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

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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00:05 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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