02/12/2025
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Organic Chemistry (1)
Organic chemistry is the study of the chemistry of compounds of Carbon.
Properties of Carbon
1. The exceptional ability of Carbon atoms to catenate i.e. to combine with one another to form straight chains, branched chains or ring compounds containing many atoms.
2. The ease with which Carbon combines with hydrogen, oxygen, nitrogen and the halogens.
3. The ability of Carbon to form single, double or triple covalent bonds.
4. Different arrangement of the same atoms within a molecule produces a variety of compounds.
Characteristics of Organic Compounds
1. Organic Compounds are mostly covalent. They are stable because of the Carbon-Carbon bonds.
2. Most organic compounds are non-polar, unless the compounds consist of very electronegative elements like chlorine or the hydroxyl group.
3. Organic compounds are generally soluble in non-polar solvents like benzene or ether.
4. They are generally insoluble in water, except in cases where the compound contains the hydroxyl group (OH).
5. Organic compounds generally have low melting and boiling points compared to inorganic compounds.
6. Most organic compounds are thermally unstable, decomposing into simpler molecules when heated to temperatures above 500°C.
7. Most organic compounds are inflammable and burn exothermically in a plentiful supply of air to yield Carbon (IV) oxide and water.
8. Reactions involving organic compounds tend to be much slower than the ionic reactions in inorganic chemistry.
Terminologies in Organic Chemistry
Homologous Series
A homologous series is a family of organic compounds which follows a regular structural pattern in which each successive member differs in its molecular formula by CH₂ group or relative molecular mass of 14 a.m.u. (atomic mass units).
The simplest series is the alkane.
Alkanes are a series of hydrocarbons with a general molecular formula of CₙH₂ₙ₊₂ where n is a whole number with a value of one or more.
Each individual member of a homologous series is referred to as a homologue.
Other homologous series include:
• alkenes, CₙH₂ₙ
• alkynes, CₙH₂ₙ₋₂
• alkanols, CₙH₂ₙ₊₁OH
• alkanoic or carboxylic acids, CₙH₂ₙ₊₁COOH
Characteristics of a Homologous Series
1. All members of the series share a general molecular formula e.g. CₙH₂ₙ₊₂ for the alkanes.
2. Each successive member in a series differ in molecular formula by the addition of a –CH₂ group or relative molecular mass of 14 a.m.u.
3. Chemical properties of the members are similar but with a gradual variation along the series.
4. All members can be prepared by the same general methods.
5. The physical properties change gradually as the number of carbon atoms per molecule increases.
(II) Alkyl Group
This includes the univalent group derived from the alkanes by the loss of a hydrogen atom, e.g. methyl group (–CH₃).
Alkyl group has a general formula CₙH₂ₙ₊₁ and is named after the parent alkane by replacing "ane" with "yl".
The alkyl group is given the symbol "R".
Examples:
• Methyl — CH₃
• Ethyl — C₂H₅
• Propyl — C₃H₇
• Butyl — C₄H₉
• Pentyl — C₅H₁₁
(III) Functional Groups
A functional group is an atom, a radical, or a bond common to a homologous series and which determines the main chemical properties of the series.
The functional group for:
alkenes (=)
alkynes (≡)
alkanols (-OH)
carboxylic (-COOH)
alkanoates (-COO)
alkanals (-CHO)
alkanones (-CO)
primary amines (-NH₂)
Effect of the Alkyl and Functional Group
The functional group determines the chemical properties of a compound, while the alkyl group affects the physical properties of a compound.
Saturated & Unsaturated Compounds
Organic compounds containing atoms joined only by single covalent bonds are said to be saturated, e.g. the alkanes.
Unsaturated Compounds
Compounds that contain Carbon atoms joined by double or triple covalent bonds are said to be unsaturated, e.g. alkenes and alkynes.
Formulae of Organic Compounds
1. Empirical Formula:
This is the simplest formula of a compound. It indicates the relative number of each kind of atom present in a molecule of a substance.
2. Molecular Formula:
This is a more useful formula than the empirical formula. It indicates the actual number of each kind of atoms in a molecule of a substance.
