Stereochemistry: Crash Course Organic Chemistry #8 - Free Educational videos for Students in K-12

Stereochemistry: Crash Course Organic Chemistry #8 - 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 Debbie Chakravarty and welcome back to
00:09	Crash Course Organic Chemistry in 1990 . While trying to
00:13	detect life on MArs the american engineer . Dr Gilbert
00:16	Levin wondered if martian life would eat the same food
00:19	as life on earth . So in the samples he
00:21	sent to MArs on the viking lander , he included
00:24	some D glucose , a right handed sugar that most
00:27	life on earth uses for energy . But he also
00:29	sends some of the left handed version of that compound
00:32	, L glucose in case Martians preferred the opposite food
00:35	by the way . Because the aipac nomenclature for right
00:38	handed and left handed glucose is really a mouthful .
00:41	We're going to just use their common names here .
00:43	When Dr Levin was getting his samples ready , he
00:46	found that the taste of L glucose was the same
00:48	as D glucose and he found that humans can't digest
00:52	glucose because our enzymes don't recognize it . If we
00:55	can't digest al glucose , that means it won't be
00:57	converted into energy or stored as fat . So theoretically
01:01	we could eat as much of the sweet molecule as
01:04	we wanted . Dr Levin thought he stumbled upon a
01:06	sweet surprise that was better than any sugar substitute that
01:09	already existed with the less artificial taste . But it
01:13	turns out that it's just tooting expensive to make L
01:15	glucose . So this sugar substitute unfortunately never made it
01:19	to market . The story reinforces what we've been saying
01:21	about how structure affects what chemicals can do . The
01:24	right handed version of glucose provides energy while the left
01:27	handed version gets ignored by your bodies , it's all
01:30	because of tiny geometric differences and specifically stereo chemistry .
01:36	Mhm . Mhm . Yeah . Yeah . Biology ,
01:47	chemistry and biochemistry have all established that the shape of
01:50	molecules is important to life as we know it .
01:53	And in this series we've learned the term is summer
01:56	to describe molecules that have the same parts as each
01:58	other with small differences to constitutionalism . Others have the
02:02	same molecular formula , but the atoms are connected in
02:05	different ways . And the geometric I summers we've talked
02:08	about our in molecules with double bonds because the attached
02:11	groups can be arranged differently around the bond . If
02:14	they're on the same side , we call it .
02:16	This is a summer or if they're on the opposite
02:18	sides , it's the transit summer . A geometric I
02:21	summer is just one kind of stereo is summer stereo
02:24	is numbers have the same atoms connected in the same
02:26	bond but they differ in the spatial relationships between those
02:30	atoms . Something that isn't a stereo . I Summer
02:32	is two identical pairs of sunglasses . I can set
02:35	them across from each other so they're mirror images .
02:38	Then I can pick up one pair and turn it
02:40	around so they would melt into each other . If
02:42	they could , that means they're super imposible and have
02:45	the same spatial relationship . If I took out one
02:48	lens on each pair , they're still mirror images .
02:51	But no matter how I flip them around , the
02:54	dark lenses won't line up so they're non super imposible
02:57	mirror images . You don't even need cheap sunglasses to
03:00	see this . Let's take a look at our hands
03:02	. If my palms are facing each other , I
03:04	can line them up so the thumb and the pinky
03:06	meat . So they're mirror images . But if I
03:09	placed one on top of the other , they won't
03:12	perfectly line up . So they're non super imposible .
03:15	In chemistry , we say that anything with the non
03:17	super imposible mirror image has chirality . The simplest example
03:20	of chirality is a carbon with four different groups attached
03:24	to it . This kind of central carbon goes by
03:26	many names but we'll call it the Cairo center or
03:29	chirality center . We can check whether this whole molecule
03:32	is Cairo by building it and doing the same test
03:34	we did with our hands or those half sunglasses first
03:37	will draw the molecules mirror image . We can see
03:40	that the reflection can't be superimposed on the original molecule
03:43	no matter how you turn them , the four different
03:45	groups will never line up . These two molecules are
03:48	a pair of non super impossible mirror images . And
03:51	because that phrase is kind of a mouthful , we'll
03:53	call a pair of these Cairo molecules and nan tumors
03:57	and Antonio is from the greek for opposite because they're
03:59	opposite images by now you've probably noticed that we do
04:02	a lot of drawing in organic chemistry so surprise .
