Cyclohexanes: Crash Course Organic Chemistry #7 - Free Educational videos for Students in K-12

Cyclohexanes: Crash Course Organic Chemistry #7 - By CrashCourse

Transcript


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 tab okay Chakravarty and welcome
00:08	back to Crash course Organic Chemistry . What do Saturn
00:12	a diamond and Giant's Causeway in Ireland all have in
00:16	common hexagons . From honeycombs to the shells of tortoises
00:20	. Hexagons appear all over the natural world . Even
00:23	when you push bubbles together they'll make hexagons . But
00:27	the scientific reasons why hexagon seem to be everywhere are
00:30	debatable . Some people consider hexagons a space saving wonder
00:33	. For example , pencil companies realize they could pack
00:36	more hexagonal pencils in a box and save storage space
00:39	. So that's why every number two is hexagonal hexagons
00:43	are even in the arrangement of carbon atoms like the
00:45	close packed structure that gives diamond , it's famous hardness
00:48	and in graphite hexagonal sheets of carbon conducting one direction
00:52	but not the other . In this episode we'll uncover
00:55	the secrets of one of organic chemistry's favorite manifestations of
00:58	this shape . The cyclo hexane molecule . Yeah .
01:05	Mhm . Yeah . Yeah . As we learned last
01:13	time , cyclo alcanzar named like other alcan's except they
01:16	have the prefix cyclo . Right before the root name
01:19	. A plain old five carbon rings would be called
01:21	cyclops maintain . If we have just one substitute print
01:24	, we don't need a number . Like metal cyclops
01:26	maintain . But if there are two or more substitutes
01:28	, the carbons are numbered to give those substitutes the
01:31	lowest possible numbers and the substitutes are put in alphabetical
01:34	order . Like we normally do for example one methyl
01:38	to methyl cyclo painting . A cyclo al cane can
01:40	be named as a substitute to like when the ace
01:43	I click or no ring part of the molecule has
01:45	more carbons . Or if the chain has an important
01:48	functional groups . For example , for cyclo propel helped
01:51	one . I cyclo alcan's have two distinct faces because
01:54	they don't have free rotation around their bonds . In
01:57	a cyclo al came with two substitutes pointing towards the
01:59	same face of the ring , We add the prefix
02:02	cysts and if they point towards opposite faces of the
02:04	ring , we add the prefix trans . The most
02:07	common cyclo alcanzar , cyclo plantains and cyclo hexane is
02:10	because of what we talked about last episode . They
02:13	have low ring strain , so they're more stable .
02:15	Ring string comes from a combination of two things .
02:17	There's angular strain or deviating from the ideal angle of
02:21	109.5° for sp three hybridized carbons and there's two original
02:25	strain or having bonds in an eclipsed confirmation . Nowadays
02:28	we know it causes ring strain and we know that
02:30	high strain means more energy and less stability . But
02:34	organic chemists initially figured out ring strain and lots of
02:37	other things about chemical reactions by setting compounds on fire
02:41	. To see how let's go to the thought bubble
02:43	combustion reactions are when hydrocarbons burn in oxygen releasing energy
02:47	stored in their bonds . One way to think about
02:49	combustion is that plants incorporate energy from the sun into
02:53	molecules . So when we burn wood in a campfire
02:55	or ancient plants that became fossil fuels , it's kind
02:58	of like we're undoing photosynthesis . Besides using heat to
03:01	toast marshmallows , organic chemists can also measure the heat
03:04	produced in a combustion reaction to learn about the formula
03:07	of chemical compounds and the energy stored in their bonds
03:10	in the inner chamber of an instrument called a bomb
03:13	calorie emitter . We burn a compound measure the temperature
03:16	change and use that measurement to calculate the energy of
03:19	the reaction . Don't worry , it's safe , but
03:21	if there was a bunch of energy in a closed
03:23	system like this , that's bomb , hence the name
03:26	. Organic chemists use bomb calor imagery to quantify ring
03:29	strain by comparing the heat released from the combustion of
03:32	an al Kane with the cyclo al caine . Any
03:34	extra heat from the cyclo al Kane has to be
03:36	from the energy of the ring strain being released .
