Alkyne Reactions & Tautomerization: Crash Course Organic Chemistry #18 - By Math and Science
Transcript
00:0-1 | You can review content from Crash course Organic Chemistry with | |
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00:05 | devices . Hi , I'm Dave okay Chakravarty and welcome | |
00:08 | to Crash course Organic chemistry double bond containing compounds are | |
00:12 | pretty abundant in nature but compounds with all kinds triple | |
00:15 | bonded carbons are not . There are a few naturally | |
00:18 | occurring all kinds like sticky toxin and water hemlock and | |
00:22 | histrionic , a toxin that the harlequin poison frog uses | |
00:25 | to protect itself . But many al kinds aren't poisonous | |
00:28 | and aren't naturally occurring . They're made in a lab | |
00:31 | like to common ingredients in birth control pills , ethinyl | |
00:35 | estradiol , a synthetic estrogen and Nora syndrome , a | |
00:38 | synthetic progesterone . Natural estrogen and progesterone are expensive , | |
00:43 | hard to purify and relatively scarce . Plus we need | |
00:46 | a higher concentration of the natural compounds to get the | |
00:49 | same effect as their synthetic replacements . So even though | |
00:52 | they're not as common alcohol containing molecules are really important | |
00:56 | , organic chemistry is really about how chemical reactions can | |
00:59 | make compounds that make human lives better from medicines to | |
01:02 | materials . We're trying to build on the building blocks | |
01:05 | that nature provides . So with that as motivation let's | |
01:09 | learn about alkaline reactions . Yeah . Mhm . Yeah | |
01:20 | . Yeah . Yeah . Remember that the carbons in | |
01:23 | a triple bond have sp hybridization . And if an | |
01:26 | sp hybridized AL kind is found at the end of | |
01:28 | a molecule , it's called a terminal al kind , | |
01:30 | terminal AL kinds always have a hydrogen atom attached to | |
01:33 | them . And the increased s character of the bond | |
01:36 | means that a hydrogen attached to those carbons is very | |
01:38 | weakly acidic with piquet is around 25 . So if | |
01:42 | we make a super strong base like the anti and | |
01:44 | of ammonia with a terminal AL kind , we can | |
01:47 | make negatively charged carbon containing compounds called carbon ions . | |
01:51 | You might also hear them called a civilized and ions | |
01:54 | after the simplest al Qaeda acetylene carbon ions have a | |
01:57 | formal negative charge . So their nuclear files , but | |
02:00 | they're especially cool nuclear files because they can make carbon | |
02:02 | carbon bonds , even though organic chemistry is full of | |
02:05 | carbon carbon bonds , making one is a pretty big | |
02:07 | deal . It's not easy . This might not be | |
02:09 | very obvious until later in this series , but many | |
02:12 | organic chemists aim to make huge molecules with lots of | |
02:15 | carbon carbon bonds . So the re activities of these | |
02:18 | carbon ions can help one way they form carbon carbon | |
02:21 | bonds is an calculation reaction , which looks like this | |
02:25 | . Also , carbon ions can attack carbondale groups which | |
02:28 | are those polar carbon oxygen double bonds . The lone | |
02:31 | pair of electrons attacks the partially positive carbon , forming | |
02:34 | a carbon carbon bond and pushing electrons onto the oxygen | |
02:37 | . We have a charged intermediate here . So as | |
02:40 | a second step , we add in a source of | |
02:41 | protons , water in this case and form an alcohol | |
02:44 | . The acidity of hydrogen atoms on carbon carbon triple | |
02:47 | bonds makes terminal al kinds unique . But like all | |
02:50 | kinds , all kinds of pI bonds that are also | |
02:52 | nuclear Felix . So some alkaline reactions are pretty similar | |
02:55 | to the alkaline reactions we've learned in the past two | |
02:57 | episodes . Remember halogen nation where we added halogen is | |
03:01 | like bromine or chlorine . Across the double bond , | |
03:03 | they can also be added across a triple bond . | |
03:06 | To look at the reaction mechanism , we can see | |
