[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:17.00,0:00:19.00,Default,,0000,0000,0000,,In the early days of organic chemistry,
Dialogue: 0,0:00:19.00,0:00:22.00,Default,,0000,0000,0000,,chemists understood that molecules were made of atoms
Dialogue: 0,0:00:22.00,0:00:24.00,Default,,0000,0000,0000,,connected through chemical bonds.
Dialogue: 0,0:00:24.00,0:00:27.00,Default,,0000,0000,0000,,However, the three-dimensional shapes of molecules
Dialogue: 0,0:00:27.00,0:00:31.00,Default,,0000,0000,0000,,were utterly unclear, since they couldn't be observed directly.
Dialogue: 0,0:00:31.00,0:00:34.00,Default,,0000,0000,0000,,Molecules were represented using simple connectivity graphs
Dialogue: 0,0:00:34.00,0:00:37.00,Default,,0000,0000,0000,,like the one you see here.
Dialogue: 0,0:00:37.00,0:00:40.00,Default,,0000,0000,0000,,It was clear to savvy chemists of the mid-19th century
Dialogue: 0,0:00:40.00,0:00:44.00,Default,,0000,0000,0000,,that these flat representations couldn't explain
Dialogue: 0,0:00:44.00,0:00:46.00,Default,,0000,0000,0000,,many of their observations.
Dialogue: 0,0:00:46.00,0:00:49.00,Default,,0000,0000,0000,,But chemical theory hadn't provided a satisfactory explanation
Dialogue: 0,0:00:49.00,0:00:51.00,Default,,0000,0000,0000,,for the three-dimensional structures of molecules.
Dialogue: 0,0:00:51.00,0:00:57.00,Default,,0000,0000,0000,,In 1874, the chemist Van't Hoff published a remarkable hypothesis:
Dialogue: 0,0:00:57.00,0:01:01.00,Default,,0000,0000,0000,,the four bonds of a saturated carbon atom
Dialogue: 0,0:01:01.00,0:01:03.00,Default,,0000,0000,0000,,point to the corners of a tetrahedron.
Dialogue: 0,0:01:03.00,0:01:06.00,Default,,0000,0000,0000,,It would take over 25 years
Dialogue: 0,0:01:06.00,0:01:10.00,Default,,0000,0000,0000,,for the quantum revolution to theoretically validate his hypothesis.
Dialogue: 0,0:01:10.00,0:01:14.00,Default,,0000,0000,0000,,But Van't Hoff supported his theory using optical rotation.
Dialogue: 0,0:01:14.00,0:01:17.00,Default,,0000,0000,0000,,Van't Hoff noticed that only compounds containing a central carbon
Dialogue: 0,0:01:17.00,0:01:21.00,Default,,0000,0000,0000,,bound to four different atoms or groups
Dialogue: 0,0:01:21.00,0:01:24.00,Default,,0000,0000,0000,,rotated plane-polarized light.
Dialogue: 0,0:01:24.00,0:01:26.00,Default,,0000,0000,0000,,Clearly there's something unique about this class of compounds.
Dialogue: 0,0:01:26.00,0:01:29.00,Default,,0000,0000,0000,,Take a look at the two molecules you see here.
Dialogue: 0,0:01:29.00,0:01:34.00,Default,,0000,0000,0000,,Each one is characterized by a central, tetrahedral carbon atom
Dialogue: 0,0:01:34.00,0:01:36.00,Default,,0000,0000,0000,,bound to four different atoms:
Dialogue: 0,0:01:36.00,0:01:39.00,Default,,0000,0000,0000,,bromine, chlorine, fluorine, and hydrogen.
Dialogue: 0,0:01:39.00,0:01:41.00,Default,,0000,0000,0000,,We might be tempted to conclude that the two molecules
Dialogue: 0,0:01:41.00,0:01:45.00,Default,,0000,0000,0000,,are the same, if we just concern ourselves with what they're made of.
