Chapter 22: Organic & Biological Molecules: Hydrocarbons, Polymers, Biomolecules

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Imagine for a moment a spider web, you know, glistening with dew.

It's just amazing, like nature's engineering, right?

And it's spun from this substance,

super strong and flexible, we call an organic polymer.

Yeah, it's incredible stuff.

And what's truly wild is that this delicate thing, it's fundamentally built from the same basic element that makes up, well, almost everything around us.

Simple life forms, complex human creations, everything.

Carbon.

Carbon really is the star.

Welcome to the deep dive.

Today we're jumping into the fascinating world of organic and biological molecules.

We're pulling insights from chapter 22 of Zumdahl, Zumdahl and de Kass' chemistry, the 11th edition.

Good source material there.

And our mission really is simple.

Give you a clear, hopefully engaging shortcut to understanding these essential building blocks.

Think of it as your guide for mastering these chem concepts for college, but all through listening.

No visuals needed.

We'll try to paint a picture with words.

Exactly.

We'll demystify the chemistry, show you why it matters in your world, and maybe uncover some surprising facts along the way.

Sounds like a plan.

So let's unpack this central idea first.

Why is carbon so, I don't know, special?

Well, carbon really stands out because of its amazing ability to bond strongly, not just to itself, forming long chains and rings, but also to loads of other non -metals, hydrogen, oxygen, nitrogen, sulfur.

Right.

And this versatility, this ability to create complex structures, that's the entire foundation of organic chemistry, you know, the study of carbon containing compounds.

It's a massive field, millions of known compounds, and the number just keeps going up.

I remember learning that way back, people actually believed organic compounds had some kind of mystical life force.

Like they could only come from living things.

That's right.

The vitalism theory.

It was a dominant idea for a long time.

So how did we get past that?

Well, that whole idea was famously shattered in 1828.

Friedrich Willer, he synthesized urea, which is definitely an organic substance found in urine, but he made it from an inorganic salt, ammonium cyanate.

Just in the lab.

Just by heating it in his lab.

Yeah.

Yeah.

It's a huge paradigm shift.

It basically proved that the line between living and non -living compounds, chemically speaking, wasn't some kind of insurmountable barrier.

Wow.

That's a powerful revelation.

So, okay, fast forward to today.

What's the real world impact of all this carbon chemistry?

Oh, it's immense.

I mean, look around you.

The synthetic fibers in your clothes, the plastics that shape pretty much everything, the drugs that heal us, the fuels that power, well, everything.

It's everywhere.

It's absolutely fundamental.

Organic chemistry is deeply woven into our daily lives.

Okay.

Let's start our deep dive into the specifics then.

How about the simplest class?

Hydrocarbons, just carbon then hydrogen.

Exactly.

And we split them into two main types,

saturated and unsaturated.

Think of it maybe like a sponge.

Okay.

A saturated hydrocarbon, which we call an alkane, is like a full sponge.

Every carbon atom is bonded to four other atoms, all single bonds.

It's holding the maximum number of hydrogens it possibly can.

Saturated, got it.

Then you have unsaturated hydrocarbons.

These are things like alkenes, which have a carbon -carbon double bond, or alkenes with a triple bond.

They're like a sponge that's not full.

They have loom to add more atoms because those multiple bonds can break open and let other atoms attach.

Makes sense.

And alkenes, structurally, they're interesting.

Methane is just one carbon, then ethane, propane.

But even when we call them straight chain, they're not really straight, are they?

No, not at all.

They actually zigzag in 3D space.

Each carbon in an alkane has four single bonds, and those bonds want to get as far apart from each other as possible.

This leads to what chemists call tetrahedral geometry, roughly 109 .5 degree angles.

So yeah, definitely a zigzag, not a straight line.

Okay.

And with millions of these compounds, naming them must be important.

How does that work for, say, Branstalkane?

Right.

You need a system, the IUPAC system.

Basically, you find the longest continuous chain of carbon atoms that gives you the root name, like hex for six carbon, so hexane.

Okay.

Then any smaller carbon groups attached to that main chain are called alkyl substituents.

