[sharbeldam]

So if we wanna predict the product of addition of alpha beta unsaturated ketones/aldehydes, the books say that if it's a weak base like amines then the conjugate product is formed (1,4). but clayden book puts water as a hard nucleophile, i guess because its polar but at the same time it's a weak base? so according to that, even if its a weak base, it gives the 1,2 product (Direct)... a bit confusing no? because paula book states if it's a weak base it should give the conjugate product.

[BlitzHypercharge]

I would say that Paula Bruice is a bit vague here as the line of a weak and strong base is not explicitly defined.I would say that H2o would be a hard nucleophile attacking the carbonyl and performing 1,2 addition.

[hollytara]

As with many things, creating binary categories (weak base, strong base; soft Nucleophile, hard Nucleophile) isn't always a good match with reality where there is a wide range of strengths and "hardness". 

[sharbeldam]

So to make it simple theory wise, I better go by clayden categories of hard/soft Nucleophile instead of paula’s General rule yes?

Or did you have a better way to solve problems and predict products?

[hollytara]

It also makes a difference if it is under acidic or basic conditions.  Amines are more nucleophilic than water, they will react with unsaturated carbonyls as the free amine.  Water usually won't.  You either have to add base and then the reaction is hydroxide (not water) or add acid, and then the reaction is with the protonated intermediate.  So thinking about nucleophilicity is the best place to start.

[sharbeldam]

So what you are saying is that despite that water is considered a hard nucleophile, it's not strong enough without a base, so it wont give a direct 1,2 product... interesting. i wonder why they dont explain EVERYTHING in the book. just generally

[OrganicH2O]

I think there is also the issue of kinetics vs thermodynamics. The 1,4 product is (always, I think?) more stable than the 1,2 addition product, because the C=O pi bond is stronger/more stable than the C=C pi bond. So for many nucleophiles it doesn't matter which site gets attacked faster. If the nucleophile adds reversibly, it can equilibrate to the 1,4 addition product over time. Even fairly strong bases like alkoxides can be adding reversibly.

[rolnor]

I think its complex problem, for one thing the product must be stable and for example water adding to a carbonyl generally dont give a product you normally find exept for compounds like chloral hydrate etc. its wrong to try and find a set of rules that cover all examples of this important field although there are rules that does work fine for many cases.
This video is good I think;

https://m.youtube.com/watch?v=04NYWxuD6d4

[sharbeldam]

I understand thank you, but i watched a video also from the university of california (https://www.youtube.com/watch?v=fZ1GEyNX_zI) at minute 30:00, she considers ROH and amines soft nucleophiles in contrary to the video you sent and clayden's book table.

I just wanna know if you had an alpha beta unsaturated carbonyl with alcohol or amines, where do u guys attack it? is it reversible or not? NH2 and OR should be bad leaving groups, so i would say attack the carbonyl, but why does some sources like the video i watched last say otherwise?

[hollytara]

It is complicated. 

If you react ammonia with methyl acrylate, you will get aza-Michael addition, which is a 1,4 addition. 

If you react hydroxylamine with acrolein, you will get the oxime - which is a 1,2 addition. 

Amines with acrolein will do both 1,2 and 1,4 addition - see SYNLETT 2014, 25(17), 2442–2446

Both amine nucleophiles, both unsaturated carbonyls. 

[OrganicH2O]

You mentioned NH2 as a leaving group when talking about amines. But the leaving group would really be NH3, or RNH2, etc (a neutral leaving group). And alkoxides are more like "medium" leaving groups in this context. Still good enough to add reversibly.

In this video she posted, it looks like she is saying "milder" rather than soft or hard. She mostly references the pKa of the conjugate acid. The pKa of the conjugate acid is a good indication of whether the reaction is irreversible or reversible. It doesn't tell you directly about hard or soft properties. NaH for example is an extremely strong base, but also fairly soft because it only has one proton in the nucleus pulling on the electrons (naked H minus like this is usually just a base, however, and not a nucleophile).

Many texts will emphasize kinetics or only thermodynamics, when both aspects are actually important. In the video you referenced she says grignards only add 1,2, even though it is well documented that they sometimes have a preference for adding 1,4. This is a common "lie" they tell in Sophomore organic and it is best to just believe the lie at first, because remembering every case is very difficult.

[rolnor]

My guess is that more than 90% of alkylGrignards add 1,2 not 1,4. So the lie is a good rule in most cases. You can not cover all exceptions and examples in a video or chapter in a textbook and this is true for all fields of chemistry I think, you have to accept this.