Alkene Addition Reactions: Crash Course Organic Chemistry #16 - Free Educational videos for Students in K-12

Alkene Addition Reactions: Crash Course Organic Chemistry #16 - By CrashCourse

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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 dorky Chakravarty and welcome to
00:08	Crash course Organic Chemistry , The Portuguese Explorer Vasco da
00:12	Gama sought a sea route to India in 14 97
00:15	to bring black pepper and other spices back to europe
00:18	, which helped kick off the age of discovery .
00:20	So in some way the pursuit of black pepper and
00:23	the organic chemical peppering changed the world . Named for
00:27	the tropical vine paper . Nanogram peppering triggers the spicy
00:31	receptors in our mouths that lead to a little bit
00:33	of pain but flavorful pain because it makes spicy food
00:37	taste good . The E double bonds and peppering can
00:40	be converted to cyst bonds in a rare isomerization reaction
00:43	with sunlight and these icebergs of peppering don't have the
00:46	same heat to them . It's unclear if this isomerization
00:49	is why old ground pepper isn't super hot and if
00:52	you want to become an organic chemist to investigate that
00:54	mystery , go for it with the spicy pepper inspiration
00:57	though . Let's focus on more chemical reactions involving Calkins
01:02	. Yeah . Mhm . Yeah . Over the past
01:13	few episodes , we've been doing reactions with all kinds
01:15	that follow the same general pattern . Alcanzar nuclear filic
01:19	and can attack electro files . So the pi bond
01:21	gets broken into sigma bonds . Form two groups get
01:24	added to the former alkaline , one to each carbon
01:26	on either side of the double bond , but that's
01:29	a mouthful . So organic chemists say those two groups
01:32	get added across the double bond and we call these
01:35	addition reactions before we dive into these puzzles which can
01:38	feel huge and messy . Let's touch base . Organic
01:41	chemistry is full of patterns and we can use those
01:44	patterns to predict instead of memorize reaction products for ALK
01:48	in addition reactions , there are three key questions we
01:50	can ask to help us figure out what's going on
01:52	. Think of these questions as three moves that combine
01:55	to make up a dance , a cool fighting combo
01:57	or a secret handshake . Except that dance or combo
02:02	or handshake is just a specific kind of addition reaction
02:04	with a special name . Question number one , what
02:07	are we adding across the double bond ? Maybe we're
02:09	adding hydrogen bromide like we have in previous episodes .
02:12	So there's a proton on one carbon of the former
02:14	double bond and there's a bro mean on the other
02:17	carbon . Or maybe we're adding water across the double
02:19	bond H . On one side and O . H
02:21	. On the other . And if it is water
02:24	, we call it hydration . Question number two ,
02:26	where will the group add on an asymmetrical molecule ?
02:29	For example , the left hand carbon of the double
02:31	bond in this molecule is bonded to three carbons .
02:34	And the right hand carbon of the double bond in
02:36	this molecule is bonded to two hydrogen . As a
02:39	refresher from episode 14 , we learned Markov Markov's rule
02:42	, which tells us that a proton adds to the
02:44	carbon of the double bond that has the most hydrogen
02:46	. We call that Markov Dickov edition with some special
02:50	reactions . These groups can add in the opposite orientation
02:53	and if a proton adds to the carbon with less
02:55	hydrogen , it's anti Mark kostikov edition in general .
02:59	This question is defining a reactions tendency to bond groups
03:02	to one atom over another in an asymmetrical molecule ,
03:05	a property called regio selectivity . And question number three
03:09	, what is the expected stereo chemistry of the added
03:12	groups here ? We need to pay attention to how
03:15	the groups add in three D space . If the
03:17	groups were adding add to the same face of the
03:19	double bond , it's called Sin Edition or if they
03:22	add on opposite faces , it's called Anti edition .
03:25	That's it . These three questions are the key to
03:28	deciphering the secret handshakes of addition reactions . Let's start
03:31	with an addition reaction called hallucination . We're adding chlorine
03:35	or bromine across the double bond , both of which
03:38	are in the halogen group of the periodic table .
03:40	That answers question number one . By the way ,
03:42	we typically perform this reaction in a non nuclear Felix
03:45	solvent like carbon tetrachloride . For question number two ,
03:48	we're adding the same group abe roaming on both sides
03:52	. So retail selectivity doesn't matter here . And for
03:55	question number three , see that one grooming adds to
03:57	the top of the ring and one grooming adds to
03:59	the bottom of the ring . So this is anti
04:01	edition . We've got to step through the reaction .
