# What are some common mistakes students make with synthesis reactions?

Sep 19, 2015

Oftentimes I see people use reactions that are similar to other reactions, except they used the wrong one. Or, they used a reaction that would cause a deactivation of the starting reactant.

Some common reactant combinations that look similar...

${\text{Cl"_2, "CH"_2"Cl}}_{2}$ --- simple trans-additive dichlorination on an alkene or alkyne

${\text{Cl"_2, "FeCl}}_{3}$ --- addition of chlorine on benzene ring

${\text{CH"_3"C"("=O")"Cl", "AlCl}}_{3}$ --- Addition of acetyl group to benzene ring, with $C l$ as a leaving group

$\text{Cl"_2, Delta"/} h \nu$ --- radical chlorination of an alkane using thermal/light energy catalysis

Or, maybe someone wants to use a grignard reagent on a carboxylic acid. Won't work. It won't attack the carbonyl carbon nearly as much as it deprotonates the carboxyl hydrogen. You would have to convert it to an ester.

$\text{R'MgBr"" + ""RCOOH" cancel(=>) "R"("R'CO"^(-))"OH}$

${\text{R'MgBr"" + ""RCOOH" => "R'H"" + ""MgBr"^(+)" + ""RCOO}}^{-}$