Organic Chemistry Hydrocarbons 1

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 2

Carbon has 4 valence electrons but can bond to fewer than 4 atoms and form double and triple bonds 3

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. 4

Alkanes – saturated hydrocarbons (all single bonds) Formula for butane: C 4 H 10 General Formula for alkanes: C n H 2n+2 5

Alkanes 6

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 7

Naming Alkanes To name alkanes: Count the number of carbons Find the corresponding Greek root Add “-ane” to indicate it is an alkane Organic chemists call this n-pentane, where n indicates the longest straight chain 8

Branched alkanes To name branched alkanes: 1) Find the parent compound (the longest continuous chain) and add “-ane” to the Greek root heptane 9

To name branched alkanes: 2)Find the branch(es) not included and add “-yl” to the Greek root 10

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 11

Naming alkanes heptane ethyl The branching group is called the R group Here, R = CH 2 CH 3 12

structural isomer: molecule with the same number and type of atoms as another molecule but has a different bonding pattern. n-butane (C 5 H 12 ) and isobutane (C 5 H 12 ) are structural isomers n-butaneisobutane 13

2-methyl-propane isobutane methyl group at position “2” methyl group at the second-to-last position 4 carbons in total Naming alkanes same molecule 14

Draw and name the structural isomers of pentane (C 5 H 12 ). Make a chain of 5 carbons and add hydrogens. n-pentane 2-methyl-butane 15

Structural isomers Draw and name the structural isomers of pentane (C 5 H 12 ). We can remove 2 carbons and form 2 branches in one position. isopentane n-pentane 16

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) 17

Interm Intermolecular attractions are also called van der Waals attractions olecular attractions are also called van der Waals attractions strong London dispersion Dipole-dipole Dipole-dipole Hydrogen bonding bonding Types of intermolecular attractions Between polar molecules Between nonpolar molecules Intermolecular attractions weak Hydrocarbons 18

Properties of hydrocarbons London dispersion Between nonpolar molecules Hydrocarbons With weak intermolecular attraction forces, small hydrocarbons are gases at room temperature. 19

Properties of hydrocarbons As hydrocarbon chains become longer, attraction forces become stronger. Longer hydrocarbons are liquids at room temperature. 20

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 21

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 3,300 o C (6,000 o F) 22

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 bond Add “-yne” to indicate a triple bond 23

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 bond Add “-yne” to indicate a triple bond 24

Isomers Stereoisomers Same bonding order Different spatial arrangement Structural isomers Same formula Different bonding order Geometric isomers Butene trans configuration (R groups opposite sides of the C=C bond) cis 25

Isomers Stereoisomers Same bonding order Different spatial arrangement Structural isomers Same formula Different bonding order Geometric isomersOptical isomers The central carbon is attached to four different groups. Optical isomers are two different molecules! 26

Aromatic hydrocarbons Cinnamon, cloves, wintergreen and vanilla beans have pleasant, distinctive smells What else do they have in common? 27

Aromatic hydrocarbons What else do they have in common? Benzene ring Aromatic hydrocarbons contain one or more benzene rings 28

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. C6H6C6H6 Aromatic hydrocarbons 29

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 : 30

Stereoisomers Same bonding order Different spatial arrangement Structural isomers Same formula Different bonding order Geometric isomersOptical isomers cistrans Section Review : 31

Hydrocarbons have different properties depending the functional groups attached to them 32

Functional groups Common functional groups 33

Alcohols ROH 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 34

Ethers RORROR Early use of diethyl either as an anesthetic Ethers are volatile because intermolecular attractions are weak 35

Aldehydes RCHRCH O The C O group is also called the carbonyl group A wide variety of familiar smells and flavors come from aldehydes 36

RCR’ 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 Acetone Acetone is also used as a cleaning agent in the lab and in industry because it mixes well with water and dissolves organic substances. 37

Aldehydes and ketones RCHRCH O RCR’ O R and R’ can be the same, but do not have to be Glucose Fructose 38

Aldehydes and ketones Glucose Fructose 6-membered ring 5-membered ring 39

Aldehydes and ketones glucosefructose 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 40

RCHRCH O RCR’ O RORRORROH Alcohol Common functional groups Ether Aldehyde Ketone R and R’ can be the same, but do not have to be 41

Carboxylic acids RCOH 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 42

Carboxylic acids RCOH O Carboxylic acids are weak acids in aqueous solutions R COOH(aq) + H 2 O(l) R COO – (aq) + H 3 O + (aq) 43

Amines RNH 2 Amines are organic molecules that contain an amino (NH 2 ) group. Alanine is one of the amino acids that make up all the proteins in our bodies Chlorpheniramine (allergy medication) 44

Amines RNH 2 Amines are weak bases in aqueous solutions R NH 2 (aq) + H 2 O(l) R NH 3 + (aq) + OH – (aq) 45

Esters RCOR’ 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. 46

Esters RCOR’ O Isobutylacetate 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! 47

Esters RCOR’ O Esters 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 48

RCOR’ O RNH 2 RCOH O RCHRCH O RCR’ O RORRORROH Alcohol Common functional groups Ether Aldehyde Ketone Carboxylic acidAmineEster 49

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.

Chlorination is an example of a substitution reaction Substitutions

Dehydrogenation Dehydrogenation reaction: an alkane becomes an unsaturated hydrocarbon by losing H 2. 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 H 2.

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 H 2.

Predict the product of the hydrogenation of 2-pentene (C 5 H 10 ):

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 Substitution an example is chlorination, where a hydrogen atom is replaced with a chlorine atom Dehydration alkanes become unsaturated by losing H 2 Addition an example is hydrogenation Hydrogenation alkenes and alkynes become saturated hydrocarbons with the addition of H 2 Partial hydrogenation process 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 Substitution an example is chlorination, where a hydrogen atom is replaced with a chlorine atom Dehydration alkanes become unsaturated by losing H 2 Addition an example is hydrogenation Hydrogenation alkenes and alkynes become saturated hydrocarbons with the addition of H 2 Partial hydrogenation process through which trans fats are produced

Polymerization Addition polymerization monomers are linked using their double bonds Condensation polymerization a small molecule such as water is lost during linkage formation Reactions of alkanes Substitution Dehydration Addition (ex: hydrogenation) Reactions of alkenes and alkynes