Substitution A substitution reaction occurs when a hydrogen atom is removed from a hydrocarbon and replaced by a halide substituent. When a bromine molecule absorbs energy, the covalent bond is broken resulting in the formation of bromine atoms. These atoms are good examples of radicals very unstable and highly reactive particles. Ex 1: Replace one H with a Br for every mole of Br 2 Apr 25 6:18 PM 1
Substitution Reactions R + H R Halogen + Halogen Halogen H Halogen Substitution1 2
Ex 2: 2 Br Ex 3: 3 Br Br Ex 4: 4 Bromine atoms can replace all four of the hydrogen atoms in methane but you will require 4 moles of Br Br (Br 2 ). Br Br Br Apr 25 6:23 PM 3
Ex 5: Structural isomerism is the existence of two or more structural formulas for one chemical formula. Apr 25 6:22 PM 4
Ex 6: Draw and name the structural formulas for possible isomeric products of a reaction between propane and two molecules of chlorine. Answer Stage 1: The first chlorine molecule reacts with propane. The products of the first step of the reaction are 1 chloropropane or 2 chloropropane. Apr 25 6:28 PM 5
Stage 2a: If the second chlorine molecule reacts with 1 chloropropane; then the possible isomers are: 1,1 dichloropropane, 1,2 dichloropropane, and 1,3 dichloropropane. Apr 25 6:31 PM 6
Stage 2b: If the second chlorine molecule reacts with 2 chloropropane; then the possible isomers are: 1,2 dichloropropane and 2,2 dichloropropane. Apr 25 6:32 PM 7
Benzene Benzene behaves chemically like an alkane (a saturated compound) and not like the alkenes and alkynes (unsaturated compounds.) The hybrid carbon to carbon bonds of the benzene ring are very stable and are not easily broken like the double and triple bonds Since the hybrid bond is not easily broken, reactions between halogens and benzene result in the substitution of hydrogen with halogen atoms. Apr 25 6:37 PM 8
Ex 7: Write an equation using structural formulas to illustrate a reaction between: a. benzene and chlorine Apr 25 6:39 PM 9
b. one benzene molecule and two chlorine molecules Feb 22 8:19 PM 10
Ex 8: Write an equation using structural formulas to illustrate a reaction between: a. methane and chlorine May 1 6:57 PM 11
b. ethane and two moles of iodine Feb 22 8:21 PM 12
Addition Reactions Alkenes and alkynes are unsaturated hydrocarbons containing at least one double or triple bond. They do not undergo substitution reactions; instead, they undergo addition a reaction in which substituents are added to both carbons involved in the multiple bond. Alkenes and alkynes are chemically more reactive than alkanes because of the presence of the multiple carbon to carbon bonds. In alkenes, a double bond is reduced to a single bond and in alkynes, a triple bond is reduced to either a double or a single bond depending on the amount of the substituent available for addition. Apr 25 6:41 PM 13
Addition Reactions C C X Y + C C X Y Addition 14
Ex 1: Predict the products of addition reactions involving: a. ethene and chlorine. The product is 1,2 dichloroethane. Apr 25 6:42 PM 15
b. 1 butene and chlorine. May 1 6:37 PM 16
c. cyclohexene and fluorine. The product is 1,2 difluorocyclohexane. The halogen atoms are added at the location of the double bonded carbon atoms. The reaction is spontaneous unlike substitution reactions, which require light energy to break the covalent bonds in the diatomic halogen molecules. Apr 25 6:43 PM 17
Ex 2: Predict the products of addition reactions between: a. one molecule of ethyne and one molecule of chlorine b. one molecule of ethyne and two molecules of chlorine Apr 25 6:36 PM 18
Ex 3: Predict the product of a reaction between ethene and hydrochloric acid Apr 25 6:47 PM 19
Ex 4: Predict the product of a reaction between ethene and bromine: Ex 5: Predict the product of a reaction between propene and hydrogen: May 1 7:10 PM 20
Ex 6: Predict the product of a reaction between propene and hydrobromic acid May 1 7:10 PM 21
