basicity trend

[recyrb]

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can someone explain what it means, that basicity gets stronger as we go to the left on the periodic table.

if this is the case why are CN- and N3- weak bases but OH- or RO- strong bases, both cn and n3 are 'more left' on the periodic table than oxygen.

thanks
booo

 

[MrFantastik]

When I think of acid/base trends on the periodic table I usually only determine the the trend for acidity and then know that the trend for basicity(is this a word?) is the opposite.

For example, when talking about acidity we know HF > H2O > NH3 > CH4

Therefore the basicity of their conjugate bases is CH3- > NH2- > OH- > F-

If that wasnt enough of an explanation let me know cuz theres more to it but I think it might not be necessary.

 

[recyrb]

I have in my notes from chads videos, during his distinguishing Sn2E2Sn1E1 that SN2- uses weak bases such as N3- and CN- why are these weak bases??

did i misunderstand that segment??
Thanks

 

[wizi]

I have in my notes from chads videos, during his distinguishing Sn2E2Sn1E1 that SN2- uses weak bases such as N3- and CN- why are these weak bases??

did i misunderstand that segment??
Thanks

I think the best one to answer this question should be Chad. You should post this question on his forum, he ll answer it for you personally.
🙂

 

[dental13]

Yeah I know, he didn't really explained why CN- and N3- are Strong Nuc but weak base. Then, I guess we just have to memorize this fact.

Did you asked Chad personally? if you did, please explain the reason
thanks

 

[loveoforganic]

can someone explain what it means, that basicity gets stronger as we go to the left on the periodic table.

if this is the case why are CN- and N3- weak bases but OH- or RO- strong bases, both cn and n3 are 'more left' on the periodic table than oxygen.

thanks
booo

As in the examples that MrFantastik gives below, those trends only apply when you're considering analogous structures. For example, there's some giant carbon compound (don't remember the name) that's actually a strong acid (C-H) due to steric issues and resonance or some such. This isn't the same as comparing the C-H in methane vs the O-H in water.

When I think of acid/base trends on the periodic table I usually only determine the the trend for acidity and then know that the trend for basicity(is this a word?) is the opposite.

For example, when talking about acidity we know HF > H2O > NH3 > CH4

Therefore the basicity of their conjugate bases is CH3- > NH2- > OH- > F-

If that wasnt enough of an explanation let me know cuz theres more to it but I think it might not be necessary.

Yeah I know, he didn't really explained why CN- and N3- are Strong Nuc but weak base. Then, I guess we just have to memorize this fact.

Did you asked Chad personally? if you did, please explain the reason
thanks

Just kinda have to know that they're weak bases. Can't deduce that for sure from structure. Knowing that, you can tell they're very good nucleophiles because they are both so-so bases and linear, which makes them take up very little space (they easily squeeze into places, e.g. the C-X carbon of an alkyl halide).