Petroleum Fractions and Their Uses

• Organic chemistry focuses on carbon and its compounds, especially hydrocarbons and their derivatives.

Chapter Overview

• Carbon has unique features that allow it to form chains, rings, and isomers.
• Organic chemistry is important in daily life.
• Carbon sources include coal, petroleum, and natural gas, with varying availability in Pakistan.
• Refining, reforming, and cracking of petroleum yield various products organized in tabular form.
• Petroleum serves as a source of different fuel types.
• Organic compounds are classified based on their carbon skeleton.
• Functional groups determine the chemical properties of organic compounds.
• Structural isomerism is a key feature of organic compounds.
• Cis-trans isomerism results from restricted rotation around carbon-carbon double bonds.
• Hybridization theory helps in understanding bonding types and shapes of organic compounds.

Introduction to Organic Chemistry

• Early chemists distinguished organic compounds from inorganic ones based on origin and properties.
• Organic compounds were sourced from living matter, while inorganic compounds came from non-living sources.
• Early chemists believed organic compounds could only be made by living things, a theory called vital force theory.
• Friedrick Wohler disproved this theory by synthesizing urea, an organic mammal compound, from ammonium cyanate, a mineral substance.

Modern Definition

• After urea synthesis from ammonium cyanate millions of organic compounds were analyzed.
• Carbon is essential in all organic compounds, often with hydrogen.
• Oxygen, nitrogen, and sulphur may also present.
• Some carbon compounds like CO, CO2, carbonates, and bicarbonates are studied as inorganic compounds due to historical reasons..
• Organic compounds' chemical forces mirror those in inorganic compounds, leading to a modern redefinition of organic chemistry.
• Organic chemistry studies carbon and hydrogen compounds (hydrocarbons) and their derivatives.

Features of Organic Compounds

Peculiar Nature of Carbon

• Carbon creates numerous compounds due to its linking ability, forming chains or rings, called Catenation.
• Carbon forms stable single and multiple bonds with oxygen, nitrogen, sulphur, resulting in various sizes, shapes and structures.

Non-ionic Character

• Organic compounds are mainly covalent, and do not give ionic reactions.

Similarity in Behaviour

• Organic compounds exhibit similar behaviour, exemplified by homologous series, reducing study to a few series.

Complexity

• Starch (C6H10O5)n structure, where n is several thousands is complex.
• Proteins are complex molecules, with masses ranging from thousands to a million.

Isomerism

• Isomerism occurs commonly; different compounds may have the same molecular formula but different structural formulas.

Organic Reactions

• Organic compound reactions are slow, with generally low yields, attributed to their molecular nature.

Solubility

• Most organic compounds don't dissolve in water, but do in non-polar solvents like benzene and petroleum ether.

Importance of Organic Chemistry

• Organic chemistry importance is immense, with nearly all reactions in living systems being organic.
• Life molecules, including proteins, enzymes, carbohydrates, lipids, vitamins, and nucleic acids, contain thousands of carbon atoms.
• Dependency has grown on natural organic compounds for food, clothing and medicines,.
• Chemists have synthesized plastics, synthetic rubber, preservatives, medicines, fertilizers,textile fibres, pesticides detergents and varnishes protecting shortages of naturally occurring products.

Sources of Organic Compounds

• Petroleum, coal, and natural gas are primary sources of organic compounds known as fossil fuels, formed over time from decayed plants and animals.

Coal

• Coal formed from trees buried approximately 500 million years ago.
• Bacterial and chemical reactions on wood converted it to peat inside the earth crust.
• High temperature and pressure then transformed the peat into coal.
• Coal serves as an important solid fuel and produces organic compounds through carbonization or destructive distillation.
• Heated coal without air (500-1000°C) becomes coke, coal gas, and coal tar.
• Coal tar contains many organic compounds extracted through fractional distillation.
• Pakistan's coal resources estimated at 184 billion tonnes by Geological Survey of Pakistan.
• Around 80% of coal in Pakistan is used to bake bricks, with some for domestic use.
• The government is making efforts to use coal in industry by establishing coal-based units.
• Sindh Coal Authority and other directorates support expanding coal utilization for power generation with incentives.

Natural Gas

• Natural gas is vital for countries like Pakistan due to a lack of coal and mineral oil.
• Consists of low boiling hydrocarbons, mainly methane, formed by decomposing organic matter.
• Being cheap in Pakistan, natural gas is used for power generation, fertilizer industries, cement industries as fuel.

Petroleum

• Mineral oil becomes petroleum when refined.
• Petroleum formed by slow chemical and biochemical decomposition of sedimentary rocks.
• When extracted, petroleum looks like a dark liquid known as 'crude oil'.
• Crude petroleum is separated through fractional distillation.

Cracking of Petroleum

• Fractional distillation of petroleum produces only about 20% gasoline.
• High demand for gasoline is met by converting surplus petroleum fractions like kerosene and gas oil through cracking.
• Cracking breaks higher hydrocarbons with high boiling points into lower, more volatile hydrocarbons.
• Higher hydrocarbons C16H34 split according to a reaction into C7H16 + 3CH2=CH2 + CH3-CH=CH2.
• The C-C bonds in long chain molecules break to form smaller alkanes and alkenes.
• Product composition depends on cracking conditions.

Thermal Cracking

• Thermal cracking is breaking down large molecules with heat and pressure, which creates unsaturated hydrocarbons such as ethene and propene.

