Ranking Basicity? Chad's Ochem Quiz

[bamtori]

Here's my logic (after looking at the answer).

Stability is proportional to conjugate acid strength, so molecules that are:
more stable = weaker base = stronger acid (it can hold it's ground when deprotonated due to resonance, dipole induction, etc)

The question asks which is the STRONGEST BASE, and since stability and basicity are inversely proportional, I should be looking for the LEAST STABLE molecule?

Ranking acids seemed pretty intuitive, just haven't had enough practice ranking base strength.

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[discensdentibus]

Think of the electrons. Which lone pair is more available to be a donor? A sp2 or sp3 hybridized Nitrogen LP? The arene is stable but nitrogen is conjugated with it making its electrons less available. Less available electrons account for a weaker base.

 

[bamtori]

Think of the electrons. Which lone pair is more available to be a donor? A sp2 or sp3 hybridized Nitrogen LP? The arene is stable but nitrogen is conjugated with it making its electrons less available. Less available electrons account for a weaker base.

That's definitely one way to think about it. Adding to that logic of electron availability, when you compare O and N, Nitrogen would be more willing to donate electrons because Nitrogen is less electronegative than Oxygen, making Nitro-containing molecules more basic.

 

[discensdentibus]

that's a fantastic way to get your brain ticking. If you stick a negatively charged NH2 and OH in a pot with 1 H+, that -NH2 will snatch it even if -OH beats him to it first.

 

[emminent]

Also think of it as this way; more unstable the compound is the more basic it is. More stable => more acidic.

for example: COOH has resonance with O's and very stable so very acidic

In chad's example choices you see that the stable ones have resonance whereas the correct choice doesn't have resonance.

 

[ZPederson11]

^^^ agreed. No need to overthink this one. They all have resonance besides the correct one which is the most basic