Title 2. HYDROCARBONS (58-103).pdf ✅

X–Chemistry (Vol–II) 58 Narayana Group of Schools Olympiad Class Work Book CONCEPT FLOW CHART H Y D R O C A R B O N S Alkanes Methods of preparation Chemical properties Uses Alkenes Methods of preparation Chemical properties Uses Alkynes Methods of preparation Chemical properties Uses
X – Chemistry (Vol – II) Olympiad Text Book 59 Narayana Group of Schools Olympiad Class Work Book Vladimir Vasilyevich Markovnikov, (born Dec. 22, 1838, Nizhny Novgorod, Russia— died February 1904, Moscow), Russian organic chemist who contributed to structural theory and to the understanding of the ionic addition (Markovnikov addition) of hydrogen halides to the carbon-carbon double bond of alkenes. After studying at the universities of Kazan and St. Petersburg, Markovnikov taught at the universities of Kazan, Odessa, and Moscow (1873–98). Through his experiments he showed that butyric and isobutyric acids have the same chemical formula but different structures; i.e., they are isomers. In 1869, while developing his theory of the mutual influence of atoms in chemical compounds, he noted that when hydrogen halides are added to an alkene, the hydrogen attaches to the carbon with more hydrogens already attached, whereas the halogen attaches to the carbon with fewer hydrogens attached. Why hydrogen bromide exhibited both Markovnikov as well as reversed-order, or anti- Markovnikov, addition, however, was not understood until Morris Selig Kharasch offered an explanation in 1933. Vladimir Markovnikov [1838 – 1904] HYDROCARBONS
X–Chemistry (Vol–II) 60 Narayana Group of Schools Olympiad Class Work Book HYDROCARBONS ALKANES: Introduction:  The term hydrocarbon is self-explanatory which means compounds of carbon and hydrogen only. Abbreviated form of LPG is liquefied petroleum gas, CNG stands for compressed natural gas and LNG is liquefied natural gas obtained by liquefaction of natural gas.  Petrol, diesel and kerosene are obtained by fractional distillation of petroleum found under the earth’s crust. Coal gas is obtained by the destructive distillation of coal.  LPG is used as a domestic fuel with least pollution. Kerosene oil is also used as a domestic fuel but it causes some pollution. Automobiles need fuels like petrol, diesel, and CNG.  Hydrocarbons are also used for the manufacture of polymers like polythene, poly propene, polystyrene etc. Higher hydrocarbons are used as solvents for paints. They are also used as the starting materials for manufacture of many dyes and drugs. Example: Benzene,xylene,etc. Classification of Hydrocarbons:  Hydrocarbons are classified into aliphatic hydrocarbons and aromatic hydrocarbons.Aliphatic hydrocarbons are of two types : i) Saturated Hydrocarbons ii) Unsaturated Hydrocarbons i) Saturated hydrocarbons: These are the compounds in which all the four valences of carbon are satisfied by atoms or groups. These are also called paraffin’s. Example: Alkanes C H H H H C H H H C H H H Methane Ethane ii) Unsaturated hydrocarbons: These are the compounds in which two carbon atoms are linked by double or triple bonds. Example: Alkenes and Alkynes Ethylene CH CH 2 2  ; Acetylene CH CH 
X – Chemistry (Vol – II) Olympiad Text Book 61 Narayana Group of Schools Olympiad Class Work Book Aromatic hydrocarbons: Compounds containing at least one benzene ring or cyclo compounds which obey Huckle’s rule are aromatic.(4n+2) electrons. Example: Benzene,Toluene. Alkanes:  Alkanes are saturated hydrocarbons.  General formula of alkanes is CnH2n2 , R –H ,R – CH3 ,R– (CH2 ) n – R.  Methane is the first member of this family and it is found in coal mines and marshy places.  Alkanes under normal conditions are inert and cannot react with acids, bases and other reagents So these are called paraffins.(Latin:Parum = little, affinis = affinity)  Carbon undergoes sp3 hybridisation and has tetrahedral geometry.  H-C-H bond angle in alkane is 0 1 109 28 .  Alkanes contain C – C and C – H sigma bonds. Preparations of Alkanes: Catalytic Reduction of Alkene or Alkyne from unsaturated hydrocarbons (Sabatier - Senderson’s):  Alkenes and alkynes on hydrogenation in presence of finely divided catalysts like platinum, palladium, nickel or PtO2 form alkanes.  PtO2 is called Adam’s catalyst. ' 2 Ni R CH CH R H      ' R CH CH R    2 2 3 2 2 3 2 3 0 300 Ni C CH CH CH H CH CH CH     0 0 Ni 200 300 C H H H C C H H C C H H H H H         0 0 Ni 2 200 C 300 C H H H C C H 2H H C C H H H           Platinum and palladium can catalyse the reaction at room temperature but Nickel as a catalyst requires higher temperature and pressure.