More Stereochemical Relationships: Crash Course Organic Chemistry #9 - Free Educational videos for Students in K-12

More Stereochemical Relationships: Crash Course Organic Chemistry #9 - 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
00:08	to Crash course Organic Chemistry In episode eight , we
00:11	discovered that some molecules had non super imposible mirror images
00:15	called indian tumors and tumors have almost all of the
00:18	same chemical and physical properties , like the same melting
00:21	and boiling points , so it's tough to separate them
00:24	, but they interact differently in Cairo environments , like
00:27	how the receptors in our nose and on our tongues
00:30	are pretty sensitive to carl molecules to an anti MERS
00:33	might have very different smells and tastes . For instance
00:37	, there's our Carbone and s Carbone also known by
00:40	the mouthful of an Aipac name to metal five prop
00:44	one and two . Well psycho hex two and one
00:47	on . So I'm gonna stick with Carbone to .
00:49	Most people are Carbone smells and tastes like experiment while
00:53	s Carbone smells and tastes like carraway , those earthy
00:56	tasting seeds that get sprinkled on top of rye bread
00:59	. Now I don't know about you , but I
01:00	don't want to go around chemistry lab tasting and smelling
01:03	random chemicals to figure out what they are . It
01:06	sounds kind of dangerous . So organic chemists can tell
01:09	a nancy . Meyers apart in other ways like using
01:12	light . Yeah , yeah . The light that surrounds
01:25	us is generally moving well , actually vibrating in all
01:28	directions , but a slotted disc or lens can filter
01:32	out some of it to leave behind light that's vibrating
01:34	in one direction called plane polarized light . Polarized sunglasses
01:38	, for example , are designed to filter out the
01:40	sunlight reflected off of horizontal services like lakes , roadways
01:44	or even the hood of a car . These surfaces
01:47	organize some of the scattered light that hits them so
01:49	it gets aligned with the flat surface when it bounces
01:51	towards us . Basically , some horizontal plane polarized light
01:55	gets reflected into our eyes . Polarized sunglass lenses have
01:59	a special coating of molecules that line up to block
02:02	a lot of this horizontal light so there's less glare
02:04	from horizontal light reflecting off flat surfaces , but other
02:08	light can pass through . And if we hold to
02:11	polarized sunglass lenses perpendicular to each other , the lenses
02:14	appear to get very dark because we're blocking both horizontal
02:17	and vertical light . By the way , this trip
02:18	is not going to work with any plain old sunglasses
02:20	you might have because non polarized lenses just generically filter
02:24	out some light . But to bring this all back
02:26	to an anti MERS , carol molecules also have cool
02:29	interactions with plane polarized light . A single and anti
02:32	armor of the Cairo molecule can rotate it left or
02:35	right . And using an instrument called a Polaroid emitter
02:38	. We can measure a molecule's ability to turn light
02:40	. A polaroid meter has a light source and several
02:43	played polarizing filters . There's also a rotate herbal one
02:47	called in analyzing filter , which is attached to a
02:50	protractor . To help us measure the angle of light
02:52	. A solution of an antimatter is placed inside a
02:55	sample chamber , which is sandwiched between the polarizing filters
02:58	and the analyzing filter . We can turn the analyzing
03:01	filter and observe how the light changes until we reach
03:04	a point where the most light possible is getting through
03:07	, which will probably involve some twisting back and forth
03:10	. Then we read the angle on the protractor to
03:12	see how much and in what direction the molecule rotated
03:15	the light from the source . Like I mentioned ,
03:17	an anti murders of Carole molecules can rotate the plane
03:19	polarized light either left or right . It's a physical
03:22	property of the molecule like boiling point and melting point
03:26	molecules that turn the light toward the left are called
03:28	love derogatory and are given the simple L . Or
03:31	minus molecules that turn the light to the right are
03:33	called dextre rhoda Torrey and are labeled D or plus
03:37	. We saw this nomenclature with L and D glucose
03:40	in episode eight because the amount that the light gets
03:43	rotated depends on things like the amount of carol molecules
03:46	we have and properties of our poll . A remote
03:48	er we can calculate the specific rotation of a molecule
03:51	using a fairly simple equation Alpha observed is the reading
03:55	from the protractor on the analyzing filter . C is
03:58	the sample concentration and L . Is a property called
04:00	the path length of the polarization . Er This gives
04:03	the specific rotation which is dependent on the wavelength of
04:05	the light and temperature at which the experiment was performed
04:08	. The tricky part is there's no easy rule to
04:11	guess whether an R n N . T . M
04:12	. R . Or an S . And M .