04:06	We'll need to drop pairs of an anti commerce to
04:08	for example , in the molecule beaten tool carbon to
04:11	is a carol center , it has a metal group
04:13	and ethyl group , an alcohol group and a hydrogen
04:16	atom . Four different groups attached to one carbon .
04:18	Like our model from a second ago . To draw
04:20	the an anti armor , we have to start by
04:22	drawing a line to represent our mirror . Next we'll
04:25	draw the reflection of the group that's closest to the
04:27	mirror . In this case the hydrogen atom . Then
04:30	we'll continue building the molecule and draw the metal group
04:33	, the alcohol group and the ethyl group . When
04:36	all of the items are there were done , another
04:38	way to draw a mirror image is to place the
04:40	mirror behind the molecule . So the solid wedges become
04:43	dashed wedges and the dashes become solid . Remember that
04:47	solid wedges mean things are coming out towards us and
04:50	dashes are pointing away from us to practice this kind
04:53	of drawing , let's look at a common asthma medication
04:56	. Albuterol , even though it looks like a pretty
04:57	complicated molecule . Albuterol only has one carbon surrounded by
05:02	four different groups . We'll highlight this carla center with
05:05	a red dot , just so we're on the same
05:06	page , so if we place the mirror behind albuterol
05:10	and draw , it's an anti armor , we only
05:12	need to make one . Change the solid wedge connecting
05:14	to the alcohol group needs to become dash . Now
05:17	, when we draw an anti Mursi , it's also
05:19	important that we give each structure a name that communicates
05:21	which one it is after all . One in the
05:24	anti more albuterol is an asthma medication , but the
05:27	other might have a different effect or do nothing at
05:30	all . To name an anti immerse , we adopt
05:32	the con angled prelaw convention where the Cairo centers of
05:35	a molecule are labeled , are for right handed and
05:38	s for left handed . Like all puzzles in organic
05:41	chemistry , we have rules we can follow , and
05:43	a pattern we can learn . This convention says that
05:45	the first step is assigning priority to the four groups
05:48	around a Cairo carbon . And just to make it
05:51	fun and nancy more priority is slightly different than functional
05:54	groups or substitution priority . When we name molecules .
05:57	To figure out priority for an anti summers , we
06:00	have to pay attention to the atomic number of different
06:03	atoms . For example , let's go back to butte
06:05	. And to all the Cairo center has a metal
06:07	group and ethyl group , an alcohol group and a
06:10	hydrogen atom attached to it . The lowest priority group
06:13	has the lowest atomic number . It's almost always a
06:16	hydrogen atom because their atomic number is one . So
06:19	here the hydrogen atom has lowest priority , and we'll
06:23	label that as four . When assigning the Cairo center
06:25	, we have to make sure the lowest priority group
06:28	is pointing away from us because that's the rule for
06:31	consistency . Otherwise the naming will get messed up .
06:33	The hydrogen is pointing away from us because there's a
06:36	dashed wedge easy . Next . The highest priority group
06:39	has the element with the highest atomic number . In
06:42	this case the alcohol group has the highest priority because
06:45	oxygen is atomic number is eight . So let's label
06:48	that as one . Then we have to prioritize the
06:50	middle groups , the metal and the ethel to do
06:54	this . We'll look at the atoms attached to the
06:55	first carbons away from the Cairo center . The metal
06:58	carbon has three hydrogen is attached to it . So
07:01	the highest atomic number is one . The ethyl carbon
07:04	has two hydrogen and another metal group attached . So
07:08	it has a carbon which has an atomic number of
07:10	six . So congratulations ethel carbon . Your higher priority
07:14	when it comes to priority will give the methyl group
07:16	of three and the ethyl group a two for both
07:18	. An anti immerse . The priority numbering will be
07:21	the same from highest to lowest . It's the alcohol
07:24	group , the ethyl group , the methyl group and
07:26	the hydrogen atom . Now we have to decide which
07:28	one is our or right handed and which one is
07:31	S . Or left handed . To do that .
