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Introduction to Organic Chemistry (1-hour unit)

1) First thoughts on ORGANIC CHEMISTRY:

a) Looking for the ELEMENTS.

-Can you name any organic compounds (OCs)?

-Do you think that ethanol, hemoglobin or DNA molecules are all OCs?

EthanolHemoglobinDNA types


-Then, what elements would you say are the 4 main constituents in OCs?

Tick them in the following Table 1:

F N Al B Na H S O Fe C
                   

Activity 1 (reading) "The amazing 4":
Check your answer by reading a brief article on the Britannica website.


Activity 2 (extra reading) "C's superpower":
Find out why C is precisely so important in OCs.

 

b) How many combinations of these atoms exist in ORGANIC MOLECULES?

Towards the concept of FUNCTIONAL GROUP:

Functional groups table


Fill in the blanks using the words given in Table 2:

Atoms Properties Families Covalent Same Groups Characteristic Functional


"________ ________ are specific combinations of ________ within molecules that are responsible
for the chemical __________ of those molecules. So, it defines the ___________ physical
and chemical properties of families of organic compounds. Particularly, molecules with the _______
functional group will undergo similar chemical reaction(s). Remember that the atoms
of functional groups are linked to each other and to the rest of the molecule by ________ bonds".

 

c) How many reactions involve ORGANIC MOLECULES?

A glimpse into the complexity of Organic Chemistry:

Organic reactions map

Stop for a moment and decide what seems more accurate in your view:

-The number of known Organic Reactions is huge/disregardable.
-There are many/few types of Organic Reactions running in biological systems.
-The field of study ranged by Organic Chemistry is wide/narrow.
-It is true/false that Organic Reactions never require a catalyst to facilitate the process.

 

2) Let's focus on the simplest Organic Molecules: ALKANES, a type of HYDROCARBONS.

Watch the following video (you may switch the subtitles on or check the transcription below) and answer the coming questions:
 

-Which are the two chemical elements that appear in any hydrocarbon?

-Why are alkanes the simplest of all hydrocarbons?

-Can you name three reactions in which alkanes take part?

-Describe in your own words what a catalyst is.

 

Activity 3 (extra reading) "Molecules' multiple identity":
How would you define what is an isomer?
Give one example involving two alkane molecules (clue: structural isomery).

 

 

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YOUTUBE VIDEO TRANSCRIPT
(in case you need to check any words with a dictionary on Multidict.net; a copy of this transcript in .docx format is also available at one of the Link Buttons):

0:00

You've heard this before, but it bears repeating. Carbon is the element of life.

0:03

So much so that when we explore other planets the first thing we look for is compounds that contain carbon.

0:08

In fact, there was a time when we thought carbon compounds could only be produced by living things.

0:13

So early chemists called them, as we still do today organic compounds.

0:18

Scientists back then considered biological molecules to be almost mystical in origin.

0:22

Until, 1828 when German chemist Friedrich Wöhler discovered that urea, a component of urine,

0:28

could be synthesized simply by heating ammonium cyanate, an inorganic compound.

0:33

That proved biological molecules were just chemicals that could be created and manipulated in the lab.

0:38

Suddenly a new branch of chemistry was born, organic chemistry. It's like my favorite chemistry.

0:44

So what is it about carbon though, that makes it so special? Well, a lot of things.

0:49

Like silicon, which we talked about a few weeks ago, carbon is in group 14 on the periodic table,

0:54

and like all of the elements in that group, it has 4 valence electrons.

0:59

In carbon those 4 electrons can bond to other atoms in a really promiscuous number of configurations

1:04

to form all kinds of structures.

1:07

Which is why carbon is to biology, which silicon is to geology.

1:10

Just as silicon forms the basis, not only for sand,

1:13

but also most of the rocks on earth, carbon is the foundation of most biological molecules.

1:19

Really all biological molecules...right? Yup.

1:23

The simplest organic molecules are pure hydrocarbons containing only carbon and hydrogen. Hydro-carbon.

1:29

They are where we're going to start our six week exploration of organic chemistry.

1:33

And they're a good place to start, partly because they play by the most straight forward rules.

1:38

When all carbons in a pure hydrocarbon are bound to the maximum number of atoms, 4 atoms each,

1:42

so that there are no double or triple bonds anywhere; these compounds are considered to be full or saturated.

1:48

That means that all the carbons have 4 bonds, either with other carbon atoms or with hydrogen atoms,

1:52

in which case the hydrogens are bound to one carbon.

1:55

No questions, no exceptions.

1:57

These are the simple rules that govern some of the world's most useful, or at least, used compounds.

2:01

The hydrocarbons that we use as diesel fuel, gasoline, methane, propane.

2:05

You're gonna learn what these and other compounds look like, what they're names mean,

2:09

and how they take part in the reactions that fuel our lives.

2:12

Welcome to organic chemistry!

2:14

[Theme Music]

2:24

The fully saturated hydrocarbons I just described are usually called by the much simpler name, alkanes.

