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Home , Alkane, Hydrocarbon, Hydrogen fluoride, Hydrogen halide

Reactions: Addition, Substitution and Elimination Today’s Objectives:

1) Define, illustrate and provide examples of simple addition, substituion, elimination and esterification (condensation)

2) Predict products and write and interpret balanced equations for the above reations

Section 10.2,10.3 and 10.4 (pg. 419-444) Hydrocarbon Reactions

1. Addition

and + H2(g)  ()

alkenes and alkynes + HX (or X2)  organic halides 2. Substitution

alkanes and aromatics + X2  organic halides 3. Elimination  alkenes + (dehydration) organic halides + OH-  alkenes + halide + water

4. Esterification (already covered) carboxylic + + water 1. Addition Reactions: reaction of alkenes and alkynes with , a compound, or a compound.  Addition reactions usually occur in the presence of a catalyst

a) Addition with H2(g) (also called hydrogenation)

1. Addition Reactions: reaction of alkenes and alkynes with hydrogen

gas, a halogen compound, or a hydrogen halide compound

b) Addition of a halogen

1,2-dichloroethane is a useful and is used to produce chloroethene, the used to make PVC. See Pg. 417 equation

Since addition reactions involving multiple bonds are very rapid, the product 1,2-dibromoethene can easily undergo a second addition step to produce 1,1,2,2-tetrabromomethane.

Excess promotes this second step. 1. Addition Reactions: reaction of alkenes and alkynes with hydrogen gas, a halogen compound, or a hydrogen halide compound

c) Addition of an HX (hydrogen halide)  Show both possible when predicting the products

The addition of hydrogen halides (HF, HCl, HBr or HI) to unsaturated compounds can produce structural isomers, since the hydrogen halide can add in different orientations. However, the type of isomers produced are not always equal.

For example only a tiny amount of 1-chloropropane is produced compared to 2-chloropropane in the above reaction. Practice Addition Reactions

 For each of the following questions, draw condensed structural diagrams and name all products

1. ethene + bromine  1,2-dibromoethane

2. + ethene 

3. 3-methylbut-1-yne + excess hydrogen 

2-methylbutane __ 

2. Substitution Reactions – breaking of a C-H bond in an or an aromatic ring and replacing it with another or group of

 Usually occur slowly at room temperature, so light may be necessary as a catalyst

 Often substitutes a halogen for a hydrogen  No change in saturation

Propane contains hydrogen atoms bonded to end and the middle atom, so two different products (isomers) are formed, in unequal proportions 2. Substitution Reactions – breaking of a C-H bond in an alkane or an aromatic ring and replacing it with another atom or group of atoms

Benzene rings are stable, like alkanes, so they react slowly with , even in the presence of light.

Would all three isomers be created equally? NO

As with alkanes, further substitution can occur in rings, until all hydrogen atoms are replaced by halogen atoms (in the presence of excess halogens) Practice Substitution Reactions

 For each of the following questions, draw condensed structural diagrams and name all products

1. +  1-fluoropropane + 2-fluoropropane + hydrogen F - F H - F

2. +  chloroethane + hydrogen chloride

3. Elimination Reactions – involves eliminating atoms or groups of atoms from adjacent carbon atoms; decreases the level of saturation a) Alkane cracked into an alkene (uses high temperatures)

b) Alcohol is reacted with a catalyst to produce an alkene and water (dehydration – removes a water molecule from the alcohol)

a) halide reacts with a ion (OH-) to produce an alkene (dehydrohalogenation – removes a hydrogen and halogen atom) Practice Elimination Reactions

 Write a equation for the preparation of but- 2-ene from chlorobutane, in the presence of a strong

 Write a structural formula equation for the preparation of but- 2-ene from butan-2-ol

Reaction Complete Addition Elimination Substitution Esteri- type fication Reactants Hydrocarbon* ene or yne + alcohol or alkane or alcohol + HOH, X , HX, alkyl halide aromatic + X carboxylic + O2 2 2 or H2 acid

Products CO2(g) + alcohol, alkyl alkene + HOH alkyl halide ester + H2O(g) or (l) halide*, or HX water alkane Other triple or single to slow; needs acid double to double uv light catalyst single needed Other more bonds* fewer bonds* Today’s homework

 Pg. 422 #7,8 (Addition and Substitution)

 Pg. 433 #18-19 (Elimination)

 What is coming up tomorrow?   STS Connections