[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:02.26,0:00:03.83,Default,,0000,0000,0000,,I made this video to
Dialogue: 0,0:00:03.83,0:00:07.34,Default,,0000,0000,0000,,try and help some people understand how\Ncis and trans
Dialogue: 0,0:00:07.34,0:00:10.59,Default,,0000,0000,0000,,geometric isomers work.
Dialogue: 0,0:00:10.59,0:00:14.59,Default,,0000,0000,0000,,I'm hoping it will be useful to some people,\Nand
Dialogue: 0,0:00:14.59,0:00:19.38,Default,,0000,0000,0000,,before we begin, some definitions.\NStructural isomers have the same
Dialogue: 0,0:00:19.38,0:00:22.90,Default,,0000,0000,0000,,molecular formula but a different\Nstructural formula.
Dialogue: 0,0:00:22.10,0:00:25.57,Default,,0000,0000,0000,,There are two examples of structural\Nisomers here.
Dialogue: 0,0:00:25.57,0:00:29.44,Default,,0000,0000,0000,,If you look at them, the sequence of\Natoms within the structures
Dialogue: 0,0:00:29.44,0:00:32.95,Default,,0000,0000,0000,,are different, even though the molecular\Nformulas are the same.
Dialogue: 0,0:00:32.95,0:00:35.95,Default,,0000,0000,0000,,Geometric isomers are different.
Dialogue: 0,0:00:35.95,0:00:38.97,Default,,0000,0000,0000,,They will have the same molecular and\Nstructural formula,
Dialogue: 0,0:00:38.97,0:00:45.97,Default,,0000,0000,0000,,but a different arrangement of atoms in\Nspace.
Dialogue: 0,0:00:46.18,0:00:47.10,Default,,0000,0000,0000,,Before we start
Dialogue: 0,0:00:47.10,0:00:50.26,Default,,0000,0000,0000,,talking about alkenes and their geometric isomers,
Dialogue: 0,0:00:50.26,0:00:54.70,Default,,0000,0000,0000,,I think a good starting point is a simple
Dialogue: 0,0:00:54.70,0:00:57.33,Default,,0000,0000,0000,,alkane. This is 1,2-dichloroethane. It's
Dialogue: 0,0:00:57.33,0:01:01.14,Default,,0000,0000,0000,,got single bonds between the two\Ncarbon atoms,
Dialogue: 0,0:01:01.14,0:01:04.86,Default,,0000,0000,0000,,and if this was the structure of the molecule,
Dialogue: 0,0:01:04.86,0:01:08.22,Default,,0000,0000,0000,,I could draw a picture of it. And,
Dialogue: 0,0:01:08.22,0:01:12.90,Default,,0000,0000,0000,,it would look, in terms of fully expanded,
Dialogue: 0,0:01:12.90,0:01:15.59,Default,,0000,0000,0000,,like the top diagram above. I've got two chlorines
Dialogue: 0,0:01:15.59,0:01:19.55,Default,,0000,0000,0000,,up top, two hydrogens on the bottom and there's a hydrogen left and a hydrogen right
Dialogue: 0,0:01:19.55,0:01:24.93,Default,,0000,0000,0000,,that are slightly obscured because of the geometry.
Dialogue: 0,0:01:24.93,0:01:28.94,Default,,0000,0000,0000,,The top diagram is a expanded structural formula.
Dialogue: 0,0:01:28.94,0:01:33.39,Default,,0000,0000,0000,,It shows exactly, all the bonds in the structure where the bottom one is a condensed
Dialogue: 0,0:01:33.39,0:01:37.88,Default,,0000,0000,0000,,structural formula. It still shows us the\Nsequence of all the atoms in the molecule, but
Dialogue: 0,0:01:37.88,0:01:39.40,Default,,0000,0000,0000,,it's much, much faster to write.
Dialogue: 0,0:01:39.40,0:01:42.89,Default,,0000,0000,0000,,The thing about this model is that
Dialogue: 0,0:01:42.89,0:01:47.49,Default,,0000,0000,0000,,the molecule could be viewed from many\Ndifferent angles.