2:29

The simplest of the alkanes is one you've heard of before, methane, or CH4, the main compound in natural gas.

2:35

The next simplest alkane contains 2 carbons side by side, each one of them in bonded to 3 hydrogen atoms.

2:41

This is ethane, C2H6. Another gas, and it's mostly used in the production of plastics.

2:47

If we add another carbon and enough hydrogens to fill all those spaces we get our next alkane:

2:52

propane, C3H8.

2:54

Also a gas at room temperature and normal atmospheric pressure,

2:57

propane is a common fuel for cooking, heating, and vehicles,

3:01

as well as a propellant for everything from aerosol cans to paintball guns.

3:05

And we could do this all day, adding carbons to the chain and giving each compound a name,

3:10

but that would be pretty boring.

3:12

Things get more interesting, though, with the next alkane, butane, C4H10,

3:16

because there are two different forms of it.

3:19

The first is what you'd expect:

3:20

just a chain of carbons with hydrogens stuck wherever they're needed to make each carbon have 4 bonds.

3:26

This is called normal butane or n-butane.

3:29

But you can also arrange the 4 carbons differently by making a chain of 3

3:33

and then branching the fourth one off the center of the chain.

3:36

This is called isobutane or i-butane.

3:38

And even though it has the same chemical formula as n-butane, its structure gives it different properties.

3:43

For example, n-butane boils at -0.5 degrees Celsius while isobutane boils at -11.7 degrees Celsius.

3:49

These different structures for compounds that have the same molecular formula are called isomers.

3:53

As you add more and more carbon atoms to the molecule, there are more and more ways that you can arrange them.

3:58

So the number of atoms is butane only allows for 2 isomers, n-butane and isobutane.

4:03

But pentane, C5H12, has 3 possible isomers and C6H14, known as hexane, has 5.

4:09

Again, I could do this all day.

4:11

But looking at this table of the number of possible isomers you could see that that escalated quickly.

4:16

The take away here is that molecules that have the same mass and number of atoms can form different structures.

4:22

And as their structure changes, their properties also change.

4:25

As a general rule, the larger and more complex alkanes are, the more densely their molecules can pack together,

4:30

which means that they tend to be liquid or solid instead of gaseous at room temperature.

4:34

So alkanes with 5 to 18 chains of carbon atoms like octane and gasoline are liquids at room temperature

4:40

and those with more than 18 carbon atoms like paraffin or other waxes are solids.

4:44

Now you're probably picking up on a lot of words that you've heard before, even outside of chemistry class:

4:49

octane, propane, methane, paraffin, and so on.

4:52

You can chalk that up to the enormous popularity of these compounds in our daily lives.

4:56

Like I said, hydrocarbons are super useful because of the types of reactions they can take part in,

5:01

which I will explain more in a bit.

5:03

But first, I think it's high time you know what these names actually mean.

5:06

Much like the general language of chemistry that we talked about months ago,

5:10

organic nomenclature has its own system of prefixes, suffixes, and numbers

5:14

that tell you what's in the compound being named.

5:17

Now you gotta know the prefixes because they indicate how many carbon atoms are present.

5:21

Here's one that I know you've heard before: meth.

5:23

Meth- in a name always indicates a molecule or branch containing one carbon atom.

5:28

So the difference between amphetamines doctors prescribe

5:31

and methamphetamines that are sold on the streets is that

5:34

methamphetamine has a methyl group, CH3 with one carbon,

5:37

where amphetamine just has a single hydrogen atom.

5:40

Hopefully, that's helpful to you. Don't do drugs.

5:42

Eth- in a name means 2carbon atoms.

5:45

Prop- means 3. But- means 4.

5:48

From there, most of the prefixes will be familiar from geometry class

5:52

and you can review them in tables and learn them.

5:55

I'm not gonna go through them all. There are a few naming rules that are specific to alkanes.

5:58

First, alkanes are always named based on the longest possible continuous chain in their structure.

6:03

For example, even though this looks like a 5 carbon chain intersecting with a 6 carbon chain,

6:08

it actually contains an 8 carbon chain if you look at it close enough.

6:12

So this is considered an octane with two carbon chain attached to one of its carbon atoms.

6:16

When shorter carbon chains are attached to longer ones like this, they're still named using the same prefixes,

6:21

but we stuff a little -yl onto the end to show that they're just attachments.

6:25

Since this attachment has two carbons, we call it an ethyl group.

6:29

And the attachment with just one carbon that turns amphetamine into methamphetamine, that's the methyl group.

6:33

Attachments are also given a number to show you where along the chain they're attached.

6:38

The long chain is always numbered carbon by carbon

6:41

in the direction that gives the attachments the lowest numbers possible.

6:44

So, if we number the chain the right way, the ethyl group will end up at position 4.

6:48

But if you do it the wrong way, it's in position 5.

6:51

Low numbers win so it's numbered from left to right in this case.