Dialogue: 0,0:01:45.00,0:01:48.00,Default,,0000,0000,0000,,However, let's see if we can overlay the two molecules
Dialogue: 0,0:01:48.00,0:01:51.00,Default,,0000,0000,0000,,perfectly to really prove that they're the same.
Dialogue: 0,0:01:51.00,0:01:55.00,Default,,0000,0000,0000,,We have free license to rotate and translate both of the molecules
Dialogue: 0,0:01:55.00,0:01:58.00,Default,,0000,0000,0000,,as we wish. Remarkably though,
Dialogue: 0,0:01:58.00,0:02:00.00,Default,,0000,0000,0000,,no matter how we move the molecules,
Dialogue: 0,0:02:00.00,0:02:04.00,Default,,0000,0000,0000,,we find that perfect superposition is impossible to achieve.
Dialogue: 0,0:02:04.00,0:02:07.00,Default,,0000,0000,0000,,Now take a look at your hands.
Dialogue: 0,0:02:07.00,0:02:10.00,Default,,0000,0000,0000,,Notice that your two hands have all the same parts:
Dialogue: 0,0:02:10.00,0:02:14.00,Default,,0000,0000,0000,,a thumb, fingers, a palm, etc.
Dialogue: 0,0:02:14.00,0:02:17.00,Default,,0000,0000,0000,,Like our two molecules under study,
Dialogue: 0,0:02:17.00,0:02:20.00,Default,,0000,0000,0000,,both of your hands are made of the same stuff.
Dialogue: 0,0:02:20.00,0:02:25.00,Default,,0000,0000,0000,,Furthermore, the distances between stuff in both of your hands are the same.
Dialogue: 0,0:02:25.00,0:02:27.00,Default,,0000,0000,0000,,The index finger is next to the middle finger,
Dialogue: 0,0:02:27.00,0:02:30.00,Default,,0000,0000,0000,,which is next to the ring finger, etc.
Dialogue: 0,0:02:30.00,0:02:33.00,Default,,0000,0000,0000,,The same is true of our hypothetical molecules.
Dialogue: 0,0:02:33.00,0:02:35.00,Default,,0000,0000,0000,,All of their internal distances
Dialogue: 0,0:02:35.00,0:02:38.00,Default,,0000,0000,0000,,are the same. Despite the similarities between them,
Dialogue: 0,0:02:38.00,0:02:40.00,Default,,0000,0000,0000,,your hands, and our molecules,
Dialogue: 0,0:02:40.00,0:02:43.00,Default,,0000,0000,0000,,are certainly not the same.
Dialogue: 0,0:02:43.00,0:02:46.00,Default,,0000,0000,0000,,Try superimposing your hands on one another.
Dialogue: 0,0:02:46.00,0:02:48.00,Default,,0000,0000,0000,,Just like our molecules from before,
Dialogue: 0,0:02:48.00,0:02:51.00,Default,,0000,0000,0000,,you'll find that it can't be done perfectly.
Dialogue: 0,0:02:51.00,0:02:54.00,Default,,0000,0000,0000,,Now, point your palms toward one another.
Dialogue: 0,0:02:54.00,0:02:56.00,Default,,0000,0000,0000,,Wiggle both of your index fingers.
Dialogue: 0,0:02:56.00,0:03:00.00,Default,,0000,0000,0000,,Notice that your left hand looks as if it's looking
Dialogue: 0,0:03:00.00,0:03:02.00,Default,,0000,0000,0000,,in a mirror at your right.
Dialogue: 0,0:03:02.00,0:03:05.00,Default,,0000,0000,0000,,In other words, your hands are mirror images.
Dialogue: 0,0:03:05.00,0:03:08.00,Default,,0000,0000,0000,,The same can be said of our molecules.
Dialogue: 0,0:03:08.00,0:03:11.00,Default,,0000,0000,0000,,We can turn them so that one looks at the other
Dialogue: 0,0:03:11.00,0:03:14.00,Default,,0000,0000,0000,,as in a mirror. Your hands - and our molecules -
Dialogue: 0,0:03:14.00,0:03:18.00,Default,,0000,0000,0000,,possess a spatial property in common called chirality,
Dialogue: 0,0:03:18.00,0:03:20.00,Default,,0000,0000,0000,,or handedness.
