Alkyne Reactions & Tautomerization: Crash Course Organic Chemistry #18 - Free Educational videos for Students in K-12

Alkyne Reactions & Tautomerization: Crash Course Organic Chemistry #18 - By Math and Science

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00:0-1	You can review content from Crash course Organic Chemistry with
00:02	the Crash course app available now for android and IOS
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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