Lecture 2:Organic Chemistry:

Carbon Chemistry

Let’s review bonding & Lewis Structures

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What is pencil lead made of if it isn't lead?

• Pencil lead is a mixture of graphite and clay.

• Graphite is one form of the element carbon.

• Other forms of carbon are diamond - the hardest naturally occurring substance on the earth, soot, charcoal and coke.

What is pencil lead made of if it isn't lead?

• Pencils used to be made with lead, many years ago. Lead is poisonous and so sucking the end of your pencil could be quite dangerous.

• We now use graphite and clay because it is safer and because we can make pencils of different hardness

Chemistry of Living Things

• Living things are a lot like laboratories…• There’s some serious chemistry going on

inside.• Your body is an incredibly complex chemical

machine taking in chemicals & food, and causing countless reactions to occur every second.

• Biochemistry is the study of substances & processes occurring in all living organisms.

What are living things made of?

I’m made of what???

• Guess how many elements your body is made up of?• 25 elements make up all living

things• About 97% of your body’s mass

is made of just 4 elements: oxygen, carbon, hydrogen, & nitrogen.

• Two other major elements are phosphorous & sulfur.

Minor Elements

• Of course, other elements are also important, but they’re often found in small amounts.

• They may seem insignificant, but they’re not.

• For example, iron makes up only 0.004% of your body mass, but you can’t live without it!

Major Compounds• The human body also relies on

many compounds, especially water & salt.

• The human body typically consists of 60-65% water.

• In other words, 2/3 of your body weight is water.

• Water is important because many of our body’s chemical reactions can only occur in solutions containing water.

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Major Compounds• Blood, sweat, urine…

all mostly water!• Salt is also important because

of how it can separate into its two ions: Na+ and Cl-.

• Sodium ions regular the amount of water in our cells, while chlorine ions help our body digest food.

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The most important element is…

Carbon• If you take away the water, the rest of the human body

is 53% carbon. • It may not be the most abundant element in living

things, but it certainly is the most important. At one time, scientists thought that the chemical reactions that took place inside of living things could not occur outside of them.

• The carbon molecules were so complex, scientists thought they must have been made in some unknown way. They called these carbon compounds organic compounds

The most important element is…• The wor d “or ganic” has lot s

of meanings. Event ually, scient ist s r ealized t hat t he r eact ions occur r ing inside t he body could occur out side it as well.

• They also lear ned how impor t ant car bon is in all living t hings, because of it s abilit y t o bond wit h ot her at oms.

The most important element is…• Not all subst ances made of

car bon ar e living. Diamonds & gr aphit e ar e pur e f or ms of car bon.

• Non-or ganic car bon compounds, and compounds wit hout car bon, ar e called inorganic compounds.

What is organic chemistry?

• We used to describe organic chemistry as the chemistry of living things.

• Since the chemistry of living things is based on carbon, the chemistry of carbon compounds has come to be known as organic chemistry.

• It now includes the study of carbon compounds which are not found in living things and so is an incredibly large branch of modern chemistry.

Why is life based on the element carbon?

• There are two important properties of carbon that make it a suitable element to form the compounds in living things:

• Firstly, carbon atoms can link together to form stable chains of great length.

Why is life based on the element carbon?

• Car bon at oms bind st r ongly t o each ot her and f or m ver y lar ge molecules which ar e built ar ound t his car bon ' backbone' .

• The covalent bond bet ween t wo car bon at oms is st r ong so t hat t he backbones are stable. I n all of t hese compounds simple sub-unit s called monomer s ar e linked t oget her by condensat ion r eact ions.

What makes carbon so special?

• I t has a “cent r al” r ole in all living or ganisms.• I t has 4 valence elect r ons.• I t makes 4 covalent bonds.• I t can bond wit h any

element , but r eally loves t o bond wit h ot her car bon at oms and make long chains

Lots of ways to draw this…

3 Types of Carbon Backbones

Carbon forms long chains

• One car bon chain may cont ain hundr eds of car bon at oms. • Unlike ot her element s, car bon at oms can bond t o each

ot her t o f or m ver y long chains. • One car bon chain may cont ain hundr eds of car bon at oms.

