out of orthonitroaniline and paranitroaniline which one will go at the top of TLC plate and why
It depends upon the stationary phase and the mobile phase, to some extent; however, o-nitroaniline is LESS polar than p-nitroaniline. A polar adsorbent will hold the para isomer more strongly than the orth isomer.
Therefore, o-nitroaniline will go to the top of the TLC plate.
To determine which compound will migrate to the top of the TLC (Thin Layer Chromatography) plate, we need to consider the polarity of the compounds and the polarity of the stationary phase. The compound with lower polarity will move faster and will be closer to the top of the TLC plate.
In this case, o-nitroaniline is less polar than p-nitroaniline. This is because the ortho isomer has the nitro group (-NO2) attached to the benzene ring in a position that is closer to the amino group (-NH2). The steric hindrance between these two groups reduces the overall polarity of o-nitroaniline.
On the other hand, p-nitroaniline has the nitro group attached to the benzene ring in a position that is farther away from the amino group. This allows for higher polarity due to fewer steric hindrances.
Therefore, p-nitroaniline will have a higher polarity compared to o-nitroaniline. Consequently, in a typical TLC experiment with a polar stationary phase, p-nitroaniline will be held more strongly, and o-nitroaniline will migrate faster, resulting in it being closer to the top of the TLC plate.