Answer to Question #175153 in Organic Chemistry for Joel Kutai

Question

Construct and analyse an example of each of the following reaction mechanism types:

• Addition e.g. aldehyde or ketone with HCN

• Substitution e.g. halogenoalkane with ethanolic NaOH

• Addition-elimination e.g. aldehyde or ketone with 2,4-dintriophenylhydrazine

This section must explore and interpret the similarities and differences between each of the four mechanisms.

Answer 1

1. CH3CHO + HCN --->

CH3-CH(OH)-CN

This is a nucleophilic addition reaction in which CN- attacks the partially positive carbonyl carbon. There is a shift of pi electrons towards the oxygen atom on the carbonyl group. This pi electron attacks H+ ion to form OH. Hence, ethanalcyanohydrin is generated as the product.

2. CH3Cl + NaOH---> CH3OH + NaCl

This is a nucleophilic substitution bimolecular reaction (SN2 reaction). Chloride ion is displaced by the strong base OH-. Hence methanol (an alcohol) is generated.

3. CH3CHO + H2N-NH-C6H4(NO2)2--->H3C-CH=N-NH-C6H5(NO2)2 + H2O

2,4-dinitrophenylhydrazone(DNP) is the product formed. The process is a condensation reaction(condensation= addition + elimination) in which two hydrogen atoms are lost by 2,4-dinitrophenylhydrazine and one oxygen atom by ethanal to give water.