Question

can someone expain why part B is no reaction ?????

В. Br- NaCN No Reaction CH CH Answer

Answer 1

ANSWER:

If it were to occur, this reaction would be an example of Nucleophilic substitution reaction proceeding via SN2 mechanism.

In SN2 reaction, the substrate(alkyl bromide in this case) should be sterically unhindered, mostly 1° in nature; the nucleophile should be strong and the solvent used should be polar aprotic i.e., the solvent molecule should have a net dipole moment but should not contain a H atom joined to highly electronegative atom like F, O, N etc.

Some solvents used in S02 reactions are - actone acetone - СНА CH₂ criz-C- CH₂ JO O=n DMSO (Dimethylsulfoxide) CH₂ - CH₂ THE ( Tetrahy dron furan) etc. In your question, NaCN gives : CN: which is a strong nucleophile & presence of OMSO below the reaction arrow indicate this is a SN2 reaction. But, as said earlier, the Rx used in this reaction should be. I whereas Bra n is a 3 alkyl bromide & very CN cannot approach it reaction occurs. sterically hindered. Hence, from the backside & no