Ch. 10 - Addition ReactionsWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

Hydroboration-oxidation of terminal alkynes leads to formation of aldehydes. (If the alkyne is not terminal, it will just yield a ketone). 

Concept #1: Anti-Markovnikov addition of alcohols to terminal alkynes yields aldehydes.   

Transcript

Alright so remember that we have 3 different ways to add alcohol we had hydration we had Oxymerc we had one more and that was hydroboration, remember what was kind of interesting about hydroboration is that it did everything opposite, hydroboration is actually going to be anti-markovnikov addition of alcohol so what that means is that if once again I have the blue site and I have the red site which one is it going to add to? Well it would actually add to the less substituted position so would it would add right here, OK? So once again notice that I'm getting an enol I'm still getting a vinyl alcohol the difference is that it's just in a different position, OK? Now notice my reagents really quick just notice that I said BH3 or another Boron source that's because hydroboration there's a lot of different borons such as that your professors could use so you just have to be aware of the one that your professor likes to use, OK? And then obviously the bottom part was the oxidation step so now I've got the enol how do I figure out what the product looks like? Same process, I'm going to switch the position of the double bond and the H so what that means is that in my final product what I'm going to get is now instead a double there I'm just going to get a single bond and instead of a single bond to the O, I'm going to get a double bond to the O, OK? So what this means is that where did the extra H go? The extra H went here because for right now there was only one H here and now there's going to be two Hs so there's that original H and then there's that extra H, that extra blue H or whatever was this H here and it transferred, OK? So now notice what kind of molecule this is I just drew a terminal Carbonyl this actually has a hydrogen at the end this is actually going to lead to the formation of Aldyhides, OK? So when you do a markovnikov addition of water that's going to be a ketone product, OK? When you do an anti-markovnikov addition of water what you're going to lead to is an anti-markovnikov alcohol or enol which then turns into an aldihyde, now notice that in general the still called the keto form, OK? If you were to say just in terms of totamers this is the enol totomer this is the keto totomer but this specific molecule happens to be an aldehyde because the carbon is right at the edge and it has one H on it, OK? So just something that you guys need to be aware of it's something that could definitely come up so you guys just need to know what's going on, alright? So I hope that made sense let me know if you have any questions.

This reaction yields an anti-Markovnikov vinyl alcohol, which will tautomerize into a carbonyl on the terminal position, which is the definition of an aldehyde.