04:03	To understand why this happens though . Let's look at
04:06	the mechanism of cyclo obtained with molecular bro . Ming
04:08	. Remember hbr is a strong acid and completely dissociates
04:12	in water . This means that bromide br minus is
04:15	pretty stable on its own . So the nuclear feel
04:17	like al came can attack bro ming pushing off br
04:20	minus informing a cat eye on . But here's a
04:23	possible dilemma . Thinking about stereo chemistry . The bromide
04:26	iron could attack a planer carbo cat eye on on
04:28	either face of the ring . That would give us
04:30	a mixture of sin and anti edition . But experimentally
04:34	that doesn't happen here . We only get the anti
04:37	product . So there's something tricky going on that prevents
04:40	the Sin edition . We don't form a simple carbo
04:43	cat eye on here . If we think about grooming
04:45	donating a pair of its electrons to the nearby positive
04:48	charge , we form a structure called ever ammonium ion
04:51	. This high energy bridge helps stabilize the positive charge
04:55	to get straight to the bar . Ammonium ion ,
04:56	we need to adjust our arrow pushing for the first
04:58	step the alcan attacks br minus has kicked off .
05:02	And we also show a lone pair from the bro
05:05	. Mean we attacked reaching back to attack the al
05:07	keen to form the bridge . The ammonium ion is
05:09	a major contributor to the residents hybrid and blocks the
05:12	face of the ring . So the remaining bromide ion
05:15	is forced to attack the opposite side of the ring
05:18	and its anti edition to some of our combo .
05:20	Kita halogen nation . We've got this note card will
05:23	make one for all these reactions . Now let's learn
05:26	a twist on halogen nation . An addition reaction called
05:28	jala hydrant formation . Hello comes from halogen and the
05:32	hydrant comes from water . Think hydration . So for
05:35	question number one , we're still adding chlorine or bromine
05:37	across the double bond . Just in a solvent like
05:40	water . That's also a nuclear file because there are
05:43	many solvent molecules around . We get a different final
05:46	product to see what I mean . Let's predict the
05:48	product if we had an asymmetrical alki in such as
05:50	E three metal pen to in and reacted with molecular
05:53	chlorine , but this time using water as a solvent
05:56	first . The nuclear Felix alcan attacks chlorine , like
05:59	what we saw with rumination , A Caronia my on
06:01	forms to stabilize the positive charge , stereo . Chemically
06:04	speaking , the caroni umbridge can be sticking up or
06:07	down , which ultimately means that we'll get equal amounts
06:10	of these to an anti immerse reacting with water to
06:13	make our final products . If you remember all the
06:15	way back to episode eight and nine , that's a
06:17	receipt emmick mixture . Now , it's time to think
06:19	about question number two . The next step in hello
06:21	, hydrant reaction involves a water molecule . As our
06:24	nuclear filic attacker , oxygen's lone pair is going to
06:27	attack at the side where we can draw carbo cat
06:29	eye on . That contributes more to the resonance hybrid
06:32	, which is the tertiary one . So we would
06:34	expect water to add to the more substituted side of
06:37	the bond . And this reaction is regio selective for
06:40	question number three , the caroni um iron blocks in
06:43	edition . So the water molecule adds anti and then
06:46	a second water molecule deep rotates the ox sodium ion
06:49	, forming an alcohol roof in the final products they're
06:52	called clara hydrants because this is a hallow hydrate formation
06:55	reaction , we can sum up Hello hydro information with
06:58	this note card , Both of the addition reactions we
07:02	just learned involved allegations and Calkins , but an episode
07:06	14 we looked at acid catalyzed hydration and acid catalyst
07:10	helped us add water across the double bond . This
07:13	reaction involves a 12 hydride shift but not all acid
07:17	catalyzed hydration is due . If you want a detailed
07:19	reaction mechanism , you can go watch episode 14 .
07:22	But here's the note card to compare it with the
07:24	other reactions we're learning in this episode to add a
07:27	nuclear file like water without carbo catalon rearrangements , we
07:31	can use a reaction called oxy mercury emission reduction .
07:34	To help remember this , think of mercury as a
07:37	tiny red stop sign but planet blocking shifty carbo cat
07:41	ions . The name oxy mercury ation means using a
07:44	mercury atom to help add oxygen across the double bond
07:47	and the reduction part is how we get rid of
07:49	the mercury adam after it's done its job . So
07:52	for question number one , we're adding a nuclear file
07:54	with an oxygen in it across the double bond .
07:57	With the help of mercury acetate . We're going to
07:59	use water here to be consistent with our other reactions
08:02	. But we can also use alcohols in this reaction
08:05	and forming either as the product . Let's start by
08:07	looking at our reaction arrow next to the one we
08:10	have mercury to acetate and water . What's interesting about
08:13	metal complexes , like our mercury friend here is that
08:15	the bonds aren't as tight as organic molecules , which
08:19	means the attached groups disassociate easily . Are Mercury too
08:22	, can either be attached to one or two acetate
08:24	molecules at any time in solution and what its single
08:27	bonded , the mercury has a formal positive charge .
08:30	That makes our first step pretty clear . Mercury to
08:32	acetate is our cat eye on and electro file .
