Organic Chemistry Hydrocarbons 1. Carbon Carbon can form covalent bonds with itself and create...

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Organic ChemistryHydrocarbons

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Carbon

• Carbon can form covalent bonds with itself and create networks

• No other element has this ability

• Each carbon atom can make four single bonds and form a tetrahedral structure

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Carbon has 4 valence electrons but can bond to fewer than 4 atoms and form double and triple bonds

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Hydrocarbons – the simplest organic compounds

In an unsaturated hydrocarbon, the double or triple bond can be broken and carbon can bond to one more atom.

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Alkanes – saturated hydrocarbons (all single bonds)

Formula for butane: C4H10

General Formula for alkanes:Cn H2n+2

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Alkanes

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Saturated hydrocarbons (all single bonds) are called alkanes

Butane

When you observe the structure

of butane, you see that a “straight” chain is really not straight nor linear

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Naming Alkanes To name alkanes:Count the number of carbonsFind the corresponding Greek rootAdd “-ane” to indicate it is an alkane

Organic chemists call this n-pentane, where n indicates the longest straight chain

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Branched alkanes To name branched alkanes:

1) Find the parent compound (the longest continuous chain) and add “-ane” to the Greek root

heptane

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To name branched alkanes:

2)Find the branch(es) not included and add “-yl” to the Greek root

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• Start counting from the shortest end of the parent compound

• (here, it is position “4” from both ends)

To name branched alkanes:

3) Find the position at which the branch(es) is (are) located on the parent compound

Name: 4-ethyl-heptane

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Naming alkanes

heptane

ethyl

1 2 3 4

The branching group is called the R group

Here, R = CH2CH3

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structural isomer: molecule with the same number and type of atoms as another molecule but has a different bonding pattern.

n-butane (C5H12) and isobutane (C5H12) are structural isomers

n-butane isobutane

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2-methyl-propaneisobutane

methyl group at position “2”

methyl group at the second-to-last position

4 carbons in total

Naming alkanes

same molecule

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Draw and name the structural isomers of pentane (C5H12).

• Make a chain of 5 carbons and add hydrogens.

n-pentane

2-methyl-butane

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Structural isomers

Draw and name the structural isomers of pentane (C5H12).

We can remove 2 carbons and form 2 branches in one position.

isopentanen-pentane

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Petroleum chemistry

• Isooctane is better for the car engine because it burns more slowly and more completely than octane.

• At the gas pump, unleaded 87 has 87% isooctane and 13% octane.

octane

isooctane(2,2,4-trimethyl-pentane)

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IntermIntermolecular attractions are also called van der Waals attractionsolecular attractions are also called van der Waals attractions

strong

London dispersion Dipole-dipoleDipole-dipole Hydrogen bondingbonding

Types of intermolecular attractions

Betweenpolar molecules

Betweennonpolar molecules

Intermolecular attractionsweak

Hydrocarbons

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Properties of hydrocarbons

London dispersion

Betweennonpolar molecules

Hydrocarbons

With weak intermolecular attraction forces, small hydrocarbons are gases at room temperature.

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Properties of hydrocarbons

As hydrocarbon chains become longer, attraction forces become stronger. Longer hydrocarbons are liquids at room temperature.

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n

Polyethylene

Unsaturated hydrocarbons

Ethene or ethylene is a gas at room temperature.

It can be used to create the polymer polyethylene in plastics

unsaturated hydrocarbon

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Unsaturated hydrocarbons

Acetylene torch

unsaturated hydrocarbon

Ethyne or acetylene is a hydrocarbon that contains a triple bond.

There is more energy in a triple bond than in a double or single bond.

Acetylene torches reach temperatures up to 3,300oC (6,000oF)

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Naming unsaturated hydrocarbons

To name unsaturated hydrocarbons:

1) Count the number of carbons

2) Find the corresponding Greek root

3) Add “-ene” to indicate a double bondAdd “-yne” to indicate a triple bond

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Naming unsaturated hydrocarbons

To name unsaturated hydrocarbons:

1) Count the number of carbons

2) Find the corresponding Greek root

3) Add “-ene” to indicate a double bondAdd “-yne” to indicate a triple bond

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Isomers

Stereoisomers Same bonding orderDifferent spatial arrangement

Structural isomers Same formulaDifferent bonding order

Geometric isomers

Butenetrans configuration(R groups opposite sides of the C=C bond)

cis

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Isomers

Stereoisomers Same bonding orderDifferent spatial arrangement

Structural isomers Same formulaDifferent bonding order

Geometric isomers Optical isomers

The central carbon is attached to four different groups.

