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