04:13	T . M . R . Will be lever Rhoda
04:15	Torrey or dextrose auditory polar imagery is an experimentally determined
04:19	property , which means we have to stick in the
04:21	end . Tremors in a polaroid meter to see how
04:23	they rotate light . No shortcuts . Sorry , for
04:26	example , it was experimentally found that the S .
04:29	And anti more of Carbone rotates plane polarized light to
04:32	the right . To indicate that in its name we
04:35	can add A plus S . Plus Carbone . The
04:37	R . And anti more was found to rotate plane
04:39	polarized light to the left , so it's R minus
04:42	Carbone . So I guess there's one tiny shortcut here
04:45	opposite in anti mars will turn plane polarized light in
04:48	the same amount in opposite directions . When we only
04:51	have one in anti murder in the sample chamber of
04:53	a polaroid meter , it's called an optically pure sample
04:56	, the light will rotate one way by a certain
04:58	experimentally determined amount . But if we mix an equal
05:01	amount of S plus Carbone and ar minus Carbone in
05:04	the sample chamber , we have a systemic mixture .
05:07	The light rotations cancel each other out , so we'd
05:09	observe no change in the angle of plane polarized light
05:12	. Sometimes chemical reactions make more of one an anti
05:15	more than another . So when that happens we can
05:18	use the known rotation of an optically pure sample and
05:21	the observed rotation of whatever mixture we have to find
05:24	the an anti american excess . This tells us the
05:27	percentage of each an anti armor in the mixture ,
05:29	knowing what products we have is important because a set
05:32	of an anti MERS can have really different properties in
05:35	Cairo environments , like a chemical reaction or as medicines
05:38	in our bodies . One could be helpful while another
05:42	could be deadly . Polar imagery can help keep us
05:44	safe and informed Not only that , but polar imagery
05:47	is actually how we discovered stereo chemistry and an anti
05:50	immersed in the first place . With a little help
05:52	from wine . Let's go to the thought bubble .
05:55	Sometimes you might open a bottle of wine and find
05:57	some crystals that grow on the cork or settled at
06:00	the bottom . These crystals , or salts derived from
06:03	tart eric acid , which is commonly found in grapes
06:05	. As early as 18 32 we knew that rhetoric
06:08	acid salts could rotate plane polarized light . However ,
06:11	in 18 38 there were reports of a tart uric
06:14	acid solution derived from the commercial production of the chemical
06:17	that didn't rotate plane polarized light . These reports reached
06:20	the desk of a young french biologist named louis Pasteur
06:24	. Yes , that louis Pasteur who became known for
06:26	pasteurization bacteria and other pivotal scientific ideas . The idea
06:31	that presumably similar solutions of torturing acid salts both could
06:35	and couldn't rotate plane polarized light was very bothersome to
06:39	young louis . So he got some of the powder
06:41	tart uric acid with no optical activity . And you
06:44	said about growing crystals by letting the solvent slowly evaporate
06:48	like growing rock candy on a string from a super
06:51	concentrated solution of sugar and water . Then using a
06:54	microscope pasture noticed that the salt crystals grew into different
06:57	shapes to be clear . A visible difference in an
07:00	anti more crystals is rare . It was mostly luck
07:03	that he was studying torts eric acid . He separated
07:05	the two different crystals using just a tweezer made solutions
07:08	out of both types and found that the two solutions
07:11	rotated plane polarized light in equal but opposite directions .
07:15	This was the first description of an isolated set of
07:18	an anti murders and this event is often considered the
07:20	start of the study of stereo chemistry . Thanks thought
07:23	bubble . Fresh off our history lesson , it might
07:26	be helpful to revisit all the summers we've encountered so
07:28	far . The first thing to remember is that this
07:30	summer's all have the same molecular formula . In episode
07:33	six , we met confirmation ally Summers . When we
07:36	looked at newman projections , one molecule can have many
07:39	of these I summers because they only differ in how
07:41	the groups are arranged as we rotate around sigma bonds
07:45	, constitutionalism . Others have different connections between the same
07:48	number and type of atoms and stereo . It simmers
07:50	have atoms connected in the same order , but different
07:53	spatial relationships between them stereo . Its members that have
07:56	non super imposible mirror images like S Carbone and our
08:00	Carbone are in anti members . We also have miso
08:03	compounds which are sort of in the same family of
08:05	molecules . They have two or more Cairo centers but
08:08	aren't kyra molecules because they have an internal plane of
08:11	symmetry . We'll talk more about these in a minute
08:14	. Finally , we have stereo customers that are not
08:16	mere images at all , which are called diastolic murmurs
08:19	. We also know geometric I summers like the cysts
08:22	in transit summers around a double bond . These can
08:25	technically be classified as diarrhea MERS , but we organic