03:08 | the nuclear electrical bond attacks the electra filic molecular bro | |
03:11 | me . And even though there's an extra carbon carbon | |
03:14 | bond in their ABR ammonium ion still contributes to the | |
03:17 | residents structure and stabilizes the positive charge . Like with | |
03:20 | all kinds , The bar ammonium ion structure blocks one | |
03:23 | face of the compound and our major product is formed | |
03:25 | by anti edition of the second bromide ion . But | |
03:28 | we're not done yet . These products are Calkins which | |
03:31 | also react with halogen . So there's basically nothing stopping | |
03:34 | this hydrogenation reaction from going and going until it forms | |
03:38 | a tetra bromide products . We can control side reactions | |
03:40 | a little bit with the amount of halogen we add | |
03:42 | like adding one or two molecules of die bromide to | |
03:45 | one al Qaeda molecule , but it's pretty tricky to | |
03:48 | control alkaline halogen nation reactions . On the other hand | |
03:51 | , the addition of hydrogen Halide is a bit more | |
03:53 | predictable with certain substrates . We spent a lot of | |
03:56 | time with this reaction and all kinds like when we | |
03:58 | were first exploring edition reactions in episode 14 , when | |
04:02 | we have an al Qaeda and hydrogen bromide , the | |
04:04 | nuclear feel like attack happens like we'd expect and the | |
04:06 | hydrogen bromide ads across the triple bond . If the | |
04:09 | alkaline is a terminal al kind , this edition will | |
04:12 | follow more cosmic office rule as a reminder , this | |
04:14 | means that the proton will add to the side of | |
04:16 | the triple bond with the hydrogen atom . To unpack | |
04:19 | that a little more . The carbon of the triple | |
04:21 | bond on the left side has a metal substitute and | |
04:23 | no hydrogen . And the carbon on the right side | |
04:26 | of the triple bond is bonded to one hydrogen . | |
04:28 | So the protein from hydrogen bromide will add radio selectively | |
04:31 | to the right , which forms a more stable secondary | |
04:34 | vinyl carbo cat eye on as opposed to a primary | |
04:37 | one . This is called a vinyl carbo cat eye | |
04:38 | on because the positive charge sits on a carbon carbon | |
04:41 | double bond . The attacks step creates a vinyl Halide | |
04:44 | a term we use to describe a halogen directly attached | |
04:47 | to the carbon of a double bond . And remember | |
04:50 | Alcanzar still reactive . So if we start with two | |
04:52 | molecules of hydrogen bromide to one molecule of AL kind | |
04:56 | , the reaction will keep going . We add a | |
04:58 | second hydrogen bromide across the double bond . Also following | |
05:01 | more cabinet competition , we're showing terminal all kinds here | |
05:04 | because this reaction is radio selective when the alkaline isn't | |
05:08 | at the end of a molecule called an internal AL | |
05:10 | kind . The reaction is hard to control . We | |
05:13 | get complex pictures of products because there's no difference in | |
05:16 | carbo cat eye on stability . Okay , cool . | |
05:18 | We have to AL kind reactions in our back pocket | |
05:20 | , both of which were similar to the halogen and | |
05:22 | alkaline reactions . We can add water using similar reactions | |
05:25 | to for example , we could do a mercury catalyst | |
05:28 | hydration reaction . The name tells us a couple of | |
05:30 | things will be using a mercury compounds , specifically mercury | |
05:33 | to sulphate H G S 04 which will get back | |
05:36 | unchanged at the end because it's a catalyst and we'll | |
05:38 | be adding some water across the triple bond . That's | |
05:41 | the hydration . The first step of this reaction is | |
05:44 | the alkaline attacking the mercury cat ion with a positive | |
05:47 | to charge . While the sulfate ion ion just floats | |
05:49 | around as a spectator , the mercury ads so that | |
05:52 | the more stable carbo cat eye on forms , we | |
05:54 | get a secondary vinyl carbo cat eye on stabilized by | |
05:57 | residents with the mercury India my on as opposed to | |
