Question

Nitration of Methyl Benzoate-

1. I obtained a meta isomer. Why did this isomer form in preference to the other isomers? Draw arrow-pushing mechanisms as a part of your explanation.

The reagents used were HNO₃ , H₂SO₄ , ice bath , ice cold methanol (for recrystallization).

Answer 1

Refer to the image attached. The arrow pushing mechanism has been shown in detail.

Note that -

1). -COOC(CH3) is a deactivating group. It means that the pi electrons of benzene are pulled away from the benzene ring by -COOC(CH3). As can be seen in the arrow pushing mechanism, at the ortho and para sites, there exists +ve charge.

2). The Nitration reaction is an ELECTROPHILIC reaction, ie, the Nitrate ion seeks out areas RICH in electrons. As shown by the arrow pushing mechanism, the ortho and para sites are +ve charged, implying they are NOT attractive sites for an electrophilic attack.

This is the reason why meta product is preferentially obtained.

In case the answer is not clear, feel free to leave a comment. I will be very glad to help you out.