Determining SN1, SN2, E1, and E2 Reactions: Crash Course Organic Chemistry #23 - Free Educational videos for Students in K-12

Determining SN1, SN2, E1, and E2 Reactions: Crash Course Organic Chemistry #23 - By Math and Science

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00:0-1	Hi I'm Debbie Chakravarty and welcome to Crash course Organic
00:02	Chemistry . Have you ever played an adventure game ,
00:05	the sort of thing where you start with a character
00:07	, get some equipment and go on a quest .
00:09	We can imagine organic chemicals as these kinds of characters
00:12	are adventuring protagonist is our substrate . Different substrates can
00:16	be sorted into classes which can undergo different transformations .
00:20	Specifically , our heroes can take on incredible new forms
00:23	through the substitution and elimination reactions . We've been learning
00:26	for the past few episodes in this episode , we'll
00:29	learn how to beat this adventure game , how to
00:31	take any substrate combined with any nuclear file and predict
00:34	what kind of new adventurer the transformation will produce .
00:41	Mhm mm . First of all , let's set up
00:49	our world to reveal the rules that are substitution and
00:53	elimination reactions must follow . In terms of starting characters
00:56	, we have a few fundamental classes . Metal ,
00:59	primary secondary and tertiary substrates are substrate is always an
01:03	sp three hybridized carbon and the classes refer to how
01:06	many carbon substitutes they have . Primary is one ,
01:10	secondary is two , and tertiary is three . So
01:12	a tertiary substrate is our bulky ist . Character options
01:16	are substrates encounter different nuclear files , which changed the
01:19	substrate through a chemical reaction . We can think of
01:21	nuclear files as different magic potions , some are stronger
01:25	, some are weaker , and the transformative potion effect
01:27	depend on what the substrate is and the surrounding reaction
01:31	conditions in our world . If a character is in
01:34	a desert kingdom , a potion could work differently than
01:36	it would on a character in an icy cavern .
01:39	And there are four major transformations in this world types
01:42	of substitution and elimination reactions . If you need more
01:45	of a refresher rewatch , episodes 20 through 22 in
01:48	both SN one and the one mechanisms a carbo ,
01:51	cattle and intermediate forms in the SN one substitution reaction
01:54	, the nuclear file can attack the carbo Catalan from
01:57	either side . So we get a mixture of stereo
01:59	I summers at a Cairo carbon . And in the
02:01	one elimination reaction , the nuclear file acts as a
02:04	base deep resonating the substrate . And we get an
02:06	al keen . On the other hand , both S
02:08	. And two and E . Two mechanisms happen in
02:10	one single step in the S . And two substitution
02:13	reaction . The nuclear files backside attack on the substrate
02:16	. Inverts the stereo chemistry at a Cairo carbon .
02:18	And in the E . Two elimination reaction we need
02:21	an anti perry planer leaving group and beta hydrogen for
02:24	the nuclear file to D protein eight the substrate creating
02:27	an alkaline . Okay , let's look at how different
02:29	potions or nuclear files transform our characters or substrates .
02:34	We'll start with the smallest character class metals since they
02:37	only have one carbon , there are no beta hydrogen
02:40	. So they can't do an E . To transformation
02:43	. They also can't form stable carbo cat ions ,
02:45	which means they're resistant to any SN one and E
02:48	one reactions that leaves us with only one option .
02:51	Metal substrates only do S and two reactions no matter
02:53	what nuclear file they encounter . And in fact with
02:57	poor nuclear files , metal substrates either don't do anything
03:00	or react so slowly . That is just not worth
03:03	it . I mean come on , we need to
03:04	take our a potion and get on with this adventure
03:07	. Let's take a look at a specific metal substrate
03:09	Roma , methane and its reaction with three different nuclear
03:12	files in each case are starting character is transformed by
03:15	an SN two reaction . There's only one carbon .
03:18	So there's only one place each nuclear file can go
03:20	. And one option for our characters . Final form
03:23	the reaction product easy . Next let's look at primary
03:26	sub streets . These characters have more carbons than metal
03:29	substrates , but the leaving group is at the end
03:31	of the chain . So primary substrates also don't form
03:34	very stable cargo cat ions , which rules out S
03:37	and one and E one reactions . And if they
03:39	encounter a poor nuclear file , not much will happen
03:42	. Mostly . We CSN to substitution reactions . For
03:45	example , there's the Williamson it verification named after its
03:49	discoverer , english chemist alexander William Williamson . Our character
03:52	here is a primary alcohol . Hey lied and our
03:55	potion is a strongly nuclear filic Alcock side . After
03:58	an sN two transformation , our hero becomes an ether
04:01	. But primary substrates can also undergo E two elimination
04:04	reactions when there's a certain type of potion or nuclear
04:07	file , specifically when primary substrates encounter a strong ,
04:11	bulky base . Starik hindrance makes it tricky for the
04:14	big base to displace the leaving group with a backside
04:17	attack so it just grabs one of the beta hydrogen
04:19	is and runs that's elimination . Not substitution . Now
04:23	. Primary substrates also have some special sub classes primary
04:27	Elik and primary bons Ilic substrates . These substrates have
04:30	double bonds or bending rings that stabilize carbo cat ions
04:33	by resonance . Also , polar protest conditions slow down
04:36	the effects of our nuclear file potions so the nuclear
04:39	file doesn't attack immediately . There's time for a carb
04:42	acadian to form and we'll get sN one reactions .
