2009 DAT: OC #71 - can someone explain this?

[I Brush My Teeth]

Could someone help me out as to why the answer is C? I put A because I thought that the Br would leave in an SN2 reaction with the CN.

I'm also not 100% sure what the 2nd reaction does.. any help would be greatly appreciated

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[510586]

Turns NH2 into N2 Then that turns into CN. using CuCN

 

[enamel88]

Do you have DAT destroyer? if you look at the diazonium road map, it has the exact reagents. The Sn, Hcl converts the NO2 to an NH2. Then the NaNo2, HCl converts the NH2 to a diazonium salt making it N2+Cl-. Then with the CuCN, it just substitutes CN for the salt. Hope it helps.

 

[DAT Destroyer]

Could someone help me out as to why the answer is C? I put A because I thought that the Br would leave in an SN2 reaction with the CN.

I'm also not 100% sure what the 2nd reaction does.. any help would be greatly appreciated

First of all, when a Halogen (Br in this case) is attached to a benzene, it is called an Aryl Halide. It will not undergo any Sn2 or E2 reactions, no matter what the nucleophile is. You cannot do a backside attack since the benzene ring is too bulky.

In this problem, the first step converts (reduces) NO2 into NH2. The second step makes a Diazonium salt (N2+). N2 is a very good leaving group. The last step, CuCN, will replace N2+ with a nitrile group. This is one of the several diazonium salt reactions. They are great tool for synthesis.

Hope this helps.