Dialogue: 0,0:01:47.49,0:01:50.39,Default,,0000,0000,0000,,And, if I want to view it from say, this angle, I would actually draw
Dialogue: 0,0:01:50.39,0:01:54.79,Default,,0000,0000,0000,,I would actually draw the
Dialogue: 0,0:01:54.79,0:01:58.81,Default,,0000,0000,0000,,two chlorines left and right and the hydrogens up and down, up and down on each side.
Dialogue: 0,0:01:58.81,0:02:03.20,Default,,0000,0000,0000,,It's still the same molecule, just viewed\Nfrom a slightly different angle,
Dialogue: 0,0:02:03.20,0:02:06.57,Default,,0000,0000,0000,,and to show that on paper,
Dialogue: 0,0:02:06.57,0:02:09.69,Default,,0000,0000,0000,,I could have gone those two chlorines in in two different arrangements.
Dialogue: 0,0:02:09.69,0:02:12.91,Default,,0000,0000,0000,,It could also set possibly with the two chlorines
Dialogue: 0,0:02:12.91,0:02:16.86,Default,,0000,0000,0000,,both looking downwards, in which case
Dialogue: 0,0:02:16.86,0:02:21.18,Default,,0000,0000,0000,,I would draw the structural formula like that.\NEvery single one of these
Dialogue: 0,0:02:21.18,0:02:24.66,Default,,0000,0000,0000,,are all equivalent. It's still\Nthe same thing,
Dialogue: 0,0:02:24.66,0:02:28.86,Default,,0000,0000,0000,,just viewed from different angles. But,\Nthere's
Dialogue: 0,0:02:28.86,0:02:33.49,Default,,0000,0000,0000,,one more trick that this molecule can do and\Nthat is is that
Dialogue: 0,0:02:33.49,0:02:36.62,Default,,0000,0000,0000,,whenever there's a single bond present,
Dialogue: 0,0:02:36.62,0:02:41.87,Default,,0000,0000,0000,,the atoms on each end of it can rotate about the axis of that bond,
Dialogue: 0,0:02:41.87,0:02:45.13,Default,,0000,0000,0000,,that means that
Dialogue: 0,0:02:45.13,0:02:51.23,Default,,0000,0000,0000,,this one here can spin on this axis\Nof the bond, and this one here can also do
Dialogue: 0,0:02:51.23,0:02:52.18,Default,,0000,0000,0000,,the same.
Dialogue: 0,0:02:52.18,0:02:55.69,Default,,0000,0000,0000,,So, both of these atoms have that spin movement available to
Dialogue: 0,0:02:55.69,0:02:58.73,Default,,0000,0000,0000,,spin around as they wish.
Dialogue: 0,0:02:58.73,0:03:03.77,Default,,0000,0000,0000,,And that means that I don't necessarily\Nhave to have the two chlorines
Dialogue: 0,0:03:03.77,0:03:07.18,Default,,0000,0000,0000,,sticking out side by side. They could be in any
Dialogue: 0,0:03:07.18,0:03:10.89,Default,,0000,0000,0000,,other possible position relative to\Neach other.
Dialogue: 0,0:03:10.89,0:03:15.19,Default,,0000,0000,0000,,So, that means that this molecule could also\Nbe drawn
Dialogue: 0,0:03:15.19,0:03:19.85,Default,,0000,0000,0000,,like this, in which case
Dialogue: 0,0:03:19.85,0:03:23.89,Default,,0000,0000,0000,,there is a chlorine
Dialogue: 0,0:03:23.89,0:03:29.23,Default,,0000,0000,0000,,above and below on each side and hydrogen are taking up
Dialogue: 0,0:03:29.23,0:03:33.49,Default,,0000,0000,0000,,the other remaining spots. Still the exact\Nsame molecule
Dialogue: 0,0:03:33.49,0:03:36.37,Default,,0000,0000,0000,,because all I've done to change that from
Dialogue: 0,0:03:36.37,0:03:42.20,Default,,0000,0000,0000,,what it was originally to what it is now
Dialogue: 0,0:03:42.20,0:03:47.30,Default,,0000,0000,0000,,is just rotated the molecule internally\Nwithin its own structure.