07:33	Let's draw an arrow around both molecules from highest priority
07:37	. One to lowest priority or four on one .
07:39	An anti armor . The arrow points in a clockwise
07:42	arc , which means it's the are an anti armor
07:44	. So the molecule is to our Butin tool on
07:47	the other , we have a counter clockwise arc .
07:50	So it's the S and anti armor and we call
07:52	it to S . Butin tool . If you have
07:54	a three D . Molecule set on hand , you
07:55	can figure out an anti armor names in three D
07:58	. If you want , just hold on to the
07:59	lowest priority group . In this case the hydrogen like
08:02	you're admiring a sunflower and the hydrogen is the stem
08:05	. Then you can twist the molecule from highest to
08:08	lowest priority . If you're twisting it right , it's
08:10	the are an anti armor , and if you're twisting
08:12	it left its the S . And anti armor ,
08:14	like all things are go the only way to get
08:15	better at assigning chirality is practice . So let's assign
08:19	R . And S to the albuterol . An anti
08:21	commerce to one group bonded to the Cairo center is
08:24	an alcohol group with a solid wedge , so it's
08:26	coming out towards us . The other two groups around
08:29	the Cairo center are in the same plane , so
08:31	the fourth group is an implied hydrogen atom pointing away
08:34	from us . If it helps , we can always
08:36	draw that hydrogen ourselves with the dashed wedge , now
08:39	that we have our four groups , we can assign
08:41	priority to them . The hydrogen is the lowest priority
08:44	again , and it's pointing away from us . So
08:46	we're good . We can label it with the four
08:48	, and again , we have an alcohol group ,
08:50	and oxygen's atomic number is eight . So that's the
08:53	highest priority . And we can label it with a
08:55	one to assign the middle priorities will look one step
08:58	away from the Cairo center , the carbon to the
09:01	left of the Cairo center is bonded to two carbons
09:04	, and the carbon to the right of the Cairo
09:06	center is bonded to two hydrogen and a nitrogen .
09:09	Because nitrogen has an atomic number of seven compared to
09:12	carbon six . The right group wins priority . Sorry
09:15	, carbon . So we'll label the winter two and
09:17	the loser three . If we draw the arc again
09:20	or imagine spending a three D molecule , we can
09:22	see that it goes clockwise . So this molecule is
09:25	the are an anti armor or our albuterol . So
09:28	the other one is S albuterol . But if we
09:31	label it's groups with priority and draw the arc ,
09:34	it's not counterclockwise . Like the S and anti armor
09:36	should be . You know how I keep saying that
09:38	we want the lowest priority group pointing away from us
09:42	. It's for this exact situation . Let's draw in
09:44	the fourth group again , which is the hydrogen with
09:46	a solid wedge . The hydrogen atom is coming out
09:49	of the page at us . So we need to
09:52	redraw the molecule with the hydrogen pointing away from us
09:55	. To make our an anti armor naming rules work
09:57	. Imagine grabbing that hydrogen bond like flower stem ,
10:00	the art goes counter clockwise , and the naming makes
10:04	sense . Sometimes we're faced with an even more brain
10:06	bending molecule where the lowest priority group is in the
10:09	same plane as the Cairo center . So a quick
10:12	trick is to invert the hydrogen with whatever is pointing
10:14	back away from us and label it inverted . To
10:18	remember that we did this flip next . We can
10:20	use our toolkit to assign R . Or S to
10:22	the Cairo center of the inverted structure . In this
10:25	case it's an R . But then we need to
10:27	switch the inverted structure back . So the original carol
10:30	center is an S . So I don't know .