04:45	For example , here's a reaction with the primary Ben's
04:47	Ilic substrate that forms of ether . We can see
04:50	that hydrochloric acid is a product which is another hint
04:53	that we have an SN one reaction . Remember from
04:55	episode 21 when we see an acid as a reaction
04:58	or product than SN one . If we increase the
05:01	strength of our nuclear file or switch from a more
05:03	sluggish polar product environment to an A product . Won
05:06	the special substrates act like other primary substrates in favour
05:10	sN two reactions . Time for some secondary characters and
05:13	no , I don't mean sidekicks . Secondary substrates include
05:16	some of the most important potions and reaction conditions to
05:19	learn because they have the most competing mechanisms . Secondary
05:22	substrates have all the traits of less bulky character classes
05:25	that allow for SN . Two and E . Two
05:27	reactions , but they also have some branching , which
05:29	means more stable carbon cat ions and that S .
05:32	N . One and E . One reactions are possible
05:34	to to start . Let's look at an SN one
05:36	transformation example with a secondary substrate and acetic acid as
05:39	our nuclear file that hint from episode 21 about acids
05:43	and SN one applies again and these are polar protest
05:46	conditions that slow down our nuclear files and give carbo
05:49	Catalans time to form in SN one reactions . The
05:51	nuclear file can attack either face of the carbo cat
05:54	eye on . So if our substrate had a Cairo
05:56	carbon and in this case it has to . The
05:58	stereo chemistry gets scrambled here . We get a mixture
06:01	of dietary MERS as products . Remember from episode nine
06:05	, these can occur when a compound has more than
06:07	one Kyrill center and as a result his stereo it
06:09	simmers that aren't mirror images of each other . The
06:12	non reacting carol center from the starting materials keeps its
06:15	configuration in both products but the reacting carol center ends
06:18	up our and one diets terry , Moran S and
06:20	the other . But here's why we have to be
06:22	so careful when our secondary character drink this potion ,
06:25	we're not guaranteed in S . And one transformation substitution
06:29	and elimination can compete once a carbo caddy informs the
06:33	nuclear file can D . Protein eight , our substrate
06:35	. So some anyone products get formed to Now ,
06:38	let's look at an S . And two transformation with
06:40	our top isolated alcohol as our substrate . In a
06:42	weekly basic nuclear file , D . M . S
06:44	. O . As the Sullivan gives us polar .
06:46	A product conditions which tends to give the nuclear file
06:49	a bit of a boost . In other words ,
06:51	polar a product condition strengthen our potions so even a
06:54	weak nuclear file can attack our substrate , favoring an
06:57	SN two reaction and inverted stereo chemistry in the product
07:01	. Now , if a secondary substrate encounters a strongly
07:03	basic nuclear file , we tend to see E .
07:06	Two reactions . Like I said . Lots of computing
07:09	mechanisms with this character class , stronger bases are very
07:12	reactive and quickly steal a beta hydrogen so long as
07:15	it's ante peri platter to the leaving group . Of
07:17	course , this Newman projection reminds us why we get
07:20	the alkaline as our final form . It has to
07:22	do with the anti Perry planner hydrogen and leaving group
07:25	rotating around the carbon carbon bond . Pop back to
07:28	episode 22 If you need a refresher . This example
07:30	shows another way that the surrounding reaction conditions affect how
07:34	our nuclear file potions work . Notice this reaction was
07:37	heated . Maybe this part of the game is in
07:39	a desert and he favors elimination reactions . To understand
07:43	why this is true , we have to remember our
07:44	gibbs free energy equation from episode 15 delta G equals
07:48	delta H minus T . Times delta S increasing the
07:52	temperature . Makes the entropy factor more significant , which
07:54	means we end up with a more negative delta G
07:57	. So with higher heat , a reaction that increases
08:00	entropy is more likely to happen spontaneously . Elimination reactions
08:04	create more entropy than substitution reactions because they give us
08:07	a greater number of products we get a whole extra
08:10	molecule by comparison because the base runs off with a
08:12	beta hydrogen . Now it's time for tertiary substrates are
08:15	final class of characters . With all their branches tertiary
08:18	substrates are really good at forming stable carbo cat ions
08:21	. So S and one in the one reactions are
08:23	possible with weak nuclear files being the bulky ist character
08:27	class means that tertiary substrates have a lot of Starik
08:29	hindrance to and can't undergo . S . And two
08:32	reactions . Nuclear files can get close enough to attack
08:35	the electro filic carbon from behind . So our only
08:38	all at once reaction choice is e to elimination substitution
08:41	and elimination reactions compete . So we have to pay
08:44	close attention to the nuclear files that favor one transformation
08:47	over the other . For example , here are some
08:49	tertiary substrates in two different reactions hydrochloric acid or water
08:54	, bromine and water are good nuclear files but poor
08:57	basis . So they're not so great at grabbing protons
08:59	. That means they favor substitution over elimination and are
09:02	only substitution option is S . N . One to
09:05	encourage elimination over substitution . We can pick a different
09:08	reactant sulfuric acid , which forms the conjugate base by
09:12	sulfate and ion when it loses a proton . Remember
09:15	from episode 22 A by sulfate ion is a poor
09:18	nuclear file , but it can act as a base
09:21	. That means it's better at grabbing a proton and
09:23	E one elimination is favored with our tertiary and Ben's
09:26	Ilic substrate . Now let's check out an example of
09:29	an E . Two elimination reaction . The key here
09:32	is the strong base which usually gives us E2 when
09:35	tertiary or secondary substrates transformed through elimination . Usually the
09:40	major product that forms is the most substituted alkaline .