Dialogue: 0,0:03:47.30,0:03:50.48,Default,,0000,0000,0000,,The same thing would apply
Dialogue: 0,0:03:50.48,0:03:55.80,Default,,0000,0000,0000,,to any simple single-bonded carbon chain.
Dialogue: 0,0:03:55.80,0:04:01.23,Default,,0000,0000,0000,,This is four carbons all in a line. But, I don't necessarily have to draw them like that
Dialogue: 0,0:04:01.23,0:04:05.87,Default,,0000,0000,0000,,because with all these bonds having free rotation, I could draw three
Dialogue: 0,0:04:05.87,0:04:09.32,Default,,0000,0000,0000,,in a row and one down. Or, I could draw
Dialogue: 0,0:04:09.32,0:04:12.51,Default,,0000,0000,0000,,one up and one down,
Dialogue: 0,0:04:12.51,0:04:15.80,Default,,0000,0000,0000,,or I could draw the whole thing in some sort of "n" shape, or as
Dialogue: 0,0:04:15.80,0:04:19.47,Default,,0000,0000,0000,,some sort of "u" shape.
Dialogue: 0,0:04:19.47,0:04:22.54,Default,,0000,0000,0000,,Exactly which one I draw is really
Dialogue: 0,0:04:22.54,0:04:26.46,Default,,0000,0000,0000,,irrelevant because it's all the same\Nmolecule, just twisted
Dialogue: 0,0:04:26.46,0:04:30.27,Default,,0000,0000,0000,,internally. Of course, for clarity,
Dialogue: 0,0:04:30.27,0:04:34.17,Default,,0000,0000,0000,,a structural formula will generally have all atoms in a row, or
Dialogue: 0,0:04:34.17,0:04:38.00,Default,,0000,0000,0000,,if you draw the skeletal formulas,
Dialogue: 0,0:04:38.00,0:04:45.00,Default,,0000,0000,0000,,generally, it will be drawn as a bit of a zig-zag.
Dialogue: 0,0:04:50.51,0:04:51.30,Default,,0000,0000,0000,,Alkenes
Dialogue: 0,0:04:51.30,0:04:54.70,Default,,0000,0000,0000,,are different
Dialogue: 0,0:04:54.70,0:04:57.80,Default,,0000,0000,0000,,because they have a double bond between\Nthe carbon atoms
Dialogue: 0,0:04:57.80,0:05:01.35,Default,,0000,0000,0000,,and that limits what kind of rotation is\Navailable
Dialogue: 0,0:05:01.35,0:05:05.90,Default,,0000,0000,0000,,for those atoms. But, first of all, if we looked at this one here, it's
Dialogue: 0,0:05:05.90,0:05:08.52,Default,,0000,0000,0000,,1,2-dichlorobutene (really 1,2-dichloroethene).
Dialogue: 0,0:05:08.52,0:05:12.70,Default,,0000,0000,0000,,And, I could hold this
Dialogue: 0,0:05:12.70,0:05:16.61,Default,,0000,0000,0000,,in a couple of different positions to get\Nthe different perspectives. So, this one here
Dialogue: 0,0:05:16.61,0:05:19.86,Default,,0000,0000,0000,,probably matches this, yes it does. So,
Dialogue: 0,0:05:19.86,0:05:23.78,Default,,0000,0000,0000,,on the left, we've got the chlorine up top and on the right, we've got the chlorine on the
Dialogue: 0,0:05:23.78,0:05:28.42,Default,,0000,0000,0000,,bottom. But, the exact time molecule flipped over,
Dialogue: 0,0:05:28.42,0:05:32.50,Default,,0000,0000,0000,,we could now draw it as having the chlorine on one side down
Dialogue: 0,0:05:32.50,0:05:36.30,Default,,0000,0000,0000,,on the left, and on the right hand side, it's\Nnow up.
