene you can see -ve charge in o-, p- position, similarly in nitrobenzene you can see positive charge in o-, p- positions, and $\ce{-OH}$ group attached to electron deficient carbon or positively charged carbon release $\ce{H+}$ more easily. Considering all this condition second option is the only option where carbon to which $\ce{-OH}$ is attached is getting positive charge and not getting a negative charge, so $\ce{-OH}$ is ready to loose $\ce{H+}$.
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The right answer should be 3 as the $\ce{NO2}$ group has a negative mesomeric effect, which is only possible with 3. In 2, due to steric inhibition of resonance, it exhibits only -I effect, and although 3 contains H-bonding, it slightly affects acidity.
The right answer should be 3 as the $\ce{NO2}$ group has a negative mesomeric effect, which is only possible with 3. In 2, due to steric inhibition of resonance, it exhibits only -I effect, and although 3 contains H-bonding, it slightly affects acidity.
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