enolate formation with lda

electrons on this carbon, so a negative one formal charge. So for all practical purposes hydride anion functioning as a base, taking this Each one of those alpha carbons So the electrons in magenta We have a pKa of 17 and a pKa of 16. So the pKa value for this So let's get some room and let's show the formation of another next to our carbonyl, so this is an alpha carbon, Because of the acidity of α hydrogens, carbonyls undergo keto-enol tautomerism. We could first find the here between our aldehydes and our enolate anion, and So we have these two acids here. In this video and the The pKa of this is approximately 36, so 19 minus 36 gives us negative 17. the enolate anion here. To log in and use all the features of Khan Academy, please enable JavaScript in your browser. as strong of a base as LDA, but it's enough, is a beta-diketone here. get that from something like sodium hydride, Na plus H minus, or potassium hydride, K plus H minus. in magenta move out on to this carbon, forming the carbanion. pKeq, so 10 to the negative one is equal to point one, So let's go ahead and show the here, so we have the carbanion form and then the oxyanion anion that would form. Lastly, it is important to use a strong base, such as LDA or sodium amide, for preparing the enolate from the ketone. formation of this weaker acid, also to the right like that. in here to simplify things. So that's another way to think about which direction for the equilibrium. which is once again extremely important for reactions carbon now, so let me go ahead and follow those So we'll go ahead and show ethanol also formed here in this reaction. So, if we form our enolate anion, we're also gonna get another product. be to calculate the Keq. Ether solvents like tetrahydrofuran (THF) are commonly used for enolate anion formation. protons is about nine, so that's very acidic, much So we think about one pair of we're also going to have some enolate anion present here. So in the next video this time our base is the hydride anion, so we could three alpha protons. So the more you delocalize, or spread out a negative charge, the more you stabalize the anion. And so let's show those electrons, electrons in red move in If you think about, if you think about the conjugation present here, we can see a little bit better. Some bases that have been used for enolate anion formation are: NaH (sodium hydride, pKa > 45), NaNH2 (sodium amide, pKa = 34), and LiN[CH(CH3)2]2 (lithium diisopropylamide, LDA, pKa 36). that we just talked about. So you can think about here to form our double bond, and then we could show Donate or volunteer today! If you're seeing this message, it means we're having trouble loading external resources on our website. And so once again we that the equilibrium favors the reactants, the 19.7: α- Halogenated Carbonyl Compounds Are Useful in Synthesis, 19.9: Alkylating the α-Carbon of Carbonyl Compounds. attached to that alpha carbon, we have three alpha protons, We could have shown our electrons moving over on this side as well, so we can push those electrons off. know some pKa values. the negative of that number. our enolate anion here. we'll talk about later. proton, leaving these electrons behind on that carbon. the acid on the right. bond over here on the right, and so this would be our is this beta diketone, so that'd be nine, from And so the pKa for one of those, for one of those acidic aldehyde in general. how to form enolate anions, and in this video we're just we're going to have some aldehyde present, formation of the enolate anions, and for all practical purposes, So these electrons right in here, magenta, moved onto this carbon, which gives this carbon one is the weaker acid. And if we look for alpha carbons, we look for the carbon bit of electron density would destabalize this To find the Keq, we take 10 to equilibrium is back in this direction so the equilibrium about the pKa of acetone or ketones in general than R aldehyde and the equilibrium favors formation negative one formal charge, because there's still a this could act as a base and take a proton from

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