Ex 7: Predict the product of a reaction between ethene and hydrogen Ex 8: Predict the product of a reaction between ethyne and two hydrogen + 2H 2 Ex 9: Predict the product of a reaction between ethyne and hydrogen + H 2 May 1 7:15 PM 22
An Application of the Addition Reaction The decolourization of bromine water is an important test for the presence of a double carbonto carbon bond. The reaction is spontaneous. Bromine, which has a characteristic bright orange color does not react as easily with saturated hydrocarbons. Apr 14 9:48 PM 23
Elimination Reactions : Halogen substituents can be removed from an alkyl halide in a reaction involving a base. The organic product of an elimination reaction is an unsaturated hydrocarbon. Apr 30 2:00 PM 24
Ex 1: Write a chemical equation to show the conversion of 2 chlorobutane to an unsaturated hydrocarbon. It removes a hydrogen from either carbon #1 or carbon #3. The hydroxide ion combines with the hydrogen to produce water, and the eliminated chlorine atom becomes a chloride ion. Apr 14 9:59 PM 25
Ex 2: Write a chemical equation to show the conversion of 1 bromoethane to an unsaturated hydrocarbon. + KOH + H 2 O + KBr May 1 7:30 PM 26
Ex 3: Write a chemical equation to show the conversion of 1 chloropropane to an unsaturated hydrocarbon. + NaOH + H 2 O + NaCl May 1 7:59 PM 27
Reactions producing Alcohols... Addition Reactions Ex 1: Predict the product of a reaction between ethene and water The water molecule splits into hydrogen and a hydroxyl. These species are added t ethene at the location of the double bond. The product is ethanol. Apr 25 6:48 PM 28
Ex 2: Predict the product of a reaction between 2 pentene and water + HOH or May 16 10:19 PM 29
Ex 3: Predict the product of a reaction between ethyne and two moles of water 1,2 ethandiol, commonly known as ethylene glycol or radiator antifreeze May 16 11:11 PM 30
Ex 4: Predict the product of a reaction between butene and water + HOH May 16 11:10 PM 31
Reactions with Alcohols... Elimination Reactions: Alkenes can be produced by elimination of a water molecule from an alcohol. This reaction involves the use of an ac catalyst. A catalyst is a substance that speeds up a chemical reaction without being consumed. The acid catalyst in the example below is represented by the symbol H +. Apr 30 2:00 PM 32
Ex 1:Predict the product of a reaction between propanol and an acid catalyst. It should be obvious that a hydroxyl group and a hydrogen atom are being eliminated from the alkyl parent. The result is the formation of a unsaturated hydrocarbon and water. Apr 30 2:01 PM 33
Ex2: Predict the product of a reaction between ethanol and an acid catalyst. May 16 11:20 PM 34
Ex 3: Predict the product of a reaction between cyclohexanol and an acid catalyst May 16 11:21 PM 35
Ex4: Predict the product of a reaction between 3 pentanol and an acid catalyst H + + H 2 O An important application of this reaction type is the ripening of fruit in warehouses. The ripening process is stimulated when a plant produces ethene. If unripened fruit is stored under the right conditions, the productio of ethene is inhibited allowing for long term storage. In order to initiate the ripening process, the fruit has to be exposed to ethene. This is where an elimination reaction involving ethanol becomes important. Feb 27 9:44 PM 36
Reactions producing Esters Esterification Esterification: Esters are produced when alcohols and carboxylic acids are reacted in the presence of an acid catalyst May 17 10:20 PM 37
Esterification O O R (carboxylic acid) C O H H + R C (ester) O R' + + R' O H H O H (alcohol) (water) Esterification 38
x 1: Predict the product for reaction between methanol and butanoic acid May 17 10:21 PM 39
Ex 2: Predict the product for reaction between ethanoic acid and ethanol May 17 10:23 PM 40
Ex 3: Predict the product for reaction between ethanoic acid and 1 butanol May 17 10:24 PM 41
Ex 4: Predict the product for reaction between of ethanoic acid and methanol. May 17 2:47 PM 42
Jun 2 11:18 AM 43