05:59 | a primary carbo cat eye on next , a water | |
06:02 | molecule attacks are newly formed vinyl carbo cat eye on | |
06:05 | and with a 12 punch . Another molecule of water | |
06:08 | deep resonates this ion forming an alcohol . This is | |
06:11 | a pit stop in our water molecule is officially added | |
06:14 | , but we're not done with the whole reaction mechanism | |
06:17 | , We still need to get rid of the mercury | |
06:18 | to restore our catalyst so the alcan attacks the hydro | |
06:21 | nia . My on that we just made this forms | |
06:23 | a carbo cat eye on on the side that has | |
06:25 | resonance stabilization thanks to oxygen being all generous in sharing | |
06:29 | a pair of electrons . The structure has a lot | |
06:31 | of positive charge built up . So mercury is happy | |
06:34 | to get out of there , leaving its electrons behind | |
06:36 | . And this reforms the double bond , the alcohol | |
06:39 | group and are free floating catalyst . Our product has | |
06:41 | a special duo , a double bond next to an | |
06:44 | alcohol . So we still parts of the words alkaline | |
06:46 | and alcohol to call it in . In all this | |
06:49 | is the summary of our long and winding road map | |
06:51 | for a mercury catalyzed hydration reaction , adding water to | |
06:54 | a terminal al kind internal all kinds would again give | |
06:57 | us complex mixtures of products , but there's still more | |
07:00 | fun to be had with channels specifically . There's a | |
07:03 | type of constitutionalism are called to tumors , which differ | |
07:06 | in the location of the double bond in just one | |
07:09 | hydrogen . If the double bond is between two carbons | |
07:11 | , it's the final form . And if the double | |
07:14 | bond is between a carbon and the oxygen , it's | |
07:16 | the keto form . In fact , the evil we | |
07:18 | just made quickly undergoes to memorization to become a key | |
07:21 | tone . This happens because some of the bond energies | |
07:24 | in the keto form is greater than the sum of | |
07:26 | the bond energies for the final form . Because the | |
07:29 | key to form makes stronger bonds . We know it's | |
07:31 | more stable . Looking at our reaction mechanism , we | |
07:34 | have some hydro knee um ions which are acidic so | |
07:37 | an acid catalyzed to memorization can happen here First . | |
07:40 | The double bond in the email attacks the hydro nia | |
07:42 | my on and adds a proton so that the positive | |
07:44 | charge goes next to oxygen , where it can be | |
07:47 | resonance stabilized at this point , there are two resonance | |
07:50 | forms . The positive charge can hang out on a | |
07:52 | carbon or the oxygen . So to make the keto | |
07:55 | form a water molecule , D , protein eight's , | |
07:58 | the oxen iem ion . Overall , we added a | |
08:00 | proton on one side of the channel and removed one | |
08:02 | from the other side . So it's not too complicated | |
08:06 | to . Memorization is basically some double bond shifting and | |
08:08 | a single proton being moved around . In fact , | |
08:11 | to memorization reactions have a similar pattern is resonance , | |
08:14 | which we learned an episode 10 if we place a | |
08:17 | block around the double bond along with the atom that | |
08:19 | has electrons and a p orbital next door , we | |
08:21 | find our three adam pattern . Now swap the stuff | |
08:24 | at Adams , one in three . We move the | |
08:26 | double bond and hydrogen and switch between our keto in | |
08:29 | Enel forms so we can make a key tone from | |
08:31 | an AL kind using a mercury containing catalyst in some | |
08:34 | water . But that's not the only way to add | |
08:37 | water across the double bond . We can do hydro | |
08:39 | operation to looking at the name . You might remember | |
08:42 | that the hydration reaction with some help from carbons periodic | |
08:44 | table next door neighbor boron hydro operation happens the same | |
08:48 | way it did with an alkaline . Our nuclear filic | |
08:50 | alkaline attacks the boron re agent . We get a | |
08:52 | pit stop intermediate thanks to anti Markov Niqab edition and | |