09:43	That's site's rule , which can be really helpful when
09:45	predicting our characters final forms . In fact , we
09:48	can see it in action here with a tertiary sub
09:51	street and a sodium athoc side potion . However ,
09:54	site's rule has an exception with a special type of
09:56	potion . A nuclear file . That's a very bulky
10:00	base . For example , the bulk of sodium turpitude
10:02	oxide gets in the way to form the sites of
10:05	product . This nuclear file would need to grab a
10:07	proton from beta carbon . But as the oxygen from
10:10	the turkey to oxide ion gets closer , there's a
10:12	Sterrett clash , causing lots of repulsion which slows the
10:15	reaction down . Instead , the turkey talk side eye
10:18	on just grabs the proton from our less substituted beta
10:21	carbon , reducing the clash , speeding up the reaction
10:24	informing the less substituted non sites . F product substitution
10:28	and elimination reactions can be really tough . Trust me
10:32	, I've been there . So here's a table to
10:34	organize what we've learned , remember that . It will
10:37	take more than memorization to solve these puzzles really imagine
10:41	or game world the substrate characters and how the nuclear
10:44	file potions might transform them . And of course practice
10:48	helps . So it's time for some rapid fire problems
10:50	. We're going to put four problems on screen that
10:53	could be S . And one S . N .
10:54	Two , E . One or E . Two and
10:56	predict the likely mechanism and the products . Then we'll
11:00	work through the answers . So pause right after the
11:02	question . If you want to solve them yourself ,
11:05	Player one , are you ready to start this game
11:07	? Here's problem number one , we have a secondary
11:11	Ben's Alex substrate with methane style as our nuclear file
11:14	. Looking at the table negatively charged sulfur groups are
11:17	weak basis . So we might expect SN two .
11:21	But here we have a file and since the sulfur
11:24	is pro donated in S . H . Group ,
11:26	we have acidic or neutral conditions . Using our handy
11:29	hint remember acidic conditions favor SN one because we have
11:33	a Cairo center . We also get a mixture of
11:35	an anti hammers . And don't forget that pesky minor
11:38	product by E . One . Here's problem number two
11:42	. This time the substrate is secondary again , but
11:45	the nuclear file is in a civilized and I on
11:47	a satellite and ions are strong nuclear files and super
11:51	strong bases . Which means this reaction strongly favors elimination
11:55	, specifically E . Two . And there's a mixture
11:57	of products following sites . This rule we would expect
12:01	Beauty queen as the major product since it's more substituted
12:04	. Then looking at that major product we expect more
12:06	trans insists because that's the form where we get the
12:09	most energetically stable arrangement when the metal groups are spaced
12:12	as far apart as possible . Here's problem number three
12:17	, we have another secondary substrate with methanol , a
12:20	poor nuclear file . We also have polar proto conditions
12:23	. Looking at our reactant , we expect to see
12:26	HBR as a product which is acidic . So using
12:29	that handy hint , we think we're dealing with S
12:31	. N . One . But there's something else to
12:34	consider . The intermediate is a secondary carbo Catalan ,
12:37	which is less stable than a tertiary carbo catalon .
12:40	And if a less stable carbo Catalan can get more
12:42	stable through the migration of a C . H bond
12:45	than a rearrangement can occur . We've got to look
12:48	out for these tricks . This migration is called a
12:50	hydride shift . So we actually end up with a
12:52	tertiary carbo catalon and this substitution product . And lastly
12:56	, here's problem number four . Here we have one
13:00	more secondary sub street and sodium acetate , which is
13:03	a weak nuclear file . This is a nice simple
13:06	setup , and it reacts easily by the SN two
13:09	mechanism . That's it for this episode . Next time
13:11	we're going to be looking more at alcohols ethers and
13:14	up oxides . Until then , Thanks for watching this
13:16	episode of Crash Course Organic Chemistry . If you want
13:19	to help keep all crash Course free for everybody forever
13:22	, you can join our community on Patreon . Yeah
00:0-1	.

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