Like a methyl group is one carbon, ethyl is two.

You just use numbers to say where they are attached on the main chain.

Gives each compound a unique name.

And how do these alkenes behave,

chemically speaking?

Well, generally, they're pretty unreactive.

Those carbon -carbon and carbon -hydrogen single bonds are quite strong, so they don't react easily with things like acids or bases.

But they do burn?

Oh, absolutely.

Their most critical reaction for us is combustion, burning with oxygen.

That's why there's such vital fuels, natural gas, gasoline, butane in lighters.

It's all about combustion.

Okay.

Any other reactions?

They can undergo substitution reactions.

Usually you need something like ultraviolet light to kick it off.

A hydrogen atom gets swapped out for, say, a halogen atom like chlorine.

And this process, interestingly, had a major environmental consequence.

It was used to create chlorofluorocarbons, or CFCs.

Remember freon?

Yeah, in old fridges and spray cans.

Exactly.

Those CFCs were found to be destroying the Earth's protective ozone layer.

A huge problem.

Thankfully, the international community came together with the Montreal Protocol in 1987 and banned them.

And the ozone layer is recovering now, right?

It is, slowly but surely.

A real environmental success story, actually.

That's good to hear.

Now, carbon atoms can also form rings, cyclic alkanes.

You mentioned small rings are reactive.

Yeah, really reactive.

Cyclopropane with three carbons in a ring and cyclobutane with four.

The reason is ring strain.

Strain.

Yeah, think about it.

Carbon wants those 109 .5 degree bond angles for its single bonds.

But in a tiny triangle like cyclopropane, the angles are forced to be 60 degrees.

In cyclobutane, they're about 88 degrees.

That's a lot of strain.

Like bending something that doesn't want to bend.

Exactly.

It makes the bonds weaker and the molecule eager to react to break open that ring and relieve the strain.

But bigger rings are okay, like cyclohexane.

Right.

Larger rings, like cyclohexane with six carbons, are much more stable.

Why?

Because they're not flat.

They can pucker up, adopt conformations like the famous chair form.

Chair form.

Yeah, it looks kind of like a lounge chair if you squint.

In that chair shape, all the bond angles can get very close to that ideal 109 .5 degrees.

So no strain, much more stable, much happier molecule.

Getting comfortable.

I like that.

Okay, let's shift gears now to the unsaturated ones.

Alkenes and alkenes.

Double and triple bonds.

What's the big deal about a double bond compared to a single?

The crucial difference is restricted rotation.

A single bond is like an axle.

The atoms can spin around it freely, but a double bond is more like two planks nailed together.

Okay, so it's rigid.

Pretty much.

You can't easily twist one carbon relative to the other around that double bond, and this fixed position has a big consequence.

Cis -trans isomerism.

Cis -trans.

Explain that.

Okay, imagine you have groups attached to the carbons of the double bond.

If two identical groups are on the same side of the double bond, we call that the cis -isomer.

If they're on opposite sides, it's the trans -isomer.

Same formula, different shape.

Exactly.

Same atoms connected in the same order, but arranged differently in space.

And this difference between cis -tubutene and trans -tubutene can really affect the molecule's properties, how it fits into enzymes, boiling point, everything.

And because they have these multiple bonds, they react differently too.

More reactive than alkenes.

Oh, much more reactive.

Their main game is addition reactions.

Atoms literally add across the double or triple bond, breaking one of the bonds in the process and single bonds.

Can you give an example?

Sure.

A really important industrial one is hydrogenation.

You add hydrogen across the double bonds in unsaturated fats, like liquid vegetable oils.

This turns them into saturated fats, which are often solids, like shortening or margarine.

Ah, so that's how they make margarine solids.

That's a big part of it, yeah.

Changes of the texture, the melting point, shelf life.

Interesting.

Okay, now let's zoom out again to a really special group.

Aromatic hydrocarbons.

Benzene is the classic example.

C6H6.

Absolutely.

Benzene is kind of the poster child for aromaticity.

It's a flat ring of six carbons, and it looks like it should have alternating double and single bonds, but it doesn't really behave that way.

Why not?

