Ch.15 Question 71

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Simone Seliger 1C
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Ch.15 Question 71

Postby Simone Seliger 1C » Sun Mar 05, 2017 7:16 pm

In this reaction mechanism, the answer key states that there are two intermediates and that the catalyst is OH-. But I remember learning that a catalyst is a molecule that is present in the beginning of the reaction and the end of the reaction (it is not used up). Based off of this knowledge, I wrote that there were three intermediates and that R was the catalyst molecule. The 3 intermediates I chose were OH-, RC(triple bond N-)OH, RC(triple bond NH)OH.

The problem a -C triple bond N group, which lead to me believe R was its own molecule.

Could someone clarify this for me? Thanks!

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Re: Ch.15 Question 71

Postby Chem_Mod » Sun Mar 05, 2017 10:41 pm

R just stands for any substituent that is unimportant to the reaction, and a part of the molecule. It does not have any catalytic properties in this context. Does the hydroxy anion appear in the midst of the reaction and is subsequently consumed? If not, it is not an intermediate. Rather, it is consumed in the first step, and reproduced during step 2. Thus there is no net consumption of the hydroxy anion, it is the catalyst.

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