08:56 | then an oxidation reaction gives us the channel . If | |
08:59 | you want that in more detail , watch episode 17 | |
09:02 | like the Enel formed in mercury catalyzed hydration reactions . | |
09:05 | This one will to memorize to produce the more stable | |
09:07 | keto form . But because we have sodium hydroxide ions | |
09:10 | floating around which our basic this is base catalyzed memorization | |
09:14 | and the mechanism looks a little different . First , | |
09:16 | the hydroxide ion attacks the alcohol of the eternal and | |
09:19 | D . Protein eights . It . This puts a | |
09:21 | negative charge on our molecule , which has two residents | |
09:23 | forms , one with the negative charge on the oxygen | |
09:26 | and one with a negative charge on the carbon . | |
09:28 | We use the carbon ion resonance form , attacked the | |
09:30 | proton on a water molecule and reform the base to | |
09:33 | make our keto form done . Even though the reaction | |
09:35 | mechanism was a little different . The overall to memorization | |
09:38 | reaction was similar , adding a proton on one side | |
09:41 | of the channel and removing one from the other side | |
09:44 | . Now that we've seen acid catalyzed and base catalyzed | |
09:47 | memorization . I want to point out another pattern that | |
09:49 | will see throughout this series . When we're doing reactions | |
09:52 | and acids will generally have positive charges lying around and | |
09:56 | when we're doing reactions in bases will generally have negative | |
09:59 | charges around , look back at our two reactions and | |
10:01 | see what I mean . And to round out this | |
10:04 | episode , let's explore . One last tool that we | |
10:06 | used on all kinds to reduction . Reduction by hydrogenation | |
10:09 | is when we add hydrogen across pi bonds to make | |
10:12 | an al Kane . With the help of a metal | |
10:14 | catalysts like platinum , palladium or nickel . We can | |
10:17 | also manage to do a partial hydrogenation on an AL | |
10:19 | kind to form an al keen and stop the reaction | |
10:22 | . Early lenders catalyst is a complex palladium based catalyst | |
10:26 | where some of the reactive sites on the palladium are | |
10:28 | unavailable . This keeps the reaction from going all the | |
10:31 | way to an AL came with lenders catalyst . The | |
10:33 | reaction happens on a metal surface once again . So | |
10:36 | the hydrogen is can't help but add to the same | |
10:38 | side of the AL kind , giving us the Z | |
10:40 | . I . Summer . But if we want the | |
10:43 | hydrogen to add a cross to get the Ei summer | |
10:45 | , we can use a different type of reaction and | |
10:48 | do a metal ammonia reduction . This mechanism involves radical | |
10:51 | chemistry like single electrons radical , not these gnarly waves | |
10:55 | radical . So we'll save it for the next episode | |
10:58 | . But the important takeaway here is that a radical | |
11:00 | allows the are groups to position themselves far away from | |
11:03 | each other during the mechanism and form the E . | |
11:06 | L . Came in this episode . We learn that | |
11:08 | the acidity of terminal all kinds allows us to form | |
11:10 | carbon carbon bonds . Many of the reactions that we | |
11:14 | use for al kins also happen for al kinds terminal | |
11:16 | All kinds could have good radio selectivity while internal all | |
11:19 | kinds often form mixtures of products . But reactions with | |
11:23 | the triple bond can also lead to products resulting from | |
11:26 | additions to both pi bonds like tetra allies and hydration | |
11:29 | . Reactions of all kinds can form channels which to | |
11:31 | memorize taquito compounds next time we'll get into Radical chemistry | |
11:35 | , which is pretty wild but also pretty fascinating because | |
11:38 | it gets those couch potato al canes up and moving | |
11:41 | . Thanks for watching this episode of Crash Course Organic | |
11:43 | Chemistry . If you want to help keep all crash | |
11:45 | Course free for everybody forever , you can join our | |
11:48 | community on Patreon . Yeah . |
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