Because it's electron specifically, six of its electrons aren't stuck between specific carbons.

They are delocalized.

Delocalized, meaning?

Meaning they're shared equally by all six carbon atoms in the ring.

You can imagine it like a cloud or maybe like a donut of electron density sitting above and below the plane of the ring.

Like a shared electron cloud.

Exactly.

And this delocalization gives benzene incredible stability, much more stable than you'd expect if it just had regular double bonds.

So if it's so stable, how does it react?

Not like those Elkins doing addition reactions.

Generally, no.

Benzene really resists addition reactions because that would break up its stable aromatic system, its electron donut.

Instead, it prefers substitution reactions.

Swapping things out.

Right.

One atom on the ring, usually a hydrogen, gets swapped out for another atom or group.

This way, the stable aromatic ring stays intact.

Often needs a catalyst to make it happen, though.

And where do we find these aromatic compounds?

Oh, everywhere.

They're crucial in making colorful dyes, many pharmaceuticals, plastics.

But there's a downside, too.

Some complex aromatic systems, like a molecule called 3 -vila -4 -benzpyrene, which you find in cigarette smoke and car exhaust, are known carcinogens.

Right.

So powerful chemistry, but needs careful handling.

This idea of specific groups dictating behavior leads us nightly into functional groups.

Yes.

This is a huge concept in organic chemistry.

Most organic molecules aren't just carbon and hydrogen.

They have other elements, oxygen, nitrogen, halogens, arranged in specific, predictable clusters.

These are the functional groups.

And they determine the molecule's

personality.

That's a great way to put it.

Each functional group has its own characteristic chemistry.

It dictates how the molecule will react, its properties, regardless of the size or shape of the carbon backbone it's attached to.

It's what gives organic chemistry its incredible diversity.

Okay, let's look at some key ones.

First up, alcohols.

They have that hydroxyl group, the OOH.

Right.

And that little OOH group makes a massive difference.

Think about boiling points.

Ethanol, the alcohol in drinks, has a similar size to ethane and alkane.

But ethanol boils way, higher.

Why is that?

Hydrogen bonding.

That OOH group allows alcohol molecules to form strong intermolecular attractions with each other, similar to how water molecules stick together.

Ethane can't do that.

So it takes much more energy, a higher temperature, to boil an alcohol like methanol or ethanol compared to a similar sized alkane.

Huge difference from just one oxygen atom.

And alcohols are used everywhere, right?

Ethanol in drinks, gas, a whole fuel.

Exactly.

Methanol is major industrial chemical, though it's quite toxic.

And ethylene glycol, that's the main ingredient in most car antifreeze.

Okay, next group.

Aldehydes and ketones.

They both have the carbonyl group.

A C double bonded to an O.

That's the key feature, yes.

The difference is what else is attached to that carbonyl carbon.

In a ketone, the CITO is bonded to two other carbon atoms.

A common example is acetone, the solvent and nail polish remover.

In an aldehyde, the CO is bonded to at least one hydrogen atom.

Aldehydes often have really distinctive smells, sometimes pleasant, like vanillin from vanilla beans or cinnamaldehyde giving cinnamon its scent.

But not always pleasant.

Heavenly not always.

Think of butyraldehyde that's responsible for the lovely aroma of rancid butter.

Often these are formed by oxidizing alcohols.

Okay, and related to these are carboxylic acids and esters.

Carboxylic acids, first they're acids.

Weak acids, yes.

They have the carboxyl group, which is written as COOH.

It's basically a carbonyl group and a hydroxyl group on the same carbon.

The most common one you encounter is probably acetic acid.

That's what makes vinegar sour.

Got it.

Vinegar and esters.

Esters form when you react to carboxylic acid with an alcohol.

A water molecule usually gets eliminated in the process, and esters are famous for their smells too, but typically sweet and fruity odors.

Like fruit smells.

Exactly.

The smell of bananas is largely due to an ester called enamel acetate.

Pineapple, orange, apple scents, often esters.

And a really important medicinal ester is acetyl salicylic acid.

That sounds familiar.

You know it better as aspirin, a hugely important painkiller made via an esterification reaction.