Dialogue: 0,0:05:36.30,0:05:39.14,Default,,0000,0000,0000,,It's still the exact same molecule, just
Dialogue: 0,0:05:39.14,0:05:43.11,Default,,0000,0000,0000,,one perspective versus another one.\NHowever,
Dialogue: 0,0:05:43.11,0:05:47.40,Default,,0000,0000,0000,,what this molecule can't do is
Dialogue: 0,0:05:47.40,0:05:52.49,Default,,0000,0000,0000,,rotate on the axis of this double bond.\NThat means the two carbons on the
Dialogue: 0,0:05:52.49,0:05:53.82,Default,,0000,0000,0000,,end of that double bond,
Dialogue: 0,0:05:53.82,0:05:57.40,Default,,0000,0000,0000,,cannot twist, spin independently
Dialogue: 0,0:05:57.40,0:06:00.50,Default,,0000,0000,0000,,of the other one. The double bond will not allow it. There is
Dialogue: 0,0:06:00.50,0:06:04.20,Default,,0000,0000,0000,,no ability to twist around. That means that\NI can't get this structure
Dialogue: 0,0:06:04.20,0:06:08.39,Default,,0000,0000,0000,,twisted around and get both of my chlorine atoms
Dialogue: 0,0:06:08.39,0:06:14.28,Default,,0000,0000,0000,,facing either both
Dialogue: 0,0:06:14.28,0:06:18.71,Default,,0000,0000,0000,,up or both down. So, at no stage
Dialogue: 0,0:06:18.71,0:06:21.87,Default,,0000,0000,0000,,can I turn this structure into
Dialogue: 0,0:06:21.87,0:06:25.50,Default,,0000,0000,0000,,this one. They both still have the same structural formula, in terms of
Dialogue: 0,0:06:25.50,0:06:29.56,Default,,0000,0000,0000,,the sequence of atoms in the molecule.\NIt has got a
Dialogue: 0,0:06:29.56,0:06:33.33,Default,,0000,0000,0000,,hydrogen and chlorine on the left,
Dialogue: 0,0:06:33.33,0:06:37.80,Default,,0000,0000,0000,,hydrogen and chlorine on the right, double bond between them. So,
Dialogue: 0,0:06:37.80,0:06:39.63,Default,,0000,0000,0000,,in terms of the sequence of atoms and bonds, they are identical.
Dialogue: 0,0:06:39.63,0:06:42.75,Default,,0000,0000,0000,,However, the arrangement in space of these atoms,
Dialogue: 0,0:06:42.75,0:06:45.96,Default,,0000,0000,0000,,is different and
Dialogue: 0,0:06:45.96,0:06:49.26,Default,,0000,0000,0000,,no amount rotation or manipulation
Dialogue: 0,0:06:49.26,0:06:52.52,Default,,0000,0000,0000,,can ever get them to line up with each other.
Dialogue: 0,0:06:52.52,0:06:59.52,Default,,0000,0000,0000,,So, these two here are two different\Nmolecules. We call them geometric isomers.
Dialogue: 0,0:07:00.90,0:07:04.43,Default,,0000,0000,0000,,Same structural formulas, but different\Narrangements of atoms in space.
Dialogue: 0,0:07:04.43,0:07:09.38,Default,,0000,0000,0000,,A requirement for this is that they must\Nhave a double bond between
Dialogue: 0,0:07:09.38,0:07:13.77,Default,,0000,0000,0000,,carbon atoms. Structures like this
Dialogue: 0,0:07:13.77,0:07:17.40,Default,,0000,0000,0000,,many different ways up of drawing those chlorine atoms
Dialogue: 0,0:07:17.40,0:07:20.68,Default,,0000,0000,0000,,around those carbon atoms within the same\Nmolecule
Dialogue: 0,0:07:20.68,0:07:24.65,Default,,0000,0000,0000,,because the bond can rotate to put them in
Dialogue: 0,0:07:24.65,0:07:28.85,Default,,0000,0000,0000,,any position you wish. This double bond can't rotate
Dialogue: 0,0:07:28.85,0:07:31.89,Default,,0000,0000,0000,,with means those two chlorines are forever one up
Dialogue: 0,0:07:31.89,0:07:35.64,Default,,0000,0000,0000,,and one down. This one here, they're forever either both
Dialogue: 0,0:07:35.64,0:07:40.26,Default,,0000,0000,0000,,that way, or they're both that way. So,
Dialogue: 0,0:07:40.26,0:07:43.71,Default,,0000,0000,0000,,a geometric isomer must have a double bond for starters.
