Unsaturated Hydrocarbons: Alkenes, Alkynes, Aromatics

Halogenation is the addition of chlorine or bromine (Cl2 or Br2) to the double bond.

This reaction does not require a catalyst. In this reaction the alkene becomes an

alkane. Alkynes react the same way, only 2 moles

of the chlorine or bromine are needed instead of 1 to change the alkyne to an alkane.

Example

Ethene Bromine 1,2- dibromoethane

Hydration is the addition of water to an alkene along with a small amount of strong acid (H+) as a catalyst. The resulting product is an alcohol. http://www.ausetute.com.au/hydraten.html

Acid

Ethene Water Ethanol (Ethyl alcohol)

If the same groups are attached to the double bonded carbons, there will only be one product. If there are 2 different groups attached to the double bonded carbons, there are 2 possible products. (One will be favored over the other.)

This is explained by Marovnikov’s Rule

The carbon of the C-C double bond that has the MOST hydrogen atoms receives the HYDROGEN atom being added.

The other carbon receives the OH. The resulting product is the major product that is preferred.

http://www.ausetute.com.au/hydrhala.html

Hydration of an alkyne also results in an alcohol, but is less stable. It is called an enol because at first it creates both an alkene (because of the double bond) and an alcohol.

It cannot be isolated because it quickly becomes either an aldehyde or a ketone.

Ethyne Water Ethenol Aldehyde /Ketone

Hydrohalogenation is when a hydrogen halide (HBr, HCl, or HI) is added to an alkene (as seen in the previous video.)

This reaction follows Markovnikov’s Rule.

Ethene BromoethaneChloroethaneIodoethane

Polymers- macromolecules composed of smaller molecules called monomers. Many plastics and fibers are made from alkenes or substituted alkynes. They are called addition polymers because they are made using alkene monomers.

Ethene Polyethylene(Ethylene)

Some examples of plastics include polyethylene (ethane/ethylene) which is used to make bottles and household plastics.

Polypropylene (propene/propylene) which is used to make carpeting, toys and packing material.

Condensation polymers are the combination of alkene monomers, but with the elimination of a small molecule such as water. Examples of condensation polymers include

polyesters, proteins and polysaccharides such as cellulose.

See Table 11.2

All of the same monomer makes A-A-A-A-A polymer such as polyethene.

Different monomers might be A-B-A-B-A-B polymer like polyester because an ester is found between the monomers.

1. Linear Chains- flow easily when heated, weak material, ductile, low density and melting point.

2. Branched Chains- will not flow as easily when heated, have higher melting points than linear, less ductile (stronger and stiffer).

3. Cross-linked Chains- retain shape when heated and is the type of bonding found in thermo set plastics, have a higher melting points than linear and branched, are harder but more brittle

Linear

Branched

Cross-linked

2 main types are thermo sets and thermo plastics. Thermo plastics can be reformed after heating but thermo sets cannot. Thermo plastics are recyclable and cheaper and easier to process than thermo set plastics.

Discuss the Big 6 polymers (LDPE, HDPE, PVC, PS, PP, PET)

First discovered in the early 19th century. Do not undergo additions like alkenes

and alkynes. Not recognized by having an aroma,

because many do not. Recognized for their benzene ring. Very

stable structure. Fig 11.6 shows the different

representations of the ring.

Has 6 carbons in a hexagonal arrangement with each being bonded to a hydrogen atom. The double and single bonds around the ring shift rapidly and therefore it has a resonance hybrid.

The current model says that there are overlapping orbitals. The double bonds represent the remaining electrons in p orbitals that overlap above and below the ring to form a cloud. This is represent as a circle inside the ring.

http://www.youtube.com/watch?v=6XOm3Km7r30

Benzene is the parent compound and the atom or group bonded to it is the prefix.

BromobenzeneOther examples pg. 377

Other names are based on history before nomenclature was created

Toluene, phenol, aniline, anisole (pg 377)

When 2 of the same groups are present there are 3 possible orientations. They can be named by IUPAC or the common system.

If the groups are located directly next to each other (1,2-) the prefix ortho- is used.

If there is a carbon atom between the groups (1,3-) the prefix meta- is used.

If there are 2 carbons separating the groups (1,4-) the prefix para- is used.

If 3 or more groups are attached to the ring, numbers must be used to designate their location. Names of substituents are given in alphabetical order.

In this example, toluene is the

parent chain. Bromo is on carbon

2. (2-bromotoluene)

An aromatic hydrocarbon attached to a long aliphatic group is named as a phenyl substituted hydrocarbon (has a phenol group.)

Here a butene is attached to the

benzene ring. Number thebutene so the double bond has the lowest #. That means the benzene is on carbon 4. You must name the carbon the phenyl is on first before naming the double bond.4-phenyl-2butene

Another group that may be attached to aromatics is the benzene group. (CH2)

Composed of 2 or more rings joined together. Many have been found to be carcinogenic.

Naphthalene (2 rings) is used in mothballs and may cause hemolytic anemia in humans.

Anthracene (3 rings) from coal tar, is a compound of many dyes and pigments. It is a suspected carcinogen.

Phenanthrene (3 rings) is a product of the incomplete combustion of fossil fuels and wood so it is commonly found in the environment.

Benzopyrene (5 rings) is a very potent carcinogen and is found in tobacco smoke, charcoal-grilled meat and auto exhaust.

Benzene typically undergoes substitution reactions where a hydrogen atom is replaced by another atom or group of atoms. No carbon-carbon bonds are broken A carbon- hydrogen bond is broken and the

H is replaced If the substituted atom is Cl2 or Br2, a

catalyst is required (iron or an iron halide)

If you were to add another mole of the equivalent halogen to your product, you would create 3 isomers (ortho, meta, para)

Recall figure 11.7

Benzene can react with sulfur trioxide using concentrated sulfuric acid as a catalyst. Benzenesulfonic acid is produced.

Benzene can react with nitric acid to produce nitrobenzene (nitration)

Concentrated sulfuric acid and temperatures of 50-55°C are needed as catalysts

+ H2O

Benzene Sulfur trioxide Benzenesulfonic Water

acid

Have at least 1 atom other than C as part of the ring structure.

Ex. Purine and pyrimidine (components of DNA and RNA)

Pyridine is found in nicotine Pyrrole ring is part of the porphyrin ring

(found in hemoglobin and chlorophyll)Pictures pg. 381