03:39	So we have to do a little math to get
03:41	there . For example , we can use a bomb
03:42	calorie emitter to burn a very long a cyclic al
03:45	cane and find that the average energy released per ch
03:48	two unit is 658.6 killer jewels per mole . And
03:52	when we burn cyclo propane , which we know is
03:54	a very strange ring , it releases 697.1 killer jewels
03:58	per mole per CH two units . So the ring
04:01	strain energy contributed 38.5 killer jewels per mole . We
04:05	have to multiply that by three for the three CH
04:08	two units in cyclo propane for a total of 115
04:11	killer jewels per mole . That's quite a bit of
04:13	extra energy packed into that ring . Thanks math and
04:17	thank you . Thought bubble through these sorts of combustion
04:19	experiments , the cyclo hexane ring was found to have
04:22	no ring strain , and cyclo plantain is pretty low
04:25	to both of these cyclo alcan's decreased ring strain because
04:28	their angular strain is relatively low in the pentagon .
04:32	The angles are 108 degrees and in a hex a
04:35	gone there 120 degrees . These aren't very far from
04:38	the company . 109.5 degrees for sp three hybridized carbons
04:42	. And even though flat cyclo alcan's would have bonds
04:44	in an eclipse confirmation , they can reduced orginal strained
04:47	by puckering , they poke certain atoms above and below
04:50	the molecular plane so they're not as lined up and
04:53	are slightly less strain . A puckered cyclo Pentium molecule
04:56	pokes one carbon atom above the molecular plane , forming
05:00	an envelope confirmation . We can see this a little
05:02	better by looking at a new and projection along one
05:05	of the bonds . The thing about any molecular drawing
05:07	or model is that they're static instead of the vibrating
05:10	moving molecule of reality . So the pucker of cyclops
05:13	maintain isn't stuck on one carbon . Each carbon takes
05:16	a turn poking above the molecular plane , so the
05:18	molecule is kind of constantly wobbling around . But cyclo
05:22	hexane is even more stable and free of ring strain
05:25	because it can achieve a puckered structure that has all
05:28	of the hydrogen staggered and all of the bond angles
05:31	at 109.5 degrees . This basically magical structure is called
05:35	the chair confirmation of cyclo hexane except instead of a
05:38	plush armchair that you'd want to take a nap in
05:41	. It's more like a crooked beach chair on the
05:43	deck of a cruise ship . Imagine a friend sitting
05:45	with their head up and feet down . The two
05:47	parallel lines in the middle are sort of like the
05:49	seat of the chair . And if we look along
05:51	those carbon carbon bonds , we can draw a newman
05:54	protection and see that the hydrogen are staggered . Cyclo
05:57	hexane can pucker in other ways too . With a
05:58	little bit of ring strain like in the boat confirmation
06:01	, which is also kind of honestly like a goofy
06:04	looking boat . In the boat confirmation . The foot
06:06	rest of the chair lines up with the head rest
06:08	to make a little nook . The angles between carbon
06:11	atoms are still 109.5 degrees . But now there's a
06:14	little too original strain . By drawing a Newman projection
06:17	. We can see that the hydrogen czar all eclipsed
06:19	, but there are also two flagpole hydrogen that are
06:22	sticking towards each other . To relieve strain from this
06:25	interaction . The boat twist a bit so the flagpole
06:28	hydrogen is don't get too close , sort of like
06:30	turning your head for a kiss to avoid smashing noses
06:33	. Most of the cyclo hexane molecules in a sample
06:36	will be in the chair confirmation . So it's really
06:39	important for us to learn how to draw them .
06:41	We'll practice here , starting with two parallel lines .
06:44	Next draw another set of parallel lines to make two
06:47	sideways vis . Then connect those two V . S
06:50	with the third group of parallel lines . That's the
06:52	base structure of the chair . Now we have to
06:54	stick in the hydrogen . Three on each face will
06:56	be straight vertical , up or down , and they're
06:59	all parallel to each other . These are called the
07:01	axial positions and here's a hint the V shaped points
07:04	made by the carbon atoms can help you figure out
07:06	if the axial bond goes up or down , the
07:10	V's pointing up have the actual hydrogen above the plane