Catalytic Cracking

• Catalytic cracking takes place at lower temperatures (500°C) and pressure (2 atm) using a silica (SiO2) and alumina (Al2O3) catalyst.
• It yields gasoline with higher octane number, improving gasoline quality.

Steam Cracking

• Higher hydrocarbon vapors mix with steam and heat briefly 900°C before rapid cooling.
• Suitable for obtaining lower unsaturated hydrocarbons.
• Cracking yields by-products like ethene, propene, butene, and benzene.
• Used for manufacturing drugs, plastics, detergents, weed killers, synthetic fibres and chemicals.

Reforming

• Gasoline from petroleum needs good quality.
• Poor gasoline causes engine knocking, reducing efficiency.
• The octane number shows the quality of fuel.
• Higher octane numbers reduce knocking.
• Straight chain hydrocarbons create poor fuels and have low octane.
• Isooctane or 2,2,4-trimethylpentane burns smoothly and rated 100 octane.
• Gasoline's octane number improves by reforming.
• Reforming converts straight chain to branched chain hydrocarbons with heat, and catalyst.
• The octane number can improve when blended with additives like tetraethyl lead (TEL).
• (C2H4)4Pb is an antiknock agent but combustion forms lead oxide, reducing it to metallic lead and air pollution.

Classifications of Organic Compounds

• Organic compounds are too numerous to study individually.
• They are classified into groups and subgroups.
• Broad classification in 2 classes; open chain or acyclic and cyclic compounds.

Open Chain (Acyclic)

• Contain open chains of carbon atoms, straight or branched.
• Also called aliphatic compounds.

Straight Chain

• Carbon atoms connects in series.
• Example is n-Butane (CH3-CH2-CH2-CH3)..

Branched Chain

• Contain carbon atoms attached on the sides a chain.
• Example is 2-Methylpropane Isobutane (CH₃-CH-CH₃).

Closed Chain (Cyclic)

• Contain closed chains or atom rings.
• Types include homocyclic (carbocyclic) and heterocyclic compound.

Homocyclic or Carbocyclic

• Rings consist of only carbon atoms.
• Classified as alicyclic and aromatic

Alicyclic

• Rings contain three or more carbon atoms, resemble aliphatic compounds.
• Saturated alicyclic hydrocarbons have a general formula CnH2n.
• Examples include cyclohexane and cyclopropane

Aromatic

• Carbocyclic compounds contain at least one benzene ring.
• The ring have six carbon atoms with alternating double and single bonds, shown with a circle.
• Aromatic compounds may have a side-chain or functional group attached.

Heterocyclic

• Rings have more than one type of atom; they may have nitrogen (N), oxygen (O) or sulphur (S).
• Atoms other than carbons present in the ring are hetero atoms.

Functional Group

• Functional groups impart molecule specific properties, the chemically functional parts.
• The study of organic chemistry is organized around functional groups.
• Each group defines organic families.

Hybridization

• Carbon needs to be tetravalent in compounds, even though having stable two unfilled 2p atom configuration atom has valency of 2.
• One from a 2s goes to an empty 2p, giving configuration = 1s2 2s¹ 2px 2p¹, 2p¹z
• This can explain tetravalency, hybridization explains equivalent tetravalency of carbon.

sp³ Hybridization

• All four atomic carbon orbitals mix for atoms with four attachments to give equivalent hybrid atomic orbitals.
• Degenerate sp³ hybrid orbitals go at 109.5° and give tetrahedral geometry.
• When a carbon atom makes bonds with other atoms, hybrid orbitals overlap with those other atom orbitals.
• For all compounds the carbon atom is saturated.

sp² Hybridization

sp Hybridization

Isomerism

• Isomerism contains the same molecule formula, yet different structural formulas, showing bond presence.
• The simplest hydrocarbon with structural isomers is butane , Alkanes don't show isomerism, because they exist in one structure
• Two different arrangements are possible for same molecule.

Types of Isomerism

(1) Structural Isomerism

• Structural isn't confined to HC only, arises due to arranging within molecule atom/s.

(i) The Chain Isomerism

• Arises due to the different nature in the nature of the Carbon chain- For pentane certain arrangements are possible.

(ii) Position Isomerism

• Arises due to difference between the functional group/s on carbon chains with carbon atoms being the same- For example chloropropane

(iii) Functional Group Isomerism

• the same in molecular formula, but different in structural formula ex. Dimethylether (CH3-O-CH3) Ethyl Alcohol(CH3-CH2OH

(iv) Metamerism

• Arises due to distribution of carbon atom unequal to functional group on both such sides. Ex Diethyl ether (CH3-CH2-O-CH2-CH3) , Methyl ether

(v) Tautomerism

• Atom shifting causes isomerism is arise due to shifting.

(2) Cis-Trans Isomerism/Geometric Isomerism

• Carbon atoms, joined with single bond, can free rotate. Double bonded is lock.
• With such the carbon atoms are locked with certain groups.
• KEY POINTS
• Classified in organic vs inorganic
• Synthesis in laboratory.
• Defined compounds of Carbon for Carbon chem.
• Daily compounds of nature
• Gas / Petroleum & Coal are compounds
• Developed cracking to increase yield.
• The study is organized and centred towards functionalism.
• Carbon can explain modes
• Same for but different structural is isomers- with many type differences.
• Restricted bonds are isomers by double for example.