Wow, okay.

Last functional group for now,

amines.

Nitrogen containing compounds.

Right.

Think of them as derivatives of ammonia, NH3, where one or more of the hydrogens are replaced by carbon groups.

And amines, well, they often come with characteristic odors too.

Good or bad.

Often.

Not great.

Many have fairly unpleasant fish -like smells.

Compounds like putrescine and cadaverine, as their names suggest, are amines associated with decaying tissues.

Part of nature's recycling process, I suppose.

Okay.

Let's move from these building blocks to the really huge molecules.

Yeah.

Polymers.

These are just gigantic, right?

Absolutely massive.

Polymers are long chains made by linking together many, many smaller repeating units called monomers.

Think of it like making a chain out of thousands of paperclips.

And they make up plastics fibers.

Plastics, synthetic fibers like nylon and polyester rubbers.

They fundamentally changed our world.

Modern life is almost unimaginable without synthetic polymers.

It seems like a lot of these were discovered by accident.

So many were.

Serendipity played a huge role.

Take bakelite, often considered the first truly synthetic plastic.

Leo Bakelund, around 1907, was trying to make something else entirely and kept getting this hard, terry gunk.

But he didn't just throw it away.

He experimented with it, figured out how to control the reaction, and created bakelite.

It was amazing because it was a thermoset polymer.

Meaning?

Meaning once you heated it and molded it into shape, it set permanently.

You couldn't remelt it.

Super durable, heat resistant, great insulator, perfect for early electrical components, radios, telephones.

And nylon, that was another interesting story, right?

Strength from stretching.

Yeah, Wallace Carruthers and his team at DuPont were working on long chain molecules.

They made this stuff, initially just a sticky mess.

But then, legend has it, a chemist pulled a fiber out of it with a stirring rod and noticed it was strong and silky when stretched.

Why did stretching make it strong?

When you draw nylon into a fiber, the long polymer chains, which are normally all tangled up, get aligned parallel to each other.

This alignment allows lots of hydrogen bonds to form between adjacent chains, acting like molecular velcro, holding the chains together very tightly.

That's what gives nylon its strength.

Like weaving threads into a rope.

Exactly.

And then there's vulcanized rubber.

Charles Goodyear's famous accident.

Dropped rubber mixed with sulfur onto a hot stove.

And it didn't just melt?

Nope.

It charred, but it charred.

That process, vulcanization, creates cross -links, chemical bonds, sulfur bridges, actually, that connect the long rubber polymer chains together.

This network structure is what gives rubber its durability and elasticity, essential for tires.

Okay, so how are these polymers actually made?

You mentioned monomers linking up.

There are two main mechanisms.

Addition polymerization is the simpler one.

Monomers, usually containing a double bond like ethylene, just add to each other, one after another, to form the long chain, like linking clips.

And that gives us?

Things like polyethylene.

You get different types depending on how the chains pack.

LDPE, low -density polyethylene, has branched chains, making it flexible good for plastic bags and films.

HDPE, high -density polyethylene, has linear chains that pack tightly, making it rigid use for milk jugs, bottles.

Okay.

And the other type?

Condensation polymerization.

Here, when two monomers join, a small molecule, usually water, is eliminated or condensed out.

Like the ester formation.

Exactly the same principle.

Nylon is a classic example.

It's often a copolymer, meaning it's made from two different monomers that react together, releasing water each time they link up via a peptide linkage, also called an amide bond.

Dacron, or polyester used in fabrics, is another condensation polymer.

It's amazing what chemists have engineered.

But nature's been doing this for billions of years, right?

Natural polymers.

Oh, absolutely.

Life itself is built on natural polymers.

Proteins, carbohydrates like starch and cellulose, DNA.

They're all giant molecules made from repeating monomers.

Let's talk proteins.

They do everything in the body, practically.

Pretty much.

They make up about 15 % of our body mass.

You have fibrous proteins giving structure, muscle fibers, hair, tendons, and globular proteins doing the work, transporting oxygen like hemoglobin, catalyzing reactions as enzymes, fighting disease as antibodies.

And their monomers are amino acids.