6:55

So when we put it all together, this compound is called 4 ethyl octane.

6:59

Congratulations! You just named an organic compound.

7:01

Now particularly astute and studious students would have noticed something here.

7:05

Earlier, I introduced you to isobutane, a compound with four carbons that are not all in a chain.

7:11

They call that isobutane and it is an isomer of butane,

7:14

but according to these all important rules of nomenclature, it's not actually any sort of butane at all.

7:19

The longest carbon chain is just 3 carbons long, so it's propane with one methyl group sticking off of it.

7:24

If we wanted to give a technical name for it, isobutane would be 2-methylpropane.

7:28

Though, since the second carbon is the only place where the methyl group can go without the molecule,

7:33

once again becoming butane, properly proper chemists just drop the two and call it methylpropane.

7:39

Now suppose you have more than one of the same size group attached to the same chain,

7:43

like two methyl groups on the same alkane.

7:46

In this case, you put a number for both of them

7:47

and then prefixes like di- and tri- are used to indicate multiple attachments.

7:52

So for instance, if an octane chain has methyl groups attached with second and fifth carbons,

7:57

it's called 2,5-dimethyloctane.

7:59

On the other hand, if you have attachments of different lengths,

8:02

you just name and number each one separately, being sure to list them in alphabetical order.

8:06

The structure we just used had a methyl group on it and an ethyl group on its fifth,

8:11

it would be 5-ethyl-2-methyloctane.

8:13

This is super useful for several reasons.

8:16

One, because there are trillions of ways that organic compounds can come together.

8:20

But also because you can work backwards from a name and build a structural formula from it.

8:25

Let's try that out. We're gonna build 2-ethyl-3,5-dimethylnonane.

8:30

Start with the main chain, nonane. The prefix non- indicates 9 carbons.

8:35

Then, add an ethyl group, a 2 carbon chain on number 4 and then methyl groups, just 1 carbon on carbons 3 & 5.

8:43

Our final step is to add enough hydrogen atoms to give every carbon atom 4 bonds.

8:48

And now, the molecule is complete. It's like a puzzle that we got to make.

8:52

Of course these compounds don't exist in isolation.

8:55

Like any other compound, they can undergo a whole variety of reactions.

9:00

But there are 3 types of alkane reactions that are important enough for us to cover right now right here.

9:04

The first is the kind that made alkane the most common fuel for combustion or burning.

9:09

You'll note here that I'm saying burning, a common misperception, even among chemistry students,

9:13

is that combustion somehow equals explosion.

9:16

While that would definitely make things more interesting, also more dangerous,

9:20

those two things are not synonymous.

9:22

Combustion is the type of reaction that powers your car and your propane grill,

9:27

even candles among many other alkane fuels.

9:29

The general reaction for combustion requires a hydrocarbon, oxygen, and a source of heat energy.

9:35

In this example, we're using methane, but it works the same for any pure hydrocarbon.

9:39

The only thing that changes is the coefficients.

9:41

The products of a complete combustion of a pure hydrocarbon are always

9:45

carbon dioxide and water vapor, just those two things.

9:48

The next major reaction that alkanes experience is halogenation,

9:52

when halogen atoms like fluorine or chlorine are substituted for one or more hydrogen atoms in the alkane.

9:57

For example, the rather well-known compound chloroform is more correctly called trichloromethane.

10:03

It's a molecule of methane that is reacted with a chlorine gas,

10:06

resulting in three of the hydrogen atoms being replaced with chlorine atoms.

10:10

The final reaction type is dehydrogenation, and it, somewhat obviously,

10:14

is the removal of hydrogen atoms from alkanes.

10:17

For example, ethane can be dehydrogenated by this reaction,

10:21

and as you can see, the result is that the carbon atoms are no longer saturated with hydrogen, thus,

10:26

requiring the formation of double or triple bonds to give the atoms the 4 bonds that they need.

10:31

Hydrocarbons that contain double or triple bonds have

10:33

their own specific groups with different rules, reactions, and properties than alkanes.

10:38

And those are the topic of next week's episode.

10:41

For now though, thank you for watching this episode of Crash Course Chemistry.

10:44

If you were listening, you learned about some of the different classifications of organic compounds,

10:48

the structure and properties of the simplest alkanes.

10:51

You also learned about isomers and why they're important, how to name an alkane based on its structure,

10:56

and how to build an alkane structure from its name.

10:59

And finally, you learned a few important types of chemical reactions that alkanes experience:

11:03

combustion, halogenation, and dehyrdogenation.

11:06

This episode was written by Edi Gonzalez, it was edited by Blake de Pastino,

11:09

and our chemistry consultant is Dr. Heiko Langner.

11:12

It was filmed, edited, and directed by Nicholas Jenkins. The script supervisor was Caitlin Hofmeister.

11:17

And Michael Aranda is our sound designer. Our graphics team, as always, is Thought Cafe.

 

Short url:   https://multidict.net/cs/4870