10:32	But maybe you're thinking Deb okay , this is too
10:35	easy . Please show me something a little more complicated
10:39	. Well , let me introduce you to cyclic compounds
10:42	and one more thing to think about when it comes
10:44	to chirality . For example , metal cyclo Penton has
10:47	super impossible mirror images . So we say that it's
10:50	a Cairo even though one has a metal group pointing
10:53	away from us and one has a metal group pointing
10:56	towards us . We can overlap the mirror images and
10:59	get the same arrangement of atoms . This dotted blue
11:02	line is like a mirror within the molecule , which
11:05	we call an internal plane of symmetry . Any molecule
11:08	with an internal plane of symmetry is a Cairo and
11:11	doesn't have an anti hammers , but a molecule like
11:13	three metal cyclo pentagon in doesn't have an internal plane
11:17	of symmetry . So it is Cairo . The mirror
11:20	image is different and we can't overlap them to get
11:22	the same arrangements of bonds and atoms to name these
11:25	in the anti immerse , we just need to assign
11:27	priority around the Cairo center . Again , we're basically
11:30	pros at this now . So we got this .
11:32	The double bonded carbon in the ring is highest priority
11:35	. Because it's like being bonded to two carbons .
11:37	The CH two in the ring is next because it's
11:39	bonded to two hydrogen and one carbon . The metal
11:42	group is third because it's bonded to three low priority
11:44	hydrogen and the invisible hydrogen is last like always .
11:49	That's just the way it is hydrogen . Using these
11:51	priorities , we can name three r three methyl cyclo
11:54	pent , one en and three S three methyl cyclo
11:57	pen 20 . Okay , so up until this point
11:59	we've been dealing with molecules with one Cairo center ,
12:02	but there are some molecules with to Cairo centers that
12:05	have an anti immerse to for example , look at
12:07	three , our four s four bromo hexham three ole
12:10	. We use numbered carbons to specify which Cairo center
12:13	is are and which carol center is S after doing
12:16	the whole assigning priority two groups thing . But some
12:19	molecules with two carl centers are actually a Cairo ,
12:22	which we can tell with two checks . First ,
12:25	is there a super imposible mirror image and second is
12:29	there an internal plane of symmetry ? Let's consider assists
12:32	in trans One to die brahma cyclo hexane . Both
12:35	molecules have to Cairo centers which we've marked with red
12:38	dots . Just look at them trans One to die
12:41	brahma cyclo hexane is Cairo with non super impossible mirror
12:45	images . But this one to die brahma cyclo hexane
12:48	is a Cairo . And since we've covered so much
12:51	so quickly , here's a handy flow chart to help
12:53	you with your chirality , gut checks by following these
12:56	steps . It can help you tell whether a molecule
12:58	has an anti rumors or not . Okay , time
13:00	for some rapid fire problems using that handy dandy flow
13:03	chart . If you want decided the following examples or
13:06	Cairo or a Cairo . We're going to put for
13:09	examples on screen and then tell you the answers and
13:12	you can pause this if you want to take a
13:13	second to solve them yourself . Ready . The first
13:16	problem is Cairo . See the red mark . Carbon
13:22	has four different groups . The second problem is a
13:28	Cairo , his Cairo centers , but it also has
13:31	an internal plane of symmetry . The third problem is
13:36	Cairo . It has to Cairo centers but no internal
13:40	plane of symmetry . And the last problem is also
13:46	Cairo . It just has one Cairo center which we
13:49	marked with the red dots stereo chemistry is a really
13:51	important part of our organic chemistry toolbox and even just
13:55	eight episodes in . We've got a lot of tools
13:57	for understanding all the exciting and weird and fascinating reactions
14:01	to come in this episode , we learned about how
14:03	to name Cairo centers are or S and how to
14:06	determine if molecule is Cairo or a Cairo . Next
14:10	time we'll look more closely at the properties of any
14:12	anti Emerse how they interact with light and how to
14:15	separate them so that the drugs with dr Jekyll and
14:17	mr Hyde personalities don't harm us . Thanks for watching
14:20	this episode of Crash course Organic Chemistry . If you
14:23	want to help keep all crash course free for everybody
14:26	forever , you can join our community on Patreon .
14:31	Yeah .

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