08:29	chemists more commonly referred to them as geometric I summers
08:32	. Die astronomers can also be configuration al dia streamers
08:35	which have the same adam layout , but a different
08:38	three D . Space arrangement in a pair of dice
08:40	hysteria , MERS , one or more of the Cairo
08:42	centers will be the same , but some Cairo centers
08:45	have to be different , for example , to configuration
08:48	. I'll die astronomers are two R four s ,
08:50	four promo Penton to all and to S for S
08:53	. For Roma Penton to all with all these different
08:55	kinds of ice hammers , it might look almost impossible
08:58	to look at a molecule and figure out the maximum
09:00	number of customers that can have . But thankfully ,
09:02	organic chemists have done centuries of hard work so we
09:05	can sit back and use a simple formula . And
09:08	since we have wine on the mind , lets you
09:10	start eric acid as our example . First we need
09:13	to count the number of Cairo centers in our compound
09:15	, which I'll just call end for now tart eric
09:17	acid or 23 Die hydroxy butane . Die OIC acid
09:21	has two stereo centers . So in Tartu uric acid
09:25	and equals two . Then we can use the formula
09:27	two to the power of end . To calculate the
09:29	maximum number of stereo I summers two to the power
09:32	of two is four . So tart eric acid should
09:34	have four isobars max . Let's draw them . I
09:37	think it's easiest to start with the hydrogen atoms pointing
09:40	away from me . So I'm already following the convention
09:43	that the lowest priority group is pointing away and I
09:46	don't have to do too much extra work . So
09:48	let's start with this summer and assigned the stereo chemistry
09:50	of these two Kyrill centers . First of all ,
09:52	this carbon is directly bonded to the oxygen atom of
09:55	this alcohol , which has an atomic number of eight
09:58	. The other two groups are carbons within atomic number
10:01	of six . So the alcohol is clearly the highest
10:04	priority . Now , we need to choose the higher
10:06	priority of the other two groups . Remember to think
10:09	of the car back silic acid carbon as being bonded
10:11	to three oxygen atoms , which each have an atomic
10:14	number of eight . So the car back silic acid
10:16	has higher priority over the other carbon that's bonded to
10:19	only one oxygen atom and a lowly hydrogen atom with
10:22	an atomic number of one . When we draw our
10:24	arc it points counterclockwise . So we know this carol
10:27	center is S . Now let's move over to the
10:30	other carl carbon from highest to lowest . We have
10:33	the oxygen of the alcohol , the car box silic
10:35	acid , and then the carbon with the hydrogen and
10:38	alcohol attached . And of course the hydrogen that points
10:41	into the screen is in dead last . We can
10:44	draw our ark and see this carl center is also
10:46	S . So we get a name of two S
10:48	three S . Start eric acid . Next let's draw
10:51	the mirror image of this compound . If we use
10:53	the same priorities to sign the stereo chemistry , we
10:56	get a name of two R three R tart eric
10:58	acid . Then for the 3rd december we can show
11:01	one alcohol group coming towards us and the other pointing
11:04	away from us . And finally the 4th december also
11:06	has one alcohol group coming toward us and one pointing
11:09	away from us . Just different ones . But wait
11:12	, if we look at those two , I simmer
11:14	side by side and then we rotate one around ,
11:17	we can overlap them . So the 3rd and 4th
11:20	members of tart eric acid are actually just one molecule
11:24	. This is because there's an internal plane of symmetry
11:26	that we can see if we rotate around this bond
11:29	. Now the internal plane of symmetry is clear to
11:31	see it's a miso compound and we can call it
11:34	miso tortilla , ric acid . After all that investigation
11:36	, we know that rhetoric asset has three I summer
11:38	. So we always need to think critically about the
11:41	molecules . We draw . An organic chemistry are two
11:44	to the power of N formula helps us make sure
11:46	we don't miss any I summers , but we have
11:48	to make sure that too aren't actually the same thing
11:50	. Stereo chemistry plays an important role in how molecules
11:53	interact with one another from smells to medicines . So
11:56	let's try to keep all this in mind for the
11:58	puzzles to come in this episode , we learned about
12:00	polar imagery and how an anti murders of Carole molecules
12:03	rotate plane polarized light in opposite directions , measuring an
12:07	anti America excess in an unequal mixture of an anti
12:10	Mursi with a polaroid Mitter . That rahimic mixtures contain
12:14	equal amounts of an anti Mursi and don't rotate plane
12:16	polarized light . And we did a recap of Constitutional
12:20	I simmers stereo I summers and and tumors and dietary
12:24	immerse . Next week we'll dive into water . The
12:27	molecule not an actual pool to talk about polarity and
12:30	how to show electrons moving around a structure . Thanks
12:33	for watching this episode of Crash course Organic Chemistry .
12:35	If you want to help keep all crash course free
12:38	for everybody forever , you can join our community on
12:41	Patreon . No .

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