07:13	and the downward vis have the actual hydrogen is below
07:16	the plane . And finally we add in three hydrogen
07:18	is that are parallel to the bonds one step away
07:20	, which are what we call the equatorial positions .
07:23	The equatorial hydrogen form a ring around the axle hydrogen
07:27	sort of like arts equator . This can be tricky
07:29	to wrap your head around with just words . So
07:31	we've color coded the equatorial bonds to the bonds in
07:34	the chair structure that they match . So that's one
07:37	chair confirmation . But because even low energy molecules are
07:40	constantly moving , cyclo hexane molecules are switching between confirmations
07:44	many times every second . There's one chair position where
07:47	a friend is sitting comfortably with their head up and
07:49	feet down , then there's the boat and finally there's
07:52	another chair position where their head is hanging down and
07:55	their feet are sticking up . Plus lots of in
07:57	between forms when the chair converts from one position to
08:00	the other , it's called the chair flip , but
08:02	that name can be a little misleading . A chair
08:05	flip does not mean we flip the chair upside down
08:07	and our friend falls out . We just moved their
08:10	head down and feed up . Also , all the
08:12	axial hydrogen is become equatorial hydrogen . A chair flip
08:16	also does not require bonds to be broken , they
08:19	just rotate to shift the bonded groups around . In
08:22	our all hydrogen example , both chairs are equivalent .
08:25	They're the same energetically and we might wonder why we
08:28	need to think about chair flips at all . But
08:30	let's say we swap out one of the hydrogen is
08:32	for a metal group to create metal cyclo hexane .
08:36	If we do a chair flip with this molecule ,
08:38	you can see how the metal group can switch between
08:40	an axial position or an equatorial position . And this
08:44	has chemical consequences for methyl cyclo hexane . The chair
08:47	with the metal group in the equatorial position has slightly
08:50	lower energy . So metal cyclo hexane molecules in a
08:53	sample will be in that chair confirmation as they're constantly
08:57	converting back and forth . To understand why the equatorial
09:00	metal group makes it slightly lower energy . We have
09:02	to go back to our good old tools , Newman
09:05	projections . Let's look along the sea carbon carbon bonds
09:08	in the middle . Now we can see that when
09:09	the metal group is in the axial position , it's
09:11	a ghost confirmation with respect to the head carbon ,
09:14	but in the equatorial position , the metal group is
09:17	in the anti confirmation . There's another important effect here
09:20	too . The axial metal group hysteric interactions with the
09:24	other two axle hydrogen above the ring . The crowding
09:27	introduced by pushing these groups together is called die axial
09:30	strain . This makes an energy difference between the confirmations
09:33	, as we learned in episode six and the equatorial
09:36	position is slightly prefer as more substitutes are added to
09:39	cyclo hexane . The interactions become more noticeable . For
09:43	example , let's consider cyst 13 dimethyl cyclo hexane .
09:47	If both of the methyl groups are sticking up in
09:49	the axial position , it's strongly unfavorable . Starik hindrance
09:53	kicks in and they feel crowded and uncomfortable . So
09:56	most molecules in the sample will be in the chair
09:58	confirmation where the metal groups are equatorial . But now
10:01	let's consider trans . 13 dimethyl cyclo hexane and both
10:05	chair confirmations . There's one axle metal group and one
10:08	equatorial metal group . So chair flips happen but neither
10:12	structure is energetically preferred over the other . There's an
10:15	axle metal group in each one as the group's on
10:17	the chair get even bigger and chunkier . The chair
10:20	confirmation where the substitution is in the equatorial position becomes
10:24	even more favored by the molecules . In a sample
10:26	neighboring atoms just get too crowded with too much dye
10:29	axial strain in the axial position . In fact ,
10:32	more than 99.9% of this compound has the turk bugle
10:36	group in the equatorial position . Now we've been drawing
10:39	a lot of chairs at this point and let's be
10:42	honest , you might want to flip a real chair
10:44	. I know that I do but take a breath
10:47	and when you're ready there's one more thing to learn