Dialogue: 0,0:07:43.71,0:07:48.72,Default,,0000,0000,0000,,However, there's one more requirement, and that is
Dialogue: 0,0:07:48.72,0:07:51.87,Default,,0000,0000,0000,,that each carbon within
Dialogue: 0,0:07:51.87,0:07:56.34,Default,,0000,0000,0000,,the double bond has to have
Dialogue: 0,0:07:56.34,0:08:00.19,Default,,0000,0000,0000,,two unique groups attached\Nto it. So, that carbon there
Dialogue: 0,0:08:00.19,0:08:04.27,Default,,0000,0000,0000,,has got a hydrogen and a chlorine, which are\Ndifferent from each other,
Dialogue: 0,0:08:04.27,0:08:07.38,Default,,0000,0000,0000,,and also, this one here has got
Dialogue: 0,0:08:07.38,0:08:11.30,Default,,0000,0000,0000,,a chlorine and a hydrogen that are different from each other.
Dialogue: 0,0:08:11.30,0:08:14.40,Default,,0000,0000,0000,,It doesn't matter whether or not these ones match or
Dialogue: 0,0:08:14.40,0:08:17.49,Default,,0000,0000,0000,,these ones match, it's one carbon at a time. Are they
Dialogue: 0,0:08:17.49,0:08:22.90,Default,,0000,0000,0000,,the same or are they different for both sides?
Dialogue: 0,0:08:22.90,0:08:27.47,Default,,0000,0000,0000,,If there's ever an instance where
Dialogue: 0,0:08:27.47,0:08:30.91,Default,,0000,0000,0000,,on either side of that bond,
Dialogue: 0,0:08:30.91,0:08:33.98,Default,,0000,0000,0000,,there is two groups that are the
Dialogue: 0,0:08:33.98,0:08:38.12,Default,,0000,0000,0000,,same as each other then it is not\Npossible
Dialogue: 0,0:08:38.12,0:08:41.16,Default,,0000,0000,0000,,to have this molecule arranged
Dialogue: 0,0:08:41.16,0:08:44.84,Default,,0000,0000,0000,,in any other
Dialogue: 0,0:08:44.84,0:08:48.22,Default,,0000,0000,0000,,conformation other than this.
Dialogue: 0,0:08:48.22,0:08:51.91,Default,,0000,0000,0000,,So, this one here. If I was to have this one
Dialogue: 0,0:08:51.91,0:08:55.50,Default,,0000,0000,0000,,and this one.
Dialogue: 0,0:08:55.50,0:09:00.41,Default,,0000,0000,0000,,On the surface they might look\Npossibly
Dialogue: 0,0:09:00.41,0:09:05.20,Default,,0000,0000,0000,,a little bit different because this one\Nhere has got the chlorine on the right
Dialogue: 0,0:09:05.20,0:09:09.10,Default,,0000,0000,0000,,down and this one has the chlorine on the right up.
Dialogue: 0,0:09:09.10,0:09:14.52,Default,,0000,0000,0000,,But, because the right-hand sides, sorry, left-hand sides of these
Dialogue: 0,0:09:14.52,0:09:18.29,Default,,0000,0000,0000,,both have identical groups, two chlorines on that left-hand side
Dialogue: 0,0:09:18.29,0:09:21.50,Default,,0000,0000,0000,,carbon that means that
Dialogue: 0,0:09:21.50,0:09:26.48,Default,,0000,0000,0000,,even though I can't rotate the double-bond,
Dialogue: 0,0:09:26.48,0:09:31.40,Default,,0000,0000,0000,,if I just take the whole structure and\Ntwist it over, then I've
Dialogue: 0,0:09:31.40,0:09:36.31,Default,,0000,0000,0000,,got the exact same arrangement
Dialogue: 0,0:09:36.31,0:09:40.89,Default,,0000,0000,0000,,in space. So, these aren't geometric isomers. It's the same molecule.