Molecular formula = Empirical formula × n
III. Structural Formula: is the more informative Formula used in Organic Chemistry.
The IUPAC Nomenclature for Aliphatic Compounds
The International Union of Pure and Applied Chemistry (IUPAC) put forward a system of naming which relates the name of the compound to its molecular structure.
The IUPAC Convention is to number all the carbon atoms in the longest chain starting from the end which is the closest to the branch chain or the substituent.
CH₃ – CH₂ – CH = CH₂
Not But-3-ene (The handwritten structure shows 4 carbons and a double bond, which should be But-1-ene, so I'm transcribing what I see written, but noting the likely error/typo in the original)
Rules Guiding the IUPAC Nomenclature
1. Select the longest continuous carbon chain as the root hydrocarbon and name it according to the number of carbon atom it contains.
2. Number the carbon atoms in the root hydrocarbon from the end which will give the lowest number to the substituents. The halogens are indicated by the prefixes: Fluoro–F, Chloro–Cl, Bromo–Br, and Iodo–I.
3. If the same substituent is present two or more times in a molecule, the number of this substituent is indicated by a prefix: di–(2), tri–(3), tetra–(4), etc.
4. If there is more than one type of substituent in the molecule, the substituents are named according to alphabetic order but where there are mixed substituents the inorganic are named first.
Examples:
1. CH₃ – CH₂ – C ≡ CH
But-1-yne
2. ClCH₂ – CH₂ – CH₂ – CH₂OH
1-chlorobutan-4-ol
(This should be 1-chlorobutan-4-ol or 4-chlorobutan-1-ol depending on the numbering, but 1-chlorobutan-4-ol is written).
2. CH₃ – CH₂ – CH₂ – CH(CH₃) – C(Br)(Cl) – CH₃
3-bromo, 2-dichloro, 4-methylhexane
(The written name is 3-bromo, 2-dichloro, 4-methylhexane but the substituents are likely at positions 2 and 3 on a 6-carbon chain).
Isomerism
Isomerism is the occurrence of two or more compounds with the same molecular formula but different structures.
Geometric Isomerism
Geometric isomerism is the existence of compounds with the same molecular formula, but are not identical because of different spatial arrangement of the component atoms. For instance, there are two geometric isomers of but-2-ene:
cis-but-2-ene
trans-but-2-ene
Four Reactions in Organic Chemistry
1. Substitution reaction
2. Addition reaction
3. Polymerization reaction
4. Condensation reaction
1. Substitution Reaction
A reaction in which an atom or group of atoms in an organic molecule is replaced by another atom or group.
Types of Substitution
(a) Nucleophilic substitution – e.g., attack of a nucleophile as a reactant; hydrolysis of chloroalkane.
(b) Electrophilic substitution – e.g., attack of an electrophile to get substitution; e.g., nitration of nitrobenzene.
(c) Free radical substitution – where a free radical is the attacking substituent; e.g., halogenation of alkane to form haloalkane.
2. Addition Reaction:
Addition Reaction is a reaction in which two molecules combine to yield a single molecule product.
3. Polymerization and Condensation Polymerization is the combination of two or more simple molecules to form a Complex molecules. The simple molecules are called monomers or large molecules is called polymer.
Polymerization is the process that takes place when a single substance (monomer) gives products having the same empirical formula, but different molecular weight, each of these being a multiple of that of the monomer.
4. Condensation:
This is a process whereby two or more elements join together to form a new element with the elimination of a small molecule.
5. Condensation Polymerization:
Condensation Polymerization is the process whereby two or more non-identical monomers link together to form the polymer with the elimination of a small molecule.
Polymer and Polymorphism
What is a Polymer?
A Polymer is a compound made up of large or very large (macromolecules) molecules formed by condensation of a number of similar molecules (monomers) in a linear fashion (Linear Polymers) or in a net-like structure (Cross-linked Polymers).
What is Polymorphism?
Polymorphism is the ability of certain chemical substances to exist in more than one physical form. The existence of two forms is called dimorphism.