Less reactive, more stable?

[danny89]

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Q: Which if the following nucleophiles is mos likely to react with propyl benzoate to form a new product?
A. CH2OH
B. NH3
C. CH3COOH
D. Cl-

A: NH3
When NH3 attacks propyl benzoate, it forms an amide and amides are favored to be the new product because it's less reactive than an ester, acid anhydride and acid chloride.
What do they go by to tell what is less reactive than other compounds?
And is less reactive synonymous to being more stable?
Thanks

 

[DrknoSDN]

It's based entirely on leaving group stability.
Stability is based mostly on how well an molecule can hold a given charge.

In this example the leaving group is n-propoxide with a negative charge on oxygen (fairly stable).
The NH2 subsitution reaction forms an amide (NH2). If the n-propanol tried to undergo substitution again and replace the NH2 group it would leave the NH2 group with a negative charge (very unstable as nitrogen would usually be neutral or positive.)

Just found this list: http://en.wikipedia.org/wiki/Leaving_group
Amides are the worst leaving group on the list.

 

[Teleologist]

And is less reactive synonymous to being more stable?
Thanks

Yes