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ORGANIC CHEMISTRY

Introduction

Organic Chemistry - The study of hydrocarbons and their derivatives. 

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What makes something organic? 

- Source is a living thing

- Can only be synthesized in living things

Pi Bond - Sideways overlap of orbitals

Sigma Bond - Head on head overlap of orbitals 

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Pi bond is weaker than a sigma bond. 

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COVALENT BONDING: 

One covalent bond - Sigma Bond                                e.g. in H2

Two covalent bonds - 1 Sigma Bond, 1 Pi Bond        e.g. in O2

Three covalent bonds - 1 Sigma Bond, 2 Pi Bonds   e.g. in N3

VITAL FORCE THEORY

Organic compounds cannot be created/synthesized as they do not obey the laws of chemical combination. 

The vital force theory was disproven when ammonium cyanate (inorganic substance) was turned into urea (organic substance) when heat was provided. 

This shows that organic compounds can in fact come from inorganic substances.

Catenation Property -  Carbon can make bonds with itself and other elements (different patterns e.g. rings, circles, chains) 

Hydrocarbons - Containing carbon and hydrogen only. 

H

H

C

H

H

Methane

H

H

C

OH

H

Methanol

(Derivative of a hydrocarbon)

H

O

H

C

C

OH

H

Ethanoic Acid

(Derivative of a hydrocarbon)

SATURATED HYDROCARBONS - Contain all single carbon to carbon bonds 

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UNSATURATED HYDROCARBONS - Contain double/triple  carbon to carbon bonds 

C

C

C

C

Homologous Series

A family of organic compounds having the same general formula and similar chemical properties. 

1. Alkanes 

2. Alkenes

3. Alcohols

4. Carboxylic Acids

5. Esters 

CHARACTERISTICS OF HOMOLOGOUS SERIES

  1. Same general formula

  2. Show similar chemical properties 

  3. Show gradual change in physical properties 

  4. Can be prepared/synthesized by the same general method

  5. Each successive member differs by CH2 or 14 AMU

Alkanes

  • Hydrocarbons with only singe carbon to carbon bonds (1 sigma bond) 

  • Lack of reactivity due to strong bonds 

  • High melting and boiling points

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H

H

C

H

H

Methane

H

H

C

C

H

H

Ethene

Ethene is more reactive than methane as it has a double carbon to carbon bond (1 sigma bond, 1 pi bond). Since a double carbon to carbon bond can be more easily broken, thus it is more reactive compared to methane (an alkane). 

Prefix (to show number of carbons)

1 - Meth

2 - Eth

3 - Prob

4 - But 

5 - Pent 

6 - Hex

7 - Sept

8 - Oct

9 - Non

10 - Dec

Note: 

Carbon's combination power is 4. That means it can only have a maximum of 4 bonds. This could be in the form of 4 single bonds, 2 double bonds, or 1 double and 2 single bond, etc. 

  • Normal alkanes are unbranched hydrocarbons 

  • General formula of alkanes is: 

C

n

H

2n+2

Using this formula we can say: 

When n is 1:  CH4       (Methane)

When n is 2: C2H6      (Ethane)

When n is 3: C3H8      (Propane)

NAMING ALKANES: 

1. Prefix is the number of carbons 

2. Suffix is 'ane'

ALKYL

One less hydrogen than an alkane

1. Prefix is the number of carbons

2. Suffix is 'yl' 

C

n

H

2n+1

Side chain/branched chain/substituent

H

H

H

H

H

C

C

C

C

H

H

H

H

C

H

H

H

Hydrocarbons which contain a side chain are named slightly differently. In this case this alkane would be: 

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2-MethylButanne

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How to name branched chains? 

1. Select the longest continuous carbon chain, irrespective of bends or angles (max no. of carbons)

2. Which carbon does substituent lie on (lowest possible position to branch chain) 

3. Identify the longest chain name

4. Identify the substituent name

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E.g. here, the longest possible chain of carbons is from right to left (4 carbons). The direction is right to left because the substituent is closer from left to right (it is on the second carbon in the chain from right to left, and on the third carbon in the chain from left to right). 

First we right the carbon number the substituent is on, in this case a '2'. 

Then we add a hyphen. 

After this we write the name of the substituent starting with a capital letter. (here since there is one carbon and 3 hydrogens, it is Methyl). 

The last step would be to write the name of the lonest chain starting with a capital letter. In this case the longest chain consists of 4 single carbons to carbon bonds, making it an alkane. The name would be Butane. 

Remember to write everything without any spaces, in this case: 

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2-MethylButane      

Isomers - Same molecular formula but different structural formula. 

PRACTICE QUESTIONS: 

Draw the following: 

2-MethylPropane

3-MethylHexane

3,3,4-TriMethylHexane

3,3-DiMethylHexane

3,3-DiMethylPentane

Methane

Ethane 

Propane 

(in this case, the commas show that there are three substituents, and the tri in front of methyl means that all three substituents are methyl)

REMEMBER ABOUT SUBSTITUENTS 

1. Substituents cannot be at the last carbons of a carbon chain

2. Substituents are listed in alphabetical order.

E.g. 2,3,4- EthylDiMethylPentane would mean that the ethyl substituent is located on the second carbon, and the two methyl substituents are located on the third and fourth carbons.  

  • All alkanes starting with butane exhibit structural isomerism (Structural isomers exhibit different properties) 

  • Alkanes have low chemical reactivity (considered unreactive). They undergo:  

    • Combustion reaction (complete and incomplete) ​

    • Substitution reaction (Free radical substitution) 

Alkanes are used as fuel, as they release significant amounts of energy when they are burned. 

As the carbon chain in an alkane increases, its viscosity, melting/boiling point, flammability, and volatility also increase.

