benzene a good leaving group?

[suhshi]

weird question but look at the link


http://img198.imageshack.us/img198/9012/ochem1.png


answer is C

can anybody explain?

thanks in advance

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[appulipzzz]

I think the question kinda directs you to the right answer because it says "using your knowledge of base strengths" and -OCH3 is a stronger base than CH3SH.
And I think the leaving group in C is pretty stable because of its resonance structures....

 

[wodehouse]

You can also think of each reaction as potentially going either way, with bases on either side of the reaction arrow. The reaction goes forward if it starts with a strong base and ends with a weaker one.

 

[UCB05]

weird question but look at the link


http://img198.imageshack.us/img198/9012/ochem1.png


answer is C

can anybody explain?

thanks in advance

I'd go with wodehouse's reasoning.

Notice that these are all potentially reversible addition/elimination reactions, so you have to look at the leaving group. -OH and -OCH3 are strong bases. NH3 has a lone pair and can act as a nucleophile and (iirc) -SCH3 is a reasonable leaving group. The phenol ion is resonance stabilized and the ring is electron-withdrawing, weakening its nucleophilicity/basicity. It makes the reverse reaction of C less likely and forward reaction more likely than the other 3 choices.