Not ice how t he CH2 unit s r epeat . • A ver y lar ge car bon-based molecule made of r epeat ing

unit s is called a polymer. Each unit of a polymer is called a monomer.

• Polymer s can be thousands of at oms long

Carbon forms Rings

• Car bon-based molecules also can be shaped like r ings. Most car bon r ings cont ain 5 or 6 car bon at oms.

• One of t he most impor t ant car bon r ings is benzene.• I t has 6 car bons & 6 hydr ogens , wit h alt er nat ing

double bonds.

Carbon forms Rings

• Many compounds ar e based on Benzene.• They of t en have ver y st r ong smells or ar omas,

so t hey ar e called aromatic compounds.• An example of one ar omat ic compound is a

molecule called vanillin. • Guess what t hat smells like!

•You have pr obablyhear d lot s of science f ict ionpr ogr ams on TV t alking about human beings as ' car bon-based lif e f or ms' .

Prepare to be assimilated…

Silicon is similar to carbon. Why are there no life forms based on silicon?

Silicon is unsuitable because, although it is a valence IV element like carbon (4 electrons to share), BUT the silicon-silicon covalent bond is not strong enough for it to form long stable chains. So, it can not form molecules of the complexity needed to make up cells like carbon can!

We are not silicon based life forms!

Long Chain Hydrocarbons & their Names

• The alkanes make up a series of saturated hydrocarbons, called an homologous series because they have similar properties and have the same general formula:

• The f irst four members of the series are gases at room temperature and are called:

• methane, CH4

• ethane, C2H6

• propane, C3H8

• butane, C4H10

Covalent Bonding Review

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Alkanes

• Alkanes with increasing numbers of carbon atoms have names are based on the Greek word for the number of carbon atoms in the chain of each molecule.

• So you can get, for example,• pentane (5), • hexane (6),• heptane (7)• and octane (8).

• From pentane onwards, approximately the next thirty alkanes in the series are liquids.

• Alkanes with even longer chains are waxy solids.

• They are typical covalent compounds, insoluble in water but able to mix with each other.

• Alkanes burn in oxygen to produce carbon dioxide and steam.

Lots of carbon compounds seem to be isomers. What is an isomer?

• In organic chemistry, there are many examples of different compounds which have the same molecular formula as each other,

• But different arrangements (structures) of the atoms in their molecules.

• These are called isomers.

What is an isomer?

• These compounds are said to be isomers of one another.

• Isomerism also occurs in inorganic chemistry, but it is less common.

If isomers have the same atoms in them, surely they have the same properties, so

what's the point?

• In fact, these small changes in structure can have significant effects on the properties of the substance!

• But, it is important to realize that this can have significant effects in a living system.

• One optical isomer of glucose, for example, can be used by a living cell, but the other isomer cannot.

• This is because the enzyme in the cell which recognizes glucose is sensitive to only one form.

There are two types of isomerism common in organic chemistry:

1. structural isomerism• Which have the atoms of their

molecules linked in a different order.

• This can come about in one of three ways:

Chain Isomerism

• Chain isomers of t he same compound ar e ver y similar .

• Ther e may be small dif f er ence in physical pr oper t ies such as melt ing or boiling point due t o dif f er ent st r engt hs of int er molecular bonding.

• Their chemist r y is likely t o be ident ical.

Positional Isomers

• Positional isomers ar e also usually similar . • Ther e ar e slight physical dif f er ences, but t he

chemical pr oper t ies ar e usually ver y similar .• However , occasionally, posit ional isomer s can

have quit e dif f er ent pr oper t ies

Positional Isomers

• A simple example of isomerism is given by pr opanol: • it has t he f or mula C3H8O (or C3H7OH) and t wo isomer s

pr opan-1-ol (n-pr opyl alcohol; I) and pr opan-2-ol (isopr opyl alcohol; II)

• Not e t hat t he posit ion of t he oxygen at om dif f er s bet ween t he t wo: it is at t ached t o an end car bon in t he f ir st isomer , and t o t he cent er car bon in t he second.

• The number of possible isomer s incr eases r apidly as t he number of at oms incr eases; f or example t he next lar gest alcohol, named but anol (C4H10O), has f our dif f er ent st r uct ur al isomer s.

Functional Group Isomers

• Functional group isomers ar e likely t o be bot h physically and chemically dissimilar .

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