What is chirality and how did it get in my molecules? – Michael Evans


In the early days of organic chemistry, chemists understood
that molecules were made of atoms connected through chemical bonds. However, the three-dimensional
shapes of molecules were utterly unclear, since they couldn’t
be observed directly. Molecules were represented using
simple connectivity graphs like the one you see here. It was clear to savvy chemists
of the mid-19th century that these flat representations
couldn’t explain many of their observations. But chemical theory hadn’t provided
a satisfactory explanation for the three-dimensional
structures of molecules. In 1874, the chemist Van’t Hoff
published a remarkable hypothesis: the four bonds of a saturated carbon atom point to the corners of a tetrahedron. It would take over 25 years for the quantum revolution
to theoretically validate his hypothesis. But Van’t Hoff supported
his theory using optical rotation. Van’t Hoff noticed that only compounds
containing a central carbon bound to four different atoms or groups rotated plane-polarized light. Clearly there’s something unique
about this class of compounds. Take a look at the two molecules
you see here. Each one is characterized
by a central, tetrahedral carbon atom bound to four different atoms: bromine, chlorine, fluorine, and hydrogen. We might be tempted to conclude
that the two molecules are the same, if we just concern
ourselves with what they’re made of. However, let’s see if we can
overlay the two molecules perfectly to really prove
that they’re the same. We have free license to rotate
and translate both of the molecules as we wish. Remarkably though, no matter how we move the molecules, we find that perfect superposition
is impossible to achieve. Now take a look at your hands. Notice that your two hands
have all the same parts: a thumb, fingers, a palm, etc. Like our two molecules under study, both of your hands are made
of the same stuff. Furthermore, the distances between stuff
in both of your hands are the same. The index finger
is next to the middle finger, which is next to the ring finger, etc. The same is true
of our hypothetical molecules. All of their internal distances are the same. Despite
the similarities between them, your hands, and our molecules, are certainly not the same. Try superimposing
your hands on one another. Just like our molecules from before, you’ll find that it can’t
be done perfectly. Now, point your palms toward one another. Wiggle both of your index fingers. Notice that your left hand
looks as if it’s looking in a mirror at your right. In other words, your hands
are mirror images. The same can be said of our molecules. We can turn them so
that one looks at the other as in a mirror. Your hands
– and our molecules – possess a spatial property
in common called chirality, or handedness. Chirality means exactly
what we’ve just described: a chiral object is not
the same as its mirror image. Chiral objects are very special
in both chemistry and everyday life. Screws, for example, are also chiral. That’s why we need the terms
right-handed and left-handed screws. And believe it or not,
certain types of light can behave like chiral screws. Packed into every linear,
plane-polarized beam of light are right-handed and left-handed parts that rotate together
to produce plane polarization. Chiral molecules, placed
in a beam of such light, interact differently
with the two chiral components. As a result, one component of the light
gets temporarily slowed down relative to the other. The
effect on the light beam is a rotation of its plane
from the original one, otherwise known as optical rotation. Van’t Hoff and later chemists
realized that the chiral nature of tetrahedral carbons can explain
this fascinating phenomenon. Chirality is responsible for all kinds
of other fascinating effects in chemistry, and everyday life. Humans tend to love symmetry and so if you look around you,
you’ll find that chiral objects made by humans are rare. But chiral molecules
are absolutely everywhere. Phenomena as separate as optical rotation, Screwing together furniture, and clapping your hands all involve this intriguing
spatial property.

100 thoughts on “What is chirality and how did it get in my molecules? – Michael Evans

  1. That animation was actually rather distracting with all of the dialogue boxes, I ended up reading those and not really paying attention. *sigh*

  2. 1)He did not say it has been pointed out yet.
    2) He says it because there is a possibility something like that could be brought up LATER.

  3. the pattern of reflection is one of the most obvious patterns of the universe, like the spiral or the wave. everything is yin and yang.. these slow westerners.. wait i am 1

  4. Someone gets angry with those that dont agree with them haha.Like conflict? i think so. You seem to be baiting Anti-evolutionists so that you can argue that same points over and over.

  5. Yet, at a fundamental level this reflection-symmetry is broken. The Weak Force (one of the 4 fundamental forces) explicitly breaks this symmetry (know as parity).

  6. chirality it one of these things that make organic chemistry so hard for me, thanks for the video, it helps a lot especially right before my test!

  7. If you're interested in natural shapes and patterns of the universe, learn about fractals and how they can explain the structure of plants, lightning, entire planets, circulatory systems, and more

  8. I'm not a chemist by any means but I think that the molecules on 1:48 AREN'T Chiral, because they can't be the mirror images of each other,No sure though

  9. fractals also explain our consciousness, you can apply the term fractal or resonance, ive been leaning toward resonance these days, seems to fit and concresce a little better(explains the same thing as fractal). I loved learning all about the patterns. It led me to Terence Mckenna and Alan Watts. who are easily some of the smartest minds to ever grace this planet. Alan watts talks a lot about neurological resonance, he was an utter genius.