Dialogue: 0,0:09:40.89,0:09:43.92,Default,,0000,0000,0000,,Possibly just originally viewed from a\Ndifferent angle.
Dialogue: 0,0:09:43.92,0:09:49.14,Default,,0000,0000,0000,,So this one here can't have geometric isomers.
Dialogue: 0,0:09:49.14,0:09:53.53,Default,,0000,0000,0000,,But, it does satisfy the double-bond requirements. One of the carbon atoms
Dialogue: 0,0:09:53.53,0:09:56.74,Default,,0000,0000,0000,,has got two identical group attached.
Dialogue: 0,0:09:56.74,0:10:01.10,Default,,0000,0000,0000,,That means that any different ways I\Ncan try and arrange,
Dialogue: 0,0:10:01.10,0:10:05.37,Default,,0000,0000,0000,,these groups still represent the same\Nmolecule
Dialogue: 0,0:10:05.37,0:10:14.99,Default,,0000,0000,0000,,from a different perspective. In this one\Nhere,
Dialogue: 0,0:10:14.99,0:10:18.60,Default,,0000,0000,0000,,can exist as geometric isomers because
Dialogue: 0,0:10:18.60,0:10:22.49,Default,,0000,0000,0000,,number one, there's a double-bond present\Nand number two, each codon
Dialogue: 0,0:10:22.49,0:10:28.50,Default,,0000,0000,0000,,has got two different groups attached to\Nit. So I can have this structure drawn like this
Dialogue: 0,0:10:28.50,0:10:31.62,Default,,0000,0000,0000,,or I could draw it so
Dialogue: 0,0:10:31.62,0:10:36.15,Default,,0000,0000,0000,,the two chlorines are on the same side of each other.
Dialogue: 0,0:10:36.15,0:10:40.65,Default,,0000,0000,0000,,I cannot manipulate this molecule to get\Ntheir original arrangement back again.
Dialogue: 0,0:10:40.65,0:10:44.89,Default,,0000,0000,0000,,No matter how I try because there's no rotation in here.
Dialogue: 0,0:10:44.89,0:10:49.62,Default,,0000,0000,0000,,I can never get one chlorine up and one chlorine down.
Dialogue: 0,0:10:49.62,0:10:53.56,Default,,0000,0000,0000,,So this is a different structure from the\Nother one.
Dialogue: 0,0:10:53.56,0:10:58.25,Default,,0000,0000,0000,,And, finally the original molecule we had
Dialogue: 0,0:10:58.25,0:11:02.22,Default,,0000,0000,0000,,was an alkane. An alkane
Dialogue: 0,0:11:02.22,0:11:07.00,Default,,0000,0000,0000,,by default cannot have, when it's in a\Nsingle chain,
Dialogue: 0,0:11:07.00,0:11:11.24,Default,,0000,0000,0000,,cis and trans geometric isomers because
Dialogue: 0,0:11:11.24,0:11:14.65,Default,,0000,0000,0000,,this rotation means that
Dialogue: 0,0:11:14.65,0:11:18.81,Default,,0000,0000,0000,,having the two chlorines on opposite sides or the same sides,
Dialogue: 0,0:11:18.81,0:11:23.39,Default,,0000,0000,0000,,are actually just the same molecule with different amounts of internal rotation.
Dialogue: 0,0:11:23.39,0:11:28.55,Default,,0000,0000,0000,,The lack of a double bond means any different ways of drawing this,
Dialogue: 0,0:11:28.55,0:11:30.29,Default,,0000,0000,0000,,still represent the same molecule.