Alpha amino acids specifically.

There are about 20 common ones.

They link together via those same peptide linkages we saw in nylon to form long chains called polypeptides.

What makes each protein different?

Two things mainly.

First, the sequence of amino acids.

Second, the nature of the R groups or side chains on each amino acid.

Some side chains are hydrophilic.

They like water.

Others are hydrophobic.

They avoid water.

This plays a huge role in how the protein folds up into its specific 3D shape.

And that shape is critical, right?

Proteins have different levels of structure.

Yes, absolutely critical.

We talk about four levels.

Primary structure is just the sequence, the order of amino acids in the chain, and small changes here can have massive effects.

Like how?

Well, take oxytocin and vasopressin.

They're tiny polypeptides, just nine amino acids long.

They differ by only two amino acids out of the nine.

Yet, oxytocin triggers things like uterine contractions, while vasopressin regulates blood pressure.

Totally different jobs from a sequence change.

Wow.

Okay.

What's next after primary?

Secondary structure.

This refers to local folding patterns within parts of the polypeptide chain.

Things like coils or sheets stabilize mainly by hydrogen bonding between backbone atoms.

The two main types are the alpha helix, a coil shape found in elastic proteins like hair and wool, and the pleated sheet where sections of the chain line up side by side, forming strong sheet -like structures found in like silk.

And the tertiary structure.

That's the overall unique three -dimensional shape of the entire polypeptide chain.

How the helices and sheets and loops all fold together.

This shape is absolutely crucial for the protein's function, like how an enzyme's active site is shaped to bind its target molecule.

What holds that 3D shape together?

A whole mix of interactions between those R groups.

Hydrogen bonds, ionic bonds, hydrophobic interactions pushing oily groups together, and especially desulfide linkages.

These are strong covalent bonds formed between two specific amino acids called cysteine.

They act like molecular staples holding parts of the chain together.

Is that related to getting a Bperm?

Exactly.

Getting a Bperm involves chemically breaking the disulfide bonds in your hair proteins, reshaping the hair, and then reforming the disulfide bonds in the new shape.

You're manipulating the tertiary structure.

What happens if that structure gets messed up?

That's called denaturation.

The protein unfolds, loses its specific 3D shape, and therefore loses its biological function.

Think about cooking an egg.

The white turns solid.

Right.

The heat denatures the albumin protein, causing it to unfold and tangle up, becoming solid and opaque.

Denaturation can also be caused by changes in pH, radiation, certain chemicals, heavy metals like lead or mercury.

It shows how vital maintaining that precise 3D structure is.

Yeah, definitely.

It makes you wonder if your body couldn't form hydrogen bonds in proteins, could you even survive?

Highly unlikely.

They are fundamental to protein structure and function, and so much more in biology.

Okay, let's switch to carbohydrates.

Yeah.

Sugars and starches.

Energy source.

The energy source for many organisms, yeah.

And also crucial structural materials, especially in plants.

Their monomers are monosaccharides, simple sugars like glucose and fructose.

An interesting feature of these sugars is that they often contain chiral carbon atoms, means handed.

A chiral carbon is one that's bonded to four different groups.

Just like your left and right hands are mirror images, but you can't superimpose them,

molecules with chiral carbons can exist as mirror image forms called optical isomers.

And does that matter?

Hugely in biology.

Often your body's enzymes can only recognize or process one specific handed form of a sugar or amino acid.

The other form might be useless or even harmful.

It's like trying to put a left glove on your right hand.

Got it.

And these simple sugars link up.

They do.

Two monosaccharides link to form a disaccharide, like sucrose table sugar, which is made from glucose and fructose joined by a glycoside linkage.

Link many together and you get polysaccharides.

Like starch and cellulose.

Exactly.

And here's something fascinating.

Starch, which plants use to store energy, and cellulose, the main structural component of plants, wood, cotton, they are both polymers made only of glucose monomers.

So what's the difference?

Just the type of glycoside linkage connecting the glucose units.

It's a subtle difference in geometry, alpha versus beta linkages.

But humans have enzymes, alpha glycosidases, that can break the alpha linkages in starch, allowing us to digest it for energy.