  10. That awesome moment when you see this video in your feed and you just learned about chirality a few hours ago in organic chem class.

  11. But doesn't chirality depend on perpective? If you hold a pencil such that you hands are parallel and the tip points to your left palm, then the object is chiral. But if point the pencil prependicular to your eyes, then it isn't chiral…(to give an example)

  12. Strange coincidence: I learned about chirality today for the first time while watching episode 2 (or 3) of Breaking Bad, and then this video pops up… always amuses me when I see or learn about something for the first time in my life, only to have cross my path again seemingly by pure chance on the same day. I don't believe in any significance to coincidences, but one can't shake the eerie feeling when such things happen few times in a row.

  13. Personal experience: I'm right-handed and sometimes buy jackets with left-handed zippers. It's really frustrating to zip them up with the "wrong" hand.

  14. then the pencil isn't chiral at all, he went over that with the molecule when he said it didn't matter how he orientated the molecule, it wouldn't have all the parts in the same place from the same viewpoint. he could get a mirror image, but that isn't identical.

  15. Symmetry and chirality are not the same, I think it means that since people like symmetry, we don't make objects that are (for example) bigger from one side than the other and then make the same object inverted so they look like mirrored images.

    Of course symmetric objects will look the same on the mirror, but chiral objects NEED the mirror to look the same, that's the thing.

  16. Well, not being able to translate and rotate an object on its mirror image is the definition of chirality, yes. My point is that it does not make sense to say that people don't like chirality because they like symmetry since you can make everything axially symmetric if you mirror it. And people use this to a great extent as the fleurons I borrowed from Unicode show.

  17. I felt like I got this and understood it completely, so afterwards I began re-watching this for no apparent reason until I remembered that I was really fucking baked.

  18. Definitely, it's fascinating stuff. The documentary "Fractals: The colors of infinity" makes for a great starting point for anyone who's interested.
    watch?v=qB8m85p7GsU

  19. Firstly, an account of billions of years of cosmic happenings is not an idea, it is a history. Secondly, powerful ideas and theories often escape simple explanation ( see v=wMFPe-DwULM ). If you really want to know the answer rather then make empty objections you could read a "Bang!: The Complete History of the Universe" or a similar work, or try the wikipedia page on the "chronology of the universe".

  20. What the hell are you talking about? I said nothing about the explanation of the big bang. Please read my post properly.

  21. I think you're asking the wrong question. Chiral molecules are simply two different ways of forming a molecule. It's usually based on the position of the atoms when they bond together. At no point did some event happen to "create" chirality.

  22. What Wiki says:

    "The origin of this homochirality in biology is the subject of much debate. Most scientists believe that Earth life's "choice" of chirality was purely random, and that if carbon-based life forms exist elsewhere in the universe, their chemistry could theoretically have opposite chirality. Circularly polarised radiation could have caused the selective destruction of one chirality of amino acids, leading to a selection bias which resulted in all life on Earth being homochiral."

  23. Yeah but that's chirality in organic molecules, not chirality in general. You didn't specify and i figured you meant in general because you said "after the big bang". Like i said your asking the wrong question. What I'm guessing you want to know is why life on earth only uses one out of the two. Which you answered yourself.
    Only thing I would add is that the random choice would be supported by evolution because its easier to form macro molecules if all of the parts are the same.

  24. good video! Although I found disturbing al the "funny comment bubbles"… they didn't let me concentrate on what was really important, what you were trying to teach.

  25. The evidence that homochirality could occur through natural processes in life/for the creation of life is something we can calculate using mathematical probabilities. The probability that natural processes could produce this feature is 0%.

  26. Wrong example used at 1:35 . The molecules aren't mirror images of one another, they are stereoisomers, but aren't enantiomers (as hands are), they are diastereomers (as hands aren't).

  27. If you bond a chiral object to its mirror image along the axis of reflection, isn't the resulting object achiral? 

  28. I dont understand why at 1:35 you got asymmetric molecules, but at 3:10 you got symmetric molecules? Is there a mistake?

  29. I read once that there's some work of fiction where a man's chirality gets flipped, and at first it's just amusing because his dominant hand switched, but then it turns out he can't digest food because his body molecules have the wrong chirality to interact with the food molecules correctly…

  30. BUT, if I can put my palms together, everything lines up, its a mirror, and since its all lined up perfectly, why isnt it superimposable? D:

  31. can u just give the topic detail completely by explaining Evey thing every point related to a particular point

  32. Interesting. I always though the bonded atoms around the carbon can freely rotate but they merely vibrate. Now I finally understand the chirality…

  33. ちょうど光学異性体の乳酸について勉強していたのでこの動画をみつけられて良かった

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