Optical isomers are two different molecules!

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Aromatic hydrocarbons

Cinnamon, cloves, wintergreen and vanilla beans have pleasant, distinctive smells

What else do they have in common?

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Aromatic hydrocarbons

What else do they have in common?Benzene ring

Aromatic hydrocarbons contain one or more benzene rings

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Resonance structures of benzene

Electrons are always moving, so the single and double bonds on the benzene ring are never fixed.

To show that electrons are “delocalized” and equally shared, a circle is used instead.

C6H6

Aromatic hydrocarbons

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Alkanes Greek root + “-ane”

Alkenes Greek root + “-ene”

Alkynes Greek root + “-yne”

R groups Greek root + “-yl”

Saturated hydrocarbons

Unsaturated hydrocarbons

Hydrocarbon constituents

Naming of hydrocarbons

Parent compound

Section Review:

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Stereoisomers Same bonding orderDifferent spatial arrangement

Structural isomers Same formulaDifferent bonding order

Geometric isomers Optical isomers

cis trans

Section Review:

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Hydrocarbons have different properties

depending the

functional groups attached to them

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Functional groups

Common functional groups

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Alcohols

R OH

Hydroxyl group

Alcohol can be used as a disinfectant because it breaks lipids apart and precipitates proteins

Small alcohol molecules are liquids due to hydrogen bonding, but they vaporize easily

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Ethers

R O R

Early use of diethyl either as an anesthetic

Ethers are volatile because intermolecular attractions are weak

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Aldehydes

R C H

OThe C O group is also called the carbonyl group

A wide variety of familiar smells and flavors come from aldehydes

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R C R’

O

Ketones

R and R’ can be the same, but do not have to be

Ketones are also responsible for many familiar smells and flavors

AcetoneAcetone is also used as a cleaning agent in the lab and in industry because it mixes well with water and dissolves organic substances.

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Aldehydes and ketones

R C H

O

R C R’

O

R and R’ can be the same, but do not have to be

Glucose

Fructose

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Aldehydes and ketones

Glucose

Fructose

6-membered ring

5-membered ring

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Aldehydes and ketones

glucose fructose

Carbohydrates (or saccharides) are the primary source of energy for most animals

di-saccharide

“two” “sugars”

Sucrose (table sugar): a disaccharide containing 1 glucose molecule and 1 fructose molecule

Starch (in pasta, potatoes): a polysaccharide that uses glucose molecules as a monomer

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R C H

O

R C R’

OR O RR OH

Alcohol

Common functional groups

Ether

Aldehyde Ketone

R and R’ can be the same, but do not have to be

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Carboxylic acids

R C OH

O

Red ants use formic acid as a chemical weapon

Vinegar and citrus fruits contain acetic acid

Carboxylic acids are weak acids in aqueous solutions

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Carboxylic acids

R C OH

OCarboxylic acids are weak acids in aqueous solutions

R COOH(aq) + H2O(l) R COO–(aq) + H3O+(aq)

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Amines

R NH2Amines are organic molecules that contain an amino (NH2) group.

Alanine is one of the amino acids that make up all the proteins in our bodies

Chlorpheniramine(allergy medication)

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Amines

R NH2Amines are weak bases in aqueous solutions

R NH2(aq) + H2O(l) R NH3+(aq) + OH–(aq)

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Esters

R C OR’

O

The smell of lavender comes from a molecule that contains an ester functional group

Esters are very common in nature. They are often responsible for the fragrances of flowers and ripened fruit.

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Esters

R C OR’

OIsobutylacetate

Manufacturers often add specific esters to give a better flavor to their foods and drinks.

A mixture can smell like strawberries without using actual strawberries!

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Esters

R C OR’

OEsters cannot participate in hydrogen bonding, and they vaporize easily

Polyesters are polymers that contain the ester group on the hydrocarbon chain.