08:35	So the alkaline . Our nuclear file has something to
08:38	attack . But like bro , ming and chlorine ,
08:40	the mercury has a lone pair of electrons that can
08:42	reach back and make another high energy bridge the sense
08:45	of pattern here . This makes an intermediate called a
08:47	mercury sodium ion which helps stabilize the positive charge but
08:50	also blocks any sort of 12 shifts would get with
08:53	a plain old carbo cat eye on the mercury .
08:55	Any um can form on either face of the alkaline
08:57	. Like we saw with the Caronia my on before
08:59	. We still haven't used up everything from the one
09:02	above the reaction arrow . So in this next step
09:04	, water is our nuclear file and attacks the carbon
09:07	that better stabilizes a positive charge . Then a second
09:10	molecule of water swoops in and D protein . It's
09:13	just like the 12 punch in other hydration reactions .
09:15	We've seen . That's another pattern to notice as we
09:18	do more reactions . And to answer question number two
09:21	about regional selectivity , water adds to the more substituted
09:24	carbon . Finally , we're ready to move on to
09:26	the two below the reaction era , which is sodium
09:29	boron hydride . We're actually going to skip the details
09:32	here because it's a metal reaction mechanism which gets into
09:35	inorganic chemistry . Basically all we need to know for
09:37	this series is that a hydrogen atom replaces the mercury
09:40	and we get our alcohol . And to answer question
09:43	number three , the mercury India my on blocks the
09:45	side of the double bond . So we have anti
09:47	edition of the alcohol . The really important piece to
09:50	remember here is that we get more Kalashnikov edition and
09:53	no rearrangement products . So to sum up our combo
09:56	key to oxy Mercure ation . Here's another note card
09:59	. Okay , we're going to squeeze just one more
10:02	alkaline addition reaction here . So deep breath we got
10:06	this . Our last reaction is called hydro operation .
10:09	Its name comes from the fact that we're adding water
10:11	across the double bond , which gives us hydro and
10:14	we're going to use boron to help us do it
10:16	, which gives us operation . So the answer to
10:18	question number one is we add boring and replace it
10:21	with an O . H . Overall it's like adding
10:23	water across the double bond . Like most of these
10:26	alki in addition reactions , hydro operation has two separate
10:29	steps to start the reaction . Our nuclear file ,
10:31	one metal pent one in attacks the boron containing re
10:34	agent , which we will represent here as BH three
10:37	. And in hydro operation , this kicks off a
10:39	weird chain reaction where all bonds break and form at
10:42	the same time called a concerted reaction because of boron
10:46	atom is chunkier , it has to add to the
10:48	less hindered carbon and our four member transition state looks
10:51	like this . We show the remaining two Hs from
10:54	BH three still on the boron . But in reality
10:57	those hydrogen can also add to two other alkaline molecules
11:00	. So to answer question number two , this is
11:02	anti Marconnet competition . The boron region is big ,
11:06	so the smaller hydrogen has to be added to the
11:08	more substituted carbon for question number three because the B
11:11	. And the H . R . Still attached during
11:13	this funky concerted reaction , they have to add to
11:16	the same side of the ring . So hydro operation
11:19	is always sin edition . This isn't our final product
11:22	because we still have to use the chemicals and step
11:23	to to get rid of the boring and make our
11:25	alcohol and a reaction called oxidation the peroxide H 202
11:30	and sodium hydroxide act like referees in this process ,
11:33	breaking off the boron and leaving behind the alcohol group
11:36	. We'll get into oxidation more next time . But
11:38	for now let's sum up our three combo key to
11:40	hydro operation . And here's a quick comparison of the
11:43	three alki in addition reactions that form alcohol acid catalyzed
11:47	hydration has more Kalashnikov ratio . Selectivity is not stereo
11:51	selective and can have carbo cat eye on rearrangements .
11:54	Oxy regulation has more Kalashnikov regio selectivity and blocks carbo
11:58	cat eye on rearrangements and hydro operation has anti more
12:01	kostikov regio selectivity sin stereo chemistry and no carbo cat
12:06	eye on rearrangements , depending on where we want the
12:08	alcohol . To end up , we can choose the
12:10	perfect re agent . So remember to practice recognizing these
12:13	patterns even though they might be tricky . At first
12:16	. In this episode , we began to create three
12:18	move combos for alk . In addition reactions that specify
12:21	one what is being added across the alkaline to radio
12:24	selectivity and three stereo chemistry . And we learned a
12:29	bunch of addition reactions to all claims . In the
12:31	next episode , we'll investigate even more alkaline addition reactions
12:35	, focusing on oxidation and reduction . Thanks for watching
12:38	this episode of Crash Course Organic Chemistry . If you
12:40	want to help keep all crash course free for everybody
12:43	forever , you can join our community on Patreon .
12:48	Yeah .

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