Alkenes

  • Unsaturated hydrocarbons

  • Double carbon to carbon bond

  • First member of alkene series is ethene (since double carbon bond cannot happen in methene) 

  • The general formula for alkenes is: 

C

n

H

2n

NAMING ALKENES

1. No.of carbons - position of double bond - ene

E.g. In an alkene with three carbons, and the double bond being on the second carbon, the name would be: 

Prop-2-ene 

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Remember: Always start counting the carbons from where they are closest to the double bond. Same rule as substituents and alkanes, but instead of substituents, it's the double bond with alkenes! . 

E.g. Name this alkene: 

H

H

C

C

H

H

Ethene

H

H

C

H

H

H

C

C

C

C

H

H

H

H

Step 1: Find the longest chain of carbons, begin counting from wherever the double bond is closest. In this case straight from left to right. 

Step 2: Count the carbon the substituent is on in the chain (remember that the chain starts from where the double bond is closest in alkenes, NOT the substituent). In this case, the substituent is on the third carbon. 

Step 3: Identify the name of the longest chain of carbons (in this case 4 carbons, so but)

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Add it all together in this form:

​

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So in this case it would be, 

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3-MethylBut-1-ene

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Carbon no. on which substituent is - substituent name; longest no. of carbon chain -place of double bond on longest carbon chain - ene

Cyclo-Butane

Isomer of Butene

H

H

H

C

C

H

H

C

C

H

H

H

IDENTIFYING ISOMERS

- Same molecular formula, different structural formula

- Different names

- Different physical properties 

- Shouldn't be mirror chains

- Could be from different homologous series 

  • Alkenes are more reactive than alkanes and undergo addition reactions as well as combustion reactions 

    • SPECIAL FEATURES OF ADDITION REACTIONS:​

      • You only get one single product ​

      • Product does not have a double bond

      • Always happens accross the double bond

ballgob-fig13_x028.jpg

Figure 1. Bromination of ethene (AKA ethylene), an addition reaction used to differentiate between alkanes and alkenes. Bromine reacts with ethene to turn colorless. Does not react with alkane. 

HYDROGINATION - Turns an alkene to an alkane. Used for the creation of margarine as it turns polyunsaturated bonds (oils) into saturated ones. 

BROMINATION - Differentiates between alkanes and alkenes (bromine water test). 

Functional group - Reactive part of a molecule. In the case of alkenes, it is the carbon to carbon double bond. 

CRACKING - Long chain hydrocarbons are broken into short chain hydrocarbons (more useful) and/or hydrogen.

  • Catalytic cracking - Catalyst is used

  • Thermal cracking - Heat is provided (very high temperatures)  

C

18

H

38

Alkane

C

8

H

18

+

Alkene

C

10

H

20

Can be further broken down:

2

C

5

H

10

Alkenes are used as starting compounds in many industrial processes. 

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POLYMERIZATION

- Monomers (one unit) join to make polymers (many units) 

- Ethene becomes polyethene 

addition_polymerization_of_ethene2.jpg

Figure 2. Polymerization of ethene. n stands for repeating unit. Notice that the double bond is removed in polymerization (Seeboo, 2018). 

NOTE!

Polymerization and reactions for alkanes and alkenes are not discussed in detail, but gone through as for understanding. Rely on other resources for these topics as well! 

Alcohols

  • Functional group of an alcohol is OH (hydroxl)

  • The OH group is polar and increases the solubility in water and volatility of alcohols when compared to alkanes of similar molar mass. 

  • Primary and secondary alcohols undergo oxidation and are converted to carboxlic acids, but tertiary alcohols resist oxidation. 

  • An alcohol can be called primary/secondary/tertiary depending on how many other carbons the carbon with the OH is bonded to. 

  • Alcohols undergo esterification (condensation) with carboxylic acid to make esters. 

  • The general formula of alcohols is:   

C

n

H

2n+1

OH

Naming alcohols 

1. Prefix depending on number of carbons 

2. Add 'ol' in the end. 

3. (Optional - Add the carbon number on which the OH group is bonded to between the prefix and suffix) 

4. Substituents shown in the same way as in alkenes. 

E.g. Ethanol above can also be written as ethan-1-ol. 

H

H

H

C

C

O

H

H

H

Ethanol

1-prim-sec-tert-e1410979431652.png
1.PNG

Carboxylic Acids

  • Weak acid, partially ionized in aqueous solution

  • Always start n with 0 

  • Functional group is COOH (carboxyl)

  • General formula is: 

COOH

C

n

H

2n+1

OXIDIZING AGENTS

- Acidified Potassium Dichromate VI (K2Cr2O7)

- Potassium Manganate VII (KMnO4)

Figure 3. Differentiating between primary, secondary and tertiary alcohols 

O

H

2.PNG

H

O

C

C

H

H

Ethanoic Acid

esterification.png

Figure 4. Process of esterification.  Notice how the name of the ester is made  

1. Ethanol + Methanoic Acid -> Ethyl Methanoate 

2. Propanol + Methanoic Acid -> Propyl Methanoate

3. Propanol + Propanoic Acid -> Propyl Propanoate 

4. Methanol + Butanoic Acid -> Methyl Butanoate 

ESTER LINKAGE 

O

C

O

DIFFERENCE BETWEEN ADDITION POLYMERIZATION & CONDENSATION POLYMERIZATION 

- Addition polymerization is the reaction between monomers with multiple bonds, where they join to form saturated polymers. In condensation reactions, functional groups of two monomers react together releasing a small molecule to form a polymer. 

- Saturated monomers are participating in condensation whereas in addition polymerization the monomers are unsaturated. 

- Addition polymerization is a rapid process, producing high molecular weight polymers compared to condensation polymerization. 

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