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02 Bevezetés. Szénhidrogének



Introduction to the organic chemistry, hydrocarbons


Organic compounds: compounds of the carbon


  • Electron structure: 1s2 2s2 2p2
  • Hybridisation: 1s2 2s1 2p3
  • Double bond, triple bond
  • Can be bonded to each other: long chains and different rings can be made


All other atoms besides C and H in organic compounds

  • O, N, S, P, F, Cl, Br, I


Classifying organic compounds

By the chain:

  • Open chain normal or branched
  • Closed chain

By the bonds:

  • Saturated: single bonds
  • Unsaturated: double, triple bonds
  • Aromatic: delocalized electrons in the molecule ring

By the atoms:

  • Hydrocarbons: only C and H
  • Heteroatomic compounds: C and H and heteroatoms


  • Contain only carbon and hydrogen
  • Burn to CO2 and H2O


Groups of hydrocarbons

Saturated hydrocarbons:


  • Only single bonds
  • Ancient name: paraffins (non reactive)
  • Name: -ane

Unsaturated hydrocarbons

  • Double and triple bonds

Alkenes (olefins):

  • Double bonds
  • Name: -ene


  • Triple bonds
  • Name: -yne
  • Closed chains


Cycloalkanes, cycloalkenes:

  • Ring-shaped molecule
  • Name: cyclo-


Aromatic hydrocarbons: arenes

  • Saturated hydrocarbons



Molecular structure

  • CH4
  • M = 16 g/mol
  • C-H bond: polar, covalent (ΔEN=0,4)
  • The molecule is non polar (+ and – pole is at the same place)

Physical properties

  • Colorless, inodorous gas, insoluble in polar solvents (water), soluble in nonpolar ones (oil, petrol)
  • Explosive if it is mixed to oxygene

Chemical properties

Not really reactive


  • CH4 + 2O2 = CO2 + 2H2O
  • Colorless  or pale blue flame!

Thermal decomposition: 500oC, no O2

  • 2CH4 = C2H2 + 3H2
  • Chemical properties

Reaction with steam: 1000oC, Ni catalysator

  • CH4 + H2O = CO + 3H2

Reaction with chlorine (substitution):

  • CH4 + Cl2 = CH3-Cl + HCl
  •                  monochlor-methane


  • Natural gas
  • Marsh-gas
  • Fire-damp

Used for:

  • Release energy
  • Chemical industry




Compounds with the same molecular formula but different structural formulas  

  • Constitutional: the molecular formula is the same but the sequence of the atoms is different
  • Conformational: can be converted to each other by rotation about single bonds



Features of the alkanes


  • C1-C4: gas
  • C5-C16: liquid
  • C17- : solid

Boiling point, melting point: increases as the molecular mass increases

Branched chain: boiling point is lower, melting point is higher than at the normal chain

Cycloalkanes: both of them is higher

Solubility: only in nonpolar solvents

Chemical properties

  • Combustion
  • Substitution
  • Cracking


Origin: died organisms were buried and became oil on high pressure and temperature during millions of years in oxygen-free conditions

Natural gas

Methane (99%), ethane: city gas

Propane, butane: „bottled” gas

Plus: CO2, H2S, N2, He

We use as energy source and in chemical industry (solvents, alkohol, vitamins)

Crude oil

  • Mixture of alkanes and other compounds
  • Dark brown smelly liquid

How to separate components:

FRACTIONAL DISTILLATION (fractional condensation!)

Products of distillation:

  • Petrol C5-10 (octane number!)
  • Kerosine C10-11 (aeroplanes)
  • Diesel oils C13-15 (trucks, trains, heating)
  • Lubricating oil C16-28
  • Bitumen (roads, roofs)




  • Unsaturated hydrocarbons: one double bond in the molecule


Molecular structure

  • C2H4
  • Double bond: σ (stronger)  and π (weaker) bonds

Physical properties

  • Colorless, sweet-smelling gas
  • Soluble in nonpolar solvents
  • Melting and boiling point is low (weak interactions between molecules)

Chemical properties

  • Very reactive (π bonds can be broken easily)


  • C2H4 + 3O2 = 2CO2 + 2H2O
  • Light yellow flame, black smoke (unburned carbon)