Polyester clothing made with polyethylene terephthalate (PET) fiber is popular because it does not wrinkle easily

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R C OR’

O

R NH2R C OH

O

R C H

O

R C R’

OR O RR OH

Alcohol

Common functional groups

Ether

Aldehyde Ketone

Carboxylic acid Amine Ester

Combustion of hydrocarbons

Alkanes are widely used as fuel:

Substitutions

Chlorination is an example of a substitution reaction

This reaction requires energy (such as light) to break the Cl–Cl bond and form two free chlorine radicals, Cl•

Substitution reaction: One or more hydrogen atoms are removed and replaced by different atoms.

Substitution reaction: One or more hydrogen atoms are removed and replaced by different atoms.

Chlorination is an example of a substitution reaction

Substitutions

Dehydrogenation

Dehydrogenation reaction: an alkane becomes an unsaturated hydrocarbon by losing H2.

This reaction is nonspontaneous. It needs energy (such as high temperature) as well as a catalyst.

Hydrogenation

This reaction is nonspontaneous. It needs energy (such as high temperature) as well as a catalyst.

Hydrogenation reaction: a type of addition reaction during which an unsaturated hydrocarbon becomes saturated with the addition of H2.

Hydrogenation

Removing double bonds allows hydrocarbon molecules to pack tighter.

The stronger attractive forces cause liquid oil to become a solid.

Hydrogenation reaction: a type of addition reaction during which an unsaturated hydrocarbon becomes saturated with the addition of H2.

Predict the product of the hydrogenation of 2-pentene (C5H10):

Predict the product of the hydrogenation of 2-pentene (C5H10):

Given: Structure of 2-pentene

Relationships: In hydrogenation, H atoms are added across the double bond.

Answer:

Discussion: The hydrocarbon 2-pentene is now saturated and contains only single bonds.

Hydrogenation

When the hydrogenation of unsaturated fats is incomplete, some double bonds remain and have a trans configuration

Partial hydrogenation causes food that contains oil to have a longer shelf life.

However, research now shows that trans fats are harmful to our health.

Hydrogenation

Reactions of alkanes

Reactions of alkenes and alkynes

Substitutionan example is chlorination, where a hydrogen atom is replaced with a chlorine atom

Dehydrationalkanes become unsaturated by losing H2

Additionan example is hydrogenation

Hydrogenationalkenes and alkynes become saturated hydrocarbons with the addition of H2

Partial hydrogenationprocess through which trans fats are produced

Petroleum refining

Petroleum is a blend of hydrocarbons formed from the remains of prehistoric matter

Petroleum must be refined to become useful.

Petroleum refining begins with distillation, which separates it into fractions

Polymerization

Polymerization reaction: a chemical reaction that assembles a polymer through repeated additions of smaller molecular fragments.

a monomer

Plastics and starch are examples of polymers

Addition polymerization

Polyethylene is the one of the simplest and most widely used polymers in the world. It is used to make plastic bags and shampoo bottles

Addition polymerization: the process of forming a polymer by adding monomers together using their double bonds.

Addition polymerization

Addition polymerization: the process of forming a polymer by adding monomers together using their double bonds.

ethylene

polyethylene

Condensation polymers

Condensation polymerization: a type of polymerization reaction that links monomers through the loss of a small molecule such as water.

In this reaction, a water molecule was removed.

The bond that is formed is an amide linkage.

Condensation polymers

Condensation polymerization: a type of polymerization reaction that links monomers through the loss of a small molecule such as water.

Kevlar® is another polymer formed through condensation polymerization.

It is about five times as strong as steel, and it is used in bulletproof vests.

Reactions of alkanes

Reactions of alkenes and alkynes

Substitutionan example is chlorination, where a hydrogen atom is replaced with a chlorine atom

Dehydrationalkanes become unsaturated by losing H2

Additionan example is hydrogenation

Hydrogenationalkenes and alkynes become saturated hydrocarbons with the addition of H2

Partial hydrogenationprocess through which trans fats are produced

Polymerization

Addition polymerizationmonomers are linked using their double bonds

Condensation polymerizationa small molecule such as water is lost during linkage formation

Reactions of alkanesSubstitution

Dehydration

Addition (ex: hydrogenation)

Reactions of alkenes and alkynes