Electron donating and electectron withdrawing...

[Temperature101]

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I know what are electron donating and electron withdrawing but I am having trouble grasping why they say electron donating makes a conjugate base less stable. What do they mean by using the word 'stable'? I want someone to explain clearly what that word stable meansin this case. It's been three years since I took organic; therefore, be patient with me.

 

[COTA2Phys]

If it becomes less stable, then it is more basic because those electron donating groups are pushing their negative charge towards the negatively charged atom (which would have been perfectly happy (stable) without those electrons being pushed towards it). Since, electrons repel, the negative charge will be more likely to want to grab a proton (i.e. more basic).

 

[gettheleadout]

I know what are electron donating and electron withdrawing but I am having trouble grasping why they say electron donating makes a conjugate base less stable. What do they mean by using the word 'stable'? I want someone to explain clearly what that word stable meansin this case. It's been three years since I took organic; therefore, be patient with me.

So if you take a conjugate base A- of some acid HA and put an EDG on it, now you have increased negative character in the conjugate base (makes sense because the EDG is donating electrons to a region that is already electron-rich). Excessive charge decreases stability (i.e. non-reactivity) of a compound because it increases its reactivity. The greater the negative character on a group, the more easily it can use the magnitude of that character to interact with a foreign group of positive character (in this case either a free H+ ion or a partially positive proton on some other acidic compound.)

Stability in this sense refers to the inverse of reactivity. The more negative the base, the more easily it can interact with something at least slightly positive. The more electron-donating the attached group, the more negative the base.