Dialogue: 0,0:03:20.00,0:03:23.00,Default,,0000,0000,0000,,Chirality means exactly what we've just described:
Dialogue: 0,0:03:23.00,0:03:25.00,Default,,0000,0000,0000,,a chiral object is not the same as its mirror image.
Dialogue: 0,0:03:25.00,0:03:30.00,Default,,0000,0000,0000,,Chiral objects are very special in both chemistry and everyday life.
Dialogue: 0,0:03:30.00,0:03:33.00,Default,,0000,0000,0000,,Screws, for example, are also chiral.
Dialogue: 0,0:03:33.00,0:03:37.00,Default,,0000,0000,0000,,That's why we need the terms right-handed and left-handed screws.
Dialogue: 0,0:03:37.00,0:03:40.00,Default,,0000,0000,0000,,And believe it or not, certain types of light
Dialogue: 0,0:03:40.00,0:03:42.00,Default,,0000,0000,0000,,can behave like chiral screws.
Dialogue: 0,0:03:42.00,0:03:47.00,Default,,0000,0000,0000,,Packed into every linear, plane-polarized beam of light
Dialogue: 0,0:03:47.00,0:03:50.00,Default,,0000,0000,0000,,are right-handed and left-handed parts
Dialogue: 0,0:03:50.00,0:03:55.00,Default,,0000,0000,0000,,that rotate together to produce plane polarization.
Dialogue: 0,0:03:55.00,0:03:58.00,Default,,0000,0000,0000,,Chiral molecules, placed in a beam of such light,
Dialogue: 0,0:03:58.00,0:04:01.00,Default,,0000,0000,0000,,interact differently with the two chiral components.
Dialogue: 0,0:04:01.00,0:04:06.00,Default,,0000,0000,0000,,As a result, one component of the light gets temporarily slowed down
Dialogue: 0,0:04:06.00,0:04:09.00,Default,,0000,0000,0000,,relative to the other. The effect on the light beam
Dialogue: 0,0:04:09.00,0:04:13.00,Default,,0000,0000,0000,,is a rotation of its plane from the original one,
Dialogue: 0,0:04:13.00,0:04:16.00,Default,,0000,0000,0000,,otherwise known as optical rotation.
Dialogue: 0,0:04:16.00,0:04:21.00,Default,,0000,0000,0000,,Van't Hoff and later chemists realized that the chiral nature
Dialogue: 0,0:04:21.00,0:04:24.00,Default,,0000,0000,0000,,of tetrahedral carbons can explain this fascinating phenomenon.
Dialogue: 0,0:04:24.00,0:04:29.00,Default,,0000,0000,0000,,Chirality is responsible for all kinds of other fascinating effects
Dialogue: 0,0:04:29.00,0:04:31.00,Default,,0000,0000,0000,,in chemistry, and everyday life.
Dialogue: 0,0:04:31.00,0:04:34.00,Default,,0000,0000,0000,,Humans tend to love symmetry
Dialogue: 0,0:04:34.00,0:04:36.00,Default,,0000,0000,0000,,and so if you look around you, you'll find that chiral objects
Dialogue: 0,0:04:36.00,0:04:38.00,Default,,0000,0000,0000,,made by humans are rare.
Dialogue: 0,0:04:38.00,0:04:42.00,Default,,0000,0000,0000,,But chiral molecules are absolutely everywhere.
Dialogue: 0,0:04:42.00,0:04:45.00,Default,,0000,0000,0000,,Phenomena as separate as optical rotation,
Dialogue: 0,0:04:45.00,0:04:47.00,Default,,0000,0000,0000,,Screwing together furniture,
Dialogue: 0,0:04:47.00,0:04:49.00,Default,,0000,0000,0000,,and clapping your hands
Dialogue: 0,0:04:49.00,0:04:53.00,Default,,0000,0000,0000,,all involve this intriguing spatial property.