But not cellulose?

Nope.

We lack the enzymes.

Beta glycosidases needed to break the beta linkages in cellulose.

That's why we can eat potatoes, but not wood.

Cows and termites, though, have gut microbes that can digest cellulose.

It's all down to that tiny difference in the linkage.

Incredible.

Okay.

Finally, the molecules that carry the code of life,

nucleic acids,

DNA and RNA.

The blueprint.

Exactly.

Life, as we know it, depends on cells being able to store, transmit, and use genetic information.

That's the job of nucleic acids.

So DNA, deoxyribonucleic acid, stores the info.

Right.

It's this huge molecule, usually found in the cell nucleus, containing the master plan.

And RNA, ribonucleic acid, plays various roles in actually using that information to build proteins.

And their monomers are called?

Nucleotides.

Each nucleotide has three parts.

A five -carbon sugar, deoxyribose in DNA, ribose in RNA,

a nitrogen -containing organic base, and a phosphate group from phosphoric acid.

The bases are the letters, right?

A, G, C, T.

Exactly.

Adenine A, guanine G, cytosine C, and thymine T are the four bases in DNA.

In RNA, uracil, U, takes the place of thymine.

And DNA is famous for its double helix structure.

That's right.

Discovered by Watson and Crick, building on work by Franklin and Wilkins, it looks like a twisted ladder.

The sides of the ladder are alternating sugar and phosphate groups.

The rungs are pairs of bases.

And the pairing is specific.

Absolutely specific.

And held together by hydrogen bonds.

Adenine A always pairs with thymine T, forming two hydrogen bonds.

Guanine G always pairs with cytosine C, forming three hydrogen bonds.

A with T, G with C.

This is called complementary base pairing.

And this pairing is the key to copying DNA for replication.

Precisely.

The double helix can unzip down the middle, separating the base pairs.

Then each strand acts as a template.

New nucleotides come in and pair up with their complements on the template strand.

A with T, G with C.

And enzymes link them together to build a new identical complementary strand.

Result, two perfect copies of the original DNA molecule, essential for cell division.

And how does DNA direct protein synthesis?

Okay.

So a specific segment of DNA that codes for one protein is called a gene.

The sequence of bases in that gene dictates the primary structure, the amino acid sequence, of the protein.

How does the code get used?

First, the code from the gene is transcribed onto a molecule of messenger RNA, mRNA.

This mRNA then travels out of the nucleus to the ribosomes, which are like the protein -making factories of the cell.

Then transfer RNA, tRNA molecules come into play.

Each tRNA carries a specific amino acid and has an anticodon, a three -base sequence that's complementary to a three -base codon on the mRNA.

The tRNA matches its anticodon to the mRNA codon the ribosome, delivering the correct amino acid to be added to the growing protein chain.

It happens step by step, codon by codon, building the protein according to the DNA's instructions.

That's like a molecular assembly line translating the genetic code.

It really is an incredibly precise and elegant system that underlies all of life.

Wow.

Okay.

We have taken a really deep dive today.

We went from, you know, simple hydrocarbons powering our cars all the way to the mind -boggling complexity of DNA, the actual blueprint of life.

It's quite a journey from simple chains to intricate biological machines.

We've seen how carbon's unique bonding creates this incredible variety, how functional groups give molecules their specific personalities, and how these chemical processes, both the ones we've engineered and the ones nature perfected, create the materials and systems that literally define our existence.

Hopefully you now have a clearer picture of this chemical world, both around you and inside you.

Understanding why structure leads to properties and function is really empowering knowledge.

Definitely.

It gives you a whole new lens to see the world through.

So as we wrap up, here's something to chew on.

Thinking about all these polymers, we discussed synthetic ones like bakelite or nylon, natural ones like proteins or DNA.

What single chemical breakthrough or discovery related to these large molecules do you think has had the most profound, most lasting impact on daily human life and why?

That's a great question to ponder.

There are so many contenders.

Absolutely.

Thank you for joining us on this deep dive into organic and biological molecules.

This has been a special deep dive from your Last Minute Lecture Team.

Keep learning.