10:50	remember skeletal structures of cyclo hack sane . They look
10:53	like flat hexagon . So we also have to think
10:56	about how to convert a flat structure to a chair
10:58	drawing , especially when there are two or more substitue
11:01	ints . The first step is to see what the
11:03	flat structure tells you in this molecule . For instance
11:06	, we know the solid wedge means the metal group
11:08	is coming out towards us and the dashed wedge means
11:11	the isopropyl group is pointing into the screen . So
11:14	we have to make sure these groups stay on the
11:16	correct side of the cyclo hexane . When we draw
11:18	a chair , the metal needs to be above the
11:21	plane and the isopropyl needs to be below the plane
11:24	. Next we should number the carbons with the substitue
11:26	. It's just to help us keep track of them
11:28	. These numbers don't necessarily have to be aipac official
11:31	. It's just helpful when we switch from a hexagon
11:34	to a weird beach chair . And speaking of weird
11:36	beach chairs , it's time to draw the base of
11:38	the chair and number are carbon atoms . It's really
11:41	important that we number the same way we did on
11:43	the flat cyclo hexane . So if we numbered clockwise
11:46	on the flat drawing are numbers need to be clockwise
11:49	on the chair to then we can stick in place
11:51	, holder axial and equatorial bonds on the two carbons
11:54	that have substitue ints . After that , we can
11:56	use our reference numbers to know we should put the
11:58	metal on carbon one . So it's pointing above the
12:01	plane and it's higher than the hydrogen on the same
12:04	carbon . And we put the isopropyl on carbon three
12:07	, so it's below the plane and it's lower than
12:09	the hydrogen on the same carbon . The isopropyl group
12:12	is in an axial position , but it's way bigger
12:15	than the metal group . When we flip a chair
12:17	, all of the axial substitutes become equatorial and vice
12:20	versa . So we need to do a cheerful appear
12:23	to get that Chunky group in an equatorial position ,
12:25	which is what's energetically preferred . Let's keep our eye
12:28	on carbon two and pull it down . That forces
12:31	carbon three up and the isopropyl group moves into the
12:34	equatorial position but it's still below the plane . At
12:38	the same time , the metal group moves into the
12:40	axial position as carbon one pushes up and it stays
12:43	above the plane . The axial metal group has a
12:45	lot less dye axial strain than the chunky branched isopropyl
12:49	. So this is our more stable chair . So
12:51	the big takeaway in today's episode is to practice .
12:53	It helps to practice drawing cyclo hexane is , but
12:56	if you have a model that's even better because you
12:58	can actually change the positions of all the hydrogen and
13:01	see them go from equatorial to axial . And you
13:05	also get to play with the toy and see chemistry
13:07	like more visibly . And it's okay if all this
13:10	chair stuff doesn't make any sense immediately . It's hard
13:13	to wrap your head around and takes a lot of
13:15	practice . But it's really important to know our cyclo
13:17	heck Saints . These organic molecules show up in carbohydrates
13:20	, steroids , plant molecules , pesticides in so many
13:24	other things and the confirmation is so important to the
13:27	function of these molecules . Today we talked about how
13:30	rings pucker to relieve angular and original strain , how
13:33	ring flips make axial substitutes become equatorial and how more
13:37	bulky substitutes should be equatorial when drawing cyclo hexane in
13:40	chair confirmations because that's more energetically favorable . Next episode
13:44	will be moving on to stereo chemistry which can also
13:47	be tough and dreaming about eating all the sugar we
13:50	could want . which is actually pretty easy . Thanks
13:53	for watching this episode of Crash Course Organic Chemistry .
13:56	If you want to help keep all Crash Course free
13:58	for everybody forever , you can join our community on
14:01	Patreon .

Summarizer

DESCRIPTION:

OVERVIEW:

Cyclohexanes: Crash Course Organic Chemistry #7 is a free educational video by CrashCourse.

This page not only allows students and teachers view Cyclohexanes: Crash Course Organic Chemistry #7 videos but also find engaging Sample Questions, Apps, Pins, Worksheets, Books related to the following topics.