SL Organic Chemistry

5 Characteristics of a Homologous Series

a homologous series is a group of organic compounds that:

* contain the same functional group,
* have the same general formula,
* differ by a CH2 group, 
* have similar chemical properties, 
* show a gradation in physical properties such as boiling point

Isomers

have the same molecular formula but different arrangements of atoms

Functional groups

single atoms or groups of atoms that give organic compounds their characteristic properties

Alkanes

* Homologous series: Alkanes are hydrocarbons with all single bonds (saturated)
* Alkanes are very unreactive, although they do burn and react with halogens (e.g. chlorine).
* General formula:  CnH2n+2
* Functional group:  alkyl
* Boiling points of alkanes increase with increasing number of carbons (London Dispersion Forces)

Alkane Reactions - Combustion

when a substance reacts with excess oxygen to produce fuel and water, an exothermic reaction. When the reaction is in complete, carbon monoxide and dioxide can be products.

Halogenation Step 1

Initiation

Halogenation Step 2

Propagation

Halogenation Step 3

Termination

Homolytic bond fission

occurs when a bond breaks evenly, with each atom taking one electron from the bond. This results in the formation of radicals, or free-radicals, highly reactive species with unpaired electrons

Alkenes

* Functional group:  alkenyl - a double bond
* General formula Cn H2n
* Naming
* -ene at end of root word
* Need to indicate the location of the double bond - the carbon where the double bond starts

Alkynes

* Functional group - alkynyl - a triple bond
* Naming
* -yne at end of prefix
* Need to indicate the location of the triple bond

Cis/trans isomerism

* Restricted nomenclature form
* Cis - groups are on the same side of the double bond
* Trans - groups are on the opposite side of the double bond

5 Main Reactions with Alkenes

* Hydrogenation - Addition of Hydrogen
* Hydration - Addition of Water
* Addition of Halogen - Reaction with Hydrogen Halides
* Addition of Halogen - Reaction with Halogen Gas
* Addition Polymerization

Hydrogenation - Addition of Hydrogen

* Reaction conditions:
* Nickel catalyst
* Hydrogen gas
* High temperature (about 200 °C) 
* High pressure
* Activation energy of reaction is slightly higher so gaseous mixture of H2 is passed over a heated Ni catalyst
* Used to make margarine
* Reduces the number of double bonds in polyunsaturated veg oils, which causes it to be a solid at room temp

Hydration - Addition of Water

* Reaction conditions:
* Super-heated steam (300°C)
* H3PO4 or H2SO4 is catalyst
* High pressure (60-70 atm)
* Produces an alcohol
* Used as an industrial process for making alcohol
* Water must be in the form of steam

Addition of Halogen - Reaction with Hydrogen Halides

* Reaction conditions  
* Spontaneous at room temperature 
* Reaction also occurs with HBr and HI
* Monohalogenoalkane formed

Electrophilic Addition of Halogen - Reaction with Hydrogen Halides Mechanism

Markovnikov’s Rule

When a compound HX is added to an unsymmetrical alkene, the hydrogen becomes attached to the carbon with the most hydrogens attached to it already

Formation of a Primary Carbocation Mechanism (doesn’t happen)

Formation of a Secondary Carbocation Mechanism (Favoured)

Addition of Halogen - Reaction with Halogen Gas

* Reaction conditions:
* Spontaneous at room temperature. 
* Reaction also occurs with Cl2 and I2


* Dihalogenoalkane formed because halogens exist as diatomic in their gaseous form

Electrophilic Addition of Halogen Gas to Alkene Mechanism

Addition Polymerization + Mechanism

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Ketones

* Functional group:  carbonyl  
* Naming
* Put an -anone on the end
* For chains with four or more carbons, need to indicate the location by putting the  number of the carbon it is attached to (x): “-an-x-one”
* Made from oxidation of secondary alcohols

Reaction with Ketones: Reduction to form secondary alcohol

* Need a reducing agent


* Can either use LiAlH4 or NaBH4

Carboxylic Acids

* Functional group:  carboxyl group
* Naming
* Ends in “-anoic acid”
* Since the functional group is always on the end, no need for numbers for the functional group - it’s carbon is always #1
*  Formed by complete (under reflux) oxidation of primary alcohol

Reaction with Carboxylic Acid: Reduction of carboxylic acids to form primary alcohols

* Need a reducing agent
* Can only use LiAlH4

Aldehydes

* Functional group:  carbonyl group
* Naming
* Ends in “-anal”
* Since the functional group is always on the end, no need for numbers for the functional group - it’s carbon is always #1
* Formed by oxidation of primary alcohol under distillation

Reaction with Aldehyde: Reduction of Aldehyde to form Primary Alcohol

Reduction of an aldehyde

* Need a reducing agent
* Can either use LiAlH4 or NaBH4

Alcohols

* Functional group:  hydroxyl -OH 
* Have the general formula CnH2n+1OH
* Naming
* Add -anol to the root
* If the hydroxyl group can be located at multiple points (when there are three or more carbons), indicate the location by putting the number of the carbon before the -ol
* Can be primary, secondary or tertiary

Processes to produce Alcohols

1. Fermentation
2. Hydration of ethene
3. Nucleophilic substitution of halogenoalkanes

Reactions of alcohols

1. Dehydration of alcohol
2. Combustion of alcohols
3. Oxidation of alcohols

Dehydration of alcohol

* Reaction conditions:
* H3PO4 or Al2O3 is catalyst
* High Temperature
* Atmospheric Pressure

Oxidation of Primary Alcohols

* There are two stages
* Oxidation of alcohol to an aldehyde
* distillation
* Oxidation of the aldehyde to a carboxylic acid
* heating under reflux

Esters

* Functional group:  ester
* Naming
* Name is broken into two parts
* Alcohol part has “-yl” on the end of the root and is placed at the beginning of the name
* Acid part has “-anoate” on the end of the root
* For the acid part, need to determine the root by including the carbon that is double-bonded to the oxygen

Formation of esters - Condensation/Esterification

Reactions with benzene

1. Substitution with halogens
2. Electrophilic substitution with nitric acid to produce nitrobenzene
3. Reduction of nitrobenzene to phenylamine

Substitution with halogens (Reactions with benzene)

* Reaction conditions
* AlCl3 catalyst
* Room temperature
* anhydrous conditions

Electrophilic substitution with nitric acid to produce nitrobenzene (Reactions with benzene)

* Reaction conditions
* Low temp -  maximum 50oC
* Concentrated sulfuric acid as catalyst

Electrophilic substitution with nitric acid to produce nitrobenzene Mechanism (Reactions with benzene)

Reduction of nitrobenzene to phenylamine Mechanism (Reactions with benzene)

Amines

* Functional group:  amine
* Naming
* If group position does not have to be indicated - put “amine” on the end of the root
* If group position needs to be indicated - put the carbon number-amino (“2-amino”) and then the root

Carboxamides

* Functional group:  carboxamide  
* Naming
* Put “-anamide” on the root
* No need to number because it is on the end
* Don’t forget to count the carbon attached to the nitrogen when determining the root

Nitriles

* Functional group:  nitrile
* Naming
* Put “-nitrile” after the alkane name

Ethers

* Functional group:  ether
* Naming
* Two parts to the name
* First part - the longer chain
* Determine which is the longest main chain and count carbons
* That part is named the same as the alkane name
* Second part - the shorter chain
* Determine shorter chain and count carbons
* That part gets just the root word + “oxy”
* Combine them:  root from shorter part-oxy-alkane name from longer part