Addition: fusion of 2 or more molecules without byproduct

  • Addition with halogens: C2H4 + Cl2 = C2Cl2H4 (1,2 dichloroethane)
  • Addition with hydrogen: C2H4 + H2 = C2H6 (ethane)
  • Addition with hydrogen-chloride: C2H4 + HCl = C2ClH3 (chloroethane)
  • Addition with water: C2H4 + H2O = C2H5OH (ethanol)

Polymerisation: a lot of unsaturated molecule (monomer) fuses without byproduct to a saturated large molecule (polymer):

                CH2=CH2 + CH2=CH2   =    -CH2-CH2-CH2-CH2-


  • Rare
  • Crude oil
  • Plant hormone

Used for:

  • Chemical industry: plastic, solvents, explosives
  • Plants: as a hormone induces fruit ripening



More alkenes

Name: -ene

General formula: CnH2n

Geometric isomerism: cis, trans

Physical properties: see the alkanes

Chemical properties

  • Combustion: Light yellow flame, black smoke (unburned carbon)
  • Addition: Markovnikov’s Rule (in addition HX H atoms will join to the carbon that already has more H atoms)

Presence: Crude oil

Producing: cracking crude oil

Importance: plastic industry

  • Polypropylene
  • Polyizobutylene

More double bonds

2: dienes (diolefines)

3: trienes (triolefines)

More: polyenes

  • Cumulated, conjugated, isolated

Buta-1,3-diene: can be polymerised

2-methylbuta-1,3-diene (isoprene): transparent liquid, low boiling point


  • Rubber tree: latex (caoutchouc=polyisoprene 30-35%)
  • Vulcanization (Goodyear, 1839): polyisoprene + sulphur (3-5%), heating
  • RUBBER: contains „sulphur bridges”, elastic
  • Ebonite: S content is more than 30%




  • Molecule has one triple bond
  • Name: -yne

Ethyne (acethylene)

Molecular structure

  • C2H2
  • 1 σ (stronger)  and 2 π (weaker) bonds

Physical properties

  • Transparent, colourless, inodorous gas
  • Insoluble in water, soluble in nonpolar solvents
  • Explosive when pressurized (instable)
  • Storing:   in acetone contained in a metal cylinder with a porous filling

Chemical properties:

Very reactive


  • 2C2H2 + 5O2 = 4CO2 + 2H2O, light yellow flame, black smoke (unburned carbon)
  • Total burning: high temperature (3600oC, used for welding)

Addition with

  • Halogens: halogenoalkanes: C2H2 + Cl2 = C2Cl2H2 (1,2 dichloroethene), C2Cl2H2 + Cl2 = C2Cl4H2 (1,1,2,2 tetrachloroethane)
  • H2: C2H2 + H2 = C2H4 (ethene), C2H4 + Cl2 = C2H6 (ethane)
  • HCl: C2H2 + HCl = CH2=CHCl (chloroethene, vinyl chloride)
  • (after polymerisation: polyvinyl chloride (PVC)

Presence, use

Is not present in nature (it is very reactive)

Used for:

  • Welding
  • Plastic industry
  • To produce alcohol, acetic acid





Molecular structure

  • C6H6
  • 1 delocalised electron on each carbon atom
  • 3 π bonds

Physical properties

  • Colorless liquid with sweet smell
  • Toxic, carcinogen
  • Soluble in nonpolar solvents

Chemical properties


  • 2C6H6 + 15O2 = 12CO2 + 6H2O
  • light yellow flame, black smoke (unburned carbon)


  • C6H6 + Br2 = C6H5Br + HBr
  • C6H6 + HNO3 = C6H5-NO2 + H2O


  • Crude oil, coal tar (kőszénkátrány)


  • Solvent
  • Rubber, dye, explosive, plastic and pharmaceutical industry

More arenes

Toluene (methylbenzene) (toluol, metil-benzol)

  • Sweet-smelling liquid, insoluble in water
  • Can react as an alkane and as an arene too
  • Used as a solvent and as a primary in chemical industry

Xylene (dimethylbenzene)

  • 1,2 dimethylbenzene: ortoxylene, 1,3 dimethylbenzene: metaxylene, 1,4 dimethylbenzene: paraxylene
  • Sweet-smelling flammable liquid, insoluble in water
  • Used as a solvent

Styrene (vinyl benzene)

  • Can react as an alkene and as an arene too
  • Polimerisation: polystyrene


  • White crystals with low melting point
  • Sublimation: transforms from solid to gas state without